クモ膜嚢腫の臨床病理学的検討

抄録

Twenty-one cases of arachnoid cysts were experienced in the last 5 years. Craniotomy and extirpation of the arachnoid cysts were performed on 20 cases.
Clinical features and histological findings of these cases were investigated. Ages of these patients ranged from 7 months to 70 years. Twelve cases (57%) were under the age of 20 years and the other nine cases (43%) were over 20 years old. The cysts were located in the middle fossa in 12 cases, in the frontal lobe in five cases, in the posterior fossa in three cases and in the left-sided hemisphere in one case. Symptoms were generally rather mild.
Among the 12 cases of middle fossa arachnoid cysts, only six cases showed bony changes such as elevation of the sphenoid wing in plain skull films and of the 11 cases which underwent angiographic studies, only five cases showed poor visualization of the superficial middle cerebral veins on the affected side. Arachnoid cysts were readily diagnosed by CT examination as watery low density areas with a clear-cut margin which showed no enhancement by intravenous injection of contrast media.
Metrizamide-CT and RI-cisternography were utilized in nine cases. Eight cases showed non-communicative cysts surrounded by metrizamide acummulation in the adjacent arachnoid space.
Histological examinations of the cystic membrane were performed in eight cases by taking specimens from the covering part as well as from the bottom where the membrane adhered to the cortical surface. Seven out of eight cases showed duplicated normal arachnoid membrane. This finding indicated that the cysts could be regarded as “intraarachnoid cysts”, as pointed out by Starkman.
Normal arachnoid membrane was examined histologically by taking specimens from lobectomized cortex as well as autopsied brain for comparison with the cystic membrane.
These examinations revealed an interesting arachnoidal structure which might be termed “micro-intraarachnoid cysts” in certain instances. The etiology of the primary arachnoid cyst has been considered as congenital or developmental in nature. Starkman advocated that the structure of the intraarachnoid cyst itself indicated congenital malformation of the arachnoid membrane.
However, this series included so many unexpected adult cases and also a case of posttraumatic arachnoid cyst in one identical twin. Therefore, one course of pathogenesis of the arachnoid cysts, can be postulated as a “microintraarachnoid cyst” existing in normal people starting to grow and becoming a large arachnoid cyst, triggered by some enlarging forces in head traumas or other unknown factors.