Abstract

PF is a rare, benign follicular neoplasm. Clinically, it presents as a slow growing cystic papule. Microscopic examination shows well circumscribed neoplasm with solid-cystic islands and differentiation in all components of follicle from infundibulum to hair matrix with laminated keratin in the cystic structure and matrixial differentiation. In the literature, three subtypes have been implicated; nodular, superficial, and cystic. Histopathologic differential diagnosis includes trichoblastoma, trichoepithelioma and trichofolliculoma. We present a 73 year old male whose medical history significant for seborrheic dermatitis, seborrheic keratosis and milia developed a 4 mm firm, homogenous blue, nonblanching papule on the left upper eyelid (LUE). Clinical presentation for LUE lesion was consistent with blue nevus. Microscopic examination of the LUE revealed dermal basaloid differentiation with infundibulocystic structure formation, follicular germs and papillae and stroma with melanin pigment incontinence. The lesion showed positive staining for BCL2, BER EP4, CK19, CK5/6, GATA3, LEF1, P63 and negative staining for CD34, EMA and SOX10. In light of these findings the diagnosis of pigmented PF was rendered. PF is a rare neoplasm that usually affects older population over the age of 50. Clinical diagnosis is challenging due to its rarity and nonspecific presentation. Clinically, it mimics basal cell carcinoma infundibular cyst, and trichoepithelioma. Microscopic examination is required for definitive diagnosis. Morphologically, it resembles trichofolliculoma which presents as a cystic structure with mature hair follicle differentiation without proliferation of immature basaloid tumor cells. In our case, prominent immature basaloid cell proliferation with melanin deposition in the cystic structures and incontinence to stroma was present. In the literature, this is the first PF case that presented with melanin pigmentation.

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