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- Herausgeber: John Wiley & Sons
- Kategorie: Fachliteratur
- Sprache: Englisch
Highly Commended at the Society of Authors and Royal Society of Medicine Medical Book Awards 2006
This outstanding atlas of ophthalmic pathology brings together the world famous collection of digital images from the Tennant Eye Institute in Glasgow.
Weng Sehu and William Lee have produced a unique body of information, moulding Ophthalmic Pathology and the accompanying interactive CD-Rom into the essential ‘must-have’ revision aid and reference book for ophthalmologists in training, teachers and clinical ophthalmologists worldwide.
Ophthalmic Pathology is a concise, yet informative, user friendly textbook whose unparalleled image collection will more than meet the expectations of the ophthalmological community.
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Veröffentlichungsjahr: 2012
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Contents
Preface
Acknowledgements
Chapter 1 Basics
Examination of the enucleated eye
Microscopic features
Basic pathology definitions
Type of specimens
Tissue preparation
Examination techniques
Chapter 2 Eyelid and lacrimal sac
Eyelid
Lacrimal drainage system
Chapter 3 Conjunctiva
Normal
Non-specific chronic conjunctivitis
Specific inflammatory conditions
Degenerative conditions
Tumours
Chapter 4 Cornea
Ulcerative keratitis
Degenerations
Dystrophies
Keratectasia
Malformations
Miscellaneous
Chapter 5 Orbit and optic nerve
Orbital tissue pathology
Lacrimal gland
Metastates
Optic nerve pathology
Chapter 6 Development and malformation
Normal development/embryology of the anterior segment
Anterior segment anomalies
Posterior segment anomalies
Whole eye anomalies
Chapter 7 Glaucoma
Classification
Normal drainage anatomy
Pathological examination of a glaucomatous eye
Primary open angle
Primary angle closure
Secondary open
Tissue effects
Chapter 8 Inflammation
Basics
Endophthalmitis/panophthalmitis
Chorioretinitis
Non-granulomatous uveitis
Chapter 9 Wound healing and trauma
Healing and repair in ocular tissues
Trauma
The shrunken eye (atrophia/phthisis bulbi)
Chapter 10 Retina: vascular diseases, degenerations, and dystrophies
Normal anatomy
Vascular disease
Dystrophies
Degenerations
Chapter 11 Intraocular tumours
Iris
Ciliary body
Choroid
Retina
Panophthalmic neoplasia
Index
Download Images
© 2005 K.W. Sehu and W. R. WengPublished by Blackwell Publishing LtdBMJ Books is an imprint of the BMJ Publishing Group Limited, used under licence
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First published in 2005
Library of Congress Cataloging-in-Publication Data
Sehu, K. WengOphthalmic pathology: an illustrated guide for clinicians/K. Weng Sehu, William R. Leep.; cm.includes index.
ISBN-13: 978 0 727917 79 9 (alk. paper)ISBN-10: 0 727917 79 X (alk. paper)1. Eye—Disease—Atlases 2. Eye—Diseases.[DNLM: 1. Eye Diseases—pathology—Atlases.] I. Lee, William R., 1932– II. Title.RE71.S44 2005617.7—dc22
2005001742
A catalogue record for this title is available from the British Library
ISBN-13: 978 0 727917 79 9ISBN-10: 0 727917 79 X
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Preface
Our original purpose in writing this book was to make available illustrations of the common pathological entities encountered in routine practice for junior colleagues who are undertaking postgraduate training. In so doing, we have attempted to provide an understanding of the basic processes involved in ophthalmic disease and thus this book should also be of interest to qualified ophthalmologists. Computer technology has advanced to such a level that it has enabled us to derive and modify images collected over a period of 40 years. An illustrated text has also been prepared for portable convenience. Basic clinical and management sections have been added into each chapter to provide relevant background to the pathology presented. As a result, we hope that this book will also be of value to those pathologists with an interest in ophthalmic pathology by helping to bridge the gap between laboratory and clinical practice.
Weng SehuWilliam Lee
Acknowledgements
It is our pleasure to acknowledge the help and advice we have received from Dr Fiona Roberts, Dr Ridia Lim, Professor Peter McCluskey, and Dr Harald Schilling.
Dedication
To our respective families.
Chapter 1
Basics
In order to achieve a better understanding of disease processes occurring in different regions of the eye, this section describes the technology currently employed by the histopathologist in the examination of tissue specimens referred by ophthalmologists. It is important to be aware of the range of laboratory services locally available. When there is a suspicion of infection, the relevant specialist (bacteriologist/mycologist/virologist) should be consulted for advice concerning appropriate transport media and therapy. The value of an accurate and concise history cannot be overestimated and good collaboration will be rewarding to both clinicians and laboratory specialists.
Examination of the enucleated eye
A formalin-fixed enucleated globe bears little resemblance to the in vivo appearance due to opacification of the cornea, lens, vitreous, and retina. Previous intervention, for example removal of keratoplasty tissue, can produce secondary damage to the anterior segment tissues (Figure 1.1). In routine practice, it is unwise to try to cut across the lens because this produces damage to the anterior segment but occasionally a suitable illustration can be provided (Figure 1.2). By dividing the globe in the coronal plane, the pathologist has the advantage of examination of the lens and ciliary body from the posterior aspect (Figure 1.3) and the retina from the anterior aspect (Figure 1.4). For demonstration purposes, it is possible to divide the optic nerve and the lens (Figure 1.5). In general, the globe is divided above the optic nerve and at the edge of the cornea to avoid traumatic artefact to the main axial structures. After paraffin processing, the microtomist cuts into the centre of the eye. The orientation of the extraocular muscles on the posterior aspect of the globe allows the pathologist to identify the side from which the globe was enucleated (Figure 1.6). Orientation of the specimen is vital if the correct plane of cut is to be made.
Microscopic features
These are described wherever relevant to pathology in the corresponding chapters and are therefore only illustrated briefly in this chapter. The histological features of each of the following tissues are annotated in detail:
cornea (
Figure 1.7
)
chamber angle (
Figure 1.8
)
iris (
Figures 1.8
,
1.9
)
ciliary body (
Figures 1.8
,
1.10
,
1.11
)
lens (
Figures 1.9
,
1.11
)
retina and choroid (
Figure 1.12
)
optic disc (
Figure 1.13
).
Features for identification of the age of a patient (in this case a child):
thin Descemet’s membrane
“finger-like ciliary processes”
intact, non-hyalinised ciliary muscle
absence of proliferations in the pars plana epithelium
absence of sub-RPE (retinal pigment epithelium) deposits (for example drusen).
Figure 1.1 In the current litigious climate, the only normal autopsy material available for study will be that used for donor keratoplasty. In this example, formalin fixation accounts for opacification in the cornea and lens. Damage to the iris is the result of the trephine.
Figure 1.2 The anatomical features of the anterior segment are easily recognised. Note that formalin fixation leads to opacification of those tissues (cornea, lens, zonules, and vitreous) which are normally transparent.
Figure 1.3 Dividing the eye in the coronal plane provides the opportunity to examine the ciliary body and lens in detail. In this case, there is a subcapsular cataract. The radial linear opacities in the lens substance are a common degenerative feature in the elderly globe. Note that in the pars plicata, there are ridges and troughs which explain the differing appearance of the ciliary processes in Figures 1.10 and 1.11.
