Resposta: Acantoma da Bainha Pilar

Histologicamente, há uma proliferacao epitelial orientada verticalmente com uma grande cavidade central que se abre em direcao a superficie, com um ostium estreito. As paredes da cavidade acham-se delineadas com queratinocitos que produzem uma camada cornificada tipo rede de cesta de basquete, que eh algo espessada. Numerosos agregados lobulares de celulas de coloracao eosinofilica se irradiam da cavidade cistica em direcao a derme circunjacente. Um lobulo solitario na base da lesao demonstra um tubulo central atapetado com queratinocitos ortoqueratoticos que se comunica com uma grande cavidade central.

Figure 2

Mehregan and Brownstein assigned the term "pilar sheath acanthoma" to 9 such lesions they described first in 1978. [1] Subsequently, several others have described this benign follicular hamartoma, including an in-depth analysis and review by Ackerman. [2-5] As depicted in this case, pilar sheath acanthoma resembles clinically a comedo or dilated pore of Winer, presenting as a small, skin-colored papule or nodule with a central depression or opening. The classic location described for these lesions is the upper lip, although their appearance on other areas of the head and face has been described.[4] They are usually asymptomatic.

Histologically, the differential diagnosis includes dilated pore of Winer and trichofolliculoma. Dilated pore of Winer (also usually a solitary lesion) has the histologic appearance of a large cystic cavity with a gaping ostium at the surface. The cavity is filled with basket weave cornified debris that simulates the normal stratum corneum although it may be thickened and more compact. The lesion extends deeply into the dermis or occasionally to the level of the subcutaneous fat. The most distinctive feature of dilated pore is the extension of thin retia and papillae from the cyst wall into the surrounding dermis. These are distinctly different from the lobulated masses which extend from the cavity of pilar sheath acanthoma, within which a central tubule lined with corneocytes is sometimes visible. Trichofolliculoma is another benign follicular hamartoma with a central keratin-filled crater. Many times there are hair shafts visible within it as well. In groups around the cavity, numerous secondary hair follicles radiate from the wall of the primary follicle. An outer root sheath, inner root sheath and trichohyaline granules are commonly visible in the secondary follicles of a trichofolliculoma, features not seen in pilar sheath acanthomas.

Pilar sheath acanthoma is an interesting, uncommon, benign neoplasm of the skin not associated with other disorders. No tendency toward malignancy has been described

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