A significant number of cases of
chronic subdural hematoma associated with middle fossa arachnoid
cyst has been reported in literature, but sufficiently tenable explanation for co-occurrence of both lesions has not yet proposed. In this study, authors try to elucidate mechanisms involved in development of
chronic subdural hematoma and arachnoid
cyst in the same patient. Eighteen cases with arachnoid
cyst in the middle fossa were diagnosed by CT scan during last 5 years in our institute. Among these, five patients had
chronic subdural hematoma additionally to their middle fossa arachnoid
cyst. Analysis of clinical, roentgenological data and operative findings in our five cases and reviewing of cases reported so far in the literature makes clear the following characteristics in this pathological condition. 1) Patients of
chronic subdural hematoma associated with arachnoid
cyst were obviously younger than patients with usual
chronic subdural hematoma. 2)
Chronic subdural hematoma developed in the same side to the associated arachnoid
cyst. 3) Characteristic changes in the skull on
x-ray films indicated the long lasting existence of middle fossa arachnoid
cyst. On the other hand, history of cases suggested that
chronic subdural hematomas had developed within recent 1-3 months. 4) Intracranial pressure tended to remain normal or slightly elevate. 5) Abnormal, small veins which run on the surface of the membranous
capsule of arachnoid
cyst and bridge the Sylvian fissure were not infrequently found at operation. These veins were not able to visualized on routine angiography. On the basis of these clinical and pathological characteristics, authors infer a mechanism for development of
subdural hematoma associated with arachnoid
cyst. The presence of middle fossa arachnoid
cyst must increase a compressibility of the intracranial content, especially of the ipsilateral cerebral hemisphere and it predisposes for development of
chronic subdural hematoma.(ABSTRACT TRUNCATED AT 250 WORDS)