European Journal of Cardiovascular Medicine

The adult cervical vertebrae are uniquely distinguished by the presence of the foramen transversarium (FT) in each transverse process, a key anatomical feature that sets them apart from other vertebrae [1]. This foramen serves as a conduit for the vertebral artery, vertebral vein, and a plexus of sympathetic nerves originating from the inferior cervical ganglion, with the notable exception of the seventh cervical vertebra (C7). In most cases, the vertebral artery enters the FT at the level of the sixth cervical vertebra (C6) and ascends through the foramina up to the atlas (C1) to contribute to the vertebrobasilar circulation. The FT of C7 typically transmits only the vertebral vein and is often smaller in size or, in some individuals, may even be absent [1]. Structurally, the transverse process in cervical vertebrae is a composite structure, enclosing the FT. It comprises ventral and dorsal bars, which terminate laterally as the anterior and posterior tubercles, respectively. These tubercles are interconnected laterally by the costal or intertubercular lamella, commonly referred to as the costotransverse bar [2]. This bony framework provides structural integrity but is also a site of potential anatomical variation. Variations in the number, size, and shape of the FT, such as double foramina transversaria (DFT), can significantly alter the course of the vertebral vessels. Such deviations may lead to compression or kinking of the vertebral artery, particularly during neck movements, resulting in vertebrobasilar insufficiency, a condition clinically manifested by headache, vertigo, dizziness, migraine, and syncope [3]. Given that the inner ear derives its blood supply from branches of the vertebrobasilar system, any disturbance, such as arterial spasm induced by irritation of the accompanying sympathetic plexus, can contribute to labyrinthine symptoms, including hearing loss, tinnitus, and balance disturbances, along with other neurological deficits [4]. Therefore, a comprehensive understanding of FT variations, including the presence of double foramina transversaria, is of paramount importance. Such anatomical knowledge aids radiologists and clinicians in the accurate interpretation of X-rays, CT scans, and MRI images. It also holds critical surgical relevance for orthopedic and neurosurgeons, especially during posterior approaches to the cervical spine, where inadvertent injury to the vertebral artery can have serious consequences.

Aim and Objectives: This study aimed to investigate the incidence of double foramen transversarium in dried cervical vertebrae from the population of Bihar, and to compare the findings with reported incidences among different racial and ethnic groups worldwide.

This cross-sectional osteological study was conducted on a total of 150 human cervical vertebrae, comprising 100 typical (C3–C6) and 50 atypical vertebrae (C1, C2, and C7), of unknown age and sex. These specimens were obtained from the Department of Anatomy, Bhagwan Mahavir Institute of Medical Sciences, Pawapuri, Bihar, and supplemented with samples from other medical colleges across Bihar, India. The atypical cervical vertebrae were categorized as follows: 20 atlas (C1), 15 axis (C2), and 15 vertebra prominens (C7). Each vertebra was carefully examined macroscopically for the presence, laterality, number, and morphology of double foramina transversaria (DFT). Observations were recorded and documented systematically. To ensure accuracy and standardization, high-resolution digital photographs were taken of representative specimens showing double foramina transversaria. These images were used for further morphological analysis and comparison.

Inclusion and Exclusion Criteria:

The study included intact and well-preserved cervical vertebrae, both typical (C3–C6) and atypical (C1, C2, and C7), irrespective of sex and age, provided their foramina transversaria were clearly visible and undamaged. Vertebrae exhibiting any form of gross deformity, structural damage, or fractures, particularly those affecting the transverse processes or compromising the integrity of the foramina transversaria, were excluded from the study to maintain the accuracy and reliability of observations.

Statistical Analysis

All data collected from the examination of cervical vertebrae were entered into Microsoft Excel and analyzed using Statistical Package for the Social Sciences (SPSS), version 25.0. The frequency and percentage of double foramina transversaria (DFT) were calculated in both typical and atypical cervical vertebrae. Descriptive statistics were used to summarize the incidence and morphological variations of DFT. The collected data were analyzed using Fisher’s Exact Test to assess the association between the type of cervical vertebra (typical or atypical) and the presence of double foramen transversarium. A p-value of less than 0.05 was considered statistically significant.

Out of the total 150 cervical vertebrae studied, a double foramen transversarium was observed in 23 vertebrae (15.33%). Among these, 15 vertebrae (10%) were identified as typical cervical vertebrae, while 8 vertebrae (5.33%) were atypical. Unilateral double foramen transversarium was more frequently observed than bilateral, with a total of 14 cases on the right side (9.33%) and 6 cases on the left side (4%), whereas bilateral occurrence was noted in only 3 vertebrae (2%). Although typical vertebrae showed a higher frequency of double foramen transversarium, the difference between typical and atypical cervical vertebrae was not statistically significant (P-value = 0.99, Fisher’s Exact Test) [Table 1 and Figure 1].

Table 1: Prevalence of double foramen transversarium in the study group

Figure 1: Showing the double foramen transversarium; A. Right-sided in atypical cervical vertebrae; B. Left-sided in atypical cervical vertebrae; C. Bilateral in atypical cervical vertebrae; D. Right-sided in typical cervical vertebrae; E. Left-sided in typical cervical vertebrae; F. Bilateral in typical cervical vertebrae.

