Surgical outcomes of basilar invagination type B without atlantoaxial dislocation through simple posterior fossa decompression: a retrospective study of 18 cases

Background Basilar invagination (BI) is a common disease in the craniocervical junction (CVJ) area. Posterior fossa decompression with/without fixation is a controversial surgical strategy for BI type B. This study aimed to evaluate the efficacy of simple posterior fossa decompression in treating BI type B. Methods This study retrospectively enrolled BI type B patients who underwent simple posterior fossa decompression at Huashan Hospital, Fudan University between 2014.12 and 2021.12. Patient data and images were recorded pre- and postoperatively (at the last follow-up) to evaluate the surgical outcomes and craniocervical stability. Results A total of 18 BI type B patients (13 females), with a mean age of 44.2±7.9 years (range 37–62 years), were enrolled. The mean follow-up period was 47.7±20.6 months (range 10–81 months). All patients received simple posterior fossa decompression without any fixation. At the last follow-up, compared with preoperation, the JOA scores were significantly higher (14.2±1.5 vs. 9.9±2.0, p = 0.001); the CCA was improved (128.7±9.6° vs. 121.5±8.1° p = 0.001), and the DOCL was reduced (7.9±1.5 mm vs. 9.9±2.5 mm, p = 0.001). However, the follow-up and preoperative ADI, BAI, PR, and D/L ratio were similar. No patients had an unstable condition between the C1-2 facet joints that was observed in the follow-up CT and dynamic X-ray. Conclusions In BI type B patients, simple posterior fossa decompression could improve neurological function and will not induce CVJ instability in BI type B patients. Simple posterior fossa decompression could be a satisfactory surgical strategy for BI type B patients, but preoperative CVJ stability assessment is crucial.