A Maroon Plaque in an Infant

Abstract

L arge congenital masses appropriately raise clinical concern, especially when they do not present with the classic appearance, thus requiring consideration of broad differential diagnostic categories prior to conclusive diagnosis. We discuss analysis and treatment of a vascular lesion most closely resembling a fibrous hamartoma of infancy (FHI). Report of a Case.A 13-day-old healthy female infant presented for evaluation of a "lump" on her right buttock. She was born at 37 weeks' gestation via scheduled cesarean section. Pregnancy was complicated by gestational diabetes, and birth by initial oxygen saturation of 60% that had to be normalized with supplementation. The plaque appeared asymptomatic at birth and had not changed much by the time of presentation. Physical examination revealed a 3 ϫ 2-cm maroon, firm, welldemarcated, nonblanching plaque with a palpable subcutaneous component and overlying hypertrichosis on the right buttock (Figure 1). Manipulation produced piloerection (positive pseudo-Darier sign). Histopathologic analysis revealed two predominant components, a prominent proliferation of spindle-shaped cells admixed with numerous round blood vessels lined by plump endothelial cells throughout the dermis and subcutis (Figure 2).Immunohistochemical staining results were diffusely positive for CD31 and CD34, highlighting capillary structures, and focally positive for CD68, SMA (smooth-muscle antibody), and EMA (epithelial membrane antigen). Findings for S-100 and claudin were negative. The spindle-shaped component was somewhat analogous to that of FHIs but not of involuted hemangiomas. The storiform architecture seen in dermatofibrosarcoma protuberans and endothelial multilayering or atypia to suggest malignancy were lacking. Crescent-shaped vascular spaces, spindled endothelial cells, and hyaline stroma typical of kaposiform hemangioendothelioma were not seen. Over 5 months, the plaque became larger, lighter in color, and less indurated. The patient ultimately underwent surgical excision at age 8 months.