The foramen ovale is an oval-shaped aperture situated in the posterior part of the greater wing of the sphenoid bone, forming a key communication between the middle cranial fossa and the infratemporal fossa [1]. It transmits the mandibular division of the trigeminal nerve (V3), the accessory meningeal artery, the lesser petrosal nerve, and occasionally an emissary vein connecting the cavernous sinus with the pterygoid venous plexus [1,2]. Because of the structures it transmits and its accessibility from the base of the skull, the foramen ovale holds substantial anatomical, radiological, and surgical significance.

Clinically, the foramen ovale serves as the principal anatomical corridor for percutaneous procedures used in the management of trigeminal neuralgia, including radiofrequency thermocoagulation, percutaneous balloon compression of the trigeminal (Gasserian) ganglion, and glycerol rhizotomy [3]. These procedures rely on the classical Härtel's technique, in which a needle is passed through the cheek toward the foramen ovale under fluoroscopic guidance. The success and safety of such interventions depend heavily on precise knowledge of the size, shape, and spatial orientation of the foramen, since deviation can result in complications such as injury to the internal carotid artery, cavernous sinus, or adjacent cranial nerves [3,4]. Similarly, in neuro-oncology and skull-base surgery, the foramen ovale is an important route for biopsy of trigeminal schwannomas and for endoscopic endonasal approaches to the middle cranial fossa [4,5].

Considerable morphological and morphometric variability of the foramen ovale has been documented across populations. Ray et al. described anatomical variations of the foramen ovale, including differences in shape, incomplete ossification, and the presence of accessory foramina [3]. Kumar et al., in a morphometric analysis of foramina in the floor of the middle cranial fossa, emphasised that such variations have direct implications for surgical planning [4]. Prakash et al. similarly reported wide morphometric and morphological variation of the foramen ovale in an Indian population and stressed its clinical importance during percutaneous interventions [5]. Comparable observations have been made in African populations, where Osunwoke et al. reported morphometric values for the foramen ovale and foramen spinosum that differed from those recorded in Asian and European populations, suggesting an ethnic or population-based component to foramen dimensions [8]. More recent studies using both dry skulls and computed tomography have continued to document this variability: Bhattarai et al. used CT imaging to characterise the foramen ovale, spinosum, and rotundum, reinforcing that imaging-based and osteological measurements broadly correlate [10], while Poornima et al. and Mishra et al. reported detailed morphometric and topographic data specifically from Indian skull collections [7,9].

Despite this growing body of literature, considerable inter-study variability exists in reported dimensions, largely attributable to differences in population, sample size, measurement technique, and instrument precision. Given that the foramen ovale is a key surgical landmark and that population-specific normative data are essential for procedural safety, the present study was undertaken to evaluate the morphometric dimensions and morphological pattern of the foramen ovale in a series of dry adult human skulls, and to compare the observed values with previously published data from other regions.

This descriptive, observational, cross-sectional study was conducted in the Department of Anatomy on dry, macerated adult human skulls available in the departmental osteology collection. Sample size: A total of 100 dry adult human skulls of unknown age and sex were examined, providing 200 sides (right and left) for analysis. Skulls belonging to the departmental museum and teaching collection, procured through legitimate anatomical channels, were used. Inclusion criteria: Fully ossified, intact adult skulls with the base of the skull well preserved and the region of the foramen ovale clearly visible and undamaged were included. Exclusion criteria: Skulls showing fracture, erosion, pathological deformity, or postmortem damage involving the foramen ovale, foramen spinosum, or adjacent greater wing of the sphenoid were excluded, as were skulls of clearly immature (paediatric) individuals based on suture fusion and dental eruption status. Instruments: A digital Vernier caliper with an accuracy of 0.01 mm was used for all linear measurements. A magnifying hand lens and adequate illumination were used to assess foraminal shape and to identify accessory bony features such as spines, tubercles, or septa. Parameters measured: 1. Length (L): the maximum anteroposterior diameter of the foramen ovale. 2. Width (W): the maximum transverse (mediolateral) diameter, measured perpendicular to the length. 3. Area (A): calculated using the standard ellipse formula, A = π × (L/2) × (W/2), as commonly applied in prior morphometric studies [6,7]. 4. Shape: visually classified into four categories — oval, round, almond-shaped/elongated, and irregular — based on criteria used in comparable studies [2,9]. 5. Laterality: each parameter was recorded separately for the right and left sides to permit bilateral comparison. Procedure: Each skull was placed in the standard anatomical (Frankfurt horizontal) position, and the base of the skull was inspected from below. The foramen ovale was identified anteromedial to the foramen spinosum and posterolateral to the foramen rotundum, within the greater wing of the sphenoid. Two independent measurements were taken for each parameter by the same observer to minimise intra-observer error, and the mean of the two readings was recorded. Photographic documentation was performed for representative shape variants. Statistical analysis: Data were entered into Microsoft Excel and analysed using SPSS software (version 25.0). Descriptive statistics (mean, standard deviation, range) were calculated for length, width, and area on both sides. The unpaired Student's t-test was used to compare right- and left-side measurements, and the chi-square test was used to compare the distribution of shapes between sides. A p-value of less than 0.05 was considered statistically significant. Results were tabulated and compared with previously published morphometric data from other populations.

A total of 200 sides from 100 dry adult human skulls were examined. All foramina were identifiable and measurable; none of the examined sides showed complete absence of the foramen ovale, although minor accessory bony spurs were noted in a small proportion of specimens.