Numerous researchers have extensively studied the variations in the number, size, and shape of the foramen transversarium (FT) over the years (Table 2). Taitz et al. [4], in their study on 480 foramina transversaria, reported the presence of double FT in only 34 (7%) cervical vertebrae. Among these, six vertebrae (C6 and C7) had accessory FT of equal size, while in the remaining cases, the additional foramina were smaller. They also documented three C4 and one C6 vertebrae lacking any FT and observed a single vertebra possessing triple FT.

In the present study, we observed double FT in 23 (15.33%) out of 150 cervical vertebrae, comprising 15 (10%) typical and 8 (5.33%) atypical vertebrae. Das S et al. [5], in 2005, examined 132 dried human cervical vertebrae and found only two cases (1.5%) of double FT. Sharma et al. [6] identified accessory FT in 8% of cases, i.e., 16 out of 200 cervical vertebrae, with a notably higher incidence in C6 vertebrae. Kaya et al. [3], in their analysis of 22 Byzantine cervical vertebrae, reported double FT in five vertebrae (22.72%), with three cases being unilateral and two bilateral. One vertebra also exhibited asymmetrical FT. The mean diameter of FT was found to be 6.2 mm (range: 5.7–6.5 mm) on the right side and 6.4 mm (range: 2.3–6.7 mm) on the left side. Murlimanju et al. [7] reported accessory FT in only six (1.6%) of 363 cervical vertebrae, with five bilateral and one unilateral occurrence. Laxmi C et al. [8], in a study on 210 cervical vertebrae, found double FT in 10 cases (4.76%), including 8 (3.8%) bilateral and 2 (0.95%) unilateral instances. Similarly, Chaudhari et al. [9] observed 22 vertebrae with double FT out of 133, with 14 (14.73%) showing unilateral and 8 (8.42%) bilateral occurrences.

In our current study, double FT were noted in 23 (15.33%) out of 150 cervical vertebrae, comprising 15 (10%) typical and 08 (5.33%) atypical vertebrae. Rathnakar P et al. [10] found accessory FT in only 8 (5.7%) out of 140 cervical vertebrae. Patil et al. [11], in their evaluation of 175 vertebrae, reported double FT in 10 (5.71%) cases, of which 6 (3.42%) were unilateral and 4 (2.28%) bilateral. They emphasized that unilateral double FT was more common than bilateral, and accessory FT were more prevalent in the lower cervical vertebrae, particularly C4 to C7. Karau PB and Odula P [12], in a study on 102 cervical vertebrae from the Kenyan population, found double FT in only 4 (3.9%) vertebrae. Ramachandran K et al. [13] reported 19 (15.8%) cervical vertebrae with double FT among 120 samples, comprising 10 (8.3%) bilateral and 9 (7.5%) unilateral cases. The incidence observed in our study (14.36%) closely aligns with their findings. They also classified FT into five shapes, with Type I (round) being the most common, present in 76 (63.3%) vertebrae. Murugan M et al. [14] found slightly fewer cases than ours, reporting 19 (12.6%) bilateral double FT in 150 cervical vertebrae. Katikireddi RS et al. [15] documented only 3 (3%) cases of double FT among 100 vertebrae, 2 unilateral and 1 bilateral. Yadav Y et al. [16] reported 8 (6.67%) double FT cases in 120 vertebrae, including 3 unilateral and 5 bilateral. Mishra GP et al. [17] described a unique case of a sixth cervical vertebra showing bilateral double FT without a bifid spine. Double FT, also referred to as foramen transversarium bipartitia, may occur unilaterally or bilaterally, depending on the course of the vertebral artery. While embryological factors and arterial tortuosity are considered significant contributors to its development, the precise etiology remains uncertain. There continues to be debate regarding the direct correlation between the size of FT and the vertebral artery. Hadley LA [18] and Hyyppa SE et al. [19] proposed that tortuous vertebral arteries could cause bony remodeling or destruction, thereby influencing the FT size. Additionally, Epstein BS [20] observed that the left vertebral artery tends to be larger than the right, potentially accounting for asymmetrical FT diameters. Duplicated or fenestrated vertebral arteries are often associated with variations in FT anatomy. A duplicated vertebral artery originates from two separate sources with a fusion point in the neck, located outside the spinal cord. Conversely, a fenestrated artery arises from a single source and splits into two parallel trunks, which may lie either outside or within the vertebral canal. According to available literature, only 74 cases of vertebral artery fenestration have been reported, predominantly on the left side, with just four cases (5%) being bilateral. Duplication of the vertebral artery has been documented in 22 cases, of which only one (4.54%) was bilaterally symmetrical [21].

Table 1: Comparison of studies about the prevalence of the double foramen transversarium by different authors.

Limitations of the Study: This study was limited by a relatively small sample size and the absence of information on the age, sex, and clinical history of the specimens. As it was purely observational and based on dry bones, correlations with vascular or neurological structures could not be made. Radiological confirmation was also not included.

Knowledge of the double foramen transversarium is important as it can alter the course of vertebral vessels and nerves, potentially causing neurological or vascular symptoms. It is especially relevant for spine surgeons to avoid intraoperative and postoperative complications. These variations are also valuable to anatomists, anthropologists, and radiologists for accurate interpretation of cervical vertebrae in both clinical and academic settings.

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