The posterior condylar fossa is a depression situated behind the occipital condyle on either side of the foramen magnum [1]. The purpose of this fossa is to accommodate the up-turned posterior margin of the superior articular facet of the atlas during full extension of the head at the atlanto-occipital joint. This fossa may show the presence of a foramen which is known as the posterior condylar canal. During the embryonic period, the posterior condylar canal acts as a channel for venous circulation connecting the venous sinuses within the intra and extracranial locations. After the birth of the baby, there is atrophy of the previously present system of veins and then this bony channel of the posterior condylar canal closes. It may remain persistent if the channel fails to close. The human skull has several emissary foramina for providing alternate pathways for venous drainage during compromised venous outflow. The posterior condylar canal is one such foramen providing passage to the posterior condylar vein and acts as a communication between the jugular foramen and the posterior condylar fossa. Venous anastomosis between the jugular bulb and sub-occipital venous plexus is thus allowed by the posterior condylar canal. Meningeal branches of the occipital artery are also transmitted by this canal. It also gives passage to the nerves which supply the posterior cranial fossa. Variations in the occurrence of this canal are very important for understanding alternative pathways of venous outflow. This will also help in avoiding confusion while interpreting MRI and CT examinations. If misinterpreted, it may lead to surgical interventions for wrongly presumed glomus jugulare tumors. This study will enhance the knowledge of the variations of this canal and help the surgeons operating in this region of the skull base to avoid neurovascular damage. It will also help in deciding the treatment protocol for the arteriovenous fistula of the dura using condylar veins as access routes to these fistulae.  This study aims to provide a comprehensive morphological analysis of the posterior condylar canal in the population of Bihar.

This was a descriptive observational study conducted in the Department of Anatomy, Netaji Subhas Medical College & Hospital, Bihta, Patna, Bihar. Fifty adult skulls were included in the study which were thoroughly cleaned and dried. Skulls that showed gross asymmetry or deformity especially involving the foramen magnum and occipital condyle region were excluded from the study. They were carefully examined to look for the posterior condylar canals on both sides. A probe was passed into the canal to look for the patency. If the probe was completely traversing the canal, then it was recorded as present. When the posterior condylar canal was present only as a pit or small blind canal, it was recorded as absent. The data was tabulated and the percentage of the prevalence of each type was calculated. Photographs were taken showing the posterior condylar canal being present bilaterally, unilaterally, and absent. The canal was marked with an arrowhead in the digital photograph.

Out of the fifty skulls examined, forty skulls were found to have a posterior condylar canal. twenty canals were found on the right side and twelve on the left side. Eight skulls had bilateral canals. Ten skulls did not have any patent canal.

Table 1: Prevalence of posterior condylar canal

Figure 1: Left-sided posterior condylar canal

Figure 2: Right-sided posterior condylar canal

Figure 3: Bilateral posterior condylar canal

Figure 4: Absent posterior condylar canal

Knowledge of common anatomical variations is very important in avoiding inadvertent injuries during surgeries and making correct diagnoses for planning correct treatment strategies. The posterior condylar fossa is one such region that has important anatomical variations in the form of the presence of the posterior condylar canal, which is very useful for surgeons operating in the vicinity of the posterior cranial fossa. There have been several studies conducted previously over different population groups. There has been a wide variation in the results obtained by previous authors, some of which are corroborative with the present study while others show differences from the present study. Ginsberg et al [2] conducted their study on gross specimens as well as on HRCT scans. The posterior condylar canal was found to be bilateral in 55.9% of the skulls and unilateral in 17.6% of the skulls. On CT scans, the posterior condylar canal was identified bilaterally in 31% and unilaterally in 50%.  Another study conducted on 1500 skulls