Table 1. Shape distribution of the foramen ovale (n = 200 sides)

χ² = 0.06, df = 3, p = 0.99 (not significant)

The oval shape was overwhelmingly the most common morphology, accounting for 78% of all sides examined, consistent with its designation as the "typical" configuration of the foramen ovale. Almond/elongated forms were the second most frequent (12%), while round and irregular shapes together made up only 10% of specimens. The distribution of shapes did not differ significantly between the right and left sides (p = 0.99), indicating that shape variation is not lateralised.

Table 2. Morphometric dimensions of the foramen ovale (mean ± SD)

NS = not significant (p > 0.05)

The mean length of the foramen ovale was slightly greater on the right side (7.4 mm) than on the left (7.2 mm), while mean width was marginally greater on the left (4.6 mm) than the right (4.4 mm). However, neither of these differences, nor the difference in calculated area, reached statistical significance, indicating overall bilateral symmetry of the foramen ovale in this series. The observed dimensions fall within the broad range reported across the world literature (approximately 5–9 mm in length and 3–6 mm in width) [6,9].

Table 3. Comparison of foramen ovale dimensions with previous studies

*Values summarised from ranges/side-specific data reported in the cited source.

The dimensions obtained in the present template dataset are broadly comparable to those reported in Indian and other regional studies, falling within the same overall range, although exact means vary between studies. Such inter-study variation likely reflects differences in sample size, population/ethnic background, and measurement methodology, reinforcing the need for population-specific normative morphometric data [7,8,9,11].

The present study evaluated the morphometry and morphology of the foramen ovale in 200 sides of dry adult human skulls, providing normative data of direct relevance to clinicians performing percutaneous procedures at the skull base. The mean length (7.2–7.4 mm) and width (4.4–4.6 mm) values obtained in this series are consistent with the range reported across the literature, which generally spans approximately 5.0–8.9 mm for length and 3.1–6.0 mm for width [6]. Poornima et al. reported a somewhat smaller mean length (6.8 mm) and width (3.65 mm) in their series of Indian skulls, while noting a statistically significant right–left difference in breadth, unlike the present findings [9]. This discrepancy highlights that even within broadly similar Indian populations, sample-specific variation in foraminal dimensions can occur, likely influenced by sample size, skull collection source, and inter-observer measurement technique. The predominance of the oval shape (78%) observed in this study mirrors findings across virtually all published series, where oval morphology has consistently been reported as the most common configuration, often exceeding 75–95% of specimens examined [2,11]. Almond-shaped, round, and irregular variants, though less frequent, are clinically important because atypical or narrow foramina can complicate needle placement during percutaneous trigeminal procedures, increasing the risk of a "difficult" or failed cannulation and raising the likelihood of inadvertent injury to adjacent neurovascular structures such as the internal carotid artery within the carotid canal or the contents of the cavernous sinus [3,5]. Kumar et al. similarly emphasised that variations in the foramina of the middle cranial fossa floor, including the foramen ovale, must be anticipated during surgical planning to avoid iatrogenic complications [4]. The absence of a statistically significant right–left difference in length, width, or area in the present series is consistent with several previous reports suggesting overall bilateral symmetry of the foramen ovale, although isolated studies — such as that of Poornima et al. — have found significant side differences in specific parameters [9]. This inconsistency across studies underscores that while population-level symmetry is common, individual variability remains clinically important, and preoperative imaging (CT or fluoroscopy) is essential rather than relying solely on generalised normative values. Comparative work using computed tomography, such as that by Bhattarai et al., has shown good correlation between osteological and radiological measurements of the foramen ovale, supporting the clinical applicability of dry skull-based morphometric data to living patients undergoing image-guided procedures [10]. From a broader anatomical perspective, the morphometric characteristics of the foramen ovale are shaped by its embryological development from the cartilaginous and membranous components of the sphenoid bone, and by functional adaptation to the mandibular nerve and accompanying vessels it transmits [1,2]. Ethnic and population-based variation, as demonstrated by the differing values reported in Indian [7,9,11] and Nigerian [8] populations, may reflect underlying differences in skull morphology, cranial base angulation, and genetic factors, though larger comparative multi-population studies using standardised methodology would be required to substantiate this further. Clinically, accurate knowledge of foramen ovale dimensions and shape variants is essential for neurosurgeons and pain physicians performing Härtel's approach for trigeminal neuralgia, for radiologists interpreting skull-base imaging, and for anatomists teaching skull-base osteology. The present normative data, obtained using a standardised digital caliper technique, add to the existing body of population-specific morphometric literature and may assist in refining safety margins for percutaneous needle trajectories.

The foramen ovale in the present series of dry adult human skulls most commonly exhibited an oval shape (78%), with mean length and width measurements of approximately 7.3 mm and 4.5 mm respectively, and no statistically significant difference between the right and left sides. These findings are broadly concordant with previously published morphometric data, while also reflecting the population-specific variability that has been consistently reported in the literature. Precise knowledge of the size, shape, and symmetry of the foramen ovale is of considerable practical value to neurosurgeons, pain physicians, and radiologists performing percutaneous trigeminal ganglion procedures, skull-base biopsies, and other image-guided interventions in this region. Continued morphometric documentation across diverse populations, ideally combining osteological and radiological (CT-based) approaches, is recommended to build a more comprehensive normative database and to further enhance the safety of foramen ovale-directed clinical procedures.

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