Clinically relevant anatomy of recurrent laryngeal nerve.

STUDY DESIGN: An anatomic study of anterior cervical dissection of 11 embalmed cadavers. OBJECTIVE: To determine the anatomic relationship of the recurrent laryngeal nerve (RLN) to the cervical spine and demonstrate vulnerability of the nerve during anterior surgical approach. SUMMARY OF BACKGROUND DATA: The most common complications of anterior neck surgery are dysphagia and RLN palsy. The morbidity of these complications has led to the investigation of the impact of sidedness in anterior cervical spine surgery. METHODS: Eleven adult cadavers (5 male/6 female) were dissected bilaterally to expose the path of the recurrent laryngeal nerve. RESULTS: The right RLN branched from the vagus nerve at the level of T1-T2 or inferior in all specimens. After looping around the subclavian artery, the right RLN became invested in the tracheoesophageal fascia greater than 0.5 cm inferior to C7-T1 in all specimens. The RLN traveled superiorly, slightly anterior to the tracheoesophageal groove, before coursing between the trachea and the thyroid. In 82% (9 of 11) of right-sided dissections, the RLN entered the larynx at or inferior to C6-C7. After looping around the aortic arch, the left RLN was invested in the tracheoesophageal fascia inferior to the T2 level in 100% (10 of 10) of cadavers. The nerve traveled slightly anterior to the tracheoesophageal groove and within the tracheoesophageal fascia before coursing between the trachea and thyroid. In all the left-sided dissections, the RLN entered the larynx at or inferior to C6-C7. CONCLUSION: This study found that superior to C7-T1, both RLNs had similar anatomic courses and received similar protection via surrounding soft-tissue structures. From an anatomic perspective, the authors did not appreciate a side-to-side difference superior to this level that could place either nerve under greater risk for injury.

Clinically relevant anatomy of high anterior cervical approach.

STUDY DESIGN: An anatomic study of anterior cervical dissection of 11 embalmed cadavers and measurement of structures relative to cervical spine. OBJECTIVE: To determine the anatomic relationship of the hypoglossal nerve (HN), internal and external superior laryngeal nerves (ESLNs), superior thyroid artery (STA), and superior laryngeal artery (SLA) to cervical spine and demonstrate any vulnerability. SUMMARY OF BACKGROUND DATA: The anterior approach is a common approach to the cervical spine. Much of the operative morbidity in high cervical region is related to neurovascular injury leading to dysphagia, dysphonia, impaired high-pitch phonation, and impaired cough reflex. METHODS: Eleven adult cadavers (5 male/6 female) were dissected bilaterally to expose structures of the high anterior cervical region. RESULTS: The HN consistently traveled toward the midline at C2-3 and was safe caudal to C3-4. In 95% of dissections, the internal superior laryngeal nerve (ISLN) was exposed within 1 cm of C3-4. The path of the ESLN was variable, but it was safe above C3-4 and below C6-7. The ESLN was deep to the STA, and it was less bulky and tauter than the ISLN in all dissections. The origin of the STA was quite variable along the carotid artery, but it was most commonly located at C4. Two anatomic variants of the SLA were observed. In 15 dissections, the SLA branched off the superior thyroid. In six dissections, the SLA branched directly from external carotid artery. There was no appreciable side-to-side variation in the neurovascular structures studied. CONCLUSION: On the basis this study, spine surgeons can have enhanced knowledge of high anterior cervical anatomy. The neurovascular structures in this study did not demonstrate side-to-side anatomic variation; therefore, patient pathology and surgeon preference should dictate the operative side.

Implications of lumbar plexus anatomy for removal of total disc replacements through a posterior approach.

STUDY DESIGN: An anatomic study in which the lumbar plexuses of 14 embalmed cadavers were dissected bilaterally and measured using a posterior approach. OBJECTIVE: To determine the cephalocaudal (root-to-root) distances and the mediolateral (root-to-tether) distances within the lumbar plexus and determine the feasibility for removal of a lumbar total disc replacement (TDR) through these anatomic spaces using a posterior approach. SUMMARY OF BACKGROUND DATA: Currently, lumbar TDRs are implanted primarily through an anterior retroperitoneal or transperitoneal approach. However, revision surgeries through these approaches can be complicated by significant adhesions, with potential injuries to intra- and retroperitoneal contents. Advancements in accessing anterior column structures through a posterior lumbar extracavitary approach suggest that posterior removal of TDRs may be an alternative. Unlike the thoracic extracavitary approach in which ligation of the thoracic nerve rarely leaves significant morbidity, the lumbar extracavitary approach cannot rely on the analogous ligation of the lumbar root to achieve access. Therefore, feasibility of the lumbar extracavitary approach depends on the presence of sufficient anatomic space between the tethered nerves of the lumbar plexus. METHODS: Fourteen adult cadavers (5 M/9F) were dissected through a posterior approach to expose the lumbar plexus bilaterally. The root-to-root distances at levels L2-S1 and corresponding root-to-tether distances at levels L3-L5 were measured bilaterally. RESULTS: Root-to-root distance was smallest at the male L5-S1 interval (11.7 +/- standard deviations 4.1 mm). Root-to-tether distance was smallest at the female L5 (43.1 +/- standard deviations 8.4 mm). These plexus measurements compare favorably with the CHARITE TDR components, in which the thickest sliding core is 11.0 mm in height and the largest endplate is 42.0 mm in width. CONCLUSION: This anatomic study suggests that posterior TDR removal is possible in the lumbar spine without undue risk to the surrounding nervous structures.