Spinal Accessory Nerve Duplication – A Rare Anatomical Consternation During Neck Dissectio

Prevention of the spinal accessory nerve (SAN) is an indispensable aspect of the functional neck dissection surgery to avoid highly disabling shoulder syndrome postoperatively. This requires comprehensive knowledge of the anatomy of SAN and its variations. Rare anatomical variations like SAN duplication can result in an inadvertant injury to the SAN. We report a case of duplication of SAN, which was encountered while doing a functional neck dissection surgery for oral squamous cell carcinoma. No iatrogenic injury occurred during the surgery and neither there was any SAN dysfunction post-operatively. Meticulous dissection and consistent identification of SAN, along with vast anatomical knowledge is the key to the preservation of the nerve during the surgery. This report aims to broaden our anatomical knowledge of SAN and also discuss the clinical implications and literature pertaining to the duplication of SAN.

The Role of IONM in Reducing the Occurrence of Shoulder Syndrome Following Lateral Neck Dissection for Thyroid Cancer

Lateral neck dissection (LND) leads to a significant morbidity involving accessory nerve injury. Modified radical neck dissection (MRND) aims at preservation of the accessory nerve, but patients often present with negative functional outcomes after surgery. The role of neuromonitoring (IONM) in the prevention of shoulder syndrome has not yet been defined in comparison to nerve visualization only. We retrospectively analyzed 56 thyroid cancer patients who underwent MRND over a period of six years (2015–2020) in a high-volume institution. Demographic variables, type of surgical procedure, removed lymph nodes and the metastatic node ratio, pathology, adoption of IONM and shoulder functional outcome were investigated. The mean number of lymph nodes removed was 15.61, with a metastatic node ratio of 0.2745. IONM was used in 41.07% of patients, with a prevalence of 68% in the period 2017–2020. IONM adoption showed an effect on post-operative shoulder function. There were no effects in 89.29% of cases, and temporary and permanent effects in 8.93% and 1.79%, respectively. Confidence intervals and two-sample tests for equality of proportions were used when applicable. Expertise in high-volume centres and IONM during MRND seem to be correlated with a reduced prevalence of accessory nerve lesions and limited functional impairments. These results need to be confirmed by larger prospective randomized controlled trials.

Low Frequency-Repetitive Nerve Stimulation and Factors Affecting Decremental Response in Amyotrophic Lateral Sclerosis: A Retrospective Study of 449 Cases

A number of studies have demonstrated that decremental response to low frequency repetitive nerve stimulation (LF-RNS) is frequently observed in amyotrophic lateral sclerosis (ALS). However, due to the small sample size involved in previous studies, large discrepancies exist about the positivity rates of LF-RNS tests and factors affecting decremental response. This retrospective study of 449 cases, the largest sample size ever reported, shows that the overall positivity rate of LF-RNS is 49.9%. 3Hz RNS delivered to the accessory nerve has the best sensitivity and highest positivity rate. It obviously increases in response to upper limb onset, disease progression rate < 0.5 score/month, definite ALS and electromyography positive(EMG(+)) in sternocleidomastoid muscle. There is a linear increase in the decrement percentage of CMAP amplitude at 3Hz RNS delivered to the accessory nerve in response to longer disease duration, longer MUP duration and greater MUP duration increment percentage. These findings substantially advance the understanding of RNS results in ALS patients and effectively instruct clinical application.