Histopathology and Frozen-Section Interpretation
What to recognize
Candidates must identify BCC (nodular, infiltrative, morpheaform), SCC, and melanoma on frozen sections, and recognize artifacts unique to frozen tissue: freeze artifact, chatter, and cautery distortion. Know that frozen sections are typically stained with hematoxylin and eosin and that melanoma and some adnexal tumors require immunohistochemistry, which may not be available on frozen tissue - a key practical limitation.
Margin interpretation
Understand the difference between a positive margin (tumor at the inked edge), a close margin, and an equivocal margin requiring deeper levels. Know that inflammation, fibrosis from prior treatment, and adnexal structures can mimic tumor. Perineural and perivascular invasion must be specifically sought.
Traps
A classic trap: interpreting cautery artifact as tumor or missing small infiltrative strands amid fibrosis. Another: assuming frozen section is equivalent to permanent section for all tumors; melanoma and some adnexal carcinomas are often better assessed on permanent sections or with immunohistochemistry.
Rule of thumb
When tumor is seen, map its exact location (clock-face position and peripheral vs deep) before deciding the next stage. Example: tumor at 6 o'clock peripheral and deep margin means the next stage must include both that edge and underlying tissue, not just a peripheral strip.