Diagnosis and treatment of middle fossa arachnoid cysts and subdural hematomas.

Nine cases with temporal fossa arachnoid cysts were diagnosed by computerized tomography (CT). Five patients also had subdural hematomas, three of them following head trauma. When the hematoma was chronic and of equal hypodensity with the cyst, a clear-cut differentiation was not possible from the CT scan. The presence of a subdural hematoma could only be suggested by thickened arachnoid structures crossing the hypodense area, indicating the wall between cyst and hematoma. The cyst could often be diagnosed by bulging of the skull bone and a temporal lobe defect. Differences in density between cyst and hematoma, such as in subacute subdural hematoma, delineated both entities. Typical examples are demonstrated. Treatment consisted of evacuation of the hematoma and excision of the cyst in all cases.