Safe surgical zone during TORS radical tonsillectomy:An anatomical and radiological study

Objective:Parapharyngeal space contains intricate vascular anatomy(external and internal carotid arteries)that might be inadvertently injured during the dissection in this plane.None of the bony landmarks can be used during the transoral robotic surgery(TORS)radical tonsillectomy as these landmarks lie lateral to the internal carotid artery(ICA)and external carotid artery(ECA)in transoral approach.Our study aims to identify the safe surgical limits during the dissection of parapharyneal space in TORS radical tonsillectomy and to correlate the same with radiological study.Material and methods:Fifteen cadavers(30 head and neck regions)and 50 CT-Angiogram of neck(100 head and neck regions)were included in the anatomical and radiological study respectively.The vertical midpoint of anterior tonsillar pillar(palatoglossus muscle)was taken as the reference point and all the measurements were done at the level of reference point both for anatomical and radiological study.Distance between tonsillar fossa and ECA,distance between tonsillar fossa and ICA,relation between ECA and styloglossus and relation between ICA and stylopharyngeus at reference level were studied.Results:The mean distance of ECA from the tonsillar fossa at the reference point was 18.2 mm in the anatomical study and 16.2 mm in the radiological study.The mean distance of ICA from the tonsillar fossa was 23.4 mm and 23.3 mm in the anatomical study and radiological study.There was no significant difference between the anatomical and radiological findings for both the mean distance between ECA and ICA to the tonsillar fossa(p value was 0.45 and 0.30 respectively).ECA was located posterolateral to styloglossus in 24 cases(80.0%)and 79 cases(79.0%)in the anatomical and radiological study respectively.ICA was found posterolateral to stylopharyngeus in 21 cases(70.0%)and 69 cases(69.0%)in the anatomical and radiological study respectively.Conclusion:The muscular plane between styloglossus and stylopharyngeus can be used as an envelope to locate the ECA and ICA that lie medial to these critical vascular structures during TORS.We propose to divide the parapharyngeal space into two compartments(anterior and posterior)based on the surgical perspective of inside-out anatomy.The anterior compartment houses styloglossus muscle with ECA posterolateral to it and the posterior compartment has stylopharyngeus and ICA posterolateral to it.