Fibrofolliculomas and trichodiscomas

Fibrofolliculomas and trichodiscomas consist of 2- to 4-mm, yellow-white, smooth, dome-shaped lesions often on the face. The lesions can be solitary or multiple. Multiple fibrofolliculomas have been described in association with trichodiscomas and acrochordons . This triad is now referred to as the Birt-Hogg-Dube syndrome and is inherited in an autosomal dominant fashion .

In patients with the Birt-Hogg-Dube syndrome the lesions are present in considerable number mainly on the face and neck. In such cases, the trichodiscomas are clinically indistinguishable from the fibrofolliculomas . In this syndrome, there is an increased risk for the development of renal tumors and colonic polyps . In a patient reported with a large connective tissue nevus, fibrofolliculomas were present in large numbers within as well as around the connective tissue nevus .

Besides occurring in association with multiple fibrofolliculomas, multiple trichodiscomas also occur without them, as small papules either widely disseminated or localized to one area .

Histopathology

Fibrofolliculomas exhibit a central distorted hair follicle that is surrounded by a mantle of basophilic, fibrous stroma . Numerous thin, anastomosing bands of follicular epithelium extend into this stroma .

Trichodiscomas are seen in the dermis as an area of fine fibrillary connective tissue containing ectatic blood vessels . Epithel ial hyperplasia resembli ng foil icular structures, including those seen in fibrofolliculomas, is often seen. A hair follicle is usually found at the margin of the lesion . Trichodiscomas have been regarded as hamartomas of the mesodermal component of hair disks .

The pedunculated acrochordons seen in association with multiple fibrofolliculomas may contain only dermal connective

tissue. However, in some instances, they contain thin, anastomosing strands of epithelium; they are regarded as fibrofolliculomas displaying the configuration of an acrochordon .

Additional Studies

Birt-Hogg-Dube syndrome is associated with mutations in the folliculin gene on chromosome 17p; the gene is believed to function as a tumor suppressor, but the function of this molecule is unclear . Steffen and Ackerman considered that histopathologically, fibrofolliculoma and trichodiscoma are hamartomas of follicular epithelium, follicular mantles, and perifollicular connective tissue . The immunophenotypic characteristics of syndromic-associated and sporadic types are identical and consist of perifollicular spindle cells that are positive for vimentin and CD34 and negative for factor XIII. These findings suggest that these lesions originate from the hair follicle mantle tissue. However, in some instances, they contain thin, anastomosing strands of epithelium; they are regarded as fibrofolliculomas displaying the configuration of an acrochordon .