Building Blocks of Dermatopathology
BAD DermpathPRO Learning Hub: Glossary of Terms
Module-1 : Skin Basics
Glossary of dermatopathological terms
Acanthosis is thickening of the epidermis and elongation of the rete ridges due to thickening of the spinous layer +/- enlargement of rete pegs. Typical examples include chronic eczematous reactions.
Anagen is the growth phase of the hair follicle.
Apoptotic cell has a dark, condensed nucleic chromatin (pyknosis), margination of chromatin under the nuclear membrane, followed by fragmentation of the nucleus (karyorrhexis). Apoptosis of basal layer keratinocytes are called ‘Civatte bodies’ (in lichen planus and other lichenoid type reactions) or ‘sunburn cells’ (in acute sunburn).
Epidermal atrophy is characterised by the reduction in the number of epidermal cells leading to leading to reduced thickness of the epidermis.
The basement membrane is a thin, non-cellular layer between the epidermis and dermis
Bulla(e) large fluid-filled blister(s) arising from separation within the epidermis (intraepidermal blister) or below the basement membrane (subepidermal blister). Small blisters are called vesicles.
Catagen is the involutional phase of the hair cycle. There is apoptosis of the cells of the lower part of the hair follicle.
Crust is the dry concretion of parakeratotic keratinocytes, serum and inflammatory cells within the stratum corneum.
A cyst is a thin walled closed capsule or sac like structure, filled with fluid, solid or semisolid material. Cysts have an epithelial lining. A pseudocyst is a similar lesion but lacks a epithelial lining.
Dermal oedema is the process by which fluid leaks out from blood and lymphatic channels into the surrounding dermis leading to separation of the collagen bundles.
The dermis is the fibrous layer of the skin immediately below the epidermis. This layer contains predominantly collagen but also elastin fibres which contribute to the pliability of the skin . Also contains blood vessels, nerves, adnexal structures like hair follicles, eccrine (sweat) glands, sebaceous glands and other structures. The dermis has 2 distinct regions:
- the uppermost papillary dermis containing fine collagen fibrils
- the thicker, deeper layer which as coarse collagen bundles.
Dyskeratosis is the presence of premature or altered/ abnormal keratinocyte differentiation. Histologically the abnormal keratinocytes have increase/accumulation of keratin filaments leading to a hypereosinophilic cytoplasm (pinker on H&E) and shrunken hyperchromatic nuclei (ie, they are small and dark-staining).
Elastosis is a histological process of increasing the amount of elastic fibres in the skin. Elastic fibres are responsible for the pliability of the skin, contributing to dexterity of the fingers.
The epidermis is the top most layer of the skin. It consists of 4 layers, from deepest to most superficial:
- Stratum basale (basal layer)
- Stratum spinosum (spiny layer)
- Stratum granulosum (granular layer)
- Stratum corneum (horny layer)
- The stratum basale contains the regenerative cells of the epidermis and is sometimes called the ‘Malphigian layer’.
Epidermotropism is the abnormal migration of atypical lymphocytes into the epidermis of the skin. It is the hall mark of early stage cutaneous T-cell lymphoma (mycosis fungoides). The term is sometimes used to refer to invasion of malignant cells into the epidermis.
Exocytosis is the random migration of inflammatory cells, such as lymphocytes, neutrophils, basophils, into the epidermis. It is induced by cytokine release in inflammatory processes of the epidermis.
Fibrosis is the process by which the body lays down collagen as part of the healing process.
A granuloma is a chronic inflammatory pattern characterised by the localised aggregation of histiocytes with or without other inflammatory cells (eg plasma cells, eosinophils, neutrophils), with or without necrosis, with or without vasculitis, with or without calcification, with or without foreign bodies. May be due to infection or chronic inflammatory disease or reactions to foreign material.
Haemosiderin deposition is the process by which iron released from degraded extravasated red blood cells are deposited in the dermis on the skin leaving dark brown or rusty-orange marks. Commonly seen on lower legs following any inflammatory process eg capillaritis, venous stasis eczema.
Hypergranulosis is an increase in the intracellular granules of keratinocytes within the of granular layer. Commonly seen in viral warts.
Hyperkeratosis is thickening of the epidermis due to thickening of the stratum corneum with normal epidermal differentiation. In normal skin, there is a loose ‘basket weave’ appearance. In hyperkeratosis there is usually thickening and lamination or compaction of the stratum corneum.
Hyalinisation of collagen
Hyalinisation (or homogenisation) of collagen refers to degeneration of the collagen of the superficial dermis giving a smooth, granular layer. Commonly seen in lichen sclerosus.
