Pacinian collagenoma: a distinct form of sclerotic fibroma

Sclerotic fibroma (storiform collagenoma) is a rare benign skin tumor. A solitary tumor, as well as multifocal lesions, are found either sporadically, or associated with Cowden syndrome. The tumor usually presents as clinically asymptomatic, slowly growing papule or nodule on the skin of the head, neck, and upper extremities. Microscopically the lesion is sharply demarcated, composed of hyalinized bands of collagen with low cellularity and a distinctive irregularly whorled or storiform pattern. We describe a case of a unique variant of this tumor in the scalp of a 33-year-old male. The tumor was microscopically composed of concentrically arranged collagen bundles with prevailing type III collagen, which resembled an enlarged Vater-Pacini corpuscle, with low density of CD34-positive and glucose transporter 1-negative spindle shaped cells. The specific microscopic appearance is suggestive of the term "Pacinian collagenoma" for this unique benign tumor.