Orientation of the Foramen Ovale: An Anatomic Study With Neurosurgical Considerations

Sphenoidal Foramen Ovale in the Slovenian Population: An Anatomical Evaluation with Clinical Correlations

The foramen ovale (FO) is a crucial feature of the skull base, serving as a passage for clinically important neurovascular structures. The present study aimed to provide a comprehensive morphometric and morphologic analysis of the FO and highlight the clinical significance of the anatomical characterization. A total of 267 FO were analyzed in skulls obtained from deceased inhabitants of the Slovenian territory. The anteroposterior (length) and the transverse (width) diameters were measured using a digital sliding vernier caliper. Dimensions, shape, and anatomical variations of FO were analyzed. The mean length and width of the FO were 7.13 and 3.71 mm on the right side and 7.20 and 3.88 mm on the left side. The most frequently observed shape was oval (37.1%), followed by almond (28.1%), irregular (21.0%), D-shaped (4.5%), round (3.0%), pear-shaped (1.9%), kidney-shaped (1.5%), elongated (1.5%), triangular (0.7%), and slit-like (0.7%). In addition, marginal outgrowths (16.6%) and several anatomical variations were noted, including duplications, confluences, and obstruction due to a complete (5.6%) or incomplete (8.2%) pterygospinous bar. Our observations revealed substantial interindividual variation in the anatomical characteristics of the FO in the studied population, which could potentially impact the feasibility and safety of neurosurgical diagnostic and therapeutic procedures.

Morphologic and Morphometric Measurements of the Foramen Ovale: Comparing Digitized Measurements Performed on Dried Human Crania With Computed Tomographic Imaging. An Observational Anatomic Study

The foramen ovale (FO) of the sphenoid bone is clinically important for the interventional treatment of trigeminal neuralgia. Percutaneous procedures applied to treat the chronic pain condition typically involve the cannulation of this oval-like foramen located at the base of the skull. Anatomic variations of the FO have been reported to contribute to difficulties in the cannulation of this structure. Computed tomography (CT) can help the surgeon improve the accuracy and safety of the intervention. However, even with navigation technology, unsuccessful cannulation of the FO has been reported. The aim of this observational anatomic study was to define morphometric and morphologic data of the FO and to investigate for potential differences between measurements taken on dried human crania and digitized measurements of the FO measured on CT images. One hundred eighteen FOs were evaluated. Twenty FOs underwent CT scanning. The mean length of the foramen was 7.41±1.3 mm on the left side and 7.57±1.07 mm on the right. The mean width of the foramen was 4.63±0.86 mm on the left side and 4.33±0.99 on the right. The mean area on the left side was 27.11±7.58 and 25.73±6.64 mm 2 on the right. No significant left-right differences were found for any of these dimensions. The most important conclusion that we can draw is that the measurements can indeed be performed on CT images to obtain an accurate picture of the morphology. Considering the surgical importance of the FO and taking into consideration the limitations this study added to scientific knowledge, this study was constructive as far as neurosurgeons and anatomists are concerned.

Narrow ovale foramina may be involved in the development of primary trigeminal neuralgia

Background

The etiology of primary trigeminal neuralgia remains unclear and is worthy of further study; In this study, the morphometric characteristics of ovale foramina between various groups were compared and analyzed to explore the novel cause of primary trigeminal neuralgia.

Methods

High-resolution three-dimensional reconstruction images from head computed tomography of 109 patients with primary trigeminal neuralgia affecting the third branch of the trigeminal nerve and 46 healthy controls were retrospectively reviewed. Among the 109 primary trigeminal neuralgia patients, 79 patients with apparent neurovascular compression (not simply contact) demonstrated on MRI or during surgery were divided into the classical trigeminal neuralgia group and 30 patients with MRI showing no significant abnormalities were divided into idiopathic trigeminal neuralgia group. The morphometric parameters including the area, width and length of ovale foramina were examined through the use of radiologic methods.

