Applied Anatomy Of The Superior Laryngeal Nerve

Part I Applied anatomy of the external laryngeal nerve and superior thyroid arteryObjective:The topographic relationship between the external laryngeal nerve(ELN)and the superior thyroid artery(STA)were observed,in order to provide the anatomical foundations for protecting the ELN during surgery.Methods:Fifty-seven cadavers(114 sides)fixed with formalin were collected at random.The ELN and STA were carefully dissected and analyzed under a 6-power magnifier.Results: The cervical sympathetic chain(CSC)of 90 sides was anastomosed with the ELN(CSC-ELN loop).For the 27.7%(25/114)low-position CSC-ELN loops observed,the neurovascular relationship between the STA and ELN was classified into four types:(4)the branches of the STA overlapped the CSC-ELN loop;(4)the glandular branch of the STA passed through the CSC-ELN loop;(4)the muscular branch of the CSC-ELN loop and the laryngeal branch of the STA coursed together;(4)the branches of the STA and the CSC-ELN loop were interlaced.Conclusion: Our study suggested that the variable morphology of the CSC-ELN loop and its complicated topographic relationship to the STA,which should be kept in mind when attempting to avoid the nerve injury.Two specisl surgical procedures would be recommen.First,the vessels should be individually isolated and then ligated during thyroidectomy.Second,a special attention should be paid to protect the coricothyroid branch of CSC-ELN loop from injury,when the anteriomedial branches of the STA are ligated during larynxsurgery.Part II Applied anatomy of the internal superior laryngeal nerve and superior laryngeal arteryObjective:the classification,localization,distribution of the internal superior laryngeal nerve(ILN)and the origin,variation of the superior laryngeal artery(SLA)were observed,in order to provide the anatomical foundations for the surgery,such as operation of Laryngectomy etc.Methods:Fifty-seven cadavers(114 sides)fixed with formalin were collected at random.The distribution of ILN branches and the origin,variation of SLA were carefully dissected and analyzed under a 6-power magnifier.Results: 1.The course of ILN is divided into two portions: the first portion from the place of issue to the hyoid membrane,the second portion is located in the hyoid membrane and the internal surface of the hyoid membrane to the larynx tissue,each segment may be issued branch.The ILN issues three branches: superointernal,middle and outside branches.These branches distribute in the mucosae of epiglottic cartilage,aryepiglottic fold,arytenoid cartilage,posterior 2/3 part of vacal fold.2.SLA mostly originated from STA,but also from the external carotid artery.90%(103/114)of SLA with ILN walks inwards and downward in the soft tissue space between the thyroid cartilage and cricoid cartilage after passing through the hyoid membrane;10%(11/114)of SLA mutates and the variant branch is distributed in the corresponding region of the larynx after passing through the foramen thyroideum.Conclusion: The study suggested that: 1.ILN can send out branches both in intrinsic laryngeal and extralaryngeal.These branches distribute in the mucosae of epiglottic cartilage,aryepiglottic fold,arytenoid cartilage,posterior 2/3 part of vacal fold.Therefore,surgeon should protect ILN and its branches from injury in laryngeal surgery.2.The variation of SLA is not rare.It is necessary to consider the possibility of SLA variation when SLA is not found in the normal site.