Figure 1.4 In a globe removed at autopsy, there is often autolytic swelling of the macula due to delayed fixation. The opacification of the retina is the result of formalin fixation. After cessation of blood flow, the blood columns in the vessels tend to fragment (“cattle-trucking”).
Figure 1.5 This normal globe is part of an exenteration and is fixed in gluteraldehyde. For demonstration purposes, the section passes through the centre of the optic nerve, the lens, and the pupil (left). The macula is located on the temporal side of the optic nerve, which is confirmed by the adjacent scleral insertion of the inferior oblique muscle. The distance from the optic nerve to the ora is greater on the temporal side than on the nasal side. A higher magnification of the posterior pole of the globe is shown on the right. Myelination of the axons in the optic nerve ends at the lamina cribrosa.
Figure 1.6 The orientation of the extraocular muscles in relation to the optic nerve reveals that this specimen is a left globe.
Figure 1.7 A full thickness section of the cornea (left) demonstrates the relative thinness of the epithelium and endothelium in relation to the stroma. Both cell layers are shown in higher magnification (upper right and lower right). Note the artefactual separation of the corneal lamellae.
Figure 1.8 Hyalinisation and atrophy of the circular and oblique components of the ciliary muscle is a feature of ageing, but the longitudinal fibres inserting into the scleral spur persist. In an infant (inset), the components of the ciliary muscle are intact: note the thin ciliary processes.
Figure 1.9 In the pupillary portion of the iris, the sphincter pupillae is a prominent feature and the close relationship to the lens provides the opportunity to illustrate the anterior capsule and the epithelium of lens. The iris pigment epithelium terminates at the pupillary rim in the normal eye.
Figure 1.10 In this illustration of the normal ciliary body, the relative absence of hyalinisation in the ciliary muscle suggests the younger age of the patient. This section passes through one of the troughs in the pars plicata.
Figure 1.11 The ciliary processes are lined by a two-layered epithelium corresponding to the layers of the optic cup (see Chapter 6). The stroma of the ciliary processes contains blood vessels. The equator of the lens contains the nuclear bow. This section passes through a ridge in the pars plicata.
Basic pathology definitions
The following text describes the histological appearance in basic pathological processes and serves only as an introduction. Additional illustrations are provided throughout the text.
Inflammation
For a detailed description of the functions of inflammatory cells, the reader is advised to consult specialised immunology texts. Inflammatory disease entities relevant to ophthalmic pathology are described in Chapter 8.
Cellular constituents
Polymorphonuclear leucocytes
Neutrophilic polymorphonuclear leucocytes
Acute purulent inflammation occurs after pathogenic organisms, particularly bacteria or fungi, are introduced into the ocular or orbital tissues. The predominant cell is the neutrophilic polymorphonuclear leucocyte (PMNL) which contains intracytoplasmic granules encasing lysosomal enzymes capable of destroying pathogenic organisms (Figure 1.14). The proteolytic enzymes are also destructive of normal tissues adding to the lytic enzymes secreted by pathogenic organisms.
Eosinophilic polymorphonuclear leucocytes
These possess intracytoplasmic granules which, with an appropriate stimulus from interleukin 6, release major basic protein and ribonuclease (Figure 1.15). These enzymes are often associated with reactions against protozoal parasites, such as Toxocara canis, but this response is disadvantageous in allergic conditions (for example vernal conjunctivitis) because release of enzymes leads to vasodilatation and oedema.
Mast cells
Mast cells are large mononuclear cells with intracytoplasmic pink granules (in an H&E stain) containing heparin, histamine, and prostaglandin (Figure 1.16). These cells are an important component of allergic reactions (for example vernal conjunctivitis).
Lymphocytes and plasma cells
Lymphocytes and plasma cells predominate in chronic inflammatory processes, particularly in autoimmune disorders. Both types of cells are small (Figure 1.17). Lymphocytes have a homogeneous nucleus and very little cytoplasm. Plasma cells are oval with a “cartwheel” or “clockface” nucleus, and a paranuclear clear area in the pink cytoplasm.
Granulomatous inflammatory reaction
The classic reaction is characterised by an infiltration of macrophages accompanied by lymphocytes and plasma cells. Macrophages frequently fuse to form multinucleate giant cells. Granulomatous inflammatory reactions occur during chronic infections by bacteria (for example Mycobacteria sp.) and fungi (for example Aspergillus sp.). Foreign material also stimulates a granulomatous reaction (Figure 1.18).
A granulomatous inflammatory reaction must be distinguished from granulation tissue which is formed by fibrovascular proliferation occurring as part of a healing response.
Figure 1.13 A longitudinal section through the optic nerve demonstrates the different components. The nerve fibre layer (NFL) is thickened at the edge of the disc. The prelaminar part contains non-myelinated axons which pass through the lamina cribrosa. In the retrolaminar part of the optic nerve, the axons are myelinated.
Figure 1.14 This illustration was taken from a pooled collection of polymorphonuclear leucocytes in the anterior chamber (hypopyon). These cells are recognised by their distinctive multilobed nuclei. The pink-staining material around the cells is plasma.
Figure 1.15 Eosinophilic polymorphonuclear leucocytes (PMNLs) are often part of a reaction which contains macrophages. The eosinophils possess bilobed nuclei and bright red intracytoplasmic granules which are released into the tissue (degranulation). Macrophages have relatively larger oval nuclei and have a phagocytic function.
Figure 1.16 Mast cells are mononuclear cells and are larger than PMNLs. The red granules in the cytoplasm are characteristic. These cells are easily found in the normal iris stroma, as in this example.
Figure 1.17 This chronic inflammatory reaction in the choroid contains numerous lymphocytes and plasma cells. Note the clear area adjacent to the nucleus of the plasma cell.
Figure 1.18 Implantation of hair fragments into the conjunctiva induces a foreign body giant cell granulomatous reaction.
Figure 1.19 The term “pyogenic granuloma” is a misnomer as can be seen from this illustration: there is neither evidence of pus nor of a giant cell granulomatous reaction. The congested mass of tissue consists only of radiating blood vessels in loose fibrous connective tissue. A chalazion (see Chapter 2) is present beneath the pyogenic granuloma.
Pyogenic granuloma
Clinically this condition appears as a fleshy, granular, red mass over a pre-existing defect in the conjunctiva. Most commonly a pathologist will see a pyogenic granuloma over a chalazion (Figure 1.19) or over suture material in a muscle insertion after squint surgery.
Neoplasia
Knowledge of terminology used by pathologists is essential to a clinician in the interpretation of a pathological report.
Hypertrophy
An increase in the volume of tissue by enlargement of individual cells. While this is a common phenomenon in striated muscle following repetitive use (for example weight training), it is difficult to find a suitable example in ophthalmic pathology.
Hyperplasia
An increase in the volume of tissue due to the proliferation of cells (for example response of conjunctival epithelium or epidermis of the eyelid to an irritant – Figure 1.20).
Hyperkeratosis
Thickening of the keratin-containing layer in an epidermis (for example actinic keratosis – Figure 1.20).