Results

In this study, the average minimum area, width and length of 79 ovale foramina on the affected and unaffected sides in the classical trigeminal neuralgia group were 21.83 ± 8.45, 21.94 ± 7.93 mm², 2.32 ± 0.91, 2.58 ± 0.81, 5.32 ± 1.29, and 5.26 ± 1.21 mm, respectively. No significant difference in these parameters was observed (p > 0.05). However, in the idiopathic trigeminal neuralgia group, the average minimum area, width and length of 30 ovale foramina were 21.33 ± 8.21, 22.85 ± 8.36 mm², 2.25 ± 0.90, 2.79 ± 0.96, 5.20 ± 1.27, and 5.28 ± 1.19 mm, respectively. The width on the symptomatic side was significantly smaller (p = 0.03) than that on the asymptomatic side. No significant difference in area (p = 0.48) or length (p = 0.79) was observed. In addition, when compared with the healthy control group, the area and width of ovale foramina on the symptomatic side in both groups were significantly smaller. No significant difference in length was observed.

Conclusions

By comparing and analyzing the statistical data, it can be inferred that a narrow foramen ovale is associated with primary trigeminal neuralgia, as well as its recurrence after microvascular decompression.

Anatomical dimensions and variances of the foramen ovale in adult human skulls

Background/Aim: The foramen ovale (FO) is very important in neurosurgical approaches; however, studies and developments in the literature report that no definite consensus about the cannulation of the FO is available. Therefore, more morphometric information concerning the FO is needed in addition to the previously defined morphological and morphometric features. The aim of this study was to compare the features of the foramen ovale stated in the literature and to analyze the topographic relationship between the FO and the anatomical structures around it to determine its precise location. Methods: The study included 70 sides from 35 dry skulls of unknown age and gender. Skulls with any deformity or pathology that would affect the measurements were not included in the study. All skulls were placed in the horizontal plane with the external occipital protuberance facing posteriorly, the piriform aperture facing anteriorly, and the skull base pointing upwards at a 90° angle after which it was photographed vertically with the length scale. A Nikon D5300 Digital Camera was used for the photography, and digital image processing software (Image J) was used for foramen ovale measurements. In addition, the shape of the foramen ovale was classified as oval, almond, D-shaped, slit-shaped, round, and irregular. SPSS 21.0 was used for the statistical analysis. Results: The mean anteroposterior diameter length of the FO was 6.144 mm, and the transverse diameter length was 2.885 mm. When the distribution of the shape of the FO was examined, oval and almond shapes were most common shapes (34.29%). In addition, round (12.85%), D-shaped (10%), and slit-shaped (8.57%) were obtained. According to Pearson’s correlation analysis, the highest correlation was between the distance from the carotid canal to the foramen ovale and the shortest distance from the foramen ovale to the midline (FO-CC and the FO-ML, respectively; r = 0.427). Conclusion: The morphology of the FO is important in terms of surgical and interventional approaches. In the literature, no significant differences between the right and left sides for the foramen ovale were found in contrast to our study. When the FO shape percentages were examined in most previous studies, it was seen that most of them were oval. In this study, the ratios of oval and almond shapes were the same. Morphometric measurements can give different results in every race due to the structure of the bones, which may vary according to the population. We think that presenting data on the Turkish population in this study will set an example for conducting future studies.

Infratemporal Fossa Vascular Anatomy Pertinent to Percutaneous Access to the Foramen Ovale for Treatment of Trigeminal Neuralgia: A Comparison of Cadaveric Dissection and Computed Tomography Analysis

BACKGROUND

Trigeminal neuralgia may be treated via percutaneous access to the foramen ovale (FO). Vascular complications associated with the needle trajectory can result in serious morbidity and mortality. This study aimed to correlate the vascular relationships of the FO at the skull base via cadaveric dissections and computed tomography (CT).

METHODS

Two fresh cadaver heads were injected with red and blue latex to delineate arteries and veins. Neck and infratemporal fossa dissections were carried out to delineate the vascular relationships of the FO. High-resolution head CT images of adult patients undergoing neurosurgical evaluations or procedures were analyzed for distances and sizes of skull base foramina in the infratemporal fossa.

