Spontaneous resolution of a Meckel's cave arachnoid cyst causing sixth cranial nerve palsy

A 32-year-old pregnant woman developed a progressive right sixth cranial nerve palsy as an isolated finding. Brain MRI disclosed a discrete lobulated lesion centered in the right Meckel's cave with intermediate signal on T1, high signal on T2, and diffusion characteristics similar to those of cerebrospinal fluid on apparent diffusion coefficient mapping. The initial radiologic diagnosis was schwannoma or meningioma. No intervention occurred. Shortly after cesarean delivery, the abduction deficit began to lessen spontaneously. One month later, the abduction deficit had further improved; 7 months later it had completely resolved. Repeat MRI after delivery failed to disclose the lesion, which was now interpreted as consistent with an arachnoid cyst arising within Meckel's cave. Twenty-one similar cases of Meckel's cave arachnoid cyst or meningocele have been reported, 7 found incidentally and 14 causing symptoms, 2 of which produced ipsilateral sixth cranial nerve palsies. All previously reported symptomatic patients were treated surgically. This is the first report of an arachnoid cyst arising from Meckel's cave in pregnancy and having spontaneous resolution.