Hamartoma of the Scalp with Ectopic Meningothelial Elements in a Two-Year-Old Male

A two-year-old male presented with a 1.1 cm, firm, subcutaneous scalp mass. The lesion was discovered at birth, had grown with the child’s head, and recently became painful. Magnetic resonance imaging and ultrasound demonstrated a soft tissue lesion associated with an anomalous connection between the deep venous drainage and the superior sagittal sinus, consistent with sinus pericranii. Surgical excision of the lesion was performed with obliteration of the sinus pericranii. Histologic examination showed subcutaneous tissue with fibrosis and a benign meningothelial proliferation. The cells exhibited a pseudo infiltrative pattern of growth dissecting along the connective tissue planes. The meningothelial cell population was immunopositive for epithelial membrane antigen. The diagnosis of hamartoma of the scalp with ectopic meningothelial elements was made. This is a rare diagnosis, and to our knowledge only nineteen cases have been reported in literature. The current case represents the second report of an intracranial communication, and the first reported case with an associated sinus pericranii. The potential for misdiagnosis as a malignant lesion necessitates knowledge of this entity. Keywords: Hamartoma; Ectopic Meningothelial; lesion; Benign meningothelial proliferation; Scal