RESULTS

Three infratemporal fossa dissections (2 cadaveric specimens) were performed. Mean distance of FO to internal carotid artery was 2.4 ± 0.12 cm, and mean distance of FO to middle meningeal artery was 0.8 ± 0.16 cm. Head CT images of 52 patients (104 sides) with 1-mm axial slice thickness were analyzed. Area of the FO was 31.1 ± 9.6 mm². Distance of FO to internal carotid artery was 1.70 ± 0.31 cm, and distance of FO to middle meningeal artery was 0.73 ± 0.61 cm.

CONCLUSIONS

Cadaveric delineation of vascular structures in the infratemporal fossa correlates with head CT imaging and may be used to accurately plan percutaneous access to the FO. Inadvertent puncture of the extracranial internal carotid artery is nearly impossible with good technique. The most likely source of percutaneous vascular injury is the middle meningeal artery and distal branches of the maxillary artery.

CT Evaluation of Variations in the Middle Cranial Fossa Foramina: A Potential Guide for Skull Base Surgery

OBJECTIVES

To evaluate and classify the variations of foramen ovale (FO), foramen spinosum (FS).

METHODS

Six hundred fifty-eight computed tomographies (CTs) were evaluated by 2 observers. Foramen ovale was classified as oval, almond, round, and slit-like. Duplication, absence, and confluence for FS were noted. Bony outgrowths were categorized as tubercule, bony plate, and spine.

RESULTS

Oval shaped FO was the most common subgroup. Most common FS variation was the confluence with FO. Of bony outgrowths, tubercule-shaped were the most common type and spine-shaped ones were the least. Substantial agreement for bony plate and tubercule, almost excellent agreement for all the other parameters were found between 2 observers.

CONCLUSIONS

Foramen ovale called lobulated and had not classified previously was described in this study. Computed tomography is a reliable tool for anatomical evaluation of FO and FS, which would effect the methods of middle cranial fossa surgery. Thus, radiologists should be a pathfinder about the variations of these structures.

An Anatomical Study of the Foramen Ovale for Neuromodulation of Trigeminal Neuropathic Pain

OBJECTIVE

Neuromodulation for trigeminal pain syndromes such as trigeminal neuropathic pain (TNP) necessitates accurate localization of foramen ovale (FO). The Härtel-type approach is very well-established and safe, ideal for temporary cannulation of the FO for ablative procedures such as balloon microcompression. A key shortcoming of the Hartel approach for placement of neuromodulation leads is the limited opportunity for secure anchoring. The aim of this study is to introduce a novel surgical approach for the treatment of TNP by investigating key osseous landmarks and their spatial relationships to the FO.

MATERIALS AND METHODS

Sixteen sides of cadaver heads were dissected to investigate a surgical route of the FO via transoral gingival buccal approach. Alveolar arch of the maxilla and zygomaticomaxillary suture were selected to serve as an osseous landmark for the surgical guidance to the FO. Through the intraoral route, a needle simulating electrode was traversed to aim the FO from the inferior lateral to the superior medial direction to target specific fibers of the aimed division of the nerve.

RESULTS

Visual identification and access to the trigeminal nerve at the external opening of FO was successful in all 16 hemifacial cadavers. A needle successfully targeted different regions of the trigeminal nerve by changing the angle of the trajectory allowing the needle to reach a specific division of the trigeminal nerve.

CONCLUSIONS

This study provides a novel means of approaching the FO via transoral gingival buccal access.

The emissary veins of the foramen ovale: an anatomical study using magnetic resonance imaging

PURPOSE

The emissary veins (EVs) passing through the foramen ovale (FO) are not well understood. The aim of this study was to characterize these veins using contrast magnetic resonance imaging (MRI).

METHODS

In total, 85 patients underwent thin-sliced, contrast MRI. Coronal and sagittal images were used for the analysis.

