Quantitative Study of Posterior Fossa Crowdedness in Hemifacial Spasm

OBJECTIVE: To quantitatively study the degree of posterior fossa crowdedness (PFC) in patients with hemifacial spasm (HFS) and to further investigate whether overcrowding in posterior fossa affects the efficacy and safety of microvascular decompression. METHODS: We conducted a prospective case-control study of patients diagnosed with HFS and sex-and age-matched healthy control patients. All subjects underwent high-resolution, 3-dimensional magnetic resonance imaging, and posterior fossa crowdedness index (PFCI) and cerebrospinal fluid volume (CSFV) were measured. Patients with HFS underwent primary microvascular decompression and long-term follow-up. Associations of PFCI and other factors with operative outcomes and complications were analyzed. RESULTS: The study enrolled 153 subjects: 102 patients and 51 control subjects. Compared with control subjects, patients had a more PFC (PFCI: 83.2% vs. 80.2%; P = 0.005) and smaller posterior fossa CSFV (16,248.0 mm(3) vs. 20,054.0 mm(3); P = 0.001). The mean effective space of posterior fossa cerebrospinal fluid in patients with HFS was 11.8% smaller than in control subjects (P = 0.004). Compared with men, women showed larger PFCI (83.6% vs. 82.2%; P = 0.012) and smaller PF CSFV (16,027.5 mm3 vs. 17,299.5 mm(3); P = 0.009). Sixty-one patients (59.8%) were spasmfree immediately postoperatively, and 95 (93.1%) were spasm-free at follow-up. Complication rates were 9.8% in the short term, and 2.9% at follow-up. Lower PFCI (odds ratio [OR] 0.63; P = 0.019) and severe indention (OR 1.41; P = 0.027) were significantly associated with better short-term outcomes. Greater PFCI (OR 2.05, P = 0.008) was associated with greater early complication incidence. CONCLUSION: Patients with HFS had more PFC. PFC potentially leads to cranial nerve and vascular structure crowding, which may increase HFS risk. PFC was significantly associated with poor short-term outcomes and greater incidence of early complications but not long-term outcomes and complications.