Classification
Subdural hygromas
- Differential diagnosis
- Vs benign enlargement of the subarachnoid space (benign external hydrocephalus)
- BESS: which is radiologically differentiated by the coursing of vessels through the collection and no effacement of sulci/gyri.
- Chronic Subdural haematoma
- A subdural hygroma may only be distinguished from a chronic subdural hematoma radiologically by the presence of haemorrhage and/or neomembrane formation
- MRI hygromas have CSF signal intensity on all sequences
- Mechanism
- Form after rapid absorption of acute subdural hematoma leaves low pressure subdural space into which CSF/extracellular fluid can accumulate to form subdural hygroma, subdural hygroma expands and forms membranes → Membrane liable to microhaemorrhages producing chronic subdural hematomas,
- Arachnoid tear after trauma/neurosurgery/rupture of arachnoid cyst allows CSF or CSF-like fluid to enter subdural space
Chronic subdural hematomas
- MRI high signal on T1W images owing to the presence of methemoglobin.
Subdural effusion
- Mass of proteinaceous liquid within the subdural space that appears to be associated with bacterial meningitis
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