RESULTS

The EVs of the FO were well delineated in 100% on sagittal and 97% on coronal images. On the sagittal images, these veins could be classified into the lateral, medial, and perineural types in association with the mandibular division of the trigeminal nerve (V3) segment in the FO. In 22% of the slides, the medial EV was more predominant than lateral one, while in 64% of the slides, the latter was more predominant. On the coronal images, the identified EVs of the FO coursed medially to the V3 in 68% and laterally in 72% of 165 sides. The perineural EVs most frequently coursed along both the lateral and medial surfaces of the V3. On the sagittal images, the angles formed by the midline of the V3 segment in the FO and lower margin of the FO were 81.5 ± 11.9° on the left side and 80.0 ± 12.2° on the right, while on the coronal images, they were 61.5 ± 12.1° on the left side and 64.8 ± 11.3° on the right.

CONCLUSIONS

The EVs of the FO are structures that may be characterized by a well-developed venous channel in the lateral aspect of the V3 and nearly symmetrical orientation of both V3s lying in the FO.

Angular Relationship Between the Foramen Ovale and the Trigeminal Impression: Percutaneous Cannulation Trajectories for Trigeminal Neuralgia

The debilitating pain of trigeminal neuralgia often necessitates neurosurgical intervention via percutaneous transovale cannulation. While most percutaneous treatments of trigeminal neuralgia are successful, severe adverse events resulting from failure to properly cannulate the foramen ovale (FO) have been reported. With regard to specific targeting of particular trigeminal divisions (ie, V1, V2, V3, and combinations thereof), operative techniques have been described; however, these descriptions have not included specific angulation data. This anatomic study analyzed the angular relationship between the centroid and anteromedial- and posterolateral-most aspects of the FO and the boundaries of the trigeminal impression. The study is the first to detail the angular relationship between the FO boundaries and the boundaries of the trigeminal impression in dry human skulls relative to the coronal plane. The information may be used to prevent miscannulation and also target specific branches of the trigeminal nerve for optimal operative results.

Percutaneous radiofrequency thermocoagulation for trigeminal neuralgia using neuronavigation-guided puncture from a mandibular angle

Percutaneous radiofrequency thermocoagulation (RFT) of the Gasserian ganglion is an effective treatment for primary trigeminal neuralgia (pTN). Currently Hartel anterior approach is the most commonly used method to access the Gasserian ganglion. However, this approach is associated with high recurrence rate and technical difficulties in certain patients with foramen ovale (FO) anatomical variations. In the present study, we assessed the feasibility of accessing the Gasserian ganglion through the FO from a mandibular angle under computed tomography (CT) and neuronavigation guidance.A total of 108 patients with TN were randomly divided into 2 groups (Group G and Group H) using a random number table. In Group H, Hartel anterior approach was used to puncture the FO; whereas in Group G, a percutaneous puncture through a mandibular angle was used to reach the FO. In both groups, procedures were guided by CT imaging and neuronavigation. The success rates, therapeutic effects, complications, and recurrence rates of the 2 groups were compared.The puncture success rates in Group H and Group G were 52/54 (96.30%) and 49/54 (90.74%), respectively (P = 0.24). The 2 procedural failures in Group H were rescued by using submandibular trajectory, and the 5 failures in Group G were successfully reapproached by Hartel method. Therapeutic effects as measured by Barrow Neurological Institute (BNI) pain scale (P = 0.03) and quality of life (QOL) scores (P = 0.04) were significantly better in Group G than those in Group H at 36 months posttreatment. Hematoma developed in 1/54 (1.85%) cases in Group H, and no cases of hematoma were observed in Group G (P = 0.33). In Group H, RFT resulted in injury to the unintended trigeminal nerve branches and motor fibers in 27/52 (51.92%) cases; in Group G, it resulted in the same type of injury in 7/49 cases (14.29%) (P < 0.01). In Group H, the 24- and 36-month recurrence rates were 12/51 (23.53%) and 20/51 (39.22%), respectively; in Group G, these recurrence rates were 7/49 (12.24%) and 9/49 (16.33%, P = 0.03), respectively.CT- and neuronavigation-guided puncture from a mandibular angle through the FO into the Gasserian ganglion can be safely and effectively used to deliver RFT for the treatment of pTN. This method may represent a viable option to treat TN in addition to Hartel approach.