Parakeratosis
Nuclear debris persists in a thickened keratin layer when the growth rate of the epithelium is accelerated (for example actinic keratosis – Figure 1.20).
Metaplasia
This is transformation of one cell type to another cell type (for example columnar epithelium of conjunctiva to stratified squamous in keratoconjunctivitis sicca). Two other forms of metaplasia of importance in ophthalmology are fibrous metaplasia of the retinal pigment epithelium (for example proliferative vitreoretinopathy following rhegmatogenous retinal detachment – see Chapter 10) and fibrous metaplasia of the lens epithelium (for example anterior subcapsular cataract – Figure 1.21).
Dysplasia
Irregular arrangement and loss of maturation of cells in an epithelium. The nuclei are irregular in size, shape, and chromatin distribution, and mitotic figures may be found in all levels. This can be regarded as a carcinoma-in-situ because the neoplastic cells have not penetrated the underlying basement membrane (Figure 1.22).
Mitotic figures
Mitotic division of cells involves the duplication of chromosomes and separation to form two daughter cells. A mitotic figure is most easily identified in metaphase when the nuclear material forms a broad line across the cell (Figure 1.22). Mitotic activity is a normal function of those cells which undergo “wear-and-tear” replacement (for example basal layer of epithelium). Pathologists attach great importance to the identification of mitotic figures, especially in neoplasias where an increase in mitotic activity reflects cell proliferation rates. Many examples of mitotic activity will be provided throughout this textbook to illustrate the varying appearances of the process.
Figure 1.20 Sun damage to skin results in hyperplasia of the epidermis with excessive keratin formation (hyperkeratosis) and migration of epithelial cell nuclei into the surface keratin (parakeratosis). There is still maturation of the epidermal layers from basal to surface, which makes the distinction between hyperplasia and dysplasia (see Figure 1.22).
Figure 1.21 The formation of an anterior subcapsular fibrous plaque is one complication of anterior uveitis. The fibrous tissue staining green with the Masson stain (lower) is formed by metaplasia of lens epithelial cells to fibroblasts
Atrophy
A decrease in size or number of cells. This process may be physiological or pathological. The lacrimal gland (see Chapter 5) becomes atrophic in later life (physiological) and the nerve fibre layer becomes atrophic in glaucoma (pathological).
Apoptosis
Apoptosis describes the programmed cell death which occurs in normal tissue (for example embryogenesis of the retina) and in disease. In the absence of inflammatory cell infiltration, individual cells undergoing apoptosis appear shrunken and the nuclei are fragmented (Figure 1.23). Programmed cell death is common in malignant tumours and explains the slow growth of basal cell carcinomas and uveal melanomas.
Necrosis
By comparison, in necrosis there is widespread cell death as observed in rapidly proliferating tumours such as retinoblastoma in which tumour growth exceeds the blood supply (see Chapter 11). When a population of cells dies simultaneously, the nuclei and cytoplasmic membranes disappear leaving a pale pink staining area of tissue in an H&E section.
Type of specimens
Pathological services are now used more frequently due to the importance of accountability, audit, and research.
The following types of specimen may be presented for pathological examination:
eyelid (including lacrimai sac) – biopsy
*
conjunctiva – biopsy, impression cytology, and scrape
cornea – lamellar or full thickness (penetrating keratoplasty), impression cytology, and scrape
orbit (including lacrimal gland) – biopsy + exenteration
optic nerve – biopsy or enucleation
temporal artery biopsy
globe – biopsy, evisceration, enucleation, exenteration
aqueous and vitreous tap
vitrectomy including membrane peeling
subretinal membrane – excision.
Tissue preparation
Fixatives
Fixation is essential to good histopathology because excised tissue undergoes rapid autolysis and desiccation.
Formalin
This is the traditional universal fixative solution in ophthalmic pathology because it has prolonged chemical stability and is most appropriate for immunohistochemistry.
Gluteraldehyde
If scanning or transmission electron microscopy is required for diagnosis, gluteraldehyde fixation is essential. One advantage of this fixative is that the macroscopic appearances are closer to those observed in vivo, although it is less suitable for immunohistochemistry.
Figure 1.22 This is an example of metaplasia and dysplasia in the conjunctival epithelium (upper). The normal appearance is shown below for comparison. In the upper figure, the conjunctival epithelial cells have undergone metaplasia to squamous cells. Dysplasia is characterised by a failure of maturation in the cell population which exhibits the cytological characteristics of malignancy (e.g. marked variation in nuclear size and shape and mitotic figures located outside the basal layer). Although this is a premalignant change, there is no evidence of invasion into the underlying stroma and this change is classified as carcinoma-in-situ.
Figure 1.23 Programmed cell death in individual cells occurs in both physiological and pathological processes. In this orbital rhabdomyosarcoma, the apoptotic cells can be recognised by the small fragmented nuclei in comparison with large irregular nuclei of the viable cells.
Alcohol
Alcohol (for example gin) can be used for specimen fixation in countries where formalin is not available.
Preparation
Paraffin embedding
Currently, tissue is cut to provide histological preparations after it is embedded in paraffin wax. To achieve impregnation of the tissue by wax, it is necessary to remove water (ascending concentrations of alcohol) and lipid (xylene). The wax supports the tissue during sectioning (5–10 μm in thickness) and acts as an adhesive when the section is mounted on a glass slide. A reverse process takes place to remove the wax (xylene) and rehydrate the tissue (descending concentrations of alcohol) prior to tissue staining with water-soluble conventional stains or the application of immunohistochemistry.
Paraffin blocks and sections can be stored indefinitely.
Fresh/frozen sections
If an urgent diagnosis is required during a surgical procedure, the tissue can be rapidly frozen and sections cut on a freezing microtome. Section preparation is easier when the tissue is not fixed so the specimen should be transferred to the laboratory in saline or transport media.
Fresh tissue is also more suitable for the study of fat within cellular components (for example lipid keratopathy or sebaceous carcinoma) and for immunohistochemical studies in which a full exposure of antigenic epitopes is required.
For the best preservation of tissue, specially designed transport media (for example Michel’s transport medium) should be used. Consultation with the pathologist is essential.
Plastic embedding
For transmission electron microscopy, it is necessary to embed tissue in hard plastic material (Araldite). Plastic material can be cut on a microtome to achieve the thin sections (0.05–0.06 μm) necessary for high-resolution imaging and are able to resist electron beam bombardment. Thin plastic sections (1 μm) are cut for light microscopy and stained with toluidine blue.
Macroscopic examination or specimen “grossing”
In ophthalmic pathology, specimens are often small and the initial examination requires magnification with a dissecting microscope. The specimen is measured and a description recorded before division into blocks for paraffin embedding. The methods for each tissue sample are described at the beginning of the relevant chapter. It is however appropriate to describe the methodology for the examination of a globe at this point.
Measurements
The maximum dimensions in the globe in the following sequence are measured using a calliper:
The following are examples of conditions that may alter the dimensions:
Increase (25–30 mm): axial myopia, adult glaucomatous enlargement due to uveoscleral bulging (staphyloma formation) or buphthalmos resulting from infantile glaucoma.
