The Anatomic Study Of The Extracranial Accessory Nerve And Hypoglossal Nerve

ObjectiveThe study were to obtain more useful detailed anatomic information of the extracranial accessory nerve and hypoglossal nerve and the spatial relationships of surrounding structures, to provide anatomical basis for the operation of the region. MethodsTen cadaver heads (20 sides) were used for microsurgical dissection , the whole cadaver heads injected with colored latex . Microsurgical anatomy and measurement were performed in cervix. Then exposed the whole length on the extracranial course of the accessory nerve and hypoglossal nerve . The anatomic relationships of the muscle, nerve, and vessel were carefully recorded, with special emphasis regarding the relative relationship of these structures. All stages of the dissections were photographed.Results1 , After the accessory nerve exits the skull through the jugular foramen, it weredivided into cranial roots and spinal roots. Cranial roots merged into vagal trunk or inferior ganglion. Spinal roots ran down clingly internal jugular vein, and passed through a narrow space between the internal jugular vein and styloid process. The accessory nerve was found below belly of digastric muscle. The greatest diameter was 1.58mm. Continuing inferiorly. The accessory nerve ran superficial to the internal jugular vein in 55%(11/20) and ran deep to internal jugular vein in 45%(9/20).Continuing inferiorly. The accessory nerve entered into the SCM in 60%(12/20), the accessory trunk ran deep to the SCM and the branch of the accessory nerve ran into the SCM leaving the nerve trunk by the time above the third of SCM in 40%(8/20). Continuing inferiorly and outerly, the accessory nerve was found at the posterior edge of the SCM where was at 11.08±2.44(7.60-15.20)mm above the point of the great auricular nerve going out the muscle. It passed obliquely across the floor of the posterior triangle, over the levator scapulae, and superficial to the prevertebral fascia. Continuing inferiorly and outerly and posteriorly. There was the accessory nerve paralleled to the anterior border of the trapezius muscle before it entered the muscle in 60%(12/20), the nerve entered into the trapezius muscle directly in 40%(8/20). The point entering into the muscle was middle thirds of the anterior border. The accessory nerve supplied branch to the trapezius after entering deep to the anterior border of the muscle.2 The accessory nerve and the branches of cervical plexus double innervated trapezius muscle and SCM. Communicating branches between the accessory and cervical nerve entering into those muscles were found, accessory and cervical nerve entering into those muscles respectively were found too.3 The hypoglossal nerve exited the skull from hypoglossal canal. Firstly ran at the lateral border of internal jugular vein and glossopharyngeal nerve and vagus nerve. Then ran down between internal jugular vein and internal carotid artery. At angle of mandible, the hypoglossal nerve ran along deep to posterior belly of digastric muscle. The nerve exited 1 piece of branch when it ran superficially to the point of occipital artery exiting from external carotid artery in 50%(10/20), above to the point in 15%(3/20),inferiorly to the point in 35%(7/20). Continuing, the hypoglossal nerve ran superficial to external carotid artery. The nerve ran above to the point of lingual artery exiting from external carotid artery in 85%(17/20) and superficially to the point in 15%(3/20). Then ran between digastric, stylohyoid, mylohyoid and hyoglossus. The hypoglossal nerve exited 4~6 pieces of branches in former border of hyoglossus .4 The lingual nerve exited 1 or 2 piece of branch which ran to outerly border of hyoglossus and down curvingly, the nerve joined with branches of hypoglossal nerve. The area of joint was found about at the first about 8~11mm after branches of hypoglossal nerve entering lingual muscles. When the submandibular duct passed through superficially hyoglossus . The lingual nerve and the hypoglossal nerve ranalong together : the lingual nerve was above the submandibular duct and the hypoglossal nerve was inferiorly the submandibular. Conclusion1. The transverse process of atlas and the angle of the mandible and apex of mastoid process serve as important landmarks of the accessory nerve and the hypoglossal nerve at the extracranial region .2. At posteriorly of the SCM, the accessory nerve is found at 11.08±2.44 (7.60-15.20) mm above the point of the great auricular nerve going out the SCM.3. The accessory nerve and the branches of cervical plexus double innervate trapezius muscle and SCM. Communicating branches between the accessory and cervical nerve are complicated.4. The relationship between the lingual nerve and the hypoglossal nerve is close. The most significative region in surgery is at the first 8~llmm where branches of hypoglossal nerve entering lingual muscle.5 The structure around PBDM is complicated. When the PBDM is dissected , the important blood vessel and nerve around the PBDM is identified and protected. The PBDM is also a key landmark to identify and protect the hypoglossal nerve and the accessory nerve in surgery .