A yellow-orange hairless patch on a 1-year-old

A 1-year-old boy presents with a single, L-shaped, yellow-orange hairless patch over the left preauricular skin. The patient's mother notes that he has never grown hair in that location. The mother is concerned because the area used to be smooth, but seems to be changing. The patient has a history of prematurity and low birthweight but is otherwise healthy. The ...