Access to Parapharyngeal Space - Vula - University of Cape Town

the superior constrictor muscle of thepharynx. It contains the internal carotidartery and the internal jugular vein, as wellas the lower cranial nerves IX -XII, and thesympathetic trunk. Unlike prestyloidmasses, poststyloid tumours typicallydisplace the PPS fat anterolaterally(Figures 8, 9).sympathetic trunk, and schwannomas(Figures 9, 10).External carotidInternal carotidFigure 10: Carotid body tumour in poststyloidPPS, splaying the internal andexternal carotid arteriesFigure 8: Direction of displacement of fatas seen on CT or MRI with poststyloidmass (light blue)Figure 9: CT scan of poststyloid vagalschwannoma demonstrating direction ofdisplacement of fat and medialdisplacement of carotid vesselsThe most commonly encountered massesinclude carotid body tumours, or otherparagangliomas eg of the vagus nerve andKey Diagnostic InformationOne should determine the following beforeembarking on surgery:Benign / malignant: This is generallydetermined by FNAC. The needlebiopsy may be done transcervically ortransorally, and one should not beconcerned about puncturing theinternal carotid artery with a smallneedleVascularity: A paraganglioma may besuspected on CT or MRI, andconfirmed angiographically. Vasculartumours may require preoperativeembolisation, and proximal vascularcontrol, or one may elect to treat it withradiation therapyPrestyloid / poststyloid: This is determinedclinically and radiologicallywith CT / MRI as indicated previously.This information permits narrowingdown of the differential diagnosis,planning the best surgical approach,and preoperative counselling ofpossible sequelae3

Is a prestyloid mass originating fromthe parotid gland? This informationmight determine the surgical approache.g. transcervical +/- totalparotidectomy. It may be difficult todetermine even radiologically whethera prestyloid pleomorphic adenomasimply represents ectopic salivarytissue, or is extending from the deeplobe of the parotid glandInternal & external carotid arteries:Particularly with poststyloid masses,knowledge of the position of thearteries is important in order to directthe surgerySurgical approachesFigure 11 presents a schematic summaryof the surgical approaches to the PPS.rupture (especially with pleomorphicadenomas that may seed). The tumours aresituated anywhere between the hyoid boneand generally do not extend above thelevel of the hard palate of pterygoid plates,and are situated on the medial aspect of themedial pterygoid muscle. They aretherefore readily accessible via a transcervicalsubmandibular approach. Thealternative is a transoral approach +mandibulotomy.Transcervical submandibular approach toprestyloid tumoursA horizontal skin crease incision is madeat the level of the hyoid bone. Thesubmandibular salivary gland (SSG) anddigastric muscle are identified. The facialvein is ligated and divided. The capsule ofthe gland is incised. The SSG is mobilisedin a subcapsular plane so as to protect themarginal mandibular nerve. The facialartery is identified posteroinferior to thegland where it emerges from behind theposterior belly of the digastric muscle(Figure 12).Figure 11: Approaches to PPS: transoral+ mandibulotomy (green); transcervicalsubmandibular (yellow), transparotid(blue), and transcervical + mandibulotomy(red)Prestyloid surgical approachesMasses in the prestyloid space are mostlybenign, well defined, surrounded by fat,and unlike tumours of the poststyloidspace, are generally not tethered tostructures such as major nerves andvessels. They can therefore generally beremoved by careful blunt dissection alongthe tumour capsule, avoiding tumourSubmandibularglandFacial arteryDigastricFigure 12: Exposure of the left submandibulargland, digastric muscle andfacial arteryThe facial artery is then ligated anddivided above the posterior belly ofdigastric. The submandibular gland ismobilised with gentle finger dissection in aposterior-to-anterior direction leaving the4

estricted by the vertical ramus of themandible, the parotid gland, the facialnerve and the styloid process with itsmuscular and ligamentous attachments.Masses in the poststyloid space are mostlybenign but unlike tumours of the prestyloidspace, are generally tethered to/arise frommajor nerves and vessels. Resectionrequires good exposure of the mass and themajor vessels and nerves via transcervicaland/or transparotid approach. Rarely amandibulotomy of the vertical ramus of themandible is required for additionalexposure. Patients should be cautionedabout the sequelae of vascular and lowercranial nerve injury, as well sympathetictrunk injury causing Horner’s and “1 stBite” syndromes. Preoperativeembolisation of paragangliomas reducesintraoperative bleeding.Transcervical approach to the poststyloidPPS (Figures 11, 17)The transcervical approach is suitable fortumours extending up to about the level ofthe styloid process, such as smaller carotidbody and glomus vagale tumours, as wellas lower lying schwannomas. The upperneck is exposed via a transverse skincrease incision, the X, XI, and XII nervesare identified, as are the carotid bifurcationand the internal jugular vein. The mass isthen removed using sharp dissection. Theposterior belly of digastric is eitherretracted superiorly, or divided to provideaccess deep to the parotid gland (Figure17).DigastricFigure 17: Transcervical resection ofglomus vagaleTransparotid approach to the poststyloidPPS (Figures 11, 18, 19, 20, 21)The transparotid approach is required formasses situated closer to the skull base.The superficial lobe of the parotid gland iselevated off the facial nerve, the nerve isfreed from the deep lobe, and the deepparotid lobe is resected. This exposes thestyloid process. Immediately medial to thestyloid are the contents of the poststyloidPPS. Access can be further improved byexcising the styloid process with a bonenibbler, and retracting the mandibleanteriorly (taking care to avoid excessivetension of the facial nerve), and inferiorlyby dividing the posterior belly of thedigastric.External carotidInternal carotidGlomus vagaleAccessory nerveInternal jugularFigure 18: Operative field followingresection of carotid body tumour shown inFigure 106

Author & EditorSchwannomaInternal carotidJohan Fagan MBChB, FCORL, MMedProfessor and ChairmanDivision of OtolaryngologyUniversity of Cape TownCape TownSouth Africajohannes.fagan@uct.ac.zaFigure 19: Schwannoma of poststyloidPPS located medial to internal carotidarteryThe Open Access Atlas of Otolaryngology, Head &Neck Operative Surgery by Johan Fagan (Editor)johannes.fagan@uct.ac.za is licensed under a CreativeCommons Attribution - Non-Commercial 3.0 UnportedLicenseFigure 20: Transparotid access topoststyloid PPS in Figure 15Figure 21: Additional access to poststyloidPPS in Figures 15&16 by transection ofdigastric muscle7