Key Concepts

RoundRound to polygonal rosettePolygonal rosetteSolid blackSolid color within rosetteSpots within rosette

Body Site/Regional

Key Differences

• Scalp – numerous anagen hair follicles with bulbs (arrows) in the fat (Fig. 1.1)

• Ear – vellus hair follicles (arrows) and central cartilage (*) (Fig. 1.2)

• Face – prominent hair follicles and sebaceous glands within the dermis (Fig. 1.3)

• Eyelid – vellus hair follicles (arrows) and underlying skeletal muscle (*) (Fig. 1.4)

• Cutaneous lip – epidermis with keratin and a granular layer (arrows); skeletal muscle (*) (Fig. 1.5)

• Mucosal lip – pale epithelium that lacks a granular layer and does not keratinize (Fig. 1.6)

• Areola – acanthotic, pigmented epidermis with dermal smooth muscle bundles (arrows) (Fig. 1.7)

• Back – thick dermis (Fig. 1.8)

• Axilla – undulating epidermis with deep apocrine glands (arrows) (Fig. 1.9)

• Acral – thick stratum corneum with stratum lucidum (arrow) (Fig. 1.10)

• Nail – nail plate (arrow), nail matrix (black bar), and nail bed (Fig. 1.11)

Fig. 1.11 Nail unit anatomy. B, From Telser AG, Young JK, Baldwin KM. Integrated Histology, 1e. St Louis: Mosby, 2007, with permission.

Age

Key Differences

• Young skin has small adnexal structures (arrows) and more compact dermis (Figs 1.12, 1.13)

Fig. 1.12 Dorsal hand. A,B Child. C,D Adult.

• Sun-damaged skin has characteristic solar elastosis (arrows) (Fig. 1.14)

Distribution

Extensive – more than one body part affected with multiple lesions; may preferentially affect extensor surfaces (e.g. elbows/knees) vs flexor surfaces (e.g. antecubital/popliteal fossae) or ventral vs dorsal surfaces (Fig. 1.15)

Photodistribution – can vary depending on the type of clothing worn; sun-protected sites of the face/neck generally include the central upper cutaneous lip and submental area (Fig. 1.16A; see Fig. 3.7)

Fig. 1.16 Distribution. A Photodistribution. B Double-covered sites. C Acral. D Body folds. Areas shaded in red are classically involved; light pink areas may also be involved.

Double-covered areas – generally includes sites covered by undergarments (Fig. 1.16B)

Acral – hands/feet but also the tips of the ears/nose (Fig. 1.16C)

Body folds – inframammary/intertriginous (Fig. 1.16D)

Generalized – involving the majority of the cutaneous surface (Fig. 1.17)

Dermatomal – patterns of cutaneous innervation by spinal nerve roots (Fig. 1.18A)

Fig. 1.18 Distribution patterns. A Dermatomal. B Blaschkoid. From Bolognia JL, Jorizzo JL, Schaffer JV. Dermatology, 3e. London: Saunders, 2012, with permission.

Blaschkoid – follows patterns of embryonic cell migration; while the linear pattern on the extremities is similar to the dermatomal pattern, the V-shaped curves over the trunk and the S-shapes on the abdomen are characteristic (Fig. 1.18B)