Teaching NeuroImages: Spontaneous resolution of a giant intracranial arachnoid cyst.

A giant arachnoid cyst (63 83 11 cm) of left middle cranial fossa was found incidentally in a 3-year-old boy with head MRI examination for increased head circumference (figure 1). Surgical intervention was refused by his parents since the boy was asymptomatic, and the patient was followed up. Repeated MRI performed 2 years later revealed disappearance of the cyst, and the compressed brain tissue had significantly re-expanded (figure 2). There was no history of head trauma or stroke. The spontaneous resolution of a giant intracranial arachnoid cyst is extremely rare and the mechanism is not clear.