F6Ch29c: The acidophilic portion to the right, at the top of the field, has features of the infundibular portion of a follicle. The bulk of the epithelial component is composed of basaloid cells with pale, or vacuolated cytoplasm; the patterns are of a type commonly seen in follicular hamartomas of the butterfly area of the face. In this field, atypia is mild.
The lesion of chapters 41 & 42 is a pigmented, in-situ process; destructive invasion is not identified on the available sections. There is marked papillomatosis. A neoplastic basal unit is a prominent feature. There are numerous whorls, some of which are keratinizing. The degree of atypia is moderately severe to marked. Papillary carcinoma in situ can be considered as an alternative diagnosis. The histologic features tend to elicit a search for the mental parcel, tricholemmoma, from which a pathologist would pick virtual images to compare with the images of the section.
The lesion of chapter 43 shows features of a catagen-like tricholemmoma; there are a few small areas in which cells of the superficial unit-like component have vacuolated cytoplasm. The cells of the lesion show moderately severe cytologic atypia; cells with superficial unit-like qualities have plump nuclei with marginated chromatin and a prominent nucleolus. Centrally, patterns of sclerosing entrapment are prominent. The lesion has been cut across at the base; an infiltrating carcinoma cannot be ruled out.
In chapter 44, a rather solid, expansile tumor has pushed into the dermis. Stroma is inconspicuous in the nodular component. The epidermis over the lesion is ulcerated. Atypical changes extend in the epidermis away from the nodular component; they involve a neighboring follicle. Although the interface between the nodule and dermis is sharply defined, the lesion has bulk and extends to about the level of the sebaceous glands. Patterns of minimal micro-invasion are apparent in the dermis adjacent to the follicular component.