Risk of marginal mandibular nerve injury in neck dissection

The immediate and permanent frequency of injury to the marginal mandibular branch of the facial nerve (MMN) after neck dissection has only scarcely been addressed in the medical literature. We investigated the risk of injury in 159 consecutive patients after neck dissection for various reasons in level I B and level II A, respectively. In 95 patients with oral cancer 13 (14%) of the cases had malfunction of the lower lip domain 2 weeks after neck dissection in level I B indicating paresis to the MMN. Follow-up analyses 1-2 years after the operation showed permanent paralysis in 4 to 7% of the cases in whom two of them had the nerve sacrificed for oncologic reasons during the operation. In 18 patients with parotic cancer the corresponding permanent frequency of MMN paralysis was 11.1%. In 46 patients with neck dissection in level II A but not in level I B, no paresis of the MMN was registered. Recognition of the MMN during the operation, pre- or postoperative radiation therapy, re-operation for deep hemorrhage, age, gender or postoperative infection did not have any statistically significant influence on the frequency of MMN injury. In conclusion we found a moderate risk of injury to the MMN after neck dissection in level I B whereas the corresponding risk after level II A dissection was negligible.