The specific diagnosis of a hamartoma may create diagnostic difficulties, both grossly and histologically. We observed an infant who was noted at birth to have a hyperpigmented plaque with follicular accentuation and a slight increase in the amount of hair on the anterior abdominal wall. The clinical differential diagnosis included mastocytoma, epidermal nevus, congenital pigmented nevus, and congenital Becker's nevus. The most striking feature of the biopsy specimen was the presence of large numbers of smooth-muscle fibers permeating the dermis, a finding most consistent with a diagnosis of Becker's nevus, although Becker's nevus has not previously been known to be present at birth.
Report of a Case
At birth, a 3 × 4-cm, yellow-brown, slightly hairy, barely palpable plaque (Fig 1) was noted on the anterior abdominal wall of an otherwise normal, full-term, 2.1-kg female infant. When the plaque was stroked, a slight accentuation, with rapid, brief elevation of the