Case Description
Embryologic Basis
Discussion
The superior laryngeal artery ( SLA ) which originates from the first branch of the ECA , the superior thyroid artery ( STA ) to supply the larynx , is also subject to rare variations ( Devadas , et al ., 2016 ) .
While the external carotid artery ( ECA ) and its branches are known for several variations regarding their branching pattern , the superior laryngeal artery ( SLA ) is the least variable and diverse ( Devadas , et al ., 2016 ) . Despite the fact that in the majority of cases , the SLA tends to emerge from the superior thyroid artery ( STA ) via a common trunk ; nevertheless , few reports hinted the possibility of its branching either immediately from the external carotid artery ( ECA ) ( 10 %) or , in very rare instances , as a branch of the lingual artery ( LA ) ( 1.5 %), the facial artery ( 1 %), the common carotid artery ( 0.5 %) or even as being completely absent ( Devadas , et al ., 2016 ) . Few cases have been reported in which the SLA branches off the ECA directly , while only 2 cases described its emergence from the LA ( Nayak , et al ., 2011 ) . Moreover , all the reported variations concerning the SLA were unilateral and to the left , with the right SLA branching off the right STA ( Nayak , et al ., 2011 ) ( Devadas , et al ., 2016 ) . An understanding of such variations of the SLA is essential to anatomists , radiologists and neck surgeons . This case report describes a rare bilateral variation in the origin of the SLA , whereby the right SLA arose from the right LA and the left SLA took origin from the left ECA . As such , this report , not only combines two of the least frequent variants of the SLA but is the first to report an SLA branching from the right LA in the right hemi-neck .
Case Description
After performing dissection of over 400 cadaveric specimens and reporting various types of vascular congenital anomalies , it is the first case encountered with bilateral SLA anomalies ( Jurjus , et al ., 1986 ) and ( Jurjus , et al ., 1999 ) . The cadaver was a 70-year-old Caucasian female . In her left carotid triangle , the STA branched off the ECA immediately at the level of the bifurcation of the common carotid artery . The left SLA emerged 1 cm superior to the STA , and 1.5 cm inferior to the left LA . It , then , coursed the carotid triangle antero-inferiorly and parallel to the left internal laryngeal nerve , with which it pierced the thyrohyoid membrane to supply the laryngeal region . ( Figure 1 )
As for the right carotid triangle , the STA artery was observed to rise 1 cm above the bifurcation of the common carotid and branched of 0.5 cm superior to the right STA . Then , 1.2 cm superior to the branching origin of the LA , the SLA emerged and coursed antero-inferiorly over a longer distance than the left SLA to meet the right internal laryngeal nerve and pierce together the thyrohyoid membrane to finally reach the larynx . ( Figure 2 ).
It is noteworthy the very different courses that the right and left SLA took in order to reach the thyrohyoid membrane . The right SLA branched farther away superiorly and followed a more acute antero-inferior path than the left SLA . Moreover , the right SLA seemed to have a much larger caliber than the left SLA , thus providing a larger blood supply to the larynx .
Embryologic Basis
The disparity in the distances between the STA and lingual artery , ( 0.5 cm on the right , 2.5 cm on the left ), is most likely due to the variable origin of the SLA as a result of an embryonic congenital arterial variation that leads to the lack of symmetry between the two hemi-necks of this female cadaver . As for the bilateral variation in the branching origin of the SLA , this is traced back to a variation in the embryological formation of the ECA itself . During fetal development , the ECA arises from the aortic sac at a close proximity to the anterior end of the third pharyngeal arch , after which it travels cranially ( Nayak , et al ., 2011 ) . At the moment of its sprouting , the ECA is joined by the ventral pharyngeal artery . The maxillary branch of the latter , then , communicates with the common maxillary / mandibular trunk of the stapedial artery and adds to its branches , thus leading to the known ECA branching pattern ( Nayak , et al ., 2011 ) . Any lack of synchronization or correct signaling throughout this development or even lack of easy spatial development in a forming neck , would lead to variable branching patterns of the artery . Alterations on both sides eventually led to bilateral variations in the ECA that were specifically reported as variations in the branching origins of the SLA .
Discussion
The larynx is a very complex organ , that has been coupled with numerous variations , including the ones involving the superior laryngeal nerve or the recurrent laryngeal nerve ( Nayak , et al ., 2011 ) . Only recently , variations regarding the SLA ,