Subdural Hemorrhage Without Trauma
The available evidence does not provide a specific percentage for subdural hemorrhage cases occurring without trauma, as the provided studies focus predominantly on traumatic brain injury populations and clinical decision rules for trauma-related intracranial hemorrhage.
What the Evidence Shows
Traumatic Context Dominates the Literature
The major guidelines and studies provided focus exclusively on traumatic subdural hematomas in the context of mild traumatic brain injury, with studies like CENTER-TBI and TRACK-TBI examining trauma populations 1.
Clinical decision rules (CCHR and NOC) were developed specifically for patients with witnessed trauma, requiring clear trauma history with loss of consciousness, amnesia, or disorientation 1.
Rare Non-Traumatic Cases Documented
Spontaneous acute arterial subdural hematomas are explicitly described as "rare entities" caused by hemorrhage from cortical perisylvian arteries without known precipitants 2.
One surgical series found that arteriolar subdural hematomas represent less than 5% of all acute and subacute subdural hematomas treated, though the authors note that "while the majority of arteriolar hematomas reported here and in the literature are of traumatic origin, some are undoubtedly spontaneous" 3.
In lobar intracerebral hemorrhage, subdural hematoma was present in 20% of cases (40 of 200 patients), with cerebral amyloid angiopathy identified in pathological specimens, suggesting a non-traumatic mechanism involving rupture of amyloid-laden leptomeningeal vessels 4.
Clinical Implications
When to Suspect Non-Traumatic SDH
Consider spontaneous SDH in patients presenting with acute headache, seizures, or focal neurological deficits without clear trauma history, particularly in the context of cerebral amyloid angiopathy or coagulopathy 2, 4.
Elderly patients with lobar intracerebral hemorrhage should be evaluated for concurrent subdural hematoma, as this combination carries significantly increased 30-day mortality (OR 7.60) 4.
Important Caveats
The absence of reported trauma does not definitively establish non-traumatic etiology, as minor head trauma may be forgotten or unreported, particularly in elderly patients or those with cognitive impairment 3.
Coagulopathy and anticoagulation significantly increase subdural hematoma risk and are independent predictors of poor outcomes, though these cases may still have minor unreported trauma as the precipitant 5.
The literature suggests that truly spontaneous (non-traumatic) subdural hematomas are uncommon, likely representing well under 10% of all cases, with the vast majority having at least minor trauma as a precipitating factor 3, 5.