A subdural hygroma (SDG) is a collection of cerebrospinal fluid (CSF), without blood, located under the dural membrane of the brain. Most subdural hygromas are believed to be derived from chronic subdural hematomas. They are commonly seen in elderly people after minor trauma but can also be seen in children following infection or trauma. One of the common causes of subdural hygroma is a sudden decrease in pressure as a result of placing a ventricular shunt. This can lead to leakage of CSF into the subdural space especially in cases with moderate to severe brain atrophy. In these cases the symptoms such as mild fever, headache, drowsiness and confusion can be seen, which are relieved by draining this subdural fluid. Etiology and Pathophysiology
Subdural hygromas require two conditions in order to occur. First, there must be a separation in the layers of dura mater of the brain. Second, the resulting subdural space that occurs from the separation of layers must remain uncompressed in order for CSF to accumulate in the subdural space resulting in the hygroma. The arachnoid mater is torn and cerebrospinal fluid (CSF) from the subarachnoid space accumulates in the subdural space. Hygromas also push the subarachnoid vessels away from the inner table of the skull. Subdural hygroma can appear in the first day, but the mean time of appearance is 9 days on CT scan.
In recurrent cases a craniotomy may be performed to attempt to locate the location of the CSF Leak. In certain cases a shunt can be placed for additional drainage. Great caution is used when choosing to look for the CSF leak due to them generally being difficult to spot. References
Taveras, Juan M. et al., eds. Radiology: Diagnosis, Imaging, Intervention. 1994- ISBN 0-397-57115-1; ch. 37: 9-13. Brain Inj 1998 Jul;12(7):595-603. McCluney KW, Yeakley JW, Fenstermacher MJ, et al. «Subdural hygroma versus atrophy on MR brain scans: "the cortical vein sign"». AJNR Am J Neuroradiol 1992;13: 1335–39. External links
https://thejns.org/focus/view/journals/neurosurg-focus/26/6/article-pE8.xml