Spontaneous rupture of an arachnoid cyst in an adult: illustrative case

BACKGROUND: Arachnoid cysts are common intracranial mass lesions frequently discovered as incidental findings on radiographic imaging. It is routine practice to monitor these lesions as a large majority remain stable. Although traumatic cyst rupture is a known risk, it is rare for patients to present with spontaneous rupture. OBSERVATIONS: The authors report the case of a 32-year-old patient who required emergent neurosurgical intervention for spontaneous rupture of a left hemispheric arachnoid cyst. LESSONS: Patients with ruptured arachnoid cysts can present with vague, nonspecific symptoms that may delay diagnosis. If not diagnosed and treated promptly, arachnoid cyst rupture can progress to a neurosurgical emergency as the subdural collection may cause extensive mass effect and even cerebral herniation.