13.3.2Histopathologic Recognition of Dermal Components

The Mohs surgeon should be able to easily recognize different dermal structures. In this section, we will brießy discuss the histologic criteria for some pathologic changes associated with some dermal structures.

13.3.2.1 Fibrous Tissue, Desmoplasia, and Nerves

The dermal Þbrous tissue is composed of wavy collagen bundles and spindled Þbroblasts. Desmoplasia is a dense reactive Þbrous tissue surrounding tumors. It is claimed that some tumors release Þbroblast growth factor and are associated with this surrounding ßorid desmoplasia. We described this speciÞc pattern of

Þbrosis noted in BCC and SCC which we called peritumoral Þbrosis [24]. It shows concentric layers of Þbrous tissue surrounding and/or surrounded by tumor formations and resembles carcinomatous perineural and/or intraneural invasion (Fig. 13.23). Mohs micrographic surgeons should be aware of this phenomenon to avoid triggering unnecessary steps in managing these cases, such as irradiation. Dense perineural inßammation has been associated with a higher incidenceofperineuralinvasion[25].Immunohistochemical staining for S-100 protein decorates nerve Þbrils, but not Þbrous tissue bundles (Fig. 13.24a, b). One should be careful interpreting S-100 stained sections for the presence of positive dermal dendrocytes in peritumoral Þbrosis. This is easily differentiated from the uniformly positive nerve Þbrils.

Fig. 13.24 (continued)

13.3.2.2 The Dermal Microvascular Unit

The Mohs surgeon should be familiar with the histologic changes seen within the dermal vessels. Different inßammatory diseases of the skin are usually associated with reactive endothelial cellular changes. When these vessels are cut tangentially, they could produce cytologic changes that may closely mimic carcinoma cells mainly SCC or sometimes epithelioid melanoma cells. A common example of this is the reactive endothelial cells associated with the dense lymphohistiocytic inÞltrate seen in some cases of rosacea. Deeper sections would help identify the relationship of these cells to a blood vessel. One should note also that dermal blood vessels usually run in parallel with/or associated with nerve Þbrils, the so-called neurovascular bundles. Tissue compression may create abnormal pictures depicting vessels and nerves in different positions which could mimic perineural invasion (Fig. 13.25). Dense dermal lymphocytic inÞltrate can be seen in cutaneous deposits of leukemia, JessnerÕs lymphocytic inÞltrate, and prior treatment with 5-FU or Imiquimod 5% [26].

13.3.2.3Dermal Muscles, Cartilage, and Subcutaneous Adipose Tissue

In addition to arrector pili muscle, cutaneous smooth muscles can be seen with cross-section/tangential cutting of blood vessels. Mohs surgeons should be able to identify these normal smooth muscles and differentiate them from malignant spindle cells seen in cutaneous leiomyosarcoma. Cytologic features of malignancy in the form of cytomegally, hyperchromasia, pleomorphism, and atypical mitoses would help differentiate benign from malignantsmoothmuscles.Skeletalmusclescanbeencountered in most sections of the lips, neck (platysma), face, and deeply inÞltrating cancers such as DFSP.

Cartilage is frequently seen in Mohs sections of the nose and ears. It is usually easy to interpret Mohs sections with cartilage. The latter is normally basophilic with routine H&E staining showing small, rounded, or oval chondrocytes with surrounding halos and homogeneous, structureless stroma. Cartilage tends to wash off the slides, so special slides should be used routinely for better results. These slides electrostatically attract frozen and formalin-Þxed tissue sections and bind them, while improving tissue adherence. Superfrost¨