Variously classified as hematomas (chronic subdural hematoma), effusions, or hygromas, with differing definitions associated with each. Since the appearance of imaging and the treatment is similar, Litofsky et al proposed that they all be classified as extra-axial fluid collections 1)
The difference between these lesions and “benign” subdural effusions may simply be the degree of clinical manifestation.
The following etiologies were listed in a series of 103 cases:
1. 36% were thought to be the result of trauma (22 were victims of child abuse)
2. 22% followed bacterial meningitis (post-infectious)
3. 19 occurred after placement or revision of a shunt
4. no cause could be identified in 17 patients