EFFECTIVE SHUNT-INDEPENDENT TREATMENT FOR PRIMARY MIDDLE FOSSA ARACHNOID CYST

The results of a prospective study on excision of the outer and inner membrane for symptomatic primary middle fossa arachnoid cysts in children are presented. During the period 1982-1989, among 48 cases of cyst in various locations, 18 symptomatic patients were treated by excision of both the outer and inner membranes with an opening to the basal cistern. The mean patient age was 3.2 years. All patients were evaluated by examinations, including magnetic resonance imaging (MRI), X-ray computed tomography (CT), quantitative CT cisternography (CTC), digital subtraction angiography (DSA), N-isopropyl-p[123]iodoamphetamine single-photon emission CT (IMP-SPECT) and IQ. All showed abnormal cerebrospinal fluid flow dynamics. Significant complications included massive subdural effusion in two patients and transient pulmonary edema in one. There were no recurrences during the follow-up period (mean 4.7 years). Two morphological types were noted: type I, the classical anteromedial type where the cysts are attached directly to the adjacent parasellar cisterns, and type II, the anterolateral type, where the diagonally concave anterior temporal lobe covers the adjacent cisterns, making wide opening difficult. Type I accounted for 78% of all cases, and the reduction of the cyst volume with clinical improvement was remarkable within 6 months after surgery. Angiographically, 22% of cases showed tapering and retrograde filling of the superficial middle cerebral vein. This pattern is not included in Hacker's normal variations [18] and suggests mild but chronic compression of the developing brain. Even in patients with hemispheric cyst, the reconstituted brain showed sufficient cerebral perfusion on SPECT, suggesting that the nature of this disease entity is reversible developmental arrest. These results confirm that excision is a safe, effective shunt-independent procedure for middle-fossa arachnoid cysts, especially for those of type I.