CT scanning in middle fossa arachnoid malformations.

The typical appearances of middle foss arachnoid malformations as seen by computed tomography, are presented in six cases out of 3700 unselected CT scans performed in the last two years. These lesions have well-defined borders, the anterior border often conforming to the configuration of the greater sphenoid wing, and the posterior border merging into the Sylvian fissure medially. They exhibit the same attenuation coefficients as cerebrospinal fluid (CSF), in the range of 0 to +8 EMI units. Their size is variable. They produce less mass effect than might be expected, even when their size is considerable. Their appearance does not change after infusion of contrast material. Although arachnoid malformations occur in many intracranial sites, the site of predilection appears to be the middle cranial fossa. The clinical presentation and subsequent management of the six cases is briefly described. The pathogenesis and common clincial presentation associated with these lesions is discussed.