Localisation of the petrous internal carotid artery relative to the vidian canal on computed tomography: a case-control study evaluating the impact of petroclival chondrosarcoma

Relationships of the vidian nerve and internal carotid artery: MRI and intraoperative surgical evaluation

Objective

Skull base anatomy around the internal carotid artery (ICA) is extremely complex. Among anatomical landmarks studied, the vidian canal has been thoroughly evaluated, unlike the vidian nerve (VN). Our aim is to evaluate the VN-ICA relationships, and understand their role in terms of surgical planning.

Methods

Fifty MRI examinations of 100 healthy petro-spheno-clival regions were reviewed in order to evaluate the relationship between the vidian nerve axis (VNA) and the petrous ICA. Twenty-seven cases of expanded endonasal approaches to petrous apex region were evaluated to check the VN-ICA relationship intraoperatively.

Results

MRI evaluations showed that, in 23% of cases, the VNA was below the edge of the ICA, in 45% it was at the edge of the ICA and in 32% it ended up above the edge of the ICA. Surgically speaking, in 9 of 28 petrous apex approaches, the VN ended above the inferior edge of the petrous carotid.

Conclusions

MRI evaluation adds useful information in planning the surgical approach to petro-spheno-clival regions, even if the identification of VNA, in these cases, may not be radiologically possible. Surgical experience confirms the importance of VN identification in guiding the surgeon in complex cases, and also outline the possible risks of relying only on this landmark.

The Displacement Patterns of Petrous Internal Carotid Artery and Its Morphometric Relations with Vidian Canal in Petroclival Chondrosarcomas Relevant to Extended Endoscopic Endonasal Approaches: A Radiological Study

BACKGROUND

Extended endoscopic endonasal approaches (EEAs) to petroclival chondrosarcomas (PCs) require a thorough understanding of skullbase anatomy, especially the anatomy of petrous internal carotid artery (pICA), as ICA injury is the most dreaded complication of extended EEAs. We conducted this study to determine the displacement patterns of pICA in patients with PCs.

METHODS

Contrast enhanced computed tomography scan and angiography images of patients with PCs were analyzed for following parameters-antero-posterior, cranio-caudal, medio-lateral, and direct distances between anterior genu of petrous internal carotid artery (AGpICA) and posterior end of Vidian canal (pVC). pICA encasement/narrowing by tumor was noted on magnetic resonance imaging.

RESULTS

We studied 11 patients with histopathologically proven PCs. pICA encasement/narrowing and pVC destruction were observed in one patient each. The mean antero-posterior and cranio-caudal distances on tumor side/normal side were 7.7 ± 1.9/6.4 ± 1.0 mm & 4.5 ± 1.5/3.4 ± 0.9 mm, respectively. The overall displacement was posterior & superior. Medio-lateral displacement was seen in 4 patients (lateral in 3 and medial in 1). In rest, AGpICA was centered on pVC. The mean direct distance was 9.4 ± 2.5 mm. In 3 patients with displacement seen in all three axes, direct distance was measured by the "cuboid method." Overall, posterior-superior-lateral, posterior-superior, and anterior-inferior were the common displacement patterns of AGpICA relative to pVC.

CONCLUSIONS

The displacement patterns of AGpICA in PCs are variable. An individualized approach with meticulous analysis of preoperative imaging can help in determining the relation between AGpICA and pVC. This detailed morphometric information can facilitate better orientation to altered anatomy, which can be helpful in preventing pICA injury during extended EEAs.

Imaging anatomy of the vidian canal and its clinical significance

Background

Vidian neurectomy (VN) is an effective surgical treatment for severe allergic rhinitis (AR). However, little research has been conducted on the imaging anatomy of the vidian canal (VC). This study aimed to analyze the computed tomography (CT) imaging of the VC and its surrounding structures and investigate the morphometric characteristics and clinical significance of VN.

Methods

We analyzed 118 paranasal sinus CT scans (55 male and 63 female patients), with axial, coronal, and sagittal slices being used in the study.

Results

Among the 118 patients in this study, the average length of the VC in male and female patients was 14.00±3.35 and 12.51±3.42 mm, respectively; the transverse diameter of the posterior segment of the VC in females was larger than that in males; and the length of the VC and the distance between VC and foramen rotundum (FR) in males were longer than those in females. The angle between the VC and the sagittal plane and the angle between the sphenopalatine foramen (SPF) and the VC in females were larger than those in males, and the distance between the attachment to the end of the middle turbinate (MT) and the VC was greater. Type 2 VC occupied a dominant position. The VC was mostly at the same line as the medial wall of the maxillary sinus (MS) and was located on the medial side of the medial pterygoid plate (MPTG). The highest point of the VC was mostly superior to that of the palatovaginal canal (PVC). Most of the VC was inferior to the internal carotid artery (ICA), and no cases were observed in which the VC was above the ICA. Some of the measurements of the VC and its surrounding structures were correlated.

Conclusions

The position and morphometric information of the VC could be reflected in a CT scan, which may contribute to the evaluation of VN preoperatively and postoperatively.