Inflammation is the complex coordinated multi-step process by which the body attempts to remove or contain foreign material/organisms from the body and/or repair any injury sustained by tissues. The inflammatory process may be acute or chronic in nature, reflecting the time frame over which this takes place.
Interface dermatitis generally refers to a mild lichenoid-like reaction in the interface between epidermis and dermis. There is sparse scattered lymphocytic infiltration centred around the basal layer +/- vacuolar degeneration of the basal layer. Unlike a classical lichenoid reaction, the inflammatory infiltrate does not obscure the basement membrane.
Keratinisation is the process by which epidermal cells (keratinocytes) undergo maturation and differentiation, as the cell migrates from the basal layer to the stratum corneum. There is gradual loss of nuclear function (with eventual loss of nuclei in the stratum corneum), loss of cytolasmic structures and progressive formation of keratin filaments to form the cornified envelope.
Lichenoid reaction is a dense lymphocytic inflammatory infiltrate centred on the basal layer of the epidermis and upper dermis. The basement membrane is obscured and there is often vaculolar degeneration or Civatte bodies in the basal layer of the epidermis. The lichenoid pattern of inflammation is seen in lichen planus, drug reactions, cutaneous lupus erythematosus, lichen nitidus, erythema multiforme.
Neoplasm is a proliferation and accumulation of an abnormal cell(s) due to mutation(s) or factors which promote cellular growth and/or loss of inhibition of cell death and/or loss of ability of immune function — which allow identification and destruction of abnormal cells. The cells of a neoplasm are usually derived from the same cell line (a clonal proliferation) but may come from unaffected normal skin. Neoplasms may be benign (ie, they have no potential to spread to distant sites via the blood or lymphatic system) or malignant (ie, they have the potential to spread to distant sites on the body, also called a metastasis. Neoplasms may grow locally with no propensity to spread into the blood or lymphatic systems.
Oedema is an accumulation of plasma into the tissues leading to sweeping of the layer affected. Oedema may occur in the dermal interstitium (dermal oedema), due to reduced hydrostatic pressure in blood vessels, reduced albumin or secondary to inflammation or within the epidermal layer (spongiosis).
Orthokeratosis is the normal ‘basket weave’ appearance of the stratum corneum seen in normal skin. In acral skin (palms or soles), the stratum corneum exhibits thickening and compaction (“compact orthokeratosis”).
Pagetoid spread refers to the proliferation of cells within the epidermis in a random pattern of distribution giving a ‘buckshot’ scattered appearance. This appearance can be seen in malignant melanoma, extramammary Paget disease and occasionally in squamous cell carcinoma in situ.
The panniculus is the deepest layer of the skin and is predominantly composed of fat cells.
Papillomatosis is the hyperkeratotic and undulating appearance of the epidermis above the surrounding normal skin. Papillomatosis is associated with hyperproliferation of keratinocytes. Papillomatosis may be seen in viral warts, seborrhoeic keratoses, confluent and reticulate papillomatosis.
Parakeratosis is the abnormal retention of keratinocyte nuclei within the stratum corneum. The presence of parakeratosis indicates that the epidermis has been inflamed or injured.
Peri-adnexal inflammation is the presence of lymphohistiocytic inflammation around pilosebaceous and adnexal structures, eg hair follicles, sebaceous glands, eccrine glands.
Perivascular lymphocytic infiltrate
Perivascular lymphocytic infiltrate refers to inflammation centred around the small vessels in the skin. It is usually a lymphocytic or lymphohistiocytic inflammatory infiltrate, without evidence of vascular damage/ death (vasculitis).
Pigment incontinence is the deposition of melanin in upper dermis due to inflammation affecting the melanocytes within the basal layer. Pigment incontinence is most commonly seen following, or in association with, established lichenoid reactions.
A pustule is a collection of neutrophils in the epidermis or within a hair follicle.
Scale crust is localised areas of stratum corneum, where there are parakeratosis, inflammatory cells and serum that arise from inflammatory skin disease, eg infected eczematous skin conditions.
Solar elastosis is degenerative basophilic change of elastin and collagen fibres of the dermis in chronically sun damaged skin.
Spongiosis is the widening of the intercellular spaces between keratinocytes due to intercellular oedema that occurs when the epidermis is inflamed. Spongiosis is classically seen in association with eosinophilic infiltrates in the skin (eosinophilic spongiosis) but can also be seen in association with neutrophils (neutrophilic spongiosis).
Telogen is the resting phase of the hair follicle and lasts months. Telogen occurs after catagen and precedes anagen.
Tumour is an abnormal proliferation of cells and normally implies the presence of a benign or malignant neoplasm. This term is also used by clinicians to describe a macroscopic swelling or a lump on the skin.
A vesicle is a small fluid-filled blister within or below the epidermis.