Ch14P6-L3 Folliculogenic
Myxoma

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R4547trichodiscoma220

F1Ch14 (R4547): Two sections of a small myxoma of the skin are represented. The lesion is oval in outline and superficial; It presses upon the epidermis and forms an interface with the reticular dermis. In the area of the tumor, a papillary dermis is not defined. For the upper section, there is an area of epidermal hyperplasia to the left; in this area, thin cords of epithelium are irregular in distribution. Thin strands and coarse bands of collagen are loosely spaced in the myxoid matrix. The lesion is not well circumscribed at the interface with the reticular dermis (upper lesion).

The lower lesion shows four foci in which thin, interconnected cords of squamous cells encircle rounded islands of the myxoid tumor (myxofollicular patterns). Blue arrows point to two of these areas. On the left, the myxofollicular component focally is associated with an area of fibrosis. A follicular lumen is represented in the area on the left. The lesion on this section presents a circumscribed interface with the reticular dermis. Basaloid germinative changes are not evident at this magnification.

R4547trichodiscoma200

F2Ch14: At higher magnification in the area of epidermal hyperplasia on the left, at least two of the thin cords projecting from the epidermis into the lesion have blunted extremities and show increased basophilia.

R4547trichodiscoma190

F3Ch14: Focally, anastomosing cords of small squamous cells encircle islands of the myxoid tumor. Focally, the matrix outlining some of the thin cords is distinctly fibrous. Basal cell components are not represented in this area. The myxoid component is loosely cellular; thin-wall vessels are irregularly distributed. There is a band of condensed fibrous tissue at the interface with the reticular dermis.

R4547trichodiscoma180

F4Ch14: With a different technique, the myxoid character of the lesion is accentuated. There are irregular clefts in the myxoid component. Pools of mucin are present in some of the clefts. Fibrous qualities are variable.

R4547trichodiscoma160

F5Ch14 (see also F2Ch14): in this area of epithelial hyperplasia, some of the thin cords at their extremities show basaloid qualities (germinative qualities [red arrows]). Scattered pale pink bodies in the myxoid stroma near the epidermis on the left are interpreted as colloid bodies; in areas, the stromal component has eroded the basal layer of the epidermis.

The patterns provide evidence of the interaction between the germinative portion (i.e., basal unit) of squamous epithelium and activated stroma (with myxoid stroma as an example of activated stroma); the two components expand in mutually accommodating patterns. In this field in the area with the red arrows, the basal unit of the epidermis has taken on basaloid qualties with an accentuation of the basal row of palisaded cells. In turn, the neighboring stroma is somewhat hypercellular and the nuclei of the respective stromal cells are enlarged.

The epithelial patterns might be dismissed as evidence of the “mantle change.” The exuberance of the epithelial strands might be evidence of a lack of success in a search for a proper nerve that, if encountered, would, in turn, lead to the formation of a developing hair bulb.

As one additional consideration, the strands of squamous cells - as opposed to the focus of basal cell transformation - might be evidence of tricholemmal type epithelium awaiting the formation of a trichogenic hair bulb.

The role of the “hair disk” in the development of “trichodiscoma” (F5Ch11) is mostly fanciful. Myxoid change is an optional functional attribute of fibrous tissue, particularly the specialized form that qualifies as stroma, such as the adventitial dermis.

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