By two weeks, subdural hematomas are generally liquified, with the gross appearance of 'motor oil.' On CT imaging, chronic subdural hematomas appear hypodense (blacker) than adjacent brain. Chronic subdural hematomas may also develop thick and organized membranes with prominent vasculature, which are well-demonstrated on enhanced CT or MR imaging. These vascular membranes are a common source of rebleeding leading to enlargement of the hematoma. Chronic subdural hematomas may be clinically occult, or may cause focal neurological deficits, seizures or macrocephaly. Chronic hematomas are drained by placement of burr holes and may also require craniotomy if they contain organized vascular membranes.
In children, the subject of 'chronic subdural effusion' or 'benign extra-axial hydrocephalus' deserves attention. This entity has not been uniformly defined but generally refers to infants and toddlers with a large head circumference (often > 95th percentile) and enlarged subarachnoid and/or subdural CSF spaces. Some of these children have a family history of large head circumference and usually follow a benign clinical course. Other cases are thought to result from repeated minor subdural or subarachnoid hemorrhages over time. The latter children sometimes require subdural-to-peritoneal shunting because of severe macrocephaly, chronic neurological deficit or developmental delay. Some experts maintain that benign subdural effusions can convert to hemorrhagic effusions as the result of everyday minor head trauma common in infants and toddlers. Others argue that all cases of hemorrhagic subdural effusion represent nonaccidental trauma.
With hemorrhagic subdural effusions, CT imaging demonstrates slightly higher CSF attenuation in the extra-axial spaces than in the ventricles (see Fig. 5A). MR imaging more accurately demonstrates the presence of organized membranes and loculated subdural fluid collections of varying fluid density (i.e., protein level) (see Fig. 5B). Benign subdural effusions appear in CT and MR imaging as an enlarged but otherwise normal subarachnoid space.
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