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