Spontaneous acute subdural hematoma: Etiologic spectrum, diagnostic approach, and clinical correlates

Acute subdural hematoma (ASDH) is classically associated with head trauma. In rare cases, ASDH occurs in the absence of a precipitating injury and is referred to as spontaneous acute subdural hematoma (sASDH). This entity poses a diagnostic challenge, as the underlying cause is often unclear on initial imaging. We aimed to characterize the imaging features, etiologic spectrum, and diagnostic workup of sASDH using a single-center cohort supplemented by a focused narrative review of the literature.

Adult patients diagnosed with nontraumatic ASDH at a tertiary medical center between January 2017 and May 2025 were retrospectively reviewed. Clinical presentation, imaging findings, radiologic investigations, management, and outcomes were analyzed. All cases were independently reviewed by senior neuroradiologists to confirm the absence of traumatic features. To contextualize institutional findings, a narrative review of the literature was performed, focusing on reported etiologies, imaging characteristics, and diagnostic approaches.

Among 435 patients with ASDH, 23 (5.2%) met criteria for sASDH. The median age was 69 years, and acute-onset headache was the most common presenting symptom (87%). Mean hematoma thickness was 12.0 mm, with a mean midline shift of 5.5 mm. Additional imaging beyond noncontrast CT was performed in most patients, including CTA, MRI, and catheter angiography. A probable underlying etiology was identified in 11 patients (48%), most commonly vascular or neoplastic. Twelve cases remained idiopathic despite extensive evaluation. Surgical evacuation was required in 60% of patients. At last follow-up, 57% achieved good functional recovery. The narrative review demonstrated that reported etiologies of sASDH include rupture of cortical or aneurysmal vessels, cerebral amyloid angiopathy, vascular malformations, anticoagulation-related hemorrhage, and tumor-associated bleeding. Across published series, favorable outcomes were achieved in approximately half of patients, with reported mortality rates ranging from 10% to 30%.

Spontaneous acute subdural hematoma is an uncommon but clinically significant diagnosis with heterogeneous etiologies. Careful radiologic assessment is essential to exclude traumatic features, identify underlying causes, and guide further imaging workup. A structured diagnostic approach incorporating advanced imaging modalities may improve etiologic detection and support timely clinical decision-making.