Ch16P8-L3 Catagen-like &
Follicular Matrical Tumor

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  • F1Ch16 (R4564): With pattern analysis, this would most likely be characterized as seborrheic keratosis; the basic pattern in this portion of the lesion is that of interconnected epithelial processes, scattered keratin-filled cysts, and two populations of squamous cells. The lesions sits on the surface of the skin. An isolated nest of basophilic cells sets the pattern apart from the common seborrheic keratosis. (Seborrheic keratosis might have been classified as a follicular lesion in the chapter on skin tumors in Silverberg’s Textbook of Surgical Pathology; it might have been characterized as follicular poroma?)
  • The basophilic nest is isolated in a delicate fibrous matrix; the expanse of the fibrous matrix in this area would be an unusual feature of a common seborrheic keratosis. There are scattered squamous eddies.
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    F2Ch16 (R4564): Again, the patterns basically are those of a common “seborrheic keratosis.” There is a dual population of cells. In areas (blue arrows point to one such area in which the patterns in a nest of cells contrasts with those of the surrounding epithelium), the cells have enlarged, somewhat hyperchromatic nuclei; at this magnification, this collection of cells is paler than the neighboring populations of cells. The prominence of epithelial whorls produces a pattern that is reminiscent of that seen in inverted follicular keratosis (and “irritated seborrheic keratosis”). The basic pattern in which the lesion sits upon the skin is more characteristic of a variant seborrheic keratosis.

    R4564hairmatrporo240

    F3Ch16: In areas, a basaloid quality is manifested in some of the nests. To the right, the cells have pale, finely vacuolated cytoplasm. In addition in this same area, there is a rounded microcyst that contains proteinaceous fluid.

    R4564hairmatrporo210

    F4Ch16: In this area, patterns of stromal-epithelial interaction are represented. Bulbous projections of stroma are partitioned by thin epithelial strands. A dual population of epithelial cells is represented with nests of basaloid cells among collections of less distinctive squamous cells. In some of the nests of “basaloid” cells, the cells are loosely spaced in an expanded interstitial matrix. In the basaloid components, the cells have enlarged, hyperchromatic nuclei. Focally, the stroma is clearly myxoid. In these areas, stromal cells show some variation in nuclear sizes, and staining qualities. The pattern in this localized area has a myxofollicular quality.

    R4564hairmatrporo200

    F5Ch16: In this portion of the lesion, the patterns are those of an “intraepithelial epithelioma.” The cellular rounded nests of basaloid cells are associated with a component of more common squamous cells; the rounded nests are sharply defined in a background of squamous epithelium. The papillary dermis is expanded, delicately fibrous, and vascularized. There are mild perivascular infiltrates of inflammatory cells. In the general category of intraepithelial epithelioma, hidroacanthoma simplex might be considered in the differential diagnosis, but the melanin deposits would be an unusual feature for a sweat gland neoplasm. Pigmented “hidradenomas” of the scalp have been described, but may represent compound lesions showing both follicular and sweat duct differentiation.

    R4564hairmatrporo230

    F6Ch16: The rounded nest in the center of the field is composed of basaloid cells; there is mild atypia with variation in nuclear size, outline, and staining. The central rounded nest is attached superiorly to a strand of squamous cells. In turn, there appears to be a single row of flattened squamous cells that outline the rounded nest . The myxoid stroma bulges irregularly into the epithelial component.

    A diagnosis of melanoacanthoma might be considered in areas in which tumor cells are pigmented. Such a diagnosis offers little in the way of guides to therapy. In my experience, the diagnosis merely encourages a clinician to be more aggressive.

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