Sole vein offenders confirmed by disappearance of the lateral spread response during microvascular decompression for hemifacial spasm

Sole vein offenders are rare and can be difficult to identify on preoperative magnetic resonance imaging (MRI) and intraoperative microscopy. The objective of this case review was to investigate factors resulting in successful decompression in venous offender cases. Among 234 cases of microvascular decompression surgery performed for hemifacial spasm from September 2020 to April 2022 at Konkuk University Medical Center, only two cases were identified as having a definite venous offender. We reviewed preoperative MRI and intraoperative microscopic findings and studied the correlation between decompression and lateral spread response (LSR) changes. Our two patients had possibility of a small venous offender on preoperative MRI, but it was ambiguous. A definite venous offender was identified on the operative microscopic findings and decompressed successfully, referring to the disappearance of the LSR waveform. Postoperatively, spasm disappeared or significantly improved. A venous offender is difficult to identify on preoperative MRI findings or even on intraoperative microscopic findings. In such cases, changes in the LSR waveform in response to decompressing the suspected vein can be a valuable reference for successful facial outcomes.