Trichofolliculoma is a rare benign tumor characterized by pilosebaceous follicle hamartoma; it presents mostly during adulthood as a papule or nodule usually affecting face and scalp.1-2 This benign tumor is characterized clinically by the presence of a central dilated pore with tufted hairs and corresponds histologically to a central primary follicle and many secondary vellus hair follicles originating from it. Thus far, dermoscopy description of trichofolliculoma has been lacking. Here, we describe a typical case of trichofolliculoma, particularly the special manifestation under the dermoscopy, and try to depict a new pattern of dermoscopy, which turned out to be a useful diagnostic tool.
A 29-year-old man presented to the Hospital for Skin Diseases in December 2017 with a five-year history of a nodule containing a central whitish hair plug on his left tempus (Fig. 1A). The nodule was asymptomatic and enlarged progressively. The patient was otherwise in good health. He denied trauma and proceeding or concurrent illnesses.
Dermoscopic examination revealed a well-defined, yellow macule with a central whitish hair plug surrounded by dilated capillaries (Fig. 1B). An excisional biopsy was performed, and the histopathological analysis was consistent with trichofolliculoma (Fig. 1C). No recurrence was found in three months of follow-up. The patient has given his consent for his case to be reported.
Prototypically, a trichofolliculoma consists of a central cystic space with infundibular cornification and central orthokeratin. Relatively well-developed and occasionally oddly formed vellus follicles protrude in a radial fashion from the central structure. The follicles usually display a bulb and papilla, and exhibit inner and outer sheaths as well as isthmic differentiation. In the early stages, there are few secondary vellus hair follicles originating from the primary follicle. In mature lesions, vellus hair follicles increase in number. Later stages show a thickened primary follicle and fewer secondary follicles.3 The entire structure, including the central cyst and its associated radiating follicles, is enveloped by a vascularized fibrous (angiofibroma-like) stroma. Immunohistochemical staining shows that trichofolliculomas express CK17 intensely, as well as PHLDA1 and BerEP4, two markers expressed in normal follicles and in certain follicular tumors.4 These findings indicate possible stimulation of follicular induction by unknown factors. The androgen receptors found in the stroma antagonize the β-catenin pathway in cutaneous stem cells and accelerate the senescence of hair papillae, which are also important for sebaceous differentiation.5
Thus far, there are few studies on the dermoscopic features of this disease. Its typical dermoscopic features are called “yellow clods.” The presence of keratotic plugs within the follicular structures enlarges the follicular openings and gives rise to variably large, partially confluent white to yellow clods that are also seen in pigmented actinic keratoses. The simultaneous presentation of a central whitish hair plug suggested a diagnosis of trichofolliculoma that was finally confirmed by the histopathological analysis. In addition, as a compressive result of the mass below, the superficial capillaries of the dermis became markedly dilated, as seen under a dermatoscope. While histopathological examination revealed only one longitudinal section, partial dilated capillaries could also be seen.
Until now, only two reports described the dermoscopy presentation of trichofolliculoma,6-7 one showed a “firework” pattern in a four-month-old lesion. It revealed that the dark brown projections seen in dermoscopy histopathologically correspond to nests of cells radiating from the follicular epithelium.6 Another case showed a well-defined, firm, bluish nodule with a white–pink central area, shiny white structures, dotted vessels, and a central scale, which might be compatible with a more chronic course.7 Therefore, we assume that, because the histopathology may vary according to the maturation stage, the findings of dermoscopy may also vary. The origin of the disease, various phases of the hair cycle, depth of the lesion, and even external stimulus may all affect the dermoscopic findings.
In conclusion, despite distinctive clinical features, diagnosis of trichofolliculoma is sometimes difficult because the presence of the central crater and visible hairs is only 15.5% and 12.2%, respectively, which made dermoscopy examination a potentially useful diagnostic tool. In other words, correlation among the clinicopathological features, dermoscopic pattern, and pathological examination to rule out other processes are critical. Because little is currently known, and specimens for dermoscopic examination are limited, advanced investigations are warranted.
Source of funding
The study was supported by CAMS Innovation Fund for Medical Sciences (No. CIFMS-2017-I2M-1-017).
. Gokalp H, Gurer MA, Alan S. Trichofolliculoma: a rare variant of hair follicle hamartoma. Dermatol Online J 2013;19 (8):19264.
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. Singh N, Kumar N, Chandrashekar L, et al. Umbilicated nodule over eyebrow. Dermatol Online J 2013;19 (9):19622.
. Sellheyer K, Nelson P, Kutzner H, et al. The immunohistochemical differential diagnosis of microcystic adnexal carcinoma, desmoplastic trichoepithelioma and morpheaform basal cell carcinoma using BerEP4 and stem cell markers. J Cutan Pathol 2013;40 (4):363–370.
. Romero-Pérez D, García-Bustinduy M, Cribier B. Clinicopathologic study of 90 cases of trichofolliculoma. J Eur Acad Dermatol Venereol 2017;31 (3):e141–e142. doi:10.1111/jdv.13960.
. Panasiti V, Roberti V, Lieto P, et al. The “firework” pattern in dermoscopy. Int J Dermatol 2013;52 (9):1158–1159. doi:10.1111/j.1365-4632.2011.05122.x.
. Garcia-Garcia SC, Villarreal-Martinez A, Guerrero-Gonzalez GA, et al. Dermoscopy of trichofolliculoma: a rare hair follicle hamartoma. J Eur Acad Dermatol Venereol 2017;31 (2):e123–e124. doi:10.1111/jdv.13870.