The Middle Cranial Fossa Approach To Exocranial Skull Base Regions With Temporomandibular Joint Preservation

BackgroundThe Middle Cranial Fossa Approach with Temporomandibular Joint Preservation(MCFA-TMJp)is a characteristic approach in neurosurgery for dealing with lesions in the complex exocranial skull base regions such as the pterygopalatine fossa(PPF),infratemporal fossa(ITF),and parapharyngeal space(PPS).Some surgeons believe that most tumors can be safely removed through tumor corridors and extracapsular dissection techniques without the need for meticulous identification ofsurrounding structures during MCFA-TMJp surgery.However,inadequate exposure or difficulty in distinguishing tumors from normal exocranial soft tissues due to unfamiliarity with relevant anatomy can result in unsatisfactory tumor resection or serious complications.The surgical anatomy of MCFA-TMJp is highly complex and lacks detailed description in the literature;moreover,key issues such as the extent of exposure,severity of temporal lobe retraction,and reconstruction of MCFA-TMJp have not been quantitatively analyzed or thoroughly discussed.ObjectivesThis study first establishes the theoretical foundation and provides data reference through topographic dissections,followed by detailed anatomical dissections of the approach and a brief case review,aiming to comprehensively elucidate the anatomy of MCFA-TMJp and explore relevant issues.Additionally,this study conducts an anatomical study ofthe temporal branch of the facial nerve(TBFN)to guide the dissection of skin flaps and the harvesting offascial flaps during the craniotomy process of MCFA-TMJp.Methods1.Topographic anatomy:Dissection was performed on six cadaveric heads.Under the microscope,dissections were carried out sequentially on the parotid gland,ITF,PPS,nasopharynx,petroclival area,craniovertebral junction,and PPF.The scalp over the frontotemporoparietal region was dissected layer by layer,with particular attention paid to the course of the TBFN.Each step was documented with photographs taken using the microscope’s built-in camera.2.Surgical anatomy:Ten cadaveric heads were utilized for detailed dissection of MCFA-TMJp,spanning from craniotomy to reconstruction under a microscope.The main steps included craniotomy,harvesting offascial flaps,exposure and excision of the middle cranial fossa(MCF),exposure of the PPF,ITF,PPS,nasal cavity and paranasal sinuses,nasopharyngx,temporal bone,clivus,craniovertebraljunction,and intradural extension,and reconstruction.Each step was documented with photographs taken by the microscope’s built-in camera.The Leksell frame was used to determine the spatial coordinates of selected landmarks in the target areas,which were subsequently imported into Auto CAD software for area calculation.3.Case analysis:Tumor cases involving the ITF treated with MCFA-TMJp from July2022 to September 2023 were retrospectively reviewed,with collection and analysis of patients’preoperative,intraoperative,postoperative,and follow-up data.Results1.In the temporal region,all branches of TBFN run within the subgalealfat pad.The distances from the posterior border ofthis fat pad to the lateral canthus and the keyhole were62.17±4.27mm and 27.60±2.17mm,respectively.At the upper and lower borders of the zygomatic arch,the distances from the last branch of TBFN involved in the innervation of the frontalis muscle to the tragus were 34.24±2.15mm and 28.13±1.87mm,respectively.In8 specimens(8/12,66.67%),the temporoparietal fascia,loose areolar tissue,and parietal periosteum-superficial layer oftemporalis fascia could be harvested as three separate fascial flaps with sufficient thickness.The inferior border of ITF was defined as a line connecting the upper edge ofthe submandibular gland and the posterior end ofthe mylohyoid line,with the length of the pterygomandibular raphe being 19.12±1.78mm,and the distance from the foramen oval to the upper edge of the submandibular gland where the lingual nerve crosses being 53.24±2.84mm.2.i)Fascial flap harvesting:According