Landmarks for endoscopic approach to the parapharyngeal internal carotid artery: A radiographic and cadaveric study

Endoscopic trans-eustachian tube approach: identifying the precise landmarks, a novel radiological and anatomical evaluation

PURPOSE

The endoscopic trans-eustachian approach (ETETA) is a less invasive approach to the infratemporal fossa (ITF), providing superior exposure compared to traditional transcranial approaches. The anatomy of the pharyngotympanic (eustachian) tube and adjacent neurovascular structures is complex and requires in-depth knowledge to safely perform this approach. We present a cadaveric and radiological assessment of critical anatomic considerations for ETETA.

METHODS

Six adult cadaveric heads were dissected alongside examination of 50 paranasal sinus CT scans. Key anatomic relationships of the pharyngotympanic tube and adjacent structures were qualitatively and quantitatively evaluated. Descriptive statistics were performed for quantitative data.

RESULTS

Anatomical and radiological measurements showed lateralization of the pharyngotympanic tube allows access to the ITF. The pharyngotympanic tube has bony and cartilaginous parts with the junction formed by the sphenoid spine and foramen spinosum. The bony part and tendon of the tensor tympani muscle were located at the posterior genu of the internal carotid artery. The anterior and inferior wall of the carotid canal was located between the horizontal segment of the internal carotid artery and petrous segment of the cartilaginous pharyngotympanic tube.

CONCLUSION

The combination of preoperative radiographic assessment and anatomical correlation demonstrates a safe and effective approach to ETETA, which allowed satisfactory visualization of ITF. The morphological evaluation showed that the lateralization of the pharyngotympanic tube and related structures allowed a surgical corridor to reach the ITF. Endoscopic surgery through the pharyngotympanic tube is challenging, and in-depth understanding of the key anatomic relationships is critical for performing this approach.

Surgical Landmarks for Parapharyngeal Internal Carotid Artery During Extended Endoscopic Surgery of Nasopharynx: A Cadaveric and Radiological Study

Nasopharynx is a complex region situated at the center of skull surrounded by various vital neurovascular structures. Surgical access to the nasopharyngeal space poses significant challenges due to the position of the internal carotid artery (ICA). Open approaches to nasopharynx utilize the lateral to medial anatomy but the endoscopic endo-nasal approach warrants knowledge about the medial to lateral anatomy. In this study we attempted to find the consistent surgical landmarks for parapharyngeal portion of internal carotid artery at the level of nasopharynx by means of cadaveric and radiological study. Eight fresh frozen cadavers (16 sides) and 30 CT angiography (60 sides) were included in the anatomical and radiological study respectively. Superior aspect of the torus tubarius was taken as the reference point in cadaveric study and C1-C2 interspace was used as the reference point for the radiological study. The distance between the ICA to the landmarks such as fossa of Rosenmullaer, torus tubarius, medial and lateral pterygoid plates were recorded. The mean distance of ICA to the fossa of Rosenmuller was 8.5 ± 1.4 mm and 9.1 ± 1.1 mm in the cadaveric and radiological study respectively. The mean distance between ICA to torus tubarius was 19.8 ± 1.3 mm in cadaveric and 20.6 ± 1.0 mm in radiological study. The mean distance of ICA to medial and lateral pterygoid plates were 25.3 ± 1.4 mm and 18.2 ± 1.4 mm in the cadaveric study and 25.9 ± 1.2 mm and 18.8 ± 1.3 mm in the radiological study respectively. On correlating the measurements between cadaveric and radiological study, the p values were not statistically significant (p > 0.05). The closest landmark to the ICA was the fossa of Rosenmuller. ICA was located at the same sagittal plane as that of the lateral pterygoid plate. The nasopharynx is a complex anatomical region closely related to ICA. Inadvertent injury to ICA is one of the dreaded complications of nasopharyngeal surgery. Fossa of Rosenmuller is only few millimeters away from the ICA and must be treated very cautiously. During the endoscopic approach, the ICA is at the sagittal plane as of the lateral pterygoid plate. This must be kept in mind when advancing toward the ICA by keeping intact the lateral pterygoid plate when possible and one should stay in the plane of medial pterygoid plate as the ICA lies posterolateral to it. Cadaveric dissections supported by radiological data would definitely aid surgeons to successfully perform surgeries in nasopharynx.

