Mechanism of Subdural Hematoma Resorption
Subdural hematomas are resorbed through a complex inflammatory and angiogenic process involving fibrinolysis, phagocytosis by macrophages, and gradual absorption of blood breakdown products through the dura and arachnoid membranes, though this natural resorption process is often incomplete or prolonged, particularly in chronic subdural hematomas where ongoing inflammation and neovascularization create a self-perpetuating cycle of re-bleeding and fluid accumulation. 1
Pathophysiology of Chronic Subdural Hematoma Formation and Resorption
The current understanding of chronic subdural hematoma (cSDH) pathophysiology reveals why natural resorption is often inadequate:
A positive feedback loop develops involving inflammation, angiogenesis, and persistent exudation of blood into the subdural space, which impairs natural resorption mechanisms 1
Neovascularization of the outer membrane creates fragile new blood vessels that are prone to repeated micro-hemorrhages, continuously adding to the hematoma volume and preventing effective resorption 1
Inflammatory mediators perpetuate the cycle by promoting further angiogenesis and membrane formation, creating a self-sustaining pathologic process 1
Natural History and Resorption Patterns
The natural resorption of subdural hematomas varies significantly based on several factors:
Acute subdural hematomas can sometimes resolve spontaneously in small volumes, though progression to chronic subdural hematoma formation, further enlargement, seizures, and progressive midline shift can occur when managed conservatively 2
Initial hematoma volume and severity (determined by Glasgow Coma Scale score) are more predictive of surgical need or future expansion than patient age alone 2
No significant difference in rate of volume expansion or resolution time was observed between younger (<65 years) and older (>65 years) patients in observational studies 2
Clinical Implications for Management
Given the limitations of natural resorption:
Surgical evacuation remains the standard treatment for symptomatic chronic subdural hematomas, as medical management alone is often insufficient due to the pathophysiologic mechanisms that impair natural resorption 3, 4
Burr hole drainage is the preferred first-line surgical treatment for symptomatic chronic subdural hematomas presenting with altered consciousness 3
Middle meningeal artery embolization (MMAE) has emerged as an effective treatment for promoting cSDH resorption and reducing recurrence rates by interrupting the angiogenic cycle 1
Use of subdural drains following surgical drainage significantly decreases recurrence rates (RR 0.46; 95% CI 0.27-0.76), likely by facilitating more complete evacuation and preventing re-accumulation 5
Important Caveats
Anticoagulant use does not necessarily predict worse outcomes when appropriate reversal agents are administered early, though these patients require special consideration 3, 2
Corticosteroids as adjuvant therapy are associated with higher morbidity (RR 1.97; 95% CI 1.54-2.45) without significant improvement in recurrence or cure rates, and should generally be avoided 5
Delaying surgical intervention in symptomatic patients with altered consciousness can lead to neurological deterioration and poorer outcomes 3