Biometric measurements involving the terminal portion of the thoracic duct on left level IV: an anatomic study
BACKGROUND: During a neck dissection involving the left IV level, the final segment of the thoracic duct (TD) may be injured, significantly increasing postoperative morbi-mortality. The best treatment is its prevention. However, there is a lack of helpful biometric measurements focusing on the TD termination in the literature. MATERIALS AND METHODS: The TD termination was identified and some helpful biometric measurements were obtained on 25 non-preserved cadavers. Statistical analysis was performed to analyze correlations. RESULTS: TD termination was found on the jugulo-subclavian junction (JSJ - 60%), on the left internal jugular vein (LIJV - 36%), and on the left brachiocephalic vein in 4%. A statistically significant association was found between TD termination on the JSJ and the distance between LIJV and omohyoid muscle (Measurement #1). Individuals with TD termination on the JSJ had median Measurement #1 of 34.5±12.0mm, compared with median Measurement #1 of 22.3±8.7mm among individuals with TD termination on LIJV (p=0.015 – Student´s t-test). The logistic regression showed for every 10mm increment of Measurement #1 there was 1.12x chance to find the TD termination on the JSJ (OR=1.12; CI95%:1,01-1,25; p=0.032). A 19mm cut-off was established for this distance as a diagnostic test to predict the TD termination on the JSJ, with sensitivity of 86.7% (CI95%:59.5-98.3%), specificity of 55.6% (CI95%:21.2-86.3%), PPV of 76.5% (CI95%:50.1-93.2%), NPV of 71.4% (CI95%:25.8-97.2%) and ROC AUC of 79.3% (CI95%: 58.0-92.9%). CONCLUSION: This anatomic study demonstrated the most frequent TD termination was on JSJ and Measurement #1 is able to predict the localization of TD termination.