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| ORIGINAL ARTICLE |
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| Year : 2023 | Volume
: 12
| Issue : 1 | Page : 36-41 |
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The prevalence, classification, and potential clinical implications of anatomical variations of first cervical vertebra: A computed tomographic study
Priyanka Pandey1, Swati Yadav1, Navbir Pasricha2, Shamrendra Narayan3
1 Assistant Professor, Department of Anatomy, Hind Institute of Medical Sciences, Sitapur, Uttar Pradesh, India
2 Additional Professor, Department of Anatomy, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
3 Additional Professor, Department of Radiodiagnosis, Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
| Date of Submission | 29-Oct-2022 |
| Date of Decision | 09-Jan-2023 |
| Date of Acceptance | 10-Jan-2023 |
| Date of Web Publication | 21-Feb-2023 |
Correspondence Address:
Swati Yadav
Department of Anatomy, Hind Institute of Medical Sciences, Mau, Ataria, Sitapur, Uttar Pradesh
India
 Source of Support: None, Conflict of Interest: None
DOI: 10.4103/NJCA.NJCA_217_22
Background: First cervical vertebra has different anatomical features than other cervical vertebrae. It holds globe of skull and lacks body and spine. It is composed of 2 lateral masses linked by anterior and posterior arches. Posterior atlanto-occipital membrane is attached to posterior arch whose lateral edge sometimes ossifies thus converting groove into canal. Consequently, neurovascular groove gets converted into a bony ring “ponticulus posticus”. It can cause of neck pain and headache. Knowledge of this variation is important during various orthopedic procedures involving atlas including C1 lateral mass screw placement.Congenital defects of atlantal arch a developmental failure of chondrogenesis is a rare anomaly. These defects are a benign variation discovered incidentally. Detection of these anomalies is clinically important as they can cause acute neurologic deficits, which is associated with neck extension. Study was done: To determine the prevalence of Ponticulus Posticus and to report the frequency of various types of congenital malformations of the atlantal arch. Methodology: 250 computerized tomography (CT) head and neck in axial and sagittal sections from Picture Archiving and Communication System (PACS) of Dr RMLIMS, Lucknow was studied as CT is the best method to study the bony landmarks and any anomaly. Prevalence of variations was calculated. Data was analyzed statistically using SPSS version 21 by Chi-square test. Result: Prevalence of ponticulus posticus was 32.4%. Males had higher prevalence (20.4%) than females (12%). Incomplete ponticulus posticus (24.4%) was more than complete variant (8%). There was predominance of left sided ponticulus posticus(12% vs 8.4%) Deficient posterior arch was found in 9(3.6%) cases. 6 were of type A 3 were of type B. Conclusion: This study will help in determining cause of neurological deficit in patients due to presence of above variations.
Keywords: Anatomical variations, atlas, deficient posterior arch, first cervical vertebra, ponticulus posticus
How to cite this article:
Pandey P, Yadav S, Pasricha N, Narayan S. The prevalence, classification, and potential clinical implications of anatomical variations of first cervical vertebra: A computed tomographic study. Natl J Clin Anat 2023;12:36-41 |
How to cite this URL:
Pandey P, Yadav S, Pasricha N, Narayan S. The prevalence, classification, and potential clinical implications of anatomical variations of first cervical vertebra: A computed tomographic study. Natl J Clin Anat [serial online] 2023 [cited 2023 Mar 20];12:36-41. Available from: http://www.njca.info/text.asp?2023/12/1/36/370134 |
| Introduction | |  |
Compared to other cervical vertebrae, the first cervical vertebra, or atlas, has different physical properties since it lacks a body and a spine.[1] The anterior and posterior arches connect the two lateral masses [Figure 1]. The posterior arch provides attachment to the postatlanto-occipital membrane. On rare occasions, the lateral margin of this membrane might solidify, converting the groove into a canal. The neurovascular groove consequently transforms into a bony ring known as the “ponticulus posticus (PP).”[2]
This condition may cause neck pain and headaches. It is essential to have a full awareness of these circumstances when performing operations such as the instrumentation of the atlas, which entails the insertion of screws directly into the lateral mass beneath the bony arch of the atlas and necessitates the mobilization of the C2 nerve root. If it is not recognized beforehand, persons with ponticulus posticus may appear to have a large bony arch for screw insertion, which could harm the vertebral arteries if this variation is breached.[3]
The embryological development of the first two cervical vertebrae is significantly and substantially different from the development of the remaining vertebrae. The atlas is formed by joining the caudal half of the fourth occipital somite with the cranial half of the first cervical somite. Together, these two halves make up the atlas. Its ossification is controlled by three centers, one of which is responsible for the formation of the anterior arch, while the other two are responsible for the formation of the lateral masses. This process begins in the 7th week of intrauterine life. Later on, between the ages of 3 and 5 years old, the lateral masses of a child will stretch posteromedially and eventually come together in the midline to create the posterior arch. The anterior center does not ultimately merge with the two lateral centers until the child is between the ages of 5 and 9 years old. The posterior arch defect is thought to be more of a secondary chondrification defect than an ossification of primary defect. This concept is supported by a number of evidences from autopsies and intraoperative discoveries[4] [Figure 2].
