Pilomatrixoma: An Uncommon Tumor of the Brow

A 32-year-old man presented with a mass of the left upper brow, which enlarged over 8 weeks (Fig 1, black arrow). After surgical removal, it was found to be a pilomatrixoma (or calcifying epithelioma of Malherbe; Fig 2). Pilomatrixomas are rare (<1% of all benign skin tumors), and believed to be caused by genetic alterations in hair cells causing dysregulated apoptosis. Their histology is striking: darkly staining “basophilic” cells (Fig 3, arrow), shadow cells lacking nuclei (Fig 3, asterisks), keratinization (Fig 3, star), and calcium deposits.