Morphometric and Anatomic Variations of Foramen Ovale in Human Skull and Its Clinical Importance

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.

Morphological variations and morphometry details of the foramen ovale in the Saudi population: a retrospective radiological study

The foramen ovale is one of the essential foramina in the middle cranial fossa, more precisely, in the superior surface of the greater wing of the sphenoid bone. It has essential surgical and diagnostic significance since it serves as a surgical landmark, and crucial neurovascular vessels such as the mandibular nerve and accessory meningeal artery pass through it. Therefore, understanding the morphological and morphometric variations of the foramen ovale is essential for accurately identifying, diagnosing, and managing related pathologies. The study aimed to evaluate the morphological variations and morphometric details of the foramen ovale in the Saudi population. A radiological study was conducted to observe the measurements and the shapes of the foramen ovale in the skull with its anatomical variants. Retrospective data was collected from the Department of Radiology, King Fahad University Hospital, Saudi Arabia. The sample consisted of 100 human skulls from computed tomography scans, including 50 males and 50 females. The values for the mean length, width, and distance from the midline on the right side were 6.462 mm ± 1.681 mm, 4.897 ± 1.0631 mm, and 2.4565 ± 0.51275 mm, and 6.451 ± 1.6691 mm, 4.812 ± 1.0848 mm and 2.4290 ± 0.60039 mm for the left side, respectively. The foramen shape was oval in the majority (47%), followed by round shape (31%) with no bony outgrowths such as spur in the studied foramina. Furthermore, the morphometric variation between males and females was statistically insignificant (p-value>0.05). The observed variation of foramen ovale in this study has significant anatomical and clinical applications for various diagnostic and surgical procedures.

Identification of Foramen Ovale With H-Figure Fluoroscopic Landmark Improves Treatment Outcomes in Idiopathic Trigeminal Neuralgia

BACKGROUND

Because it is traditionally difficult and time-consuming to identify the foramen ovale (FO) with fluoroscopy, we recently developed the H-figure method to acquire fluoroscopic view of FO with shorter procedure time and less radiation. However, the impact of such an H-figure approach on the clinical outcomes of trigeminal ganglion radiofrequency thermocoagulation (RFT) in treating idiopathic trigeminal neuralgia (ITN) remains unclear.

METHODS

In a 12-month follow-up retrospective cohort study, patients with ITN had fluoroscopy-guided RFT of trigeminal ganglion via either classic approach (n = 100) or H-figure approach (n = 136) to identify FO. Data of continuous variables were analyzed with a Shapiro-Wilk test for normality and subsequently with a Mann-Whitney test, and the binary data were analyzed with a χ 2 test. The primary outcome was the facial pain measured by a Visual Analog Scale (VAS) 1 year after the treatment. The secondary outcomes included the quality of the fluoroscopic FO views, the threshold voltage to provoke paresthesia, the procedure time, the number of fluoroscopic images, and the facial numbness VAS.

RESULTS

Compared with the classic approach group, the H-figure approach group was associated with better long-term pain relief after the procedure, with significantly fewer patients had pain 3 months (6.6% vs 17.0%, P = .012) and 12 months (21.3% vs 38.0%, P = .005) after the procedure, and among patients who had pain after the procedure, patients in the H-figure group had significantly less pain 6 months after the procedure (VAS median [interquartile range (IQR)]: 3 [2-6] vs 6 [4-7], P < .001). Moreover, compared to the classic approach, the H-figure approach provided better fluoroscopic view of FO, lower threshold voltage to elicit paresthesia (median [IQR]: 0.2 [0.2-0.3] vs 0.4 [0.4-0.5] V, P < .0001), with shorter procedure time (median [IQR]: 7.5 [6.0-9.0] vs 14.0 [10.0-18.0] min, P < .0001), and required fewer fluoroscopic images (median [IQR]: 4.0 [3.0-5.0] vs 8.0 [6.0-10.0], P < .0001).

CONCLUSIONS

RFT of the trigeminal ganglion using the H-figure approach is associated with superior longer term clinical pain relief than the classic approach in treating ITN.

Feasibility of Upper Cranial Nerve Sonication in Human Application via Neuronavigated Single-Element Pulsed Focused Ultrasound

Sonicating deep brain regions with pulsed focused ultrasound using magnetic resonance imaging-guided neuronavigation single-element piezoelectric transducers is a new area of exploration for neuromodulation. Upper cranial nerves such as the trigeminal nerve and other nerves responsible for sensory/motor functions in the head may be potential targets for ultrasound pain therapy. The location of upper cranial nerves close to the skull base poses additional challenges when compared with conventional cortical or middle brain targets. In the work described here, a series of computational and empirical testing methods using human skull specimens were conducted to assess the feasibility of sonicating the trigeminal pathway near the sphenoid bone region. The results indicate a transducer with a focal length of 120 mm and diameter of 85 mm (350 kHz) can deliver sonication to upper cranial nerve regions with spatial accuracy comparable to that of focused ultrasound brain targets used in previous human studies. Temperature measurements in cortical bone and in the skull base with embedded thermocouples yield evidence of minimal bone heating. Conventional pulse parameters were found to cause reverberation interference patterns near the cranial floor; therefore, changes in pulse cycles and pulse repetition frequency were examined for reducing standing waves. Limitations and considerations for conducting ultradeep focal targeting in human applications are discussed.

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.

Anatomical relationship between the foramen ovale and the lateral plate of the pterygoid process: application to percutaneous treatments of trigeminal neuralgia

Our aim was to clarify the variations in the positional relationship between the base of the lateral plate of the pterygoid process and the foramen ovale (FO), which block inserted needles during percutaneous procedures to the FO usually used for the treatment of trigeminal neuralgia. Ninety skulls were examined. The horizontal relationship between the FO and the posterior border of the base of the lateral plate of the pterygoid process was observed in an inferior view of the skull base. Skulls that showed injury to either the FO or the lateral plate of the pterygoid process on either side were excluded. One hundred and sixty sides of eighty skulls were eligible. The relationship between the FO and the posterior border of the base of the lateral plate was classified into four types. Among the 160 sides, type III (direct type) was the most common (35%), followed by type I (lateral type, 29%) and type IV (removed type, 21%); type II (medial type) was the least common (15%). Of the 80 specimens, 53 showed the same type bilaterally. In type IV, the posterior border of the base of the lateral plate is disconnected from the FO, so percutaneous procedures for treating trigeminal neuralgia could fail in patients with this type.