A 25 year-old female presented with a verrucous lesion on her medial part of her right eyebrow [Figure 1]. A clinical diagnosis of a viral wart was made and the lesion was biopsied. The histologic sections demonstrated an endo-exophytic lesion with squamous eddies and no cytologic atypia [Figures 2 and 3]. Immunoperoxidase staining for HPV was negative.
Figure 1.
A 25-year-old female with a verrucous lesion on the right medial eyebrow
Figure 2.
Endo-exophytic lesion with marked hyperkeratosis. (H and E, ×100)
Figure 3.
Numerous squamous eddies and no cytologic atypia. (H and E, ×400)
WHAT IS YOUR DIAGNOSIS?
ANSWER
Inverted follicular keratosis.
DISCUSSION
Described by Helwig in 1954, inverted follicular keratosis (IFK) is a benign lesion with a histologic appearance that can be mistaken for squamous cell carcinoma. IFK typically occurs in middle-aged and older individuals, more often in men. The face is the most common site, especially the upper lip and cheek, followed by the nose, chin, forehead, eyelid, and eyebrow. IFK has also been found on the scalp, temple, conjunctiva, neck, trunk, extremities, vulvar skin, and scrotum.[1,2,3,4,5,6] The vulvar and scrotal lesions may have been related to shaving injuries of hair follicles.[5,6] Clinically, IFK is frequently diagnosed as verruca vulgaris. Other clinical impressions include basal cell carcinoma, keratoacanthoma, and squamous cell carcinoma.[1,2,3,5] IFK can present as a cutaneous horn, even a massive one.[1,2,3,7] Dermoscopic and reflectance confocal microscopy features of IFK have been described and may be helpful in its diagnosis.[8]
Histologically, IFK is a circumscribed lesion demonstrating exophytic as well as endophytic growth with papillomatosis, hyperkeratosis, and parakeratosis. There are abundant squamous eddies, and cytologic atypia with mitotic activity may or may not be present. IFK can be mistaken for squamous cell carcinoma, especially on superficial biopsy.[1,2,3,5,6,9] IFK has histologic similarities to irritated seborrheic keratosis, keratoacanthoma, trichilemmoma, and verruca vulgaris, but most studies have found IFK to be consistently negative for HPV by immunohistochemistry, in situ hybridization and polymerase chain reaction.[1,2,3,10,11,12,13,14]
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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