Multiple, comedo-like openings filled with keratin plugs

A healthy 15-year-old girl presents with a solitary, asymptomatic lesion on her back. The lesion has been present since birth but has enlarged over the past 2 years. She denies association with previous trauma and irritation. Examination reveals multiple, comedo-like openings filled with dark lamellate keratinocyte plugs grouped in a linear distribution over a slightly hypotrophic area of 3 cm ...