Lower cranial nerve palsy after the infrafloccular approach in microvascular decompression for hemifacial spasm

BACKGROUND The infrafloccular approach was introduced as a variation in microvascular decompression (MVD) for hemifacial spasm. However, the rate of postoperative lower cranial nerve (CN) palsy can be high. This study investigated the surgical factors in relation to the occurrence of postoperative lower CN palsy. METHODS The case records of 103 patients who underwent MVD were reviewed. Dissection around the lower CNs to approach the root exit zone of CN VII was divided into two steps - incision of the rhomboid lip at the root of the lower CNs and separation of CN IX and flocculus/choroid plexus. The correlations of these steps and other characteristics to the occurrence of lower CN palsy were analyzed. RESULTS Ten of the 103 patients suffered from postoperative transient lower CN palsy. The rhomboid lip was incised in 30 cases (29.1%), separation of CN IX and flocculus or choroid plexus was necessary in 24 cases (23.3%), and both steps were required in 7 cases (6.8%). The steps showed no correlation with postoperative lower CN palsy. Posterior inferior cerebellar artery (PICA) as the offending vessel was significantly correlated with postoperative lower CN palsy (P < 0.05). CONCLUSIONS Our study showed that the offending PICA was the only significant factor for postoperative lower CN palsy. Therefore, correct dissection around the lower CNs, particularly for complicated PICA, is necessary to reduce the risk of postoperative lower CN palsy.