Decrease (15–18 mm): axial hypermetropia when the globe is shortened. Shrinkage (for example atrophia bulbi or phthisis bulbi) occurs after prolonged loss of pressure in the eye. Ocular hypotonia may be the consequence of inflammatory damage to the ciliary processes or to leakage of intraocular fluids through a defect in the corneoscleral envelope.
Transillumination
The shadow from a powerful light source behind the globe is used to locate intraocular masses.
Different cuts and terminology
The plane of section through an eye is extremely important in revealing the pathological features in a paraffin section. Cuts are carefully chosen to include all the pathological features and relationships in one plane of section.
In the horizontal plane, the paraffin sections should include the centre of the pupil, the lens, the macula, and the optic nerve (Figure 1.24). The temporal side of the eye is longer than the nasal side, so that a horizontal cut can be recognised in a section even when the retina and macula are atrophic. The inferior oblique muscle when present is useful to identify the posterior temporal sclera and overlies the macula.
The vertical plane is favoured for displaying surgery for glaucoma and cataract. However, in the case of a tumour or a foreign body, an oblique section may be required to cut across the feature of interest (Figure 1.25).
Anatomical location
For accurate clinical correlation, the ocular abnormalities should be described in their correct quadrants–referred to as superior, inferior, temporal, and nasal.
Calotte
The term “calotte” (French: “cap”) is used for the two hemispheres which are cut from the globe before the central pupil-optic nerve block (PO block) is processed through paraffin. NB: This should not be confused with “culotte” (French: “knickers/panties”)!
Stains for microscopy
Conventional histopathology
All of the conventional stains and the more sophisticated diagnostic techniques summarised in Tables 1.1 and 1.2 will be referred to in detail in subsequent chapters.
Figure 1.24 The primary cuts in a globe are important if all the features are to be displayed in a paraffin section. Upper left: a second cut in a globe is made with a large dermatome blade. The first cut reveals a small tumour adjacent to the optic nerve (right). The paraffin section passes through the centre of the nerve, the centre of the tumour, and the centre of the anterior segment. The clinical diagnosis was a retinoblastoma but pathologically the tumour was a small benign glial tumour (astrocytic hamartoma, see Chapter 11).
Figure 1.25 Oblique cuts are made in this globe to pass through a superonasal tumour in the ciliary body. The central pupil-optic nerve block is subsequently processed for paraffin histology and the calottes are retained for specialised investigation.
Table 1.1 A summary of the special stains used in routine diagnostic histopathology.
Figure 1.26 In macular dystrophy of the cornea, mucopolysaccharides accumulate in the endothelium, in the keratocytes, and in clumps beneath the epithelium. The best way to demonstrate the presence of mucopolysaccharides is to use the colloidal iron (left) or the Alcian blue (right) stains. NB: Mucopolysaccharides do not stain with H&E.
Figure 1.27 Alizarin red stain is used to identify calcium salts. This example shows calcified bone spicules within an osteosarcoma which arose in the orbit of a child who was previously treated by irradiation for a retinoblastoma. The inset shows the appearance of the tumour in an H&E section.
Figure 1.28 In an H&E section (see Figure 1.13) it is not possible to identify individual axons. The Bodian stain is one of the stains used for this purpose. Normal axons are so fine that they are not easily identified at low magnification (left). At high magnification, only segments of the sinuous axons are seen (right).
Figure 1.29 Examples of common pathogenic bacteria as seen in a Gram stain. (A) Gram positive staphylococci are dark blue in colour and occur in clumps. (B) Gram positive diplococci (Streptococcus pneumoniae) are smaller than staphylocci and possess a capsule. Both A and B can be the cause of postoperative endophthalmitis. (C) Gram negative diplocci (Neisseria gonorrhoeae) can be found in conjunctival swabs in adults with unresolving conjunctivitis and in neonates infected during birth (ophthalmia neonatorum). (D) Gram negative bacilli (Moraxella sp.) may be identified in a corneal scrape from a chronic ulcer.
Figure 1.30 Myelin sheaths are demonstrated by the Loyez stain. The inset is a transverse section through the optic nerve of a patient suffering from tobacco-alcohol amblyopia: the centre of the nerve is pale (axial demyelination). The high power view shows the transition from bundles containing sparse myelin sheaths on the left to more densely packed myelin sheaths on the right.
Figure 1.31 Masson trichrome stain is frequently used in corneal pathology. In this example, previous trauma has disrupted the Bowman’s layer and the adjacent stroma is replaced by an irregular fibrous scar tissue. The epithelium stains pink (and red cells are red!).
Figure 1.32 By comparison with an H&E stain (left), a PAS stain (right) is used to demonstrate basement membranes. In this example, there is a post-traumatic detachment of Descemet’s membrane which is incarcerated in the posterior corneal stroma. The stain also demonstrates a thickened epithelial basement membrane secondary to corneal oedema. Clefts in the stroma are artefactual and do not represent corneal oedema.
Figure 1.33 In a standard H&E section, the presence of iron in metallic foreign material in fibrous tissue cannot be determined. The Prussian blue stain demonstrates iron salts within the metallic particles and the widespread diffusion into the surrounding tissue.
Figure 1.34 The van Gieson stain is also a trichrome stain and is used to differentiate between muscle (yellow) and connective tissue (red). When combined with a stain for elastic tissue (black), fragmentation of the internal elastic lamina can be demonstrated in degenerative disease of the temporal artery.
Figure 1.35 The von Kossa stain reacts with phosphates to form a black precipitate. It is used to identify calcium phosphate complexes in tissues. In this example, the patient suffered from alkali burns which were intensively treated with phosphate buffered solutions. The extent of calcium phosphate deposition is not apparent in the H&E stained section (inset).
Other techniques
Immunohistochemistry
This technology has brought about a revolution in diagnostic and research pathology and has superseded electron microscopy. Precise identification of cells by type is achieved by applying a specific antibody to an antigenic epitope within the cell. The antibody is subsequently labelled with a chromogen which can be visualised by light or fluorescence microscopy. The number of specific antibodies which are commercially available is ever increasing (Table 1.2). For example, there are at least 25 antibodies to specifically identify T- and B-cell subsets and macrophages in benign and malignant states (Figure 1.37). Similarly, a battery of immunohistochemical reagents is applied to poorly differentiated tumours when the H&E appearance is inconclusive (for example in metastatic disease). In ophthalmic pathology, the standard brown chromogen (peroxidase-antiperoxidase: PAP) is of limited value in the study of pigmented tissues; as an alternative, red chromogens (alkaline phosphatase) are more helpful (Figure 1.37).
Electron microscopy/immunoelectron microscopy
The transmission electron microscope (TEM) focuses electrons to resolve cell structures at a high magnification (for example up to ×100 000). This was a valuable tool prior to immunohistochemistry and was mainly used to identify cell organelles (for example melanosomes) and viral particles. The principles applied in immunohistochemistry can also be applied at the ultrastructural level. Antibodies are labelled with very small gold particles that appear as black dots in micrographs. The technique can localise epitopes within cellular organelles and membranes – this is essentially a research tool.
The scanning electron microscope (SEM) focuses a raster of electrons on tissue surfaces. It is particularly useful for the study of the corneal endothelium.
