|Year : 2015 | Volume
| Issue : 5 | Page : 636-638
Atlanto-occipital fusion: A case report
Monalisa1, Subhendu Pandit2, Rajan Bhatnagar3
1 Resident, Department of Anatomy, Armed Forces Medical College, Pune, Maharashtra, India
2 Associate Professor, Department of Anatomy, Armed Forces Medical College, Pune, Maharashtra, India
3 Professor and Head, Department of Anatomy, Armed Forces Medical College, Pune, Maharashtra, India
|Date of Web Publication||10-Sep-2015|
Department of Anatomy, Armed Forces Medical College (AFMC), Pune - 40, Maharashtra
Source of Support: Nil., Conflict of Interest: None declared.
The atlas is the first cervical vertebra. In the history of anatomy, due to its primary function of supporting the skull, it has been innumerably compared with Atlas the Greek God, who holds the globe of the earth on his shoulders. This vertebra is devoid of a body and has two prominent lateral masses bearing a pair of superior concave facets and inferior smooth facets each. Atlanto-occipital fusion may be unilateral or bilateral, complete or incomplete and symptomatic or asymptomatic. In our, case atlanto-occipital fusion was observed in the skull of a male cadaver. Our study will be of significance to clinicians in the specialties of radiodiagnosis, orthopedics, neurosurgery and anesthesiology. Because of a lack of knowledge of developmental malformation in the craniocervical region, sudden death can occur during clinical manipulation. Head and neck surgeons must keep in mind that such anomaly can exist without any prior symptoms. The specimen seen represents a case of congenital fusion. The articular processes of the specimen are fused between the occipital and the atlas bones. Atlanto-occipital fusion decreases the diameter of the foramen magnum and produce neurovascular symptoms.
Keywords: Atlanto-occipital fusion, atlanto-occipital joint, foramen magnum, neurological complications
|How to cite this article:|
Monalisa, Pandit S, Bhatnagar R. Atlanto-occipital fusion: A case report. Med J DY Patil Univ 2015;8:636-8
| Introduction|| |
The atlanto-occipital joint is a synovial type of joint connected by articular capsules and by the anterior and posterior atlanto-occipital membranes. The image of a normal atlanto-occipital joint is shown in [Figure 1]. The curved surfaces of the joint are well adapted for head flexion and extension and also allow considerable amount of abduction (lateral flexion) of the skull on Atlas More Details. Superior articular facets on lateral masses of the atlas articulate with the corresponding occipital condyles forming the atlanto-occipital joint, which is a bicondylar synovial joint that permits nodding movement of the skull on the atlas. These joints also permit sideway tilting of the head. The main movement is flexion, with little lateral bending and rotation. Craniovertebral anomalies have been recorded for many years in morphological and clinicoradiological studies. It is characterized by complete or partial fusion of the bony ring of the atlas to the base of the occipital bone. The patients are commonly found to have dysplastic conditions, and 20% of cases have also been found to have isolated congenital ossification abnormalities. In the normal population, the incidence of atlanto-occipital fusion varies between 0.14 and 0.75%., The anomalies pertaining to the atlas and occipital region are clinically significant due to the presence of the first cervical nerve and vertebral artery on the superior aspect of the atlas vertebra. Compression of the vertebral artery may compromise blood flow to the brain and compression of the nerve may produce neurological symptoms. Many authors have reported neurovascular complications arising due to atlanto-occipital fusion.
| Case Report|| |
The specimen of skull showing fused atlanto-occipital joint was retrieved from the Anatomy Department burial ground. The specimen was washed in water and immersed in 6% H 2 O 2 (hydrogen peroxide) in 50:50 concentration. The specimen was immersed for 3 days and subsequently dried. It was then studied and photographs were obtained from various angles. In [Figure 2], the atlanto-occipital joint is seen from the right side, showing fusion of joint with a part of bone missing from the foramen transversarium. In [Figure 3], the atlanto-occipital joint is seen from the left side, showing fusion of the joint with a part of bone missing from the foramen transversarium. In [Figure 4], the atlanto-occipital joint is seen from below, showing both arches being normal, foramen magnum being normal and no other bony prominences being evident. In [Figure 5], the atlanto-occipital joint is seen from the posterior side showing atlanto-occipital joint fusion and posterior arch being normal. In [Figure 6], the atlanto-occipital joint is seen from the anterior side, showing anterior arch and tubercle without any bony deformity. In the specimen retrieved, total fusion of the atlanto-occipital joint was noted bilaterally. The occipital bone forms the back and base of the cranium. The inferior surface of the occipital bone contains articular processes necessary for articulation with the superior articular facet of the atlas. The articular processes are fused between the occipital and the atlas bone. The posterior arch of the atlas is maintained; however, the foramen transversarium of the atlas is damaged due to burial and subsequent handling. No other bony growths or additional foramina are visualized.
|Figure 2: Atlanto-occipital joint seen from the right side, showing fusion of the joint with a part of bone missing from the foramen transversarium|
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|Figure 3: Atlanto-occipital joint seen from the left side, showing fusion of the joint with a part of bone missing from the foramen transversarium|
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|Figure 4: Atlanto-occipital joint seen from below; both arches are normal, the foramen magnum is seen to be normal and no additional bony prominences are seen|
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|Figure 5: Atlanto-occipital joint seen from the posterior side (below). The posterior arch is normal and atlanto-occipital joint fusion is seen|
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|Figure 6: Atlanto-occipital joint seen from the anterior side (below). The anterior arch and tubercles are seen. There is no other bony deformity|
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| Discussion|| |
Embryological basis: The human occipital bone develops from four cartilaginous centers laid down in the chondrocranium around the foramen magnum and forms a fifth membranous element. The base of the occipital bone is formed by the parachordal cartilage and the bodies of three occipital sclerotomes. Therefore, the occipital bone has dual developmental origin from the cartilage as well as the membrane. Developmentally, the four cartilaginous elements comprise the basioccipital part lying anterior to the foramen magnum, with the lateral part lying on each side of the foramen magnum and the supraoccipital part lying posterior to the foramen magnum. Researchers have attributed the embryological reason for atlanto-occipital fusion due to failure to differentiate the fused caudal and cranial segments of the fourth occipital and first cervical sclerotomes.
Clinical considerations: According to McRae and Barnon, patients with atlanto-occipital fusion may have the following physical features: Low hairline, torticollis, restricted neck movements and/or abnormal short neck. Anatomically, the fusion can compress the vertebral artery, the first cervical nerve and the posterior atlanto-occipital membrane, all of which are related to the posterior arch of the atlas. Atlanto-occipital fusion can affect the postural muscles causing extension of the head and may give rise to abnormal posture. The fusion may compress the spinal cord giving rise to neurological complications due to occipitocervical synostosis. In neurological examination, the patient may reveal the following clinical findings: Neck pain, numbness, pain in limbs, weakness, abnormal head posture and posteriorly located dull aching headache., According to Greenberg, spinal cord compression always occurs when the sagittal spinal canal diameter behind the odontoid process is ≤14 mm. Spinal cord compression occurs when the sagittal cord diameter is between 15 and 17 mm. Cranial nerve findings include tinnitus, visual disturbances and lower cranial nerve palsies leading to dysphagia and dysarthria.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6]