Arachnoid cyst and associated subdural hematoma. Observations on conventional roentgenographic and computerized tomographic diagnosis.

Information about computerized tomography (CT) of arachnoid cysts of the middle fossa (ACMF) is increasing, and it appears that certain CT characteristics may be diagnostic. The association of ACMF and subdural hematoma has been emphasized previously but is not common knowledge. We present three new cases of ACMF and associated subdural hematoma studied by plain roentgenograms, EEG, conventional brain scanning, CT scanning, and angiography. The cysts were clearly shown in each case by CT scan, but no subdural hematoma was visualized in our first two cases. Angiography was necessary to establish the associated hematoma. We review and emphasize computerized tomographic characteristics that may be pathognomonic of ACMF. It is suggested that angiography be included in the study of patients symptomatic with ACMF because associated subdural hematoma is not an uncommon lesion and may fail to visualize on CT scan. Angiography still remains the most conclusive study to establish or exclude the diagnosis of subdural hematoma.