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Year : 2010  |  Volume : 20  |  Issue : 2  |  Page : 109-111
Case report: Congenital absence of the dens

1 MR Centre, GBH American Hospital, Udaipur, Rajasthan - 313 001, India
2 Department of Radiodiagnosis, R.N.T. Medical College, Udaipur, Rajasthan - 313 001, India
3 Neurology Centre, 21-C A Madhuban, Udaipur, Rajasthan - 313 001, India

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Date of Web Publication6-May-2010


A 36-year-old man presented with headache and right upper and lower limb weakness for 10 days. MRI revealed absence of the odontoid process of the C2 vertebral body, with resultant atlantoaxial dislocation along with myelomalacic changes involving the cervicomedullary junction.

Keywords: Absent; congenital; dens

How to cite this article:
Bajaj M, Jangid H, Vats A K, Meena M L. Case report: Congenital absence of the dens. Indian J Radiol Imaging 2010;20:109-11

How to cite this URL:
Bajaj M, Jangid H, Vats A K, Meena M L. Case report: Congenital absence of the dens. Indian J Radiol Imaging [serial online] 2010 [cited 2021 Mar 2];20:109-11. Available from:

   Introduction Top

Developmental anomalies of the odontoid are uncommon. The clinical importance lies in their potential to cause serious neurological complications due to atlantoaxial instability.

We report a case of congenital absence of the dens, with resultant atlantoaxial dislocation and partial fusion of the C2 and C3 vertebrae.

   Case Report Top

A 36-year-old man presented with a history of minor trauma to the head following a sudden jerk while traveling in a bus. He complained of headache and right upper and lower limb weakness. On examination, power in the right upper and lower limbs was 4/5. The right plantar reflex was extensor. No sensory deficit or bladder/bowel involvement was seen.

MRI of the brain and the cervical spine was performed, which