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Metastatic tumors and simulators

It is important to distinguish cutaneous metastases, particularly metastatic adenocarcinoma, from primary adnexal tumors of the skin. Adenocarcinoma metastatic to the skin is commonly of breast or lung origin. Focal areas of glandular differentiation may be highlighted with a mucicarmine stain. Most metastatic tumors are situated in the dermis, although occasionally epidermotropic metastases form intraepidermal nests. Pearl Positivity with both cytokeratin 5/6 and p63 or p40…

B-cell lymphoma and lymphocytic leukemia

Cutaneous B-cell lymphoproliferative disorders The primary cutaneous B-cell lymphomas share some histologic features with their nodal counterparts, but in many cases represent distinct clinicopathologic entities with significant clinical, immunophenotypic, molecular, and prognostic differences from their extracutaneous counterparts. In general, primary cutaneous B-cell lymphomas have a better prognosis than their nodal-based counterparts, and treatment strategies for them may be different. The classification system used in this chapter…

Cutaneous T-cell lymphoma, NK-cell lymphoma, and myeloid leukemia

Cutaneous T-cell lymphoma and NK-cell lymphoma Mycosis fungoides Patch stage Key Features Lymphocytes “line up” along the dermal–epidermal junction (simulates vacuolar interface dermatitis, with a “lymphocyte in every hole”) Large dark lymphocytes with irregular nuclear contours and perinuclear haloes (“lump of coal on a pillow”) Pautrier microabscesses (intraepidermal clusters of atypical lymphocytes, larger than the benign recruited dermal lymphocytes) Mild bandlike infiltrate in superficial dermis Sclerosis…

Vascular tumors

Angiokeratoma Key Features Hyperkeratosis Acanthosis Ectatic, thin-walled vessels in contact with the epidermis Resembles a “bloody seborrheic keratosis” Lymphangioma Key Features “Frog spawn” clinically Similar to angiokeratoma with lymph in vessels, but few erythrocytes D2-40+ Nevus flammeus Key Features Dilated capillary-sized vessels Angioma serpiginosum Key Features Dilated tortuous capillaries in dermal papillae and the upper dermis Vessels lack alkaline phosphatase activity Angioma serpiginosum presents as a…

Neural tumors

Neurofibroma Key Features Loose arrangement with pale myxoid stroma Haphazard spindle cells with small wavy or S-shaped nuclei Mast cells are numerous Neurofibromas may occur as solitary lesions. Multiple widespread neurofibromas characterize neurofibromatosis (von Recklinghausen disease) in which they are seen in association with café-au-lait macules, axillary freckling, and pigmented hamartomas of the iris (Lisch nodules). Diffuse neurofibroma Key Features At scanning magnification, diffuse replacement of…

Tumors of fat, muscle, cartilage, and bone

Fat Lipoma Key Features Well-circumscribed tumor with a thin capsule Mature lipocytes Inconspicuous septae Lipomas typically present as asymptomatic, mobile, soft nodules in the deep soft tissue or subcutis. Histologically, they are thinly encapsulated tumors composed of sheets of mature adipocytes that are indistinguishable from the fat cells in the subcutaneous tissue. Each adipocyte has a single vacuole and an eccentric nucleus. The thin fibrous septa,…

Fibrous tumors

Dermatofibroma Key Features Interstitial spindle cell proliferation Collagen trapping Overlying platelike acanthosis Follicular induction common Ringed lipidized siderophages or perivascular collagen donuts may be present Factor XIIIa+ CD34− All dermatofibromas demonstrate a proliferation of fibrohistiocytic cells. A curlicue pattern is typical. Another typical feature is that some areas of the tumor will be densely cellular, whereas others are sclerotic and hypocellular. The overlying epidermis is acanthotic…

Viral infections, helminths, and arthropods

Viral infections Warts Verruca vulgaris Key Features Exophytic Papillomatosis Compact eosinophilic hyperkeratosis Coarse hypergranulosis in dells Vertical tiers of round parakeratosis common above peaks Blood and serum common above peaks Koilocytes variable The biopsy will demonstrate a compact stratum corneum, coarse hypergranulosis, and papillomatosis. The papillomatosis often curves inward. Vascular ectasia is common. Koilocytes (vacuolated cells with hyperchromatic shriveled nuclei) may be present. Red cytoplasmic inclusions…

Fungal infections

Tinea Key Feature Nonpigmented hyphae in stratum corneum The stratum corneum may be basket-weave or compact and eosinophilic. It may contain parakeratosis or clusters of neutrophils. Pearl The stratum corneum in tinea is commonly basket-weave, but a narrow zone of compact eosinophilic stratum corneum is present just above the granular layer. Round hyphae cut on end are often visible in this compact layer. Pearl If it…

Bacterial, spirochete, and protozoan infections

Bacterial diseases Impetigo Key Features Neutrophilic crust Chains or clusters of cocci Impetigo recruits neutrophils to the stratum corneum. Organisms are commonly visible in hematoxylin and eosin sections. Gram stain and culture may be required. Differential Diagnosis Collections of neutrophils within the stratum corneum: psoriasis, tinea, impetigo, Candida, seborrheic dermatitis, syphilis (PTICSS) Bullous impetigo Key Features Subcorneal bulla Acantholysis in granular layer Differential Diagnosis Staphylococcal scalded-skin…