Despite being an extremely rare condition, defects in the posterior arch, also known as an unfused posterior arch, can cause sudden neurological symptoms. Posterior arch defects classification has been proposed by Currarino et al.[5] [Figure 3]. Since cervical radiography is often done after trauma, distinguishing an acute burst fracture from a congenital abnormality is crucial. Computerized tomography (CT) is the best way to evaluate the atlas ring and distinguish between acute injuries and developing clefts. An atlas arch defect patient's CT scan shows a minor defect with a smooth corticated margin.[4] | Figure 3: The Different Classes of Posterior Arch Defects Proposed by Currarino et al.[5] (Type -A) Failure of the two hemiarchs' posterior midline fusion; (Type- B) Unilateral cleft; (Type -C) bilateral cleft with a dorsal arch remnant that is still present; (Type- D) Lack of a posterior arch and an ongoing posterior tubercle; (Type- E) The complete posterior arch is absent
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This study aims to determine the prevalence of Ponticulus Posticus and to report the frequency of various types of congenital malformations of the atlantal arch.
| Materials and Methods | | |
Study design
This was an observational study (retrospective).
Inclusion criteria
This study examined the normal axial and sagittal head and neck CT images from the picture archiving and communication system (PACS) of our institution
The CT was done for various other reasons and the authors looked in these CTs for the presence of ponticulus posticus and congenital malformations of the atlantal arch.
Exclusion criteria
- Technically suboptimal scans
- Evidence of tumor and/or fracture of the cervical spine.
Data collection and analysis
The Chi-squired (χ2) test was utilized to assess the data using SPSS version 21 (IBM, Chicago, Illinois, USA).
Methodology
The study examined 250 CT head and neck scans obtained from the PACS of Dr. Ram Manohar Lohia Institute of Medical Sciences, Lucknow, after receiving approval from the Ethics Committee of IEC No.(107/20). Both axial and sagittal sections were scanned for this examination. Quantitative radiology was performed using NewTom 3G flat panel-based CT (Verona, Italy) equipment. The patient was given instructions to take a horizontal position and to lie down in such a way that the Frankfort horizontal plane was perpendicular to the table. After the patient completed these instructions, the examination could continue. The head of the patient was then positioned such that it would fit inside the circular gantry housing that is part of the X-ray tube detection system. The examination of the patient lasted for a total of 36 s as the scanner rotated completely around the patient's head. The scanner had a maximum output of 110 kilovolts and a current of 15 milliamperes. Its voxel size was 0.16 mm, and its exposure period was 5.4 s on average. The atlas vertebra was characterized using axial slices that had a thickness of 0.5 mm. On the selected axial picture, the sagittal slice of the atlas vertebrae was 1 mm thick and perpendicular to its long axis, while the coronal slices were 1 mm thick and parallel to it. Sagittal imaging detected the posterior process (PP) on the atlas vertebrae, whereas axial images detected anomalies in the atlantal arch.[6] This was due to the orientation of the PP on the atlas vertebrae, which is explained in the previous sentence.
Following parameters in the first cervical vertebra or atlas were observed and noted: Accessory foramina or pontulus posticus and congenital malformations of the atlantal arch.
| Results | | |
There were 84 (33.6%) females and 166 (66.4%) males in our study [Table 1]. Ponticulus posticus prevalence was 81 (32.4%) [Table 1]. Males were more prevalent than females (51/20.4% vs. 30/12%) [Table 2]. Normal CT of atlas vertebrae is depicted in axial and sagittal planes in [Figure 4] and [Figure 5] respectively. Incomplete variation of 61 (24.4%) outnumbered the complete ponticulus posticus 6120 (8%) [Table 3] and [Figure 6], [Figure 7]. Left-sided ponticulus posticus was more common than right-sided ponticulus posticus (12% vs. 8.4%) [Table 4]. In nine (3.6%) cases, a deficient posterior arch was found [Table 1]. Five (2%) were detected in women, whereas four (1.6%) were found in men [Table 2]. Six cases out of the nine were type A (2.4%) and three were type B (1.2%) [Table 4] and [Figure 8], [Figure 9]. In our study, types C, D, and E were not present. | Table 2: Gender wise distribution of ponticulus posticus and deficient posterior arch
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 | Figure 4: Normal CT of atlas vertebra in axial plane. CT: Computerized tomography
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 | Figure 5: Normal CT of Atlas Vertebra in Sagittal Plane. CT: Computerized tomography
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| Discussion | | |
