Timing matters: evaluating lateral spreads response disappearance as a prognostic marker in microvascular decompression for hemifacial spasm: a phenomenological study

Purpose Prognostic significance of lateral spreads response (LSR) disappearance in microvascular decompression (MVD) for hemifacial spasm (HFS) remains controversial. Still the timing of LSR disappearance and its association with overall outcomes has not been sufficiently investigated. We evaluate the prognostic significance of the timing of LSR disappearance during MVD in HFS. Methods Prospective documentation of the LSR-Status during the procedural steps was performed alongside routinely collected data. Surgical steps were categorized into three phases: Opening phase (skin incision till cisternal opening), arachnoid dissection, and actual Decompression phase. Outcome assessment was conducted after a follow-up period of at least 12 months, with favorable outcome defined as at least 90% resolution of the spasms. Results 214 patients were included with a mean age (SD) of 54.9 ± 11.6 years and a follow-up duration (SD) of 25.8 ± 15.7 months. The male-to-female ratio was 1:1.6. LSR was "not detected" in 32 patients (15.0%), with a 93.8% favorable outcome. LSR "persisted" in 22 patients (10.3%), showing only 77.3% favorable outcome. In 16 patients (7.4%), LSR disappeared during the opening phase, yielding a 100% favorable outcome. LSR disappearance occurred during arachnoid dissection in 40 patients (18.7%), with a 91.1% favorable outcome. Finally, LSR disappearance following nerve decompression was observed in 104 patients (48.6%), showing a 78.9% favorable outcome. Earlier disappearance of the LSR was associated with long-term cure (P-value < 0.05). Conclusion LSR may serve as a valuable intraoperative indicator during MVD for HFS. Early intraoperative disappearance of the LSR may predict favorable long-term outcomes. However, the disappearance of the LSR in general does not consistently correlate with surgical success.