by Boyd [3] showed the unilateral presence of posterior condylar canal in a total of 77% of cases, out of which it was bilateral in 46.6% of skulls, right-sided in 16.5%, left-sided in 13.88%, and absent in 23.81% skulls. Boyd concluded the posterior condylar canal was the largest of the emissary foramina. Krause W [4] found that 21% of skulls had bilateral presence of posterior condylar canal while unilateral was present in 38% of skulls. Kumar M [5] observed that the posterior condylar canal was present on both sides in 48.33%, left-sided in 18.33% and right-sided in 15% and 16.66% of skulls did not show any patent canal. Kavitha S et al [6] conducted their study on 156 skulls in the South Indian population. Nine skulls (5.76%) showed an absence of foramen bilaterally. Out of 147 skulls remaining, 31 skulls (21.1%) showed unilateral presence and 116 skulls (78.9%) showed bilateral presence. Out of the unilateral foramina in 31 skulls, 12 were right-sided (38.7%) and 19 were left-sided (61.3%). Out of 147 skulls, they found patent foramen in 92 skulls (62.58%) having 64 skulls (69.5%) with right-sided foramen and 28 skulls (30.4%) with left-sided foramen. Foramen was not patent in 55 skulls. Mian A A et al [7] reported that the posterior condylar foramina were present in 33%, bilaterally in 18%, and unilaterally in 14%. Another study by Kothandaraman U et al [8] showed that 26% of skulls had the presence of a posterior condylar canal, out of which bilateral incidence was 16%, whereas unilateral was 10%. The posterior condylar foramina in 60 human cadaveric skulls was observed by Vaishnani H V et al [9]. According to their research, 73.33% of cases had posterior condylar foramina. Of those, 40% had bilateral posterior condylar foramina and 33.33% had unilateral ones. 26.66% of cadaveric skulls were found to be devoid of posterior condylar foramen.

Table 2: Comparison of posterior condylar canal with previous studies.

The PCC and its connected emissary vein significantly contribute to the surgical management of tumours and dural arteriovenous fistulas in this area. They are important anatomical clues that help doctors tell the difference between the transcondylar fossa approach and the transcondylar approach. This keeps the atlanto-occipital joint from getting hurt needlessly. They have also been considered reference points for posterolateral methods, such as the juxta-condylar approach and the extreme lateral approach, which aim to reveal lesions in the jugular foramen and hypoglossal canal [10-12]. Transverse-sigmoid dural arteriovenous fistulas can enter through the posterior condylar veins and block the jugular vein. Hypoglossal dural arteriovenous fistulas can also enter through these veins. Moreover, dural arteriovenous fistulas may also affect these condylar veins [13-14]. It serves as a channel for the spread of infections because, from a clinical standpoint, it provides an additional source of venous drainage from the intracranial to the extracranial venous system. Therefore, the inconsistent patterns and gender disparities of PCC may influence surgical procedures near the occipital region. Female PCC is a more dependable and possible landmark than male PCC due to the greater consistency of female PCC compared to male PCC. Therefore, when considering the aforementioned surgical techniques, we also need to check for other landmarks in males

besides PCC. Males have higher rates of morphological differences in PCC than females; hence, surgeons need to exercise extra caution when doing endovascular treatments on male patients, as these variations may cause problems. Understanding that the internal opening of PCC varies in prevalence between the sexes will also aid in determining the entry points for this endovascular intervention. As a result, when planning and executing surgical treatments around the occipital area in both sexes, neurosurgeons may find it helpful to know the normal architecture and gender differences of PCC. Because it could be mistaken for a calcified lymph node or glomus jugulare tumour, it is important to understand this structure and how it changes during imaging investigations so that radiological scans are not interpreted incorrectly [15-17]. The gender variations observed in our study can also improve our understanding of the influences of gender on various diseases or extrinsic factors, such as neurofibromatosis, brachymicrocephaly, osteoporosis, osteopetrosis, Cruzons syndrome, and mental retardation, which can result in morphological variations of the cranial foramina [18-21].

Knowing the prevalence of the posterior condylar canal is all the more crucial in surgeries involving the base of the skull. It will be helpful not only for the anatomists who plan future research in this field but also for the radiologists, as imaging studies are very common before planning any surgery in this region. In cases of trauma to the skull's base, neurosurgeons prefer several transcondylar approaches. The occipital condyle also serves as an approach for tumors involving the occipital region. In all such cases, anatomical knowledge of the morphology of the posterior condylar canal becomes indispensable. Therefore, the current study will offer baseline data on the anatomical variations in posterior condylar canal prevalence in the North Indian population, enabling clinicians to improve medical and surgical outcomes for skull base cases.

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