Bilateral Subdural Hygromas Following Rupture of a Temporal Arachnoid Cyst in a 16-Year-Old Boy: A Case Report

Arachnoid cysts (ACs) are benign, usually asymptomatic malformations; however, following minor head trauma, rupture can result in subdural hygromas, with bilateral involvement being uncommon and management often debated. A previously healthy 16-year-old competitive boxer presented with two weeks of headache, nausea, vomiting, and diplopia after a blunt head impact. Examination revealed a right abducens palsy with early papilledema. Non-contrast head CT demonstrated a left temporal AC complicated by bilateral convexity subdural hygromas and an approximately 5-mm rightward midline shift. Given the stable initial examination, close observation was undertaken; however, with progressive signs of intracranial hypertension, a stepwise surgical strategy was implemented, consisting of right subdural drainage and fenestration of the left temporal cyst. Follow-up MRI, including cine phase-contrast sequences, confirmed communication between the cyst and basal cisterns and documented fluctuating hygroma volumes (resolution on the right with contralateral variation) without lasting neurological deficit. The clinical course was favorable, with resolution of headache and improvement of diplopia; papilledema regressed, and no cerebrospinal fluid shunt was required. This case highlights the clinicoradiological variability of post-traumatic hygromas associated with ACs in adolescents and supports a stepwise, individualized approach that prioritizes vigilant surveillance and targeted intervention, with flow-sensitive MRI helping to substantiate shunt avoidance when the clinical trajectory is improving.