Polymerase chain reaction (PCR)
Specific DNA or RNA sequences can characterise pathogenic organisms or cellular constituents. Only very small samples of tissue are required (for example aqueous or vitreous tap). This technique breaks down nuclear chromatin into sequences and a particular sequence (for example unique constituents of viruses or bacteria) under investigation is amplified to a level that allows rapid detection using gel electrophoresis.
In situhybridization
This technique also relies on the ability to cut segments of nuclear proteins with specific enzymes. The fragments are identified by immunohistochemical techniques in routine light microscopy. The advantage is that the precise location of the protein fragments can be visualised within the tissue.
Flow cytometry
This research tool is used to identify cells types within a population (for example lymphoid proliferations). A suspension of cells is labelled with fluorescent antibodies specific for antigen determinants on the surfaces of the different cell types. The flow cytometer differentiates and quantifies the different cell types (for example B and T cells).
Figure 1.36 An immunosuppressed patient who succumbed to tuberculosis. Acid-fast organisms stained with Ziehl–Neelsen were plentiful in a choroidal microabscess.
Figure 1.37 Immunohistochemistry is helpful in the diagnosis of benign and malignant conditions. In heavily pigmented tissues, it is necessary to bleach the melanin prior to application of a specific antibody labelled with a red chromogen. In this case, the angle in the trabecular meshwork is blocked by macrophages (CD68 positive) laden with melanin pigment derived from a necrotic melanoma of the ciliary body (melanomalytic glaucoma – left upper and lower). In the case of a malignant T-cell lymphoma, a brown chromogen (peroxidase-antiperoxidase: PAP) is used to label the anti-T-cell antibody (CD5, right). Note that not all the malignant cells express the epitope.
Table 1.2 A summary of the antibodies used in immunohistochemistry.
Antibody
Antigen
Diagnostic use
Anti-actin/myoglobin
Contractile filaments in smooth and striated muscle
Tumours derived from muscle, e.g. rhabdomyosarcoma (
Figure 1.38
)
Desmin
Intermediate filaments in smooth and striated muscle
Tumours derived from muscle, e.g. rhabdomyosarcoma (
Figure 1.38
)
Carcinoembryonic antigen (CEA)
High MW glycoprotein normally present in gastrointestinal epithelial cells
Metastatic adenocarcinomas to ocular tissues, adnexal skin tumours, sebaceous carcinoma
CD1–79+
Components of T and B cells, and macrophages
Many uses to identify cells in inflammatory infiltrates and in lymphomas (
Figure 1.37
)
Cytokeratin/CAM 5.2/AE1/AE3
Intermediate filaments in epithelial cells
Carcinomas derived from epidermis (
Figure 1.39
)
Epithelial membrane antigen (EMA)
Initially used for epithelial cells and carcinomas
Sebaceous carcinoma
Factor VIII-related antigen
Endothelial cell constituents
Neovascularisation and vascular tumours (
Figure 1.40
)
Glial fibrillar acidic protein (GFAP)
Glial cell constituents
Normal: glial cells and astrocytes (Müller cells) in retina
HMB45/melan-A
Intracytoplasmic antigen in melanocytes
Identifies cells of melanocytic origin (active naevi and malignantmelanomas –
Figure 1.41
)
S-100
Constituents of cells of neural crest lineage
Peripheral nerve tumours andmelanocytic tumours
Vimentin
Intermediate filaments Cells of mesenchymal origin
Differentiation of spindle cell tumours, e.g. leiomyoma
Figure 1.38 In poorly differentiated spindle cell tumours, an H&E section will not provide a specific diagnosis. In this example, an antibody against myoglobin demonstrates the protein within the cytoplasm of some of the tumour cells to confirm a diagnosis of embryonal rhabdomyosarcoma. Note that not all the tumour cells express the epitope.
Figure 1.39 In metastatic tumours, the primary site may not be evident on first presentation so that immunohistochemistry can be helpful in suggesting the origin. In this example of an orbital biopsy, CAM 5.2 labelled with peroxidase-antiperoxidase (PAP) demonstrates the characteristics of squamous epithelium. A primary bronchial carcinoma was the source. This specimen was negative for carcinoembryonic antigen which excluded a primary gastrointestinal carcinoma.
Table 1.3 A summary of routine media used in bacteriology.
Name of media
Appearance
Common pathogens cultured
Nutrient agar
Transparent pale yellow
Routine screening
Blood agar
Opaque blood red
Gram positive cocci and rods
Fungi
Chocolate agar
Opaque brown
Gram negative cocci
MacConkey’s agar
Transparent pink
Gram negative rods
Meat broth
Small bottle containing fragments of meat
Anaerobic rods
E. coli
on non- nutrient agar
Pale yellow with a surface layer
Acanthamoeba
previously a common cause of keratitis secondary to contact lens wear
Lowenstein–Jensen media
Opaque green media on a slope
Mycobacteria
Microbiology
The microbiology is here presented in context with the pathology commonly encountered in ophthalmic practice. It is important for ophthalmologists to be aware of basic microbiological techniques and the selection of media for an accurate diagnosis of infective conditions (Table 1.3). This text is not intended to be comprehensive, and for more specialised accounts the reader should consult the appropriate reference works.
Media
Organisms have specific growth requirements which are provided by the standard media (Table 1.3; Figures 1.42, 1.43). The majority of organisms will grow in normal atmosphere but some proliferate in a low oxygen environment (anaerobes).
Stains
Gram stains
The initial diagnosis of a bacterial or fungal infection can be made rapidly using a Gram stain on a smear taken from an infected site (Table 1.4; Figure 1.36).
Common organisms associated with chronic ophthalmic disease
Table 1.4 Common organisms associated with acute conjunctivitis, keratitis, and endophthalmitis.
Cocci
Staphylococcus
sp.
Streptococcus
sp.
Neisseria
sp.
Rods
Corynebacteria
sp.
Escherichia
sp.
Listeria
sp.
Klebsiella
sp.
Clostridium
sp.
Pseudomonas
sp.
Proprionibacterium
sp.: a facultative anaerobe and a common cause of late stage endophthalmitis following cataract surgery
Haemophilus
sp.
Moraxella
sp.
Common fungal pathogens
These grow on Sabauraud’s media.
Examination techniques
Postgraduate examinations will rely either on microscopic glass slides and the microscope or photomicrographs to test the knowledge of the candidates. In the former case, familiarity with a microscope is advantageous!
Microscopic glass slides
Viewing the slide with the naked eye can be invaluable in locating the essential pathology (for example intraocular or extraocular tumour) and the opportunity to measure dimensions. If the abnormality is not readily evident, a useful procedure is to examine a section of an eye from front to back, i.e. cornea, angles, iris, lens, vitreous, retina, optic nerve, and retroocular tissues.
Advice on the detection of specific pathological features is provided at the start of each chapter.
Micrographs
The use of photographic material is increasingly common. The illustrations will be of specific diagnostic pathological entities which will be similar to those presented in this text.
Figure 1.40 Factor VIII antibody is used to identify blood vessels in reactionary and neoplastic proliferations. This example is taken from an inflammatory mass in which there is striking angiogenesis in a dense inflammatory cell infiltrate (bacillary angiomatosis).
