Orbital intramuscular schwannoma.

In an 8-year-old girl with asymptomatic proptosis, computed tomographic scans showed a large medial orbital mass that contoured the globe anteriorly, bowed the optic nerve laterally, and extended posteriorly to the orbital apex. T1-weighted coronal magnetic resonance images showed the mass to be a diffusely enlarged medial rectus muscle. Histopathologic examination of a medial rectus muscle biopsy specimen disclosed a multinodular, intramuscular schwannoma, separating and infiltrating normal skeletal muscle fibers. The intramuscular location and multinodular configuration of this tumor, together with its occurrence in a child, distinguish it from previous orbital schwannomas.