| Table 8-10 Characteristic Histologic Findings |
| Histopathologic Finding | | Seen in: |
| Cornified Layer |
| | Follicular plugging | | Pityriasis rubra pilaris (PRP), lichen planopilaris (LPP), lichen sclerosus, lupus erythematosus (LE), perforating folliculitis |
| | Cornoid lamella | | Porokeratosis |
| | Compact parakeratosis with retained KHG | | Axillary granular parakeratosis |
| | “Checkerboard” and “shoulder” parakeratosis | | PRP |
| | Mounds of parakeratosis | | Psoriasis |
| | Focal parakeratosis | | Guttate psoriasis, pityriasis rosea, pityriasis lichenoides |
| | Confluent parakeratosis | | Psoriasis, Bowen’s disease, necrolytic migratory erythema (NEM) in glucagonoma syndrome |
| | Columns of parakeratosis | | Verruca vulgaris (VV), porokeratosis |
| | Alternating parakeratosis | | Actinic keratosis (AK) |
| | Sandwich parakeratosis | | Tinea |
| | Confluent hyperkeratosis | | Lichen planus (LP) |
| | Massive orthokeratosis | | Acquired digital fibrokeratoma |
| | “Church spire” papillomatosis | | Acrokeratosis verruciformis |
| | Papillomatosis | | Acanthosis nigricans, VV, seborrheic keratosis (SK), acrochordon |
| | Neutrophils in crust | | Candidiasis, psoriasis, impetigo, tinea, syphilis |
| | Munro microabscess in cornified layer | | Psoriasis (plate-like neutrophils in multilayered scale) |
| Epidermis |
| | “Claw” (epidermis) clutching a “ball” (dermis) | | Lichen nitidus |
| | Epidermal necrosis | | Herpes simplex (HSV) infection, toxic epidermal necrolysis, erythema multiforme (EM), NEM, hydroa vacciniforme, graft-versus-host disease (GVHD), acute fixed drug reaction (FDE) |
| | Atrophic epidermis | | Porokeratosis, atrophic AK, radiation dermatitis, lichen sclerosus, LE, dermatomyositis, poikiloderma, necrobiosis lipoidica, GVHD |
| | Upper pallor with normal-appearing lower epidermis | | NEM, ± acrodermatitis enteropathica |
| | Windblown appearance | | Bowen’s disease |
| | Subcorneal/intragranular split with acantholytic cells (cling on) | | Pemphigus foliaceous (sometimes can look like impetigo if neutrophils within blister cavity) |
| | Eosinophilic spongiosis (hAPPIE) | | Arthropod bite, pemphigoid, pemphigus, incontinentia pigmenti (IP), eruption (drug), contact dermatitis |
| | Foam cells in epidermis | | Balloon cell nevus |
| | Dyskeratotic or necrotic keratinocytes | | EM, pityrisiasis lichenoides et varioliformis acuta (PLEVA), paraneoplastic pemphigus, acrodermatitis enteropathica, acute FDE, IP, NEM, GVHD, radiation dermatitis |
| | Vacuolated keratinocytes (empty shells) | | Tissue-processing artifact, freezing artifact, epidermolytic hyperkeratosis |
| | Elongated keratinocytes | | Electrodessication artifact |
| | Acantholytic cells | | Darier’s disease, Hailey-Hailey disease, HSV infection, transient acantholytic dermatosis (Grover’s disease), pemphigus (acantholysis involves hair follicles), warty dyskeratoma, acantholytic SCC or AK |
| | Koilocytes | | HPV infection |
| | Multinucleated keratinocytes | | HSV (steel gray nuclei) |
| | Epidermotropic lymphocytes | | Cutaneous T-cell lymphoma (CTCL) |
| | Pagetoid cells | | Bowen’s disease, melanoma, recurrent nevus, Paget’s disease, CTCL, lymphomatoid papulomatosis (LyP), Langerhans cell histiocytosis (LCH) |
| | Dilapidated brick wall | | Hailey-Hailey disease |
| | Pautrier microabscesses | | CTCL |
| | Tombstoning of basal cells | | Pemphigus vulgaris |
| | Clumped keratohyaline granules (KHG) | | Epidermolytic hyperkeratosis, verruca (HPV infection) |
| | Squamous eddies | | Irritated seborrheic keratosis (SK), inverted follicular keratosis (IFK), SCC, trichoblastoma |
