Horner syndrome secondary to otomastoiditis.

A 5-year-old girl was brought to the emergency room with unequal pupil size, fever, and ear pain. Computed tomography and magnetic resonance imaging showed left otomastoiditis complicated with a subperiosteal abscess in the posteromedial left temporomandibular joint. Magnetic resonance angiography revealed enhancement of the left canalicular carotid vessel wall due to adjacent inflammatory process, with irritation of post synaptic sympathetic fibers, causing left Horner syndrome. Horner syndrome can be caused by apical lung tumors, carotid artery dissection, and metastatic neuroblastoma, but otomastoiditis is an uncommon etiology. Recognition and further workup of anisocoria is crucial to management of extracranial complications of otomastoiditis.