Dermatopathology. Christine J. Ko

2(B) Architecture of an epidermal tumor/process

       Dermal tumors can have various architectural patterns

      Note Benign tumors are often symmetric with a pushing border, and malignant tumors may be asymmetric and infiltrative.

Figure 2(C) Different tumors are predominantly composed of a particular cell type

       Keratinocytic: rectangular/polygonal shape, intercellular bridges, round nucleus and small nucleolus

       Melanocytic: may be nested/clustered; nevomelanocytes (red arrow): oval nuclei, small nucleolus, pseudonuclear inclusions or melanin pigment may be evident; dendritic melanocyte (green arrow): thin cytoplasmic processes extending away from cell center

       Smooth muscle: spindle cell with abundant cytoplasm, perinuclear clear space, cigar‐shaped nucleus

       Adipocytic: thin membrane with compressed nucleus

       Neural: spindle cell with tapered nucleus, pink cytoplasm (green arrows)

       Fibroblast: spindle cell with oval nucleus (yellow arrows)

       Endothelial: blue nuclei surrounding vascular spaces (red arrows)

       Hair follicle: matrical cells are round to oval and dark blue (red arrow); outer root sheath cells are pale pink (green arrow)

       Sebocytes: bubbly cytoplasm (yellow arrow) and central nucleus that may be star‐shaped (scalloped)

       Eccrine gland and duct: the gland has clear cells (blue arrow); the duct has an eosinophilic pink cuticle

       Apocrine gland and duct: the gland often shows decapitation secretion (black arrow)

Figure 2(D) Cytologic features are important in pointing toward a benign versus malignant tumor

       Malignant cells have high nuclear:cytoplasmic ratio, irregular chromatin pattern, irregular nuclear contours, irregular nucleolar shape and size

       Primarily nuclear details suggest cytologic malignancy

       Cytoplasmic features point to differentiation: keratinocytes – eosinophilic, hyalinized cytoplasm, melanocytes – fine brown pigment

Benign nevomelanocytes (left)	versus	Melanoma cells (right)
Small nucleus, abundant cytoplasm		Large nucleus, relatively little cytoplasm
Smooth nuclear border		Irregular nuclear border
Chromatin pattern nondescript		Irregular, chunky nuclear contents (chromatin)
Inconspicuous nucleolus		1 or more large, purple nucleoli

“Rash”: key concepts

       The eye can be trained to focus in on the blue areas (figure–ground separation; grouping)

       Key features include epidermal changes (A), distribution of inflammation (B), and inflammatory cell type (C)

       Parakeratosis is often present in spongiotic and papulosquamous disorders; dry parakeratosis without serum but with neutrophils is suggestive of psoriasis

       Simplistically, a dermatitis can be categorized as spongiotic, papulosquamous, or interface

Figure 3(A) Key epidermal changes

       Parakeratosis: retained nuclei in the stratum corneum

       Spongiosis: increased intercellular spaces and sometimes vesicles

       Papulosquamous: thickened epidermis with parakeratosis

       Interface (vacuolar): spaces in basal cells, which may be polygonal (squamatized), lymphocytes at junction

       Interface (lichenoid): dense band of lymphocytes between epidermis and dermis with necrotic keratinocytes

Figure 3(B) Distribution of inflammation – major patternsSee Figure 3(A) for lichenoid

Figure 3(C) The morphology of key inflammatory cells

       Lymphocyte: round blue nucleus, little cytoplasm

       Neutrophil: multilobed nucleus

       Eosinophil: bilobed nucleus with bright pink‐red cytoplasmic granules

       Histiocyte: oval nucleus

       Giant cell: multiple nuclei in one cell

       Plasma cell: clock‐faced nucleus on one side of cell, perinuclear clear space

Characteristic body sites

       The location on the body (body site) can often be determined by training the eye/brain to perceive certain features

       Figure 4: Acral (A), mucosal (B), eyelid (C), axilla (D)

Figure 4(A) Acral skin

      Note Meissner’s corpuscles (black arrow), Pacinian corpuscles (red arrow), and thick stratum corneum with a stratum lucidum (green arrow).

Figure 4(B) Cutaneous lip (top row) has keratin and a granular layer (green arrow) as well as adnexal structures

       Skeletal