Panniculitis

The inflammatory infiltrate in septal panniculitis spills over into the lobule. The inflammation in lobular panniculitis often involves the septum; therefore septal and lobular panniculitis are best differentiated by the architecture of the lobule. In septal panniculitis, the lobule is intact; lipocytes are similar in size and shape, and the scan appearance resembles a bowl of toasted oat cereal. In lobular panniculitis, the lobule is necrotic;…

Disorders of skin appendages

Noninflammatory alopecia Transverse (horizontal) sections are generally best for evaluation of noninflammatory alopecia. Vertical sections may be used if serial ribbons of sections are cut from the block. A combination of vertical and transverse sections is always acceptable. Pattern alopecia (androgenetic balding) Key Features Miniaturization of follicular units Variability in diameter of follicles (anisotrichosis) In vertical sections, hairs extend to variable depths in proportion to their…

Metabolic disorders

Mucinoses The mucinoses are a group of disorders characterized by mucin deposition in the dermis. The mucin is typically non–sulfated acid mucopolysaccharide (hyaluronic acid) that appears as wispy, faint blue threads on routine sections. It can be better appreciated with colloidal iron, Alcian blue, and toluidine blue staining. Scleredema (of Buschke) Key Features Thickened dermis Widened spaces with mucin between normal collagen bundles The mucin is…

Alterations in collagen and elastin

Lichen sclerosus (et atrophicus) Key Features Red (compact stratum corneum) White (papillary dermal pallor) Blue (lymphoid band beneath zone of pallor) Synonymous with balanitis xerotica obliterans on the glans penis Lichen sclerosus may involve skin or mucosa. Follicular plugging is common, and the plugs may resemble comedones clinically. The epidermis is commonly atrophic, and the rete pattern is effaced; however, scratching may produce pseudoepitheliomatous hyperplasia, especially…

Genodermatoses

Pseudoxanthoma elasticum Key Features Curled and frayed, calcified elastic fibers in the reticular dermis (pink or blue squiggles) Elastic tissue (Verhoeff–Van Gieson) and calcium (Von Kossa) stains highlight the distorted elastic fibers Pseudoxanthoma elasticum is an autosomal-recessive and, less commonly, autosomal-dominant disorder due to a mutation in the ABCC6 transporter gene. It results in calcification of the elastic fibers of the skin, eyes, and artery walls.…

Inflammatory vascular diseases

Leukocytoclastic vasculitis (LCV) Key Features Perivascular infiltrate with neutrophils Karyorrhexis (nuclear dust, leukocytoclasis) Expansion of the vessel wall Fibrin deposition within the vessel wall Erythrocyte extravasation Clinical lesions of leukocytoclastic vasculitis are purpuric and often palpable. Vasculitis involving arterioles commonly produces livedo reticularis or stellate infarcts. Classification of vasculitis Vasculitis is classified by the type of inflammatory infiltrate, type of vessel involved, the presence or absence…

Granulomatous and histiocytic diseases

Granulomas are discrete collections of histiocytes with or without multinucleate giant cells. Histiocytes are bone marrow derived or mesenchymal. In granulomas, their cytoplasmic membranes touch with no intervening connective tissue. Infectious etiologies, especially fungal and mycobacterial, should be excluded with special stains in any granulomatous process without obvious etiology. Examination under polarized light is required to exclude birefringent foreign material. Granulomas can be categorized into sarcoidal,…

Blistering diseases

Subcorneal vesiculobullous disorders Pemphigus foliaceus Key Features Subcorneal split Acantholysis (loss of attachments between keratinocytes) Dyskeratosis may occur within the granular layer Direct immunofluorescence demonstrates “netlike” deposition of immunoglobulin (Ig) G and C3 between keratinocytes in upper epidermis Pemphigus foliaceus is a subcorneal vesiculobullous disorder caused by autoantibodies directed at an intercellular keratinocyte adhesion protein: desmoglein 1 (160 kD). The disease usually presents with superficial crusted erosions…

Psoriasiform and spongiotic dermatitis

Psoriasis Key Features Neutrophils above parakeratosis in stratum corneum Little to no serum in stratum corneum Alternating neutrophils and parakeratosis in the stratum corneum (sandwich sign) Neutrophilic spongiform pustules Little spongiosis in adjacent epidermis Tortuous blood vessels in dermal papillae The appearance of psoriasis depends on the stage of the lesion and type of lesion. Early guttate lesions demonstrate no acanthosis. Established plaques demonstrate a characteristic…

Interface dermatitis

Lichenoid interface dermatitis Key Features Basal layer is destroyed Civatte bodies Sawtooth rete pattern Causes of lichenoid interface dermatitis Lichen planus Benign lichenoid keratosis (BLK, lichen planus–like keratosis) Lichenoid drug eruption Lichenoid graft-versus-host disease (GvHD) Hypertrophic lupus erythematosus Lichenoid regression of a melanocytic lesion (usually lentigo maligna) The biopsy in each of these conditions demonstrates a sawtooth rete ridge pattern with destruction of the basal layer,…