A young adult patient with multifocal arachnoid developmental anomalies: traumatic rupture of left middle fossa arachnoid cyst complicated by chronic subdural haematoma treated with burr-hole drainage, with early postoperative surveillance considerations

Rupture of middle fossa arachnoid cysts causing chronic subdural haematoma (CSDH) is far less common in young adults than elderly populations, especially when complicated by multiple intracranial arachnoid lesions and uncontrolled hypertension. Current debates focus on whether concurrent cyst resection should be performed alongside haematoma evacuation, yet evidence specific to young patients with multifocal developmental arachnoid anomalies remains limited. This case report analyses a young man with multifocal arachnoid cysts who developed CSDH after minor head trauma, exploring stratified treatment strategies and rational long-term surveillance. A 36-year-old male with a 7-year history of uncontrolled hypertension presented with post-traumatic progressive headache for one month. Initial cranial CT revealed a left temporal arachnoid cyst with mild subdural effusion; follow-up MRI confirmed left frontotemporoparietal CSDH with 0.8 cm midline shift, concurrent cisterna magna cyst and suspected septum pellucidum cyst. Minimally invasive burr-hole drainage was performed as first-line standard therapy. Intraoperatively, 30 mL chronic haemorrhage was drained, with immediate relief of headache. One-month postoperative CT showed near-complete haematoma absorption, while the left temporal arachnoid cyst re-emerged; this imaging finding reflects resolution of postoperative haematoma, pneumocephalus and oedema rather than de novo cyst formation. No reoperation was performed, and structured imaging follow-up was scheduled. Standard burr-hole drainage achieved effective intracranial decompression, consistent with first-line neurosurgical guidance for cyst-associated CSDH. The persistent temporal cyst on delayed imaging represents the natural anatomical status after isolated haematoma evacuation, as the cyst wall was not addressed intraoperatively. Given the patient’s young age, multifocal arachnoid developmental malformations and vascular risk factors, intensive blood pressure management and tiered imaging surveillance were recommended. For young adults with trauma-induced arachnoid cyst rupture and CSDH, burr-hole drainage remains the mandatory primary intervention for acute mass effect relief. Persistence of the native arachnoid cyst after drainage is an expected anatomical outcome rather than an adverse event. Unique risk profiles in younger patients limit direct extrapolation of recurrence data derived from elderly CSDH cohorts. Individualised management requires stratified early and long-term imaging follow-up, rigorous vascular risk factor control, and intraoperative cyst wall assessment when feasible.