Characterization of outcomes and practices utilized in the management of internal carotid artery injury not requiring definitive endovascular management

BACKGROUND

After internal carotid artery (ICA) injury during endoscopic skull base surgery, the majority of patients undergo ICA embolization or stenting to treat active extravasation or pseudoaneurysm development. However, management practices when embolization or stenting is not required have not been well described. The objective of this study was to determine how patients with ICA injury but no embolization, stenting, or ligation do long-term and ascertain the reconstruction methods utilized.

METHODS

Twenty-nine cases of ICA injury were identified in an international multi-institutional retrospective review. Of these, we identified six cases that were not treated with embolization, stenting, or ICA sacrifice. Information was available for five cases.

RESULTS

A muscle patch was used in the immediate repair of each case. A nasoseptal flap was used in one case. Prefabricated nasal tampons were used in all cases. Nasal packing was initially left in for a median of 7 days prior to removal. The initial muscle patch was reinforced with a second muscle graft in one case. One case demonstrated ICA bleeding at the time of packing removal and was repacked an additional week. Follow-up for each of these cases was at least 2 years. No cases of subsequent carotid rupture were found and none of these cases ultimately underwent endovascular stenting. Radiation or proton therapy has not been subsequently used in any of these patients.

CONCLUSIONS

This study details the reconstruction, lessons learned, and long-term follow-up for five cases of ICA injury not treated with embolization, stenting, or ligation.

Endoscopic transoral nasopharyngectomy

BACKGROUND

A minimal access technique for the management of nasopharyngeal tumors extending below the palatal plane and laterally beyond the pterygoid musculature is yet to be developed. In this study we demonstrate the feasibility of endoscopic transoral nasopharyngectomy (ETON) for resection of large nasopharyngeal lesions as a natural orifice alternative to traditional approaches.

METHODS

ETON was completed in three latex-injected specimens. Surgical freedom (SF) and angles of attack (AoA) were calculated along the internal carotid artery (ICA).

RESULTS

An endoscopic transoral approach was successfully used to identify the parapharyngeal ICA and subsequently perform a complete nasopharyngeal resection. SF and AoA (sagittal) were found to be the greatest at the anterior genu of the ICA.

CONCLUSIONS

ETON is feasible. It provides wide exposure of the skull base and proximal control of the ICA. It may be indicated for the management of nasopharyngeal tumors with inferolateral extension, involving the ICA.

Cervical-transoral robotic nasopharyngectomy: A preclinical study

BACKGROUND

We performed a preclinical study to assess the feasibility of the cervical-transoral robotic pharyngectomy procedure in surgery for nasopharyngeal cancer, where deep margins and vascular safety are key issues.

MATERIALS AND METHODS

Four cadaveric dissections were performed with the da Vinci Xi system. The first step was a robotic parapharyngeal dissection along the internal carotid artery (ICA). The second step was a type 3 transoral robotic nasopharyngectomy.

RESULTS

In each procedure, a comprehensive dissection of the parapharyngeal space was performed along the ICA up to the foramen lacerum. A type 3 nasopharyngectomy was performed transorally with an "en-bloc" removal of the parapharyngeal space, and with complete removal of the eustachian tube up to its bony part.

CONCLUSION

A comprehensive cervical-transoral robotic type 3 nasopharyngectomy with "en-bloc" removal of the parapharyngeal space and the eustachian tube proved to be technically feasible in a preclinical study.

The anatomy of the parapharyngeal segment of the internal carotid artery for endoscopic endonasal approach

Injury to the internal carotid artery (ICA) is a life-threatening complication of endoscopic endonasal approaches. The objective of this study is to illustrate the detail anatomy of the parapharyngeal segment of the ICA (PPICA) to safe endoscopic endonasal surgery. The anatomical dissection was performed in 10 cadaveric specimens and several crucial anatomical landmarks were identified and measured. In addition, 50 dry skulls were studied to further assess the relationship between the pharyngeal tubercle and carotid foramen. From the endoscopic endonasal perspective, in the median plane, the pharyngeal tubercle and the carotid foramen on both sides were located on a line. The average distance between the pharyngeal tubercle and anterior border of the external orifice of the carotid canal was measured as 25.2 ± 3.2 mm. In the paramedian plane, the PPICA was located between the levator veli palatini muscle (LVPM) and the stylopharyngeal muscle (SPM) in upper parapharyngeal space in all specimens, and the distance from the posterior border of the LVPM to the anterior border of the SPM was recorded as 15.1 ± 2.8 mm at the level of the carotid foramen. The distance from the attachment of the LVPM to the anterior border of the external orifice of the carotid canal was about 5.1 ± 0.2 mm. The fully developed stylopharyngeal fascia (SPhF) was observed in 10 cases, and the PPICA was always anteriorly enclosed by and adhered to the SPhF.