| | Horn pseudocysts | | SK, IFK, trichoepithelioma, microcystic adnexal carcinoma |
| | Basilar hyperpigmentation | | Dermatofibroma, SK, acanthosis nigricans |
| | Flattened (tabled) rete ridges | | Dermatofibroma |
| | “Saw-toothed” rete ridges | | LP |
| | Vacuolar interface change | | LE, LP, GVHD, dermatomyositis, acute FDE, lichen nitidus, erythema dyschromicum perstans (ashy dermatosis), lichenoid keratosis, lichen sclerosus, EM, PLEVA |
| Dermis |
| | Thick basement membrane | | LE |
| | Grenz zone | | Lepromatous leprosy, granuloma faciale, lymphocytoma cutis (bottom heavy), leukemia cutis (top heavy) |
| | Subtle amorphous pink deposits in papillary dermis | | Macular amyloidosis |
| | Band-like lymphocytic infiltrate | | LP, EM, lichen sclerosus, benign lichenoid keratosis, lichen striatus, halo nevus |
| | Upper dermal edema | | Polymorphous light eruption (PMLE), Sweet’s syndrome, lichen sclerosus, langerhans cell histiocytosis |
| | Melanin incontinence | | Macular amyloidosis, LE, atrophic LP, ashy dermatosis, FDE, dermatomyositis, postinflammatory hyperpigmentation, ± IP |
| | Subepidermal split with prominent eosinophils | | Bullous pemphigoid, pemphigoid gestationis, bullous drug eruption |
| | Subepidermal split with prominent neutrophils | | Dermatitis herpetiformis, bullous SLE, linear IgA bullous disease (LABD) |
| | Neutrophils in dermal papillae | | Dermatitis herpetiformis |
| | Subepidermal split with prominent lymphocytes | | Bullous LP, PMLE, lichen sclerosus |
| | Subepidermal vesicles with scant inflammation | | Porphyria cutanea tarda (PCT) |
| | Subepidermal vesicles with mast cells | | Bullous mastocytosis |
| | Fibrous stroma | | Syringoma, trichoepithelioma, morpheaform BCC, microcystic adnexal carcinoma |
| | “Bubble gum” pink stroma | | Neurofibroma |
| | Lymphocytes around sweat glands | | Lichen striatus |
| | Sweat glands with neutrophils | | Neutrophilic eccrine hidradenitis |
| | Necrosis of sweat glands | | Coma blister |
| | Invaginated pilosebaceous unit with dark-staining ducts | | Supernumerary nipple |
| | Extravasated red blood cells | | Pityriasis rosea, PLEVA, stasis dermatitis, pigmented purpuric dermatoses, vascular neoplasms, vasculitis, granuloma faciale (GF) |
| | Hemosiderin | | Hemochromatosis, pigmented purpuric dermatosis, stasis dermatitis, GF, pityriasis lichenoides, vascular neoplasms, vasculitis |
| | Vertically oriented collagen | | Acquired digital fibrokeratoma |
| | Collagen trapping at periphery | | Dermatofibroma |
| | Keloidal collagen | | Dermatofibroma, keloid |
| | Necrobiosis | | Granuloma annulare (GA), necrobiosis lipoidica diabeticorum (NLD), rheumatoid nodule, necrobiotic xanthogranuloma (NXG) |
| | Horizontal “sandwich” necrobiosis without palisading | | NLD |
| | Dermal fibrosis | | Angiofibroma, fibrous papule, hypertrophic scar, blue nevus, keloid, radiotherapy, morpheaform BCC, desmoplastic trichoepithelioma, syringoma |
| | Dermal necrosis | | Epithelioid sarcoma, malignant atrophic papulosis (Degos) |
| | Clumped calcified elastic fibers | | Pseudoxanthoma elasticum (PXE) |
| | Vasculitis | | GF, erythema elevatum diutinum (EED), polyarteritis nodosa (PAN), Henoch-Schonlein purpura, urticarial vasculitis, acute hemorrhagic edema of infancy |
| | Nuclear dust | | Sweet’s syndrome, leukocytoclastic vasculitis, GF, PAN, pyoderma gangrenosum (PG) |
| | Deep pink nodules | | Nodular amyloidosis |
| | Smooth muscle bundles | | Supernumerary nipple , leiomyoma (fascicles and bundles) |
