Hair Follicle Nevus Located on the Neck: Comparison with Accessory Tragus, Cervical Chondrocutaneous Branchial Remnants and Trichofolliculoma

Hair follicle nevus (HFN) is a rare, benign, follicular hamartoma that most frequently presents as a congenital nodule on the face. We experienced a rare case of HFN on the neck of a 14-year-old boy and performed a pilot immunohistochemical study with cytokeratin 19 (CK19) to compare the staining pattern of hair follicles in HFN and its differential diagnoses, accessory tragus, cervical chondrocutaneous branchial remnants (CCBR) and trichofolliculoma. With hematoxylin and eosin stain, HFN showed numerous tiny hair follicles in the dermis with several sebaceous and eccrine glands, and perifollicular fibrous thickening. With CK19 stain, some hair follicles in HFN and CCBR showed positive expression, a few hair follicles in accessory tragus showed weak expression, and no hair follicles in trichofolliculoma showed expression. The present report supports the view that HFN, accessory tragus and CCBR are within the same spectrum of hamartomas.