Characterization of Anatomical Landmarks for Exposing the Internal Carotid Artery in the Infratemporal Fossa Through an Endoscopic Transmasticator Approach: A Morphometric Cadaveric Study

BACKGROUND

The Eustachian tube and sphenoid spine have been previously described as landmarks for endonasal surgical identification of the most distal segment of the parapharyngeal internal carotid artery (PhICA). However, the intervening space between the sphenoid spine and PhICA allows for error during exposure of the artery. In the present study, we have characterized endoscopic endonasal transmasticator exposure of the PhICA using the sphenoid spine, vaginal process of the tympanic bone, and the "tympanic crest" as useful anatomical landmarks.

METHODS

Endonasal dissection was performed in 13 embalmed latex-injected cadaveric specimens. Two open lateral dissections and osteologic analysis of 10 dry skulls were also performed.

RESULTS

A novel and palpable bony landmark, the inferomedial edge of the tympanic bone, referred to as the tympanic crest, was identified, leading from the sphenoid spine to the lateral carotid canal. Additionally, the vaginal process of the tympanic bone, viewed endoscopically, was a guide to the PhICA. The sphenoid spine was bifurcate in 20% of the skulls, with an average length of 5.98 mm (range, 3.9-8.2 mm), width of 5.81 mm (range, 3.0-10.6 mm), and distance to the carotid canal of 4.48 mm (range, 2.5-6.1 mm).

CONCLUSION

The sphenoid spine and pericarotid space has variable anatomy. Using an endoscopic transmasticator approach to the infratemporal fossa, we found that the closest landmarks leading to the PhICA were the tympanic crest, sphenoid spine, and vaginal process of the tympanic bone.

Extended endonasal approach versus maxillary swing approach to the parapharyngeal space

BACKGROUND

The nasopharyngeal and parapharyngeal spaces are difficult for surgeons to access. Of the various external routes described, the maxillary swing has emerged as the gold standard because of its simplicity. However, its morbidity has led to the development of less invasive techniques. The purpose of our study was to compare the surgical anatomy of the maxillary swing with that of the endoscopic endonasal approach.

METHODS

Each procedure was performed on 10 anatomic specimens. The exposure and the limits obtained were evaluated. A CT scan analysis was performed.

RESULTS

The endoscopic endonasal approach extended the limits, offering wider exposure. The endoscopic endonasal approach made possible better visualization of deep structures and precise dissection of the parapharyngeal spaces. However, the maxillary swing provided better access to the oropharynx and could be completed 3 times faster.

CONCLUSION

The endoscopic endonasal approach provides excellent exposure, a wide dissection range, and precise definition of anatomic structures, making it an alternative of choice rather than the maxillary swing approach.

Finding the Petroclival Carotid Artery: The Vidian-Eustachian Junction as a Reliable Landmark

Introduction  Identifying the internal carotid artery (ICA) when managing petroclival and infratemporal fossa pathology is essential for the skull base surgeon. The vidian nerve and eustachian tube (ET) cartilage come together at the foramen lacerum, the vidian-eustachian junction (VEJ). The ICA position, relative to the VEJ is described. Methods  Endoscopic dissection of adult fresh-frozen cadaver ICAs and a case series of patients with petroclival pathology were performed. The relationship of the VEJ to the ICA horizontal segment, vertical segment, and second genu was assessed. The distance of the ICA second genu to VEJ was determined in coronal, axial, and sagittal planes. The length of the vidian nerve and ET was measured from the pterygopalatine fossa (PPF) and nasopharyngeal orifice to the VEJ. Results  In this study, 10 cadaver dissections (82.3 ± 6.7 years, 40% female) were performed. The horizontal petrous ICA was at or behind VEJ in 100%, above VEJ in 100%, and lateral to VEJ in 80%. The vertical paraclival segment was at or behind VEJ in 100%, above in 100%, and medial in 100%. The second genu was at or behind VEJ in 100% (3.3 ± 2.4 mm), at or above in 100% (2.5 ± 1.6 mm), and medial in 100% (3.4 ± 2.0 mm). The VEJ was successfully used to locate the ICA in nine consecutive patients (53.3 ± 13.6 years, 55.6% female) where pathology was also present. The VEJ was 15.0 ± 6.0 mm from the ET and 17.4 ± 4.1 mm from the PPF. Conclusion  The VEJ is an excellent landmark as it defines both superior and posterior limits when isolating the ICA in skull base surgery.