| | Calcification | | Pilomatricoma, PXE, calciphylaxis, osteoma cutis, cysts, panniculitis, calcinosis cutis, subepidermal calcified nodule |
| | Increased mucin deposition | | LE, dermatomyositis, scleromyxedema, scleredema diabeticorum, BCC (some), mucopolysaccharidosis, reticular erythematous mucinosis, GA (not NLD) , pretibial myxedema, focal mucinosis, follicular mucinosis |
| | Pool of mucin | | Myxoid cyst, mucocele, focal cutaneous mucinosis, mucinous carcinoma |
| | Ductal cells floating in mucin | | Eccrine mucinous carcinoma |
| | Tadpole-shaped ducts | | Syringoma |
| | Extracellular pool of lipid | | Eruptive xanthoma |
| | Empty vacuoles in dermis and epidermis | | Freeze artifact |
| | Pink to purple reticular network in dermis | | Gel foam artifact |
| | Drag marks | | Cutting artifact (knife mark artifact) |
| | Tiny black particles around blood vessels | | Argyria |
| | Black amorphous deposits around blood vessels | | Lead tattoo |
| | Tiny wispy gold to black granules in mouth | | Amalgam tattoo |
| | Nerve bundles | | Amputation neuroma, supernumerary digit |
| | Stromal retraction | | BCC |
| | Basaloid islands (jigsaw puzzle) | | Cylindroma |
| | “Cluster of grapes” (low power) | | Merkel cell carcinoma |
| | Hyalinized droplets | | Cylindroma |
| | Cannon or blue balls in dermis | | Eccrine spiradenoma |
| | Circular basaloid rosettes | | Eccrine spiradenoma |
| | Spindle and epithelioid melanocytes “raining” down | | Spitz nevus |
| Inflammatory Infiltrate |
| | Lichenoid infiltrate | | LP, lichenoid drug eruption, lichen sclerosus, secondary syphilis (with plasma cells), GVHD, pityriasis lichenoides, lichen striatus, CTCL |
| | Interstitial dermatitis | | GA, Well’s syndrome, Sweet’s syndrome, interstitial drug reaction, urticaria |
| | Coat-sleeving or perivascular cuffing of lymphocytes | | Erythema annulare centrifugum (no epidermal change) |
| | Superficial and deep lymphocytic infiltrate | | PMLE, secondary syphilis, gyrate erythemas, athropod bites, LE (latter includes periadnexal infiltrate) |
| | Deep infiltrate around sweat glands | | Lichen striatus |
| | “Naked” granulomas | | Sarcoidosis, tuberculosis, tuberculoid leprosy |
| | Single filing or “indian” filing of cells | | GA, congenital melanocytic nevus, lymphoma, leukemia, glomus cell tumor, metastatic breast carcinoma |
| | Increased mast cells | | Urticaria, neural tumors (i.e., neurofibroma), mucinous areas |
| | Increased plasma cells | | Mucous membrane (normal), secondary syphilis, syringocystadenoma papilliferum, hidradenitis suppurativa, acne keloidalis nuchae, NLD, LE, Rosai–Dorfman disease |
| Cells in Dermis |
| | Basaloid cells | | BCC, SK (reticulated variant), trichoepithelioma, eccrine tumors |
| | Diffuse dermal mast cells | | Mastocytosis (i.e., urticaria pigmentosa) |
| | Cells with reniform nuclei | | Langerhans cell histiocytosis (abundant pale cytoplasm) |
| | Spindle-shaped cells with elongated, wavy nuclei | | Neurofibroma |
| | Round monotonous cells | | Glomus cell tumor, poroma, mastocytosis (blue-purple granules) |
| | Pink granular cytoplasm | | Granular cell tumor |
| | Clear cells | | Clear cell acanthoma, trichilemmoma, clear cell hidradenoma, metastatic renal cell carcinoma, clear cell SCC, balloon cell nevus, Paget’s disease, clear cell syringoma, eccrine carcinoma |
| | Small cells | | Lymphocytoma cutis, cutaneous B-cell lymphoma, metastatic small cell carcinoma, CTCL, Merkel cell carcinoma |
