Acute subdural hematoma

Findings

There is acute subdural hematoma along the tentorium. This extends along the posterior interhemispheric fissure. The ventricles are prominent out of proportion to the sulci raising the possibility of obstructive hydrocephalus. The fourth ventricle is normal in size. No definite tectal mass is appreciated.

Differential diagnosis: "Bright tentorium"
- Subdural hematoma
- Epidural hematoma
- Aneurysmal bleed
- Metastatic disease to the cerebellum with local bleeding
- Isodense primary CNS tumor (meningioma) with focal bleeding

Other subdural fluid collection
- Hygroma (clear CSF, no encapsulating membranes)
- Effusion (xanthochromic fluid from extravasation of plasma from outer membrane; 20% evolve into chronic SDH)
- Empyema (peripheral enhancement, restricted diffusion centrally)

Epidural Hematoma
- Biconvex extra-axial collection
- Often associated with fracture
- May cross dural attachments, limited by sutures
- Pachymeningopathies (thickened dura)

Chronic meningitis (may be indistinguishable)
- Post-surgical (shunt, etc)
- Intracranial hypotension ("slumping" midbrain, tonsillar herniation)
- Sarcoid (nodular, "lumpy-bumpy")

Tumor
- Meningioma, lymphoma, leukemia, metastases
- Dural based, enhancing mass
- ± Skull involved


Diagnosis: Acute subdural hematoma


Key points

Acute (± 6 hrs-3 days) hemorrhagic collection in subdural space
Diagnostic clue: Crescent-shaped, homogenously hyperdense on CT, extra-axial collection that spreads diffusely over affected hemisphere
May cross sutures, not dural attachments
May extend along falx & tentorium
Compresses & displaces underlying brain
Recurrent, mixed-age hemorrhage in a child raises suspicion of non accidental trauma!
CT density & MR signal intensity vary with age & organization of hemorrhage
Protocol advice: Use wide window settings (150-200 HU) to identify small SDH

Etiology
- Trauma most common
Stretching & tearing of bridging cortical veins as they cross subdural space to drain into dural sinus
Both nonimpact as well as direct injury
Trauma may be minor, particularly in elderly

- Less common etiologies include
Dissection of intraparenchymal hematoma into subarachnoid, then subdural space
Aneurysm rupture
Vascular malformations: Dural AVF, AVM, cavernoma
Coagulopathy

Predisposing factors
- Atrophy
- Shunting (leads to increased traction on superior cortical veins)
- Arachnoid cyst (middle fossa most common site)

Epidemiology: SDH found in 10-20% imaged & 30% autopsy cases following craniocerebral trauma
Associated abnormalities: > 70% of aSDH have other significant associated traumatic lesions