Acute on Chronic Subdural Hematoma

Findings:

A large heterogeneous extraaxial collection extends along the right cerebral convexity, associated with sulcal effacement. Multiple septations are seen, with hyperdense fluid fluid levels on CT. Gradient echo image demonstrates patchy zones of linear and irregular hypointensity within the region. The collection overall does not show restricted diffusion, with some spotty hyperintensities related to blood products.

Differential Diagnosis/Discussion:

The differential diagnosis of extraaxial fluid collections includes hemorrhage, infection(empyema), subdural effusions/hygromas, and arachnoid cyst among other less likely causes. Hemorrhage is documented within this collection on both CT and MR, without the prominent diffusion restriction seen in empyema, and clearly this is not the CSF intensity/density of arachnoid cyst. The hematocrit levels indicate a component of acute/recent hemorrhage, and the hypointense hemosiderin stained septations indicate the formation of membranes in a chronic collection.

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