ABD Dermatopathology key terms

A pattern in which inflammatory cells, mainly lymphocytes, obscure the dermoepidermal junction and damage basal keratinocytes, producing vacuolar change or lichenoid banding. It is seen in lupus, lichen planus, and drug eruptions.

Intercellular edema within the epidermis that widens spaces between keratinocytes and stretches desmosomes, visible as pale separations and sometimes intraepidermal vesicles. It characterizes eczematous dermatitis.

Regular elongation of rete ridges with thinning above dermal papillae, usually accompanied by parakeratosis and diminished granular layer. It is the architectural hallmark of psoriasis and can occur in chronic spongiotic dermatitis.

A small collection of neutrophils within the stratum corneum, often near the top of a parakeratotic scale in psoriasis. It differs from spongiform pustules, which lie within the spinous layer.

An apoptotic basal keratinocyte that appears as a round, eosinophilic, anucleate body at the dermoepidermal junction or in the papillary dermis. It is common in lichenoid interface dermatitis.

A dense band of lymphocytes hugging the dermoepidermal junction and often obscuring it, with damage to basal cells. It produces the interface pattern of lichen planus and lichenoid drug reactions.

Loss of cohesion between keratinocytes caused by breakdown of desmosomal attachments, creating clefts or blisters within the epidermis. It is the primary event in pemphigus vulgaris and Hailey-Hailey disease.

A fluid-filled separation occurring beneath the epidermis, so the blister roof consists of full-thickness epidermis. It occurs in bullous pemphigoid, dermatitis herpetiformis, and epidermolysis bullosa acquisita.

Small-vessel inflammation with fibrinoid necrosis of vessel walls and nuclear dust from fragmented neutrophils. It presents as palpable purpura and is confirmed by detecting immune complexes on direct immunofluorescence.

A compact aggregate of epithelioid histiocytes, often with multinucleated giant cells and a rim of lymphocytes. It represents a chronic inflammatory response seen in sarcoidosis, infection, and foreign-body reactions.

Retention of nuclei in the stratum corneum, reflecting incomplete keratinocyte maturation. It appears as dark nuclei within the compact horn layer and is common in psoriasis, lichen simplex chronicus, and squamous neoplasms.

The vertical distance in millimeters from the granular layer of the epidermis to the deepest invasive melanoma cell, measured on a perpendicular section. It is the strongest predictor of melanoma outcome.

An anatomic staging system that records how deep melanoma invades through skin layers, from epidermis to subcutaneous fat. It is less reproducible than Breslow thickness and now mainly historical.

The early pattern of melanoma growth that spreads horizontally within the epidermis and superficial dermis without forming a tumorigenic nodule. It carries a low risk of metastasis.

A melanoma growth pattern in which tumor cells form a dermal nodule and acquire the capacity for metastasis. It is recognized by dermal mitoses and nests larger than those at the junction.

Melanoma in situ on chronically sun-damaged skin, showing a lentiginous proliferation of atypical melanocytes along the dermoepidermal junction. It often occurs on the face and may progress to lentigo maligna melanoma.

A melanocytic nevus with architectural and cytologic atypia, including junctional nesting, lentiginous spread, and nuclear enlargement. It is a marker of increased melanoma risk but is not itself malignant.

A sun-induced intraepidermal proliferation of atypical keratinocytes with parakeratosis and damage to the dermoepidermal junction. It is a precursor to squamous cell carcinoma.

Full-thickness atypia of the epidermis with loss of maturation and numerous mitoses, confined by an intact basement membrane. It is also called Bowen disease when presenting as a persistent plaque.

A malignant epithelial tumor composed of basaloid cells forming nests with peripheral palisading and stromal retraction. It grows locally and rarely metastasizes.

A benign epidermal proliferation of uniform basaloid cells with horn cysts and hyperkeratosis. It is common in older adults and has no malignant potential.

A rapidly growing epithelial tumor with a central keratin-filled crater and glassy eosinophilic keratinocytes. Many regard it as a variant of squamous cell carcinoma rather than a distinct benign entity.

A benign adnexal tumor showing islands of basaloid cells that abruptly become eosinophilic shadow cells, often with calcification. It usually presents as a firm nodule in children or young adults.

An intraepidermal adenocarcinoma, usually of apocrine origin, showing large pale cells with mucin scattered among keratinocytes. It may be primary or secondary to an underlying visceral carcinoma.

The most common cutaneous T-cell lymphoma, characterized by epidermotropic atypical lymphocytes with cerebriform nuclei forming Pautrier microabscesses. It evolves from patches to plaques and tumors.

A cluster of atypical lymphocytes within the epidermis, often surrounded by a clear halo, seen in mycosis fungoides. It reflects epidermotropism of neoplastic T cells.

A proliferation of Langerhans-type histiocytes with grooved nuclei and eosinophilic cytoplasm, often accompanied by eosinophils. It is confirmed by CD1a and langerin positivity.

A disease of increased mast cells in skin or other organs, showing round to spindle cells with metachromatic granules. Cutaneous lesions include urticaria pigmentosa and mastocytoma.

A benign fibrous histiocytoma of the dermis composed of spindle cells, collagen trapping, and a peripheral inflammatory rim. It usually presents as a firm brown nodule on the leg.

A locally aggressive spindle-cell tumor of the dermis and subcutis with a storiform pattern and uniform CD34 positivity. It infiltrates fat in a honeycomb pattern and rarely metastasizes.

A vascular tumor caused by human herpesvirus 8, showing slit-like spaces, spindle cells, and hyaline globules. It is confirmed by HHV8 immunohistochemistry.

A malignant vascular tumor of irregular anastomosing channels lined by atypical endothelial cells. It often arises on sun-damaged scalp of elderly patients or after radiation.

A benign peripheral nerve sheath tumor composed of bland spindle cells, wavy collagen, and mast cells. It may be sporadic or part of neurofibromatosis type 1.

A technique using fluorescent antibodies on frozen skin to detect in vivo-bound immunoglobulin and complement along the basement membrane or in vessel walls. It is essential for diagnosing autoimmune blistering diseases and vasculitis.

A method using antibodies tagged with a chromogen to detect specific proteins in tissue sections, helping classify tumors by lineage. Examples include S100 and SOX10 for melanocytic lesions and CD3 for T cells.

Fluorescence in situ hybridization uses fluorescent DNA probes to detect gene amplifications, deletions, or translocations in tumor cells. It supports melanoma diagnosis and sarcoma classification.