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Introduction
CHAPTER 32 Histopathology for Mohs
Micrographic Surgery
Teo Soleymani Sumaira Z. Aasi
SUMMARY
The Mohs surgeon must become expert at interpreting tangential sections and
distinguishing normal structures from tumor.
This may be challenging in certain situations depending on slide quality, section
quality, and tumor subtype.
Beginner Tips
An experienced technician is vital in the preparation of high-quality slides for
evaluation.
Aggregates of BCC may be distinguished from adnexal structures by peripheral
palisading and retraction artifact.
Examining multiple step sections may be helpful.
Look closely at lymphocytic aggregates, as they often surround tumor nests.
Expert Tips
Histopathologic interpretation of certain tumor subtypes, such as infiltrative BCC, may
be challenging.
These tumors should be differentiated from syringomas, desmoplastic
trichoepitheliomas, and microcystic adnexal carcinomas.
Donโt Forget!
The differential diagnosis for SCCIS (and occasionally SCC) includes actinic
keratosis, extramammary Pagetโs disease, inflamed seborrheic keratosis, verruca, pseudoepitheliomatous hyperplasia, and normal tangential sectioning of the epidermis.
With moderate-to-poorly differentiated SCCs, perineural invasion is of concern.
Pitfalls and Cautions
SCC may appear as single-cell infiltrates, which can be difficult to distinguish on
frozen sections without the aid of immunohistochemical stains.
There may be areas of focal necrosis, and often there is a prominent inflammatory
lymphocytic (or lymphohistiocytic) infiltrate surrounding the malignant cells.
Patient Education Points
Mohs surgery is unique in that one physician acts as both surgeon and pathologist.
Educating patients regarding the complexity of the process, and the logistics behind
tissue processing, may ameliorate stress regarding wait times between stages.
Billing Pearls
If a lesion is biopsied for the first time on the day of Mohs surgery and a frozen section
interpretation is made on the tissue, CPT code 88331 should be utilized with modifier 59.
Billing for immunohistochemical stains is in addition to standard Mohs layer billing,
and is generally billed on a per-specimen basis with code 88342 for the first antibody
followed by 88341 for each additional antibody. If multiple separately identifiable antibodies are applied to the slide, use one unit of 88344.
CHAPTER 32 Histopathology for Mohs