Sequestrated meningoceles of scalp: extracranial meningeal heterotopia.

Sequestrated meningocele of the scalp has seldom been reported and is difficult to diagnose. Clinically it resembles dermoid cyst, hemangioma, or alopecia; radiographs and computed tomographic scans reveal no cranial bone defect, and surgery discloses no communication with the cranial cavity. Histologically, the lesion is characterized by a loose arrangement of connective tissue in dermis and subcutis, associated with flattened cells around collagen fibers (meningothelial cells). Most examples are very vascular, sometimes mimicking angioma, and about one third contain small necrotic foci. The meningothelial nature of the lesion is shown by its architectural similarity to communicating meningocele, and its identical immunoperoxidase reactions with vimentin and epithelial membrane antigen. In the 12 cases reported herein, most lesions were small (1 to 1.5 cm), and all but one were noted at birth but usually not resected until the patient had reached age 1 to 4, and one not until the patient was 31 years of age. Five lesions were not midline. We have been unable on histologic grounds to determine whether meningoceles are communicating or sequestrated. Compared with 20 communicating meningoceles, the sequestrated lesions were usually smaller, found in slightly older patients, and much less likely to be associated with hydrocephalus. The local excision of scalp lesions in children should include a search for a small intracranial connection.