A newborn girl is noted to have a midline lumbar depression at birth. She is twin A born by uncomplicated vaginal delivery at 38 weeks and 5 days of gestation to a 31-year-old gravida 2, now para 3 mother after dichorionic/diamniotic twin pregnancy via in vitro fertilization. The pregnancy was otherwise complicated by diet-controlled gestational diabetes and maternal history of herpes simplex virus without lesions or prodromal symptoms at the time of delivery. Maternal medications during pregnancy included prenatal vitamins and valacyclovir prophylaxis. The infant transitions well and requires only routine care at the time of delivery.

Her initial physical examination reveals a circumferential 1 × 0.5-cm punched-out, skin-covered lesion overlying the midline spine at the level of L4-L5 vertebrae with surrounding dermal melanocytosis extending from the midline to the left flank (Fig 1). The examination findings are...

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