To the Editor:
Trichofolliculomas are benign tumors of hair follicle origin occurring most often on the face, scalp, or neck1,2 and most commonly occur in adults as a solitary papule. A characteristic clinical presentation is a white or pigmented tuft of wool-like hairs emerging from the papule's central pore but this is not always present.1
Histopathology reveals a central dilated infundibulum of a primary follicle and secondary follicles radiating from the infundibular wall of the primary follicle. The secondary follicles are small and vellus-like.
Abundant mucin is classically seen in trichogenic myxomas in which there is predominant mesenchymal component3 and has also been observed in folliculosebaceous cystic hamartoma,4 fibrofolliculomas, and angiomyxomas. We report a case of trichofolliculoma with striking abundant mucinosis.
A 54-year-old white man presented with a firm flesh-colored umbilicated papule measuring 3 mm in diameter on his jaw of uncertain duration. The lesion was otherwise asymptomatic and had not previously been treated. The provisional clinical diagnosis was either a keratoacanthoma or a molluscum contagiosum.
Microscopic examination showed a prominent dilated infundibulum filled with laminated keratin from which multiple secondary hair follicles projected into the surrounding dermis that was replaced by a prominent mucinous stroma containing scattered spindle cells (Figs. 1, 2). The mucin stained positively with colloidal iron (Fig. 3).
These findings were reported as an unusual trichofolliculoma with prominent mucinosis.
Although mucinosis is usually found particularly around hair bulbs, the gross mucinosis observed in this trichofolliculoma is unusual. In trichofolliculoma, both epithelial and mesenchymal components are represented. The perifollicular stroma is a mesenchymal element that is important in supporting follicular growth in inducing secondary follicles. In addition, the mesenchymal stroma may also result in hamartomatous and less differentiated follicular structures. Mesenchymal elements, including mucin,4 neural elements, smooth muscle, or adipose tissue, may develop to varying degrees and combinations during the process of stromal expansion. Mucin can be observed in follicular hamartomas5 such as trichofolliculoma as it is an integral part of the mesenchymal component but is usually localized to the adventitia of the secondary follicles and usually not abundantly as in our case. Abundant mucin deposits are seen especially in trichogenic myxoma, a rare variant of hair germ tumors,2 which has predominant mesenchymal component. This phenomenon is also seen in superficial angiomyxomas6 that at times are linked with Carney complex6 and fibrofolliculoma-associated mucinous papule.7
The tumor observed in our patient represents a tissue expansion of mucinosis in the setting of trichofolliculoma reflecting an exaggeration of the mucin associated with mesenchymal component seen usually with this benign follicle tumor. In our patient, the primary diagnosis was a trichofolliculoma and the mucinosis was a striking additional feature.
Penny Lim, MRCP
Steven Kossard, FACD
Skin and Cancer Foundation Australia
1. Gray HR, Helwig EB. Trichofolliculoma. Arch Dermatol
2. Headington JT. Tumors of the hair follicle: a review. Am J Pathol
3. Cohen C, Davis TS. Multiple trichogenic adnexal tumors. Am J Dermatopathol
4. Aloi F, Tomasini C, Pippione M. Folliculosebaceous cystic hamartoma with perifollicular mucinosis. Am J Dermatopathol
5. Yu-Hung Wu. Folliculosebaceous cystic hamartoma or trichofolliculoma? A spectrum of hamartomatous changes inducted by perifollicular stroma in the follicular epithelium. J Cutan Pathol
6. Allen P, Dymock R, MacCormac L. Superficial angiomyxomas with and without epithelial components: report of 30 tumors in 28 patients. Am J Surg Pathol
7. Schaffer JV, Gohara MA, McNiff JM, et al. Multiple facial angiofibromas: a cutaneous manifestation of Birt-Hogg-Dube syndrome. J Am Acad Dermatol