A 3-year-old child's mother notes that a large port wine stain on the left side of the child's face has not diminished in size since birth. This irregular, slightly raised, red-blue area is not painful, but is very disfiguring. Histologically, this lesion is most likely composed of a proliferation of which of the following tissue components?

The most common tumor of infancy is a hemangioma, and these benign neoplasms form a large percentage of childhood tumors as well. Although benign, they can be large and disfiguring. Fibromatoses are fibromatous proliferations of soft tissues that form solid masses. Lymphangioma is another common benign childhood tumor seen in the neck, mediastinum, and retroperitoneum. Lymphoblasts as part of leukemic infiltrates or lymphomas are not likely to be seen in skin, but mediastinal masses may be seen. A proliferation of neuroblasts occurs in neuroblastoma, a common childhood neoplasm in the abdomen.