Endoscopic Resection of Pterygopalatine Fossa and Infratemporal Fossa Malignancies

The endoscopic resection of pterygopalatine and infratemporal fossa malignancies allows excellent visualization and manipulation of tissues in an anatomically complex area compared with open approaches. With less approach morbidity, endoscopic endonasal surgery allows an easier recovery and earlier transition to adjuvant radiotherapy. The endoscopic approach is minimal access but rarely minimally invasive. Surgeons should not hesitate to gain wide surgical exposure of the pterygopalatine, infratemporal fossa, and petrocavernous carotid artery to ensure comfortable maneuverability and easy visualization of the tumor and its normal tissue margins. This method maximizes the chances of complete resection and effective postoperative surveillance.

The endoscopic anatomy of the middle ear approach to the fundus of the internal acoustic canal

OBJECTIVE The application of the endoscope in the lateral skull base increases the importance of the middle ear cavity as the corridor to the skull base. The aim of this study was to define the middle ear as a route to the fundus (lateral end) of the internal acoustic canal and to propose feasible landmarks to the fundus. METHODS This was a cadaveric study; 34 adult cadaveric temporal bones and 2 dry bones were dissected with the aid of the endoscope and microscope to show the anatomy of the transcanal approach to the middle ear and fundus of the internal acoustic canal. RESULTS In the middle ear cavity, the cochleariform process is one of the key landmarks for accessing the fundus of the internal acoustic canal. The triangle formed by the anterior and posterior edges of the overhang of the round window and the cochleariform process provides a landmark to start drilling the bone to access the fundus of the internal acoustic canal. CONCLUSIONS The external acoustic canal and middle ear cavity combined, using endoscopic guidance, can provide a route to the fundus of the internal acoustic canal. A triangular landmark crossing the promontory has been described for reaching the meatal fundus. This transcanal approach requires an understanding of the relationship between the middle ear cavity and the fundus of the internal acoustic canal and provides a potential new area of cooperation between otology and neurosurgery for accessing pathology in this and the bordering skull base.

Different Perspectives of Internal Carotid Artery in Transnasal Endoscopic Surgery

BACKGROUND

Several endoscopic landmarks for the internal carotid artery (ICA) have been identified, but they have always been proposed in a "static" perspective. The aim of this study was to investigate how the surgical corridor and optical distortion can influence the perception of carotid landmarks in transnasal endoscopic surgery.

METHODS

Computed tomography images of skulls in 20 subjects were analyzed. The petrous carotid angle (PCA) was calculated as the angle between the petrous carotid axis and the coronal plane connecting stylomastoid foramina. The angle of incidence (AI) on the anterior carotid genu of 3 different surgical corridors (contralateral nostril, ipsilateral nostril, and transmaxillary ipsilateral route) was evaluated. PCA, AI, and their differences were studied by Spearman's correlation test. Two cadaver heads were dissected, simulating the studied surgical corridors. The fish-eye effect was empirically quantified.

RESULTS

Mean PCA was 31° (range, 21-41°). PCA and AI are linked by an inverse proportion relationship. A transmaxillary approach always ensures the highest value of AI on the target. The cadaveric dissection qualitatively confirmed the radiologic data. The fish-eye effect can cause a compression of distance perception as high as 37%.

CONCLUSIONS

The surgical corridor and endoscope optic distortion can influence ICA visualization and the perception of its anatomic landmarks. In a 2-nostril, 4-handed approach, it is advisable to place the endoscope and instrument for dissection in the nostril that is ipsilateral to the lesion. Awareness of the different perspectives and related optical distortions is essential when working in proximity to the ICA.