Our discussion is based on two parameters--a] ponticulus posticus and b] the prevalence of deficient of the posterior arch a]. Although PP is usually considered benign anatomic variant on the atlas vertebrae, it is a significant anomaly of the posterolateral aspect of the posterior arch of the atlas, which is associated with conditions which include vertebrobasilar insufficiency, headache and cervical pain syndrome, migraine without aura, onset of acute hearing loss, and chronic tension-type headaches.[6] The PP is a bony arch on the atlas vertebrae converting the groove on the upper surface of the posterior arch of the atlas to the foramen. This foramen is called the arcuate foramen and has important anatomic structures, such as the vertebral artery and the suboccipital nerve as its contents. PP is intimately attached to the atlantooccipital membrane, and it is known to be connected to the dura. Especially during head movement, the neurodynamic process may lead to these conditions because of traction produced on the dura and hence can result in pain.[6] As per the findings of a number of researchers, the percentage of people who have ponticulus posticus (an anatomic anomaly of the C1 arch) can range anywhere from 10.91% to 68.40%[2],[7],[8],[9],[10],[11],[12],[13],[14],[15] [Table 5]. Our study reports the prevalence of this anomaly in the North Indian population and also adds to the further understanding of these bony variations of the C1 vertebra. To our knowledge, this is perhaps the only study using CT scans to assess the prevalence of PP in North India. We found a prevalence of PP in 81 (32.4%) subjects-males 51 (20.4%) and females 30 (12.4%). The prevalence of PP in our study population is in consonance with the other reported prevalence of PP [Table 5] Hong et al.,[11] on the basis of the review of the CT scans of 1013 patients in a Korean population, reported the overall prevalence of PP to be 15.6%. There was a male preponderance with a PP being present in 19.3% of the male population and 12.8% of the female population. In a meta-analysis performed by Elliott and Tanweer,[15] 10 44 studies comprising 21,789 patients and 6247 bony specimens were reviewed. They found an overall prevalence of PP to be 16.7%Recently, a new classification system was proposed by Saleh et al.[2] in the year 2018. According to this classification, “two letters were designated for each patient, consisting of either A, B, or C. The letter A signified ''typical anatomy'' specifically no bony arch or no PP, the letter B signified a partial or incomplete bony arch, and the letter C signified a complete bony arch. The first letter described the right-sided posterior arch, whereas the second letter described the left-sided posterior arch.[2]” He reported the prevalence of PP as 22.5% | Table 5: Comparison of various study reporting prevalence of ponticulus posticus
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Right C1 Arch XX  Left C1 Arch.
b]. Many theories have been proposed to understand the exact mechanism of the development of congenital anomalies of the atlas. It can be associated with several disorders such as Arnold–Chiari malformation, Klippel–Feil syndrome, gonadal dysgenesis, Down syndrome, and Turner. Genetic factors may also contribute to their origin.[4] Various authors have reported the prevalence of deficient of the posterior arch to be from 0.69% to 4%[16] [Table 6]. In our analysis, 9 (3.6%) subjects-4 (1.6%) males and 5 (2.0%) females-had a defective posterior arch having 6 type A (2.4%) and 3 type B (1.2%). In our study, types C, D, and E were not present. To the best of our knowledge, this is the first study to report the prevalence of deficient posterior arch through CT examinations in North Indian population. Senoglu et al.[17] observed congenital anomalies of 2.95% in a cohort of 1354 cases from the United States. Kwon et al.,[4] through their study of 1153 Asian patients from Korea, have found this defect only in 0.95% of cases, while Geetha[21] reported this finding in South Indian population as 4%. | Table 6: Comparison of various study reporting of deficient posterior arch
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| Conclusion | | |
Major findings of our study include
- Prevalence of Ponticulus Posticus is 32.4%
- PP was more in males than females (20.4% vs. 3o%)
- Incomplete variation 61 (24.4%) was more than the complete ponticulus posticus 6120 (8%)
- Left-sided ponticulus posticus was more common than right-sided ponticulus posticus (12% vs. 8.4%)
- In nine (3.6%) cases, a deficient posterior arch was found
- Five (2%) were detected in women, whereas four (1.6%) were found in men
- Six cases out of the nine were type A (2.4%) and three were type B (1.2%).
To sum up, the PP is a very significant anatomical variation with significant clinical importance, especially in spine surgery as more advanced C1 instrumentation techniques emerge. To prevent injuries to the vertebral artery, it is essential to have a thorough preoperative evaluation and planning through CT scans and the identification of any variations before the surgery.
Surgeons and radiologists need to have a thorough knowledge of posterior arch congenital abnormalities, even though they are rare. Asymptomatic type A and B patients are often misdiagnosed as fractures. Understanding type C through E abnormalities is important since they can cause various neurological disorders. Patients with type C and type D should be warned about activities involving strain since they can cause atlas axial instability.
Limitation of the study
This study was done retrospectively and used the CT images from PACS to document the prevalence of ponticulus posticus and deficient posterior arch, so we could not correlate these anatomical variations with various neurological deficits. Therefore, we intend to use CT in a subsequent effort to investigate the correlation between these alterations and migraine and neck discomfort.
Acknowledgment
The authors would like to thank all the authors and their affiliated departments and institutions for their seamless support during the research.
Financial support and sponsorship
Nil.
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6]
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