Syringomyelia associated with type I Chiari malformation. A 21-year retrospective study on 75 cases treated by foramen magnum decompression with a special emphasis on the value of tonsils resection.

The purpose of the present study is to evaluate retrospectively the effects of several intra-operative manipulations on the results of foramen magnum decompression (FMD) in patients having syringomyelia associated with type I Chiari malformation. Seventy-five patients having syringomyelia associated with Chiari I malformation were operated on between 1975 and 1996. This population was grouped into 4 subgroups according to the surgical protocol: group I = 42 patients with FMD alone; group II = 16 patients with FMD and third ventricle shunting; group III = 9 patients with FMD and syringosubarachnoid shunting (SSS); group IV = 8 patients with FMD and cerebellar tonsils resection. Pre- and postsurgical magnetic resonance imaging (MRI) studies were analyzed (and compared). Nine patients were lost to follow-up. The results were evaluated in the 66 remaining patients (mean follow-up: 52 months), using the Bidzinski's outcome scale (ref). Two patients (3%) died postoperatively, 31 (47%) had very good results (after additional surgery in 7), 16 (24.2%) had good results (after additional surgery in 7) and 17 (25.7%) had poor results despite further surgery in 9. A total of 27 reoperations were undertaken after primary FMD in 23 patients (35%). Thirty-nine patients (59%) had both pre- and postsurgical MRI evaluation. In 28 (72%) the syrinx had markedly decreased whereas it had remained stable in 11 (28%). Clinical results were not significantly different between the patients of groups I, II and III. Very good or good results were obtained in 24 patients (64.8%) of group I (after additional surgery in 10), in 8 (61.5%) of group II (after additional surgery in 1) and in 7 (87.5%) of group III (after additional surgery in 3). Results in group IV were as follows: 7 patients (87%) had very good results and one had a good result. With a mean follow-up of 28 months, no patient required additional surgery. Postsurgical MRI syrinx reduction was observed in all 8 patients either in the early postoperative course or on delayed followup. It is suggested that tonsils resection might enhance the results of FMD in individuals having Chiari I-related syringomyelia.