to the new TBFN localizing method,no subgalealfat pad was exposed during the harvesting offascial flap.The lengths and areas of the distal 1/3 of the three fascial flaps were 115.42±6.47mm,110.05±6.08mm,100.24±5.21mm,and 36.08±3.75cm~2,34.25±3.96cm~2,34.31±3.24cm~2respectively.ii)Exposure:All branches of the maxillary nerve and pterygopalatine maxillary artery within the PPF could be completely exposed.The lateral wall of the ITF(i.e.,the inner aspect of the mandibular ramus)could not be directly visualized under the microscope.The length of the exposed pterygomandibular raphe was 14.78±1.89mm,and the distance from the foramen oval to the distal end of the lingual nerve was 48.86±3.19mm,with the exposure close to the lower border of the ITF.Only the anteromedial part of the retrostyloid space(RSS)could be exposed,and structures such as the stylohyoid muscle and the internal jugular vein belonging to the posterolateral part of the RSS were difficult to expose.The length of the exposed parapharyngeal internal carotid artery(ICA)and the area of exposure of the RSS were 19.26±1.35mm,2.66±0.39cm~2,and 47.95±2.26mm,5.93±0.87cm~2respectively,before and after removal of the styloid process.The exposure of the retropharyngeal and prevertebral spaces could be achieved after resection of the lateral wall of nasopharynx.Skeletonization and anterior mobilization of the petrous ICA completely exposed the ventral aspect of the ipsilateral clivus and craniovertebral junction.Incision of the posterior fossa dura exposed the ventral side of the lower pons and medulla,and structures on the lateral,superior,and inferior aspects could be observed after introducing an angled endoscope.iii)Temporal lobe retraction:Mainly involving upward retraction of the temporal pole,with the maximum retraction distance being 26.54±2.27mm.iv)Reconstruction:The length and the area of the distal 1/2 of the temporalis muscle flap were95.34±4.68mm and 15.09±1.95cm~2respectively.The areas of defects in MCF,lateral wall of nasopharynx,and posterior fossa dura were 16.11±1.13cm~2,6.08±0.49cm~2,and9.19±1.21cm~2respectively.All fascial flaps could cover the defect of MCF,and all temporalis muscle flaps could repair defects in the lateral wall ofnasopharynx and posterior fossa dura.3.Totally,8 cases were included in the study,all tumors involving both the ITF and MCF,with involvement ofthe PPS in 3 cases,and involvement ofthe PPF,posterior cranial fossa,and petrous bone in 2 cases each.5 cases underwent total resection(62.5%),2 cases underwent subtotal resection(25%),and 1 case underwent partial resection(12.5%).1 case(12.5%)experienced postoperative complications(transient extradural effusion).The average follow-up period was 11.50±4.00 months,with no tumor recurrence.Apart from 1case(12.5%)where pre-existing symptoms worsened postoperatively,no new-onset neurological deficits were observed in other patients,and preoperative symptoms were partially or completely relieved.Conclusionsi)By utilizing four landmarks—the keyhole,lateral canthus,midpoint of the zygomatic arch,and articular tubercle—the course of the TBFN can be accurately localized,offering a simple and reliable method that effectively prevents injury during skin flap elevation and fascial flap harvesting.ii)MCFA-TMJp provides full exposure of the PPF,ITF,and the anteromedial aspect of the RSS,with potential extension into the nasal cavity/paranasal sinuses,oro-/nasopharynx,clivus,craniovertebral junction,and intradural areas.iii)The pedicled scalp flaps harvested during the craniotomy effectively fulfill various reconstruction needs at the conclusion ofthe surgery.iv)The approach-related complications of MCFA-TMJp are extremely rare,and in appropriately selected cases,MCFA-TMJp can achieve optimal outcomes with minimal complications.v)In live surgery,although tumors can be removed via’tumor corridor’and extracapsular dissection techniques without the need to identify each surrounding structure individually,a thorough understanding ofthe relevant anatomy is crucial.