Inverted Follicular Keratosis: A Retrospective Study Over 10 Years

Abstract

Inverted follicular keratosis (IFK) is a rare benign tumour of the follicular infundibulum characterized by exo-endophytic growing. Generally, the diagnosis of IFK is histopathologically made because clinical differentiation from other lesions is difficult. We present a retrospective series with thirteen patients with histologically confirmed IFK to evaluate the epidemiological, clinical and histopathologic characteristics of IFK. The mean age of the patients at the time of the excision was 53 years with extremes ranging from 19 to 82 years. The sex ratio M/F was 3.3. The lesions affected the face in nine patients mainly the moustache, followed by the scalp in three cases and the arm in one case, and 92% of the localizations are sun-exposed. The diagnosis was never clinically evoked. The lesion had a pink colour in ten cases and was pigmented in two cases and hypopigmented in one case. More than half of the lesions (53%) had a keratotic centre. Histopathological examination showed endophytic intradermal proliferation of basaloid cells with a variable degree of squamoid differentiation. Horn cysts were present in all cases. According to our series, the IFK occurs predominantly in young men, in the face and more specifically in the moustache. Dermoscopy may suggest the diagnosis of the IFK. In fact, a histopathological examination is the gold standard for the diagnosis of the IFK and helps differentiate these benign tumours from possible malignant neoplasms.

Keywords: Benign tumours; inverted follicular keratosis; pathology.

Figure 1

Clinical features of inverted follicular keratosis (a) affecting the cheek with keratotic centre, (b) affecting the scalp, (c) hyperpigmented lesion affecting the arm, (d) hypopigmented form affecting the cheek

Figure 2

Histopathological features: low power view showing endophytic intradermal proliferation of basaloid cells with a variable degree of squamoid differentiation (HEx25)

Figure 3

Inverted seborrheic keratosis: (a) intradermal proliferation of close-set basaloid cells organized in an endophytic configuration (HEx50). (b) Presence of pseudohorn cysts (→) (HEx100). (c) high power of pseudohorn cysts (→) and squamous eddies () (HEx100). (d) The dermis shows severe chronic inflammation (HEx100)