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arachnoid cyst, spontaneous development, suboccipital craniotomy
Intracranial arachnoid cysts are thought to be primarily congenital lesions that are commonly found incidentally on brain imaging. Other postulated pathophysiological mechanisms include meningeal infections, trauma, or iatrogenic (e.g. post neurosurgical procedures). The spontaneous appearance of these cysts is very rare. In this report we present the first case of an arachnoid cyst occurring spontaneously in a 54-year-old man presenting with progressively worsening headaches with subsequent imaging showing a new arachnoid cyst at the left cerebellopontine angle (CPA). Serial MRI tests revealed the cyst to be expanding rapidly coinciding with worsening of the patients headaches, tinnitus, and an ataxia; thus, the decision was made to offer surgical intervention. While arachnoid cysts in adults are primarily thought to follow a stable course in most cases, the rapid progression in this case suggests that close monitoring with serial imaging may be warranted.