Tumor of the follicular infundibulum is a rare benign adnexal tumor arising from the follicular infundibulum. The histopathology of the tumor is distinctive, which occurs as a platelike dermal nodule with multiple thin connections to the overlying epidermis (see the images below). The tumor usually manifests as a single lesion, but an eruptive (multiple) form may occur.
Tumor of the follicular infundibulum shows a platelike dermal tumor with anastomosing islands and cords with connections to the overlying epidermis an....
Tumor of the follicular infundibulum shows epidermal connections, horn cysts, and anastomosing islands (hematoxylin and eosin stain, 100X magnificatio....
Tumor of the follicular infundibulum shows epidermal connections, peripheral palisading, and horn cyst (hematoxylin and eosin stain, 400X magnificatio....
Follicular infundibulum tumor is a benign tumoral proliferation that arises from the follicular infundibulum. The external root sheath of the follicle has been shown to give rise to these tumors. A possible relation to sun exposure has been reported.
Follicular infundibulum tumor is uncommon. Since the original report from Mehregan and Butler in 1961, only a few new cases have been reported. The overall relative frequency ranges from 3-10 cases per 100,000 specimens examined.
No racial predilection is known for follicular infundibulum tumor.
A slight female predominance is recognized for follicular infundibulum tumor.
Most cases of follicular infundibulum tumor occur in patients older than 60 years.
The clinical features of follicular infundibulum tumor depend on the subtype, which may be either solitary or eruptive. In the eruptive form, multiple lesions develop over time. Neither subtype usually causes symptoms.
Solitary follicular infundibulum tumors have no distinctive clinical features. Usually, a solitary tumor presents as a scaly nodule up to 1.5 cm in diameter and located on the head or neck. A solitary tumor frequently is misdiagnosed as basal cell carcinoma or seborrheic keratosis.
Eruptive follicular infundibulum tumor lesions have been described in most reports as a sudden onset of multiple (up to 200), variably scaling, hypopigmented macules and papules confined to the head, neck, and upper trunk. They resemble tinea versicolor, pityriasis alba, or disseminated superficial actinic porokeratosis. Vitiligolike hypopigmented facial macules have also been reported. The terms infundibulomas and infundibulomatosis apply to the eruptive form.
An article from 2004 described a case of multiple infundibulomas manifesting as hundreds of 4- to 10-mm red-brown papules in the intertriginous areas, resembling Darier disease. A 2009 article described ill-defined, scaly, reticulated plaques on photodamaged skin resembling eczema craquel é, located on the bilateral sides of the face and neck. These plaques were of 5 years' duration and were accentuated with sun exposure. Biopsy showed multiple infundibulomas.
Rare cases have been associated with nevus sebaceous and Cowden syndrome.
The cause of follicular infundibulum tumor is unknown.
Tumor of the follicular infundibulum is a histologic diagnosis. Most cases typically resemble the original description by Mehregan and Butler. A platelike fenestrated subepidermal tumor extends horizontally under the epidermis with multiple cordlike connections to the overlying epidermis. Upon serial sectioning, connections between the pale-staining, glycogen-containing, tumoral keratinocytes and the external root sheath of adjacent hair follicles usually can be found. Peripheral palisading of the basal cells is present.
Peripheral palisading of basaloid cells frequently is observed. Pale staining results from the presence of glycogen analogous to the external root sheath and is confirmed by periodic acid-Schiff (PAS) stain with diastase digestion. A dense band or brushlike network of elastic fibers frequently is demonstrated at the border of the tumor, again analogous to the normal hair follicle. This can be observed readily using Verhoeff, van Gieson, or orcein stains.
A case report from 2001 noted foci of sebaceous differentiation within the fenestrated epithelium.
For multiple and eruptive follicular infundibulum tumors, treatment usually is unrewarding, since attempted treatment using corticosteroids, keratolytics, cryotherapy, and topical and systemic retinoids results in only partial improvement.
For solitary follicular infundibulum tumors, treatment is simple excision.
Prognosis is excellent in follicular infundibulum tumors. Follicular infundibulum tumor is benign, although malignant transformation to a basal cell carcinoma was reported twice in a patient with multiple lesions. Basal cell carcinoma and squamous cell carcinoma have also described within a field of multiple infundibulomas.
Additional case studies, both reported in 2009, have proposed conflicting views of the nature of follicular infundibulum tumor. First, Abbas and Mahalingam suggest that tumor of the follicular infundibulum is a benign epidermal reaction pattern. In their series of 74 cases, all showed benign histologic features, and, in addition, 25% were identified in association with other cutaneous lesions, which included basal cell carcinoma, actinic keratosis, desmoplastic melanoma, junctional nevus, tricholemmoma, and epidermoid cyst.
Second, in the same journal, Weyers et al made the statement that tumor of the follicular infundibulum is basal cell carcinoma. In their series of 24 cases, they noted, often only focally, changes typical of basal cell carcinoma such as peripheral palisading, germinative cells, crowding of cells, individual necrotic neoplastic cells, fibromucinous stroma, and stromal-epithelial island clefts. In addition, 5 cases were associated with obvious basal cell carcinoma, and, in some cases, recurrences were noted in completely removed basal cell carcinoma in which tumor infundibulum was present at the surgical margins.