Hair cortex comedo: a series of 34 cases.

Hair cortex comedo was described originally in an article detailing 2 cases of a comedo-like clinical lesion that was histologically a keratinous plug with cornification similar to the cortex of the hair shaft. We have collected retro- and prospectively a series of 34 cases of hair cortex comedo. In our series, there was a slight female predominance (Male:Female of 1:1.4), and the mean patient age was 28.8 years. All lesions were solitary, distributed mainly on the head and neck or trunk, and were described clinically as a blue subcutaneous papule or nodule with "cyst" as the most common clinical differential diagnosis. Histologic examination showed a solitary, vertically oriented, uniformly sized oval nodule of compact laminated corneocytes sitting in a patulous invagination lined by epithelium similar to the infundibulum, isthmus, or combinations of them; rarely matrical epithelium was identified. Entrapped melanin (30/34 cases), shadow cells (16/34 cases), and calcification (12/34 cases) were identified commonly. Remnants of a surrounding follicle were noted in 15 cases, with infundibular epithelium in 9 of the cases, isthmic epithelium in 3, and matrical or supramatrical epithelium (or both) in 3. There was an associated dense granulomatous infiltrate in the majority of the cases (25/34). Although hair cortex comedo was thought originally to be a variant of dilated pore of Winer, we believe that these distinctive lesions, which are characterized histopathologically by a uniformly sized vertically oriented dermal plug of laminated corneocytes with entrapped melanin and surrounding granulomatous inflammation, are likely derived from matrical or supramatrical cells (or both).