The course of lower cranial nerves within the neck: a cadaveric dissection study.

PURPOSE: To evaluate the course of lower cranial nerves (CNs) within the neck in relation to surrounding structures and anatomic landmarks via a cadaveric dissection study. METHODS: A total of 70 neck dissections (31 bilateral, 8 unilateral) were performed on 39 adult fresh cadavers [mean (SD) age: 38.5 (11.2) years, 29 male, 10 female] to identify the course of lower CNs [spinal accessory nerve (SAN), vagus nerve and hypoglossal nerve] within the neck in relation to surrounding structures [internal jugular vein (IJV), common carotid artery (CCA)] and distance to anatomical landmarks (cricoid cartilage, hyoid bone, digastric muscle). RESULTS: SAN travelled most commonly anterior to IJV (51.4%) at the level of jugular foramen, while travelling lateral to IJV at the post belly of digastric (55.7%) and inferior to digastric muscle (90%) in most neck dissections. Vagus nerve travelled lateral to CCA in majority (94.3%) of dissections, while medial (2.9%), posterolateral (1.4%) and posterior (1.4%) positions were also noted. Average distance of hypoglossal nerve was 27.7 (9.7) mm to carotid bifurcation, 9.3 (3.9) mm to hyoid bone, and 54.7 (18.0) mm to the inferior border of cricoid cartilage. CONCLUSION: In conclusion, our findings indicate that anatomic variations are not rare in the course of lower CNs within the neck in relation to adjacent structures, and awareness of these variations together with knowledge of distance to certain anatomic landmarks may help the surgeon to identify lower CNs during neck surgery and prevent potential nerve injuries.

Determination of the chest wall thicknesses and needle thoracostomy success rates at second and fifth intercostal spaces: a cadaver-based study.

INTRODUCTION: The purposes of this study were to measure the chest wall thicknesses (CWTs) at second intercostal space (ICS) mid-clavicular line (MCL) and fifth ICS MAL directly, and compare the actual success rates of needle thoracostomies (NTs) by inserting a 5-cm-long syringe needle. Predictive values of weight, body mass index (BMI) and CWT were also analyzed. MATERIALS AND METHODS: This study included 199 measurements of 50 adult fresh cadavers from both hemithoraces. Five-centimeter-long syringe needles were inserted and secured. Penetration into the pleural cavity was assessed, and CWTs at 4 locations were measured. Achieved power of this study for the primary aim of CWT comparison from 2nd and 5th ICSs was .94. RESULTS: Overall mean CWTs at 2nd ICS MCL and 5th ICS MAL were measured as 2.46 ± 0.78 and 2.89 ± 1.09, respectively, and 5th ICS MAL was found to be statistically thicker (P = .002). The success rate of NT at 2nd ICS MCL was 87% (95% CI, 80-94), and that at 5th ICS MAL was 78% (95% CI, 70-86; P = .3570). Only 6 (17.1%) of 35 failed NTs had a CWT greater than 5-cm. Needle thoracostomy has failed in 29 (14.9%) of 194 locations, despite a CWT less than 5-cm. Below a weight of 72 kg, BMI of 23 kg/m2, or CWT of 2.4 cm, all NTs were successful. DISCUSSION AND CONCLUSIONS: In this report, we present the largest cadaver-based cohort to date to the best of our knowledge, and we observed a statistically nonsignificant 9% more NT success rate at 2nd ICS at a power of 88% and statistically significant more success rate in males at 5th ICS was (47.7%). We also observed thinner CWTs and higher success rates than previous imaging-based studies. A BMI of 23 kg/m2 or less and weight of 72 kg or less seem to accurately rule-out NT failure in cadavers, and they seem to be better predictors at the bedside.