Glial choristoma of the temporal bone in a 7-month-old infant.

IMPORTANCE Heterotopic glial tissue is a rare, benign congenital anomaly that can present as a fibrous mass with or without overt signs of neural tissue origin, such as overlying alopecia, pigmentation, or a "hair collar" sign. These lesions are typically found in the midline area, though they have been found laterally involving the mastoid and middle ear regions. As demonstrated by this case report, a lateral scalp lesion may represent glial tissue even if fine-needle aspiration does not demonstrate neural findings. OBSERVATIONS This single case report represents a 7-month-old white infant who presented with a lateral scalp mass over the mastoid area. The mass enlarged as she grew, causing external auditory canal obstruction. Fine-needle aspiration demonstrated fibrovascular tissue, and computed tomographic imaging showed a small bony defect over the mastoid area but no intracranial communication. The final pathologic finding was consistent with glial choristoma, a rare, benign congenital lesion involving heterotopic neural tissue. CONCLUSIONS AND RELEVANCE Congenital scalp lesions can represent heterotopic neural tissue and warrant complete evaluation prior to treatment; fine-needle aspiration biopsy is not necessarily reliable to rule out neurogenic origin, as demonstrated in this case. The possibility for intracranial extension should always be considered and fully evaluated with computed tomography or magnetic resonance imaging prior to operative intervention. Most prior published case reports of heterotopic glial tissue involving the mastoid and/or middle ear spaces describe adults and suggest that such lesions were acquired later in life. This report of a lateral glial choristoma overlying the mastoid bone in an infant supports a congenital origin of this lesion.