Perineural cyst with intracystic hemorrhage following aneurysmal subarachnoid hemorrhage: A case report

RATIONALE: Most perineural cysts are asymptomatic and discovered incidentally at the time of imaging. Although enlargement of the perineural cyst (PC) through a ball-valve mechanism and resultant compression of the adjacent neural or bony structures are known to be a source of pain in PCs, the reason why asymptomatic PCs become symptomatic is unclear. The authors report a case of PC, which was presumed to become symptomatic after subarachnoid hemorrhage without enlargement of the pre-existing PC. PATIENT CONCERNS: A 47-year-old woman complained of lumbosacral pain after neck clipping for a ruptured cerebral aneurysm. DIAGNOSES: Magnetic resonance imaging (MRI) revealed a PC with intracystic hemorrhage at the S2 level. In comparison with the size of the PC on computed tomography performed 3 years ago, there was no change in the size. Electrodiagnostic studies performed 6 weeks after the onset of the pain showed subacute right S2 radiculopathy. INTERVENTIONS: With conservative treatment, her pain gradually diminished. OUTCOMES: When the lumbosacral pain improved, follow-up MRI showed that a fluid-fluid level within the PC disappeared. LESSONS: Hemorrhage from the subarachnoid space, such as spontaneous aneurysmal SAH, into the pre-existing PC can cause an asymptomatic PC to become symptomatic without getting enlarged. Stretching of the nerve root due to hemorrhage or irritation of the nerve root due to an inflammatory reaction to blood products can make asymptomatic PCs symptomatic without enlargement of PCs.