Figure 1.41 HMB45 is used for identification of melanocytic proliferations (benign and malignant). The extensive infiltration and nuclear pleomorphism indicate malignancy in this conjunctival amelanotic melanoma. Inflammatory cells within the tumour are the result of surface ulceration. The brown PAP label can be used in amelanotic melanomas but pigmented tumours require bleaching.
Figure 1.42 The standard agar plates used for isolation of pathogenic bacteria.
Figure 1.43 A positive culture on blood agar. The β-haemolytic streptococcus has haemolysed the red cells around each colony. A sample of the colony will be smeared onto a glass slide for Gram stain identification. The weak sensitivity to gentamicin is exhibited by the absence of colonies surrounding the antibiotic disc. This antibiotic is ineffective in the treatment of Gram positive cocci.
* The term “biopsy” refers to both partial removal (diagnostic) or total removal (excisional) of a suspicious mass. Fine needle biopsy is preferred in some centres to avoid unnecessary tissue damage.
Chapter 2
Eyelid and lacrimal sac
Eyelid
Diseases originating in the eyelid are commonly encountered by the clinician and thus a common source of material submitted to the pathologist. The role of the pathologist is to provide a definitive diagnosis, to ascertain the clearance of a malignant tumour so that the clinician can plan for additional treatment if necessary, and to predict recurrence. Pathology in the eyelid can vary from the most benign cysts to invasive carcinomas and the specimens can range in size from tiny fragments to exenteration specimens.
An appreciation of the normal anatomy is important in understanding the different pathological processes that can occur in the eyelid.
Normal eyelid
Anatomy
The anatomy of an eyelid can be simplified into four layers (Figure 2.1):
The anatomical grey line is located between the eyelashes and the Meibomian orifices and marks the anterior border of the tarsal plate. The mucocutaneous junction where the epithelium changes from epidermal to conjunctival type is present just behind the opening of the tarsal glands. The dermis contains blood vessels, lymphatics, and nerves, all of which can be a source of benign or malignant tumours.
In the upper lid, the levator palpebrae superioris inserts into the upper border of the tarsal plate by an aponeurosis which also contains the smooth fibres of Müller’s muscle (Figure 2.2).
How to examine an eyelid specimen
Macroscopic
A tumour will be excised close to the edge if the surgeon considers it benign. In the case of a suspected malignant tumour, the surgeon will remove surrounding normal tissue for clearance (up to 5 mm if possible). The specimens will be ellipsoid, rectangular, or pentagonal, and may extend to the full thickness of the lid. In the latter, it should be possible to identify the grey line and lashes (Figures 2.3, 2.23), and the tarsal plate in the cut surface (Figures 2.44, 2.54).
Microscopic
The specimen will be lined on one surface by epidermis which is covered with bright red (eosinophilic) keratin. The basal layer of the epidermis is undulating due to the presence of rete pegs. Small pilosebaceous follicles are present in the superficial dermis and these structures are often referred to as adnexal glands. These are the features of skin and they can only be found on the outer surface of the eyelid:
Epidermis
(
Figure 2.4
): the basal layer is cuboidal. The squamous cell layer consists of polygonal cells. The superficial cells are flattened and contain keratin granules. The horny or keratin layer is very thin in the lid. A thin space containing fine cytoplasmic processes (prickles) identifies the cells in the squamous layer. This is important as an identification feature for tumours derived from the squamous cell layer (refer to squamous carcinoma).
Melanocytes:
the cells with clear cytoplasm in the basal layer are melanocytes.
Dermis:
the fibrofatty tissue in the dermis contains elastic fibres. The arterioles, venules, lymphatics, and nerves are present throughout.
Muscle:
the striated muscle fibres of the orbicularis ocul possess nuclei which are located at the edge of the eel membrane. Smooth muscle nuclei are located centrally.
Tarsal plate:
dense collagenous tissue surrounds the elements of the Meibomian gland.
Adnexal structures:
the glands of Zeis are of sebaceous type and are located at the lid margin. The glands of Mol are of sudoriferous type (
Figure 2.1
). Accessory lacrimal glands are present at the upper edge of the tarsal plate (Wolfring) and in the fornix (Krause).
Tarsal conjunctiva:
see Chapter 3.
Infections
Bacterial
Bacterial infection occurs in the adnexal glandular structures of the eyelid producing a purulent reaction – hordeolum or stye. Organisms leading to granulomatous reactions (for example Mycobacterium leprae) are exceedingly rare.
Necrotising fasciitis
A synergistic infection of Streptococcus pyogenes (group A) and Staphylococcus aureus results in massive destruction of the eyelid and adjacent orbital tissue. Treatment requires extensive surgical clearance and high dose antibiotics. The histological appearance is that of a purulent exudate between necrotic tissue planes: clumps of bacteria are easily recognised.
Viral
Wart/verruca vulgaris
A wart appears as a solitary, slow growing, well circumscribed nodule lined on the surface by crumbly or spiky keratin. Treatment is usually by surgical excision or cryotherapy. Infection by the human papilloma virus (HPV) has been demonstrated using viral culture and immunohistochemistry.
Macroscopic examination reveals a hyperkeratotic nodule with surrounding skin. Histologically there is hyperplasia and folding of the epidermis due to viral stimulation. The major part of the tumour is formed by keratin. The diagnostic feature is the presence of cells with clear cytoplasm in the superficial layers (Figure 2.5).
Figure 2.1 This example shows the normal anatomical constituents of the eyelid. However, a small papilloma located at the eyelid margin has obstructed the ducts of the gland of Moll with secondary dilatation. The papilloma is also obscuring the anatomical grey line, which is located between the eyelashes and the ducts of the Meibomian gland; the grey line demarcates the beginning of the anterior border of the tarsal plate (superimposed black line).
Figure 2.2 In the Masson stain, muscle fibres are red and the fibrous tissue is green. The stain illustrates the location of the striated muscle fibres of the orbicularis oculi and levator palpebrae superioris. The smooth muscle bundles of Müller’s muscle are present within the aponeurosis. The lid fold is formed by an extension of the levator fibres into the skin – a feature of the Caucasian eyelid.
Figure 2.3 A wedge resection of a potentially malignant tumour which, on histology, was proven to be a neurofibroma. Note the clearance margin of normal tissue around the tumour. The inset shows the posterior aspect of the specimen.
Figure 2.4 Micrograph to show the layers of the normal epidermis. The inset shows the intercellular bridges in the squamous layer.
Figure 2.5 A wart is characterised by massive keratinisation (hyperkeratosis). The infected cells are vacuolated and contain clumps of viral particles (inclusion bodies) seen as small dense blue granules (inset). Normal skin is present at the edge of the wart.
Molluscum contagiosum
A common viral skin infection (pox virus) of childhood: it presents as umbilicated nodules that may be either solitary or multiple. The virus is spread by fomites in children or by direct contact in adults. Treatment may be conservative, although a large range of modalities are available: curettage, excision, cryotherapy and electrodessication.
Specimens may be derived from curettings or excision biopsies (Figure 2.6). The tumour may also have the appearance of a basal cell carcinoma and a wedge resection may be submitted.