| | Foamy macrophages | | Xanthomas (eruptive, tuberous, tendinous, planar), verruciform xanthoma, xanthelasma, xanthoma disseminatum, atypical fibroxanthoma (AFX), juvenile xanthogranuloma (JXG), necrobiotic xanthogranuloma (NXG), leprosy, pancreatic panniculitis |
| | Touton giant cell | | Xanthelasma, AFX, NXG |
| | Ground glass giant cell | | Multicentric reticulohistiocytosis, reticulohistiocytic granuloma |
| | Purple osteoclast-like giant cell | | Giant cell tumor of tendon sheath, malignant fibrous histiocytoma |
| | Bizarre multinucleated giant cell | | Malignant fibrous histiocytoma, pleomorphic lipoma |
| | Parasitized histiocytes His GiRL | | Histoplasmosis, granuloma inguinale, rhinoscleroma, leishmaniasis |
| | Ghost cells | | Pilomatricoma |
| | Fibroblast with red inclusion body | | Infantile digital fibromatosis |
| | Bizarre spindle cells | | Liposarcoma, leiomyosarcoma, AFX, radiation dermatitis |
| Hair |
| | Melanin clumps (casts) in follicle | | Trichotillomania |
| | Trichomalacia (deformed shaft) | | Trichotillomania |
| | Necrosis of hair follicles | | HSV |
| | Tiny vellus hairs | | Accessory tragus (rim periphery), xanthelasma, vellus hair cyst |
| | “Swarm of bees” (lymphocytic inflammation at hair bulb) | | Alopecia areata |
| | Lymphocytes and plasma cells around follicles | | Acne keloidalis nuchae |
| | Free hair shafts surrounded by multinucleated giant cells | | Acne keloidalis nuchae, folliculitis decalvans |
| | Eosinophils around hair follicle | | Eosinophilic folliculitis |
| | Mucin within follicle | | Follicular mucinosis |
| Cartilage |
| | Cartilage often present | | Accessory tragus, chondrodermatitis nodularis helicis (CNH), chondroid syringoma |
| | Degenerated cartilage | | Relapsing polychondritis, CNH |
| Fat |
| | Ghost-like fat cells | | Pancreatic panniculitis (with basophilic calcium deposition) |
| | Cystic spaces in fat | | Cold panniculitis |
| | Fat necrosis | | Erythema induratum (basophilic), lupus panniculitis (latter with lymphoid follicle-like aggregates, lymphoplasmacytic infiltrate) |
| | “Needle-shaped” clefts in fat | | Subcutaneous fat necrosis, sclerema neonatorum, post-steroid panniculitis |
| | Swiss cheese appearance | | Paraffinoma or sclerosing lipogranuloma |
| | Fat high up in lesion | | Accessory tragus |
| | Widened septae with giant cells | | Erythema nodosum |
| | Dense neutrophilic inflammation | | α-1-antitrypsin deficiency |
| | Lipomembranous changes | | Lipodermatosclerosis |
| | Chicken wire pattern (linear collapsed vessels) | | Myxoid liposarcoma |
| | Clear multivacuolated cells in fat | | Hibernoma |
| Vessels |
| | Hyalinized vessel walls
(with thick red color around vessels) | | Atrophie blanche |
| | Promontory sign, slit-like spaces | | Kaposi sarcoma |
| | Atypical endothelial cells with dissecting vascular spaces | | Angiosarcoma |
| | Intravascular thrombi | | Cryoglobulinemia, purpura fulminans, antiphospholipid syndrome, disseminated intravascular coagulation, coumadin necrosis, atrophie blanche |
| | Telangiectatic vessels in pale acellular dermis | | Radiation dermatitis |
| | Hob nailing
(endothelial cells protrude into vessel) | | Angiolymphoid hyperplasia with eosinophilia |
| | Staghorn appearance | | Hemangiopericytoma |
| | Recanalizing thrombus | | Masson’s tumor (intravascular endothelial hyperplasia) |
| | Spindle cells with RBCs “sandwiched” in between | | Kaposi sarcoma |
| | Polypoid collection of vessels | | Pyogenic granuloma |
| | Proliferation of thick-walled vessels with hemosiderin | | Stasis dermatitis |
| | Dilated engorged vessels with surrounding edema | | Granulation tissue |
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