Different tissue compartments interconnect anatomically and interact functionally. These are the reactive units of the skin.
The superficial reaction unit comprises the epidermis, the junctional zone, and the papillary body with its vascular system.
The reticular dermis with the deeper dermal vascular plexus is the second reactive unit.
The third reactive unit is the subcutaneous tissue with its septal and lobular compartments.
Hair follicles and glands are a fourth reactive unit embedded into these three units.
Pathologic processes may involve these reactive units alone or several of them together in a concerted fashion.
The heterogeneity and interaction of these individual cutaneous compartments explains why a few basic pathologic reactions lead to a multiplicity of clinical and pathologic reaction patterns.
INTRODUCTION TO SKIN PATHOLOGY
Skin biopsies play an important role in the care of patients with dermatologic disorders. Adequate knowledge of dermatopathology is crucial not only for interpreting the pathology report from the laboratory, but also for deciding how and where to perform the biopsy. The process of a skin biopsy is more complex than meets the eye, as it has been estimated that there are approximately 20 “handoff” steps in this process.1 Errors can occur at any one of these steps, and accurate communication at all points is important in minimizing medical mishaps.1,2
CHOOSING THE TYPE OF BIOPSY
Before performing a biopsy one must review the clinical differential diagnosis, which will assist in deciding whether a shave, punch, or excisional specimen is best (Table 2-1). One must also consider the anatomical location of the biopsy, and how it will affect the cosmetic result. Shave biopsies are best for cases where most of the pathology is in the epidermis or superficial dermis. Examples include nonmelanoma skin cancer (basal cell carcinoma, squamous cell carcinoma), seborrheic keratosis, actinic keratosis, verruca vulgaris, and some melanocytic nevi. For most inflammatory dermatoses, a punch biopsy produces the best results. Excisional biopsies are used for complete removal of a cutaneous neoplasm as well as in cases of panniculitis or fasciitis where substantial deep tissue is needed. Curettage should be restricted to lesions with a known diagnosis, such as a seborrheic keratosis, verruca, or basal cell carcinoma, where histopathologic examination is less important, and mostly performed for confirmation. Curettage results in fragmented and distorted tissue making evaluation by the pathologist extremely difficult.
Table 2-1Choosing the Type of Biopsy |Favorite Table|Download (.pdf) Table 2-1 Choosing the Type of Biopsy
|SUSPECTED DIAGNOSIS ||BIOPSY TYPE |
|Actinic keratosis ||Shave |
|Seborrheic keratosis ||Shave |
|Verruca ||Shave |
|BCC, SCC ||Shave most common; punch/excision |
|Blistering disease ||Punch or deep shave edge of blister |
|Contact dermatitis ||Punch |
|Connective tissue disease ||Punch |
|Mycosis fungoides ||Punch |
|Vasculitis ||Punch |
|Granulomatous process ||Punch |
|Atypical nevi ||Deep shave, punch, or excision |
|Panniculitis ||Punch (minimum 6 mm) or ellipse |