The nodule is well circumscribed (Figure 2.6). The central area of the mass is filled with necrotic cells which explain the umbilication. The infected cells in the superficial squamous layer are hyperplastic. The presence of proliferating viral particles causes the cell contents to be replaced by pink granular material. This becomes basophilic when the dead cells are shed (Figure 2.7).
Spillage of viral particles can produce a follicular conjunctivitis.
Inflammation
Chalazion
This lipogranulomatous inflammation within the Meibomian gland is common in clinical practice.
Clinical presentation
The condition in the acute stage appears as a generalised painful swelling, more commonly in the lower lid. A chalazion may resolve spontaneously or progress to the chronic stage at which there is a tense ovoid mass within the tarsal plate. The size of such masses can vary from 1 mm to several times the thickness of the eyelid.
This condition may be recurrent and it is important in the differential diagnosis to consider the possibility of a sebaceous gland carcinoma.
Pathogenesis
Initially the ducts of the Meibomian gland are obstructed by inspissated secretion of fatty material. Retention of lipid material within the gland and spillage into the surrounding tissues induces a lipogranulomatous inflammatory reaction. This process may be recurrent, but histology of multiple recurrences is mandatory to exclude sebaceous gland carcinoma (see below).
Possible modes of treatment
Incision and curettage of the persistent cystic mass are usually successful.
Macroscopic
In the early stages the submitted material is friable and pale yellow in colour while in delayed excisions the fibrous residue is white and firm.
Microscopic
Most commonly the lipogranulomatous reaction is restricted to the tarsal plate but may track anteriorly or posteriorly to mimic a malignant tumour (Figure 2.8). The free fat spaces represent the release of lipid from necrotic Meibomian gland cells.
The cellular infiltrate is a classic giant cell granulomatous reaction with lipid globules in the cytoplasm of macrophages and also within multinucleate cells (Figure 2.9). Lymphocytes and plasma cells are abundant and recurrent inflammation proceeds to reactionary fibrosis.
Tumours
Tumour-like masses in the eyelid are commonly encountered in clinical practice and often a clinical diagnosis is unreliable. The spectrum extends from a benign cyst to a highly malignant metastasising tumour. The rate of growth is an important feature in distinguishing benign from malignant variants. The majority of tumours are derived from the epidermis and are UV or viral induced. However, tumours derived from any intrinsic eyelid tissue may be encountered (for example muscle, nerve, melanocytes, adnexal).
Benign
Cysts
Sudoriferous cysts
Sudoriferous cysts, or sweat gland cysts, are derived from the ducts of the glands of Moll which are lined by a cuboidal epithelium surrounded by a smooth muscle layer (myoepithelium). The cysts appear as solitary or multiple subcutaneous translucent swellings at the lid margin. Presumed fibrosis constricts the ducts and continuing secretion of the glands leads to the development of cysts, which are easily excised in toto.
The thin walled cysts contain clear or milky fluid with a smooth interior (Figure 2.10). The characteristic histolog-ical feature is a double layer of cells on the inner surface. The inner cells are cuboidal and the outer layer is of myoepithelial origin (Figure 2.11).
Epithelial inclusion cysts (epidermoid and dermoid)
Obstruction of the duct of a pilosebaceous follicle creates cysts which are lined by stratified squamous epithelium (epidermoid or retention cysts). A dermoid cyst is a second type of cyst also lined by stratified squamous epithelium and is formed when embryonic ectodermal rests are displaced into the lid or orbit.
The essential difference between the two types is the presence of pilosebaceous follicles in the wall of a dermoid cyst.
Epidermoid cysts These firm pale nodules on the eyelid skin surface often have a punctum and clinically are referred to as “sebaceous cysts”. Continued formation of keratin within the lumen is responsible for the foul-smelling granular yellow content. Rupture of an epidermoid cyst with the release of keratin during surgery can induce a giant cell granulomatous reaction. Dividing a fixed specimen demonstrates the yellow greasy and flaky content.
The cysts are lined by stratified squamous epithelium and the lumen contains keratin (Figures 2.12, 2.13).
Figure 2.6 A wedge excision was performed because the molluscum nodule was thought to be a basal cell carcinoma. The inset shows the cut surface of a different molluscum contagiosum excised with a margin of normal skin. Note the central umbilication. The central crater contains necrotic cells, shown in detail in Figure 2.7.
Figure 2.7 Viral particles proliferating within the cytoplasm of the squamous epithelial cells have a “smudgy” pink appearance. Cell death releases the vital particles from the surface of the crater.
Figure 2.8 Extension of a chalazion into the anterior part of the eyelid led to a clinical suspicion of a sebaceous gland carcinoma and the mass was widely excised.
Figure 2.9 A florid chalazion demonstrates all the features of a lipogranulomatous reaction with prominent fat spaces and multinucleate giant cells. In biopsies of recurrent chalazia, there is often more fibrosis than is shown here.
Figure 2.10 The absence of solid material within the cavity is highly suggestive of a cyst derived from a sweat gland duct (the contents wash out when the cyst is cut open).
Figure 2.11 The fibrous wall is lined internally by an inner cuboidal cell layer and an outer flat myoepithelial layer, thus retaining the features of a normal sweat gland duct.
Dermoid cysts These cysts occur in children and are usually solitary and present as slowly growing painless masses in the upper lid.
The pathogenesis is of interest. In embryonic life, the face is formed by processes (frontal, nasal, maxillary) which extend forwards and fuse. Incarceration of ectoderm between the frontal and maxillary processes results in the formation of cysts. The incarcerated ectoderm also forms pilosebaceous follicles so that a dermoid cyst contains hairs. Rupture (spontaneous or traumatic) releases highly irritant lipid and keratin into the surrounding tissues resulting in a chronic granulomatous reaction.
Treatment is by surgical excision although care must be taken to avoid rupture and spillage of contents.
An excised specimen appears as a smooth intact ovoid mass with a thin wall containing pultaceous yellow white material and obvious hairs (Figure 2.14).
Microscopy shows the lumen to contain keratin and hair. The walls are similar in appearance to an epidermoid cyst but include hair follicles and sebaceous follicles (pilosebaceous follicles – Figure 2.15).
Xanthelasmas
Xanthelasmas are common superficial skin nodules that increase in frequency in the middle-aged and the elderly. Associated hyperlipidaemia should be suspected although more than 50% of patients are normolipaemic. The nodules are bilateral and have a pale yellow appearance (Figure 2.16). Treatment is usually conservative as the nodules often recur but for cosmesis, surgical excision, laser ablation, or topical treatments may be requested.
Microscopic examination reveals large clusters of ovoid cells with eccentric nuclei in the dermis (Figure 2.17). The cytoplasm of the cells is almost translucent and appears as pale granular material (“foamy cytoplasm”) which stains positively for fat in a frozen section.
Naevi
The term naevus is most commonly applied to a tumour formed by melanocytic proliferation. This abnormality is present at birth, but with the onset of puberty, these tumours can grow in size and pigmentation. There are three main types:
This classification is based on the anatomical location of the melanocytic proliferation. In embryonic life melanocytes migrate from the neural crest to reach the basal layer of the epidermis, i.e. at the junction between the epidermis and the dermis, hence the term junctional naevus. Arrested migration of melanocytes explains the proliferation of these cells in the dermis, i.e. intradermal naevus. Most commonly however, the two types coexist to form a compound naevus. In all forms of naevi, the immunohistochemical reactions are positive with melan-A, HMB45, and S100.
Junctional naevus
Junctional naevi appear as flat areas of increased pigmentation (black or brown) which may vary in size. The melanocytic proliferation is confined to the epidermis. Clinically, an increase in size of a flat pigmented patch with nodule formation is strongly suggestive of malignant transformation to a melanoma.
Histologically, in a junctional naevus, the melanocytic proliferation is confined to the lower layers of the epidermis and usually takes the form of small clusters of cells. It is important to appreciate that melanocytes are clear cells and pigmentation is the result of transfer of pre-melanosomes from the parent melanocytes to the adjacent epidermal cells (Figure 2.18).
Intradermal naevus
Clusters of heavily pigmented spindle cells are present in the dermis. The potential for malignant transformation is far less than for junctional naevi.
Compound naevus
The melanocytes are present in clusters within the epidermis and in the dermis, where the cells in the deeper clusters become smaller and more mature (Figure 2.19).
Benign tumours of the epidermis
The distinction between basal cell and squamous cell tumours is based on the degree of cellular differentiation and maturation. Basal cell papillomas contain cells which resemble the cells of the basal layer of the epidermis throughout the tumour. In squamous cell papillomas there is differentiation from basal cells to prickle cells, granular cells, and keratin.
Basal cell papilloma (BCP)/seborrhoeic keratosis
This common slowly growing tumour presents as a well circumscribed nodule with cauliflower-like appearance. It may be pigmented. The aetiology of this tumour is unknown. The treatment may be conservative, although the tumour is usually excised for cosmetic reasons or if there is a suspicion of malignancy.
The tumour will have the appearance of a closely excised nodular mass which projects from the skin surface (Figure 2.20). The surface is sometimes lined by flaky keratin (which is why the obsolete term “seborrhoeic keratosis” was used).
The majority of cells are uniform and basophilic (Figures 2.21, 2.22). The abnormal tumour cell surface predisposes to infection and secondary inflammation is seen as a lymphocytic infiltrate in the base of the tumour. The key histological feature is the lack of maturation from basal to squamous cell type (see Figure 2.4).
Squamous cell papilloma (SCP)
Hyperkeratotic tumours projecting from the surface of the lid are relatively common. The tumour may be of a viral aetiology or may be a benign proliferation of epidermal cells. The clinical presentation is in the form of a slowly growing, well circumscribed warty lesion. The treatment outlined in BCPs applies to SCPs.
The appearance in an excised specimen is similar to a basal cell papilloma except that the surface is heavily keratinised (Figure 2.23). Keratinisation may take the form of finger-like processes (filiform).
Figure 2.12 Low power view of a complete epidermoid cyst excised with overlying skin. The cyst contains keratin. Distortion of the adjacent duct of a sweat gland has given rise to a concurrent sudoriferous cyst.
Figure 2.13 In an epidermoid cyst, the epidermis lining the wall becomes compressed by the compacted keratin. Compare the thickness with that of the overlying epidermis which shows secondary degenerative vacuolar changes.
Figure 2.14 The diagnosis of a dermoid cyst is made when the lumen contains hair in addition to keratin and sebum (fatty materials secreted by sebaceous follicles).
Figure 2.15 The hallmark histological feature of a dermoid cyst is the presence of pilosebaceous follicles (outlined in red) in the wall, which is lined by stratified squamous epithelium.
Figure 2.16 In this patient, the upper and lower eyelids on both sides contain yellow plaques (xanthelasmas).
Figure 2.17 The plaque in xanthelasma is formed by well circumscribed masses of foamy cells (lower left). The cells have well defined cytoplasmic membranes and faintly staining granular material in the cytoplasm: this displaces the small nuclei (upper). The lipid within the cells stains positively with Oil red O (lower right).
Figure 2.18 In an active junctional naevus, the melanocytes (clear cells) transfer melanin into the squamous cells and the melanin-containing cells are carried to the surface. The difference between melanocytes with clear cytoplasm and squamous cells containing melanosomes is shown in the inset.
Figure 2.19 A compound naevus is characterised by proliferating melanocytes in the basal epidermis and clumps of “naevus cells” in the dermis. The clusters of naevus cells show varying degrees of maturation and melanin content.
Figure 2.20 A basal cell papilloma is easily identified both clinically and pathologically. The appearance is that of a cauliflower at low magnification.
Figure 2.21 This basal cell papilloma was excised with the underlying eyelid because there was a suspicion of malignancy. The tumour is growing away from the underlying dermis and is therefore more likely to be benign (“away from the patient”). The superimposed black line indicates the margins of the tumour. The basophilic appearance of the tumour is due to the presence of cells which retain the staining characteristics of the epidermal basal layer.
Figure 2.22 A basal cell papilloma is formed by cells of uniform size and shape. Intercellular spaces or bridges are not prominent.
The tumour cells show marked differentiation from basal to squamous with the formation of a granular layer and a thick keratin layer (Figure 2.24). Intercellular spaces are prominent and contain cytoplasmic bridges. Keratin formation can occur within the proliferating cells (dyskeratosis) (Figure 2.25). Inflammatory changes in the adjacent dermis can occur and are due to bacterial proliferation in the keratin.
Keratoacanthoma
This is an uncommon skin tumour with a characteristic presentation of rapid growth and hyperkeratosis. Rapid growth within 3 months produces an ovoid tumour mass with a central keratin core. It can mimic a squamous cell carcinoma both clinically and pathologically. The tumour can reach a large size and occupy most of the anterior surface of an eyelid. Spontaneous resolution can occur but surgical excision is effective.
The excision is usually wide and the specimen contains a well defined umbilicated nodule with a central keratinised core and a smooth rounded peripheral surface (Figure 2.26).
If on histology the tumour is well demarcated, of squamous type, with a flat base, and hyperkeratosis in the central part, the diagnosis is keratoacanthoma (Figure 2.27). The cellular component is relatively small and confined to a layer at the base of the tumour. Here, there are islands of well differentiated squamous cells (Figure 2.28). Normal epidermis at the edge of the tumour favours the diagnosis of keratoacanthoma because in squamous carcinomas the adjacent epidermis shows the changes of premalignancy (see below).
Premalignant changes
Actinic/solar/senile keratosis
Overexposure to sunlight is followed by precancerous changes in the epidermis. Solar keratosis is more common in Caucasians, especially those with an outdoor lifestyle. This condition can progress to squamous cell carcinoma.
Clinically, solar keratosis appears as a flat, scaly plaque of variable size (15–20 mm) and irregular periphery.
The pathogenesis is well understood – UV light to the epidermis damages the DNA control of cell proliferation.
The neoplastic proliferation is confined to sectors of the epidermis, and here there are areas where the basal cells possess the features of malignant cells (Figures 2.29, 2.30). A secondary effect of rapid cell division is that nuclei are carried through to the keratin layer (parakeratosis).
UV radiation to the dermis is associated with changes in the elastin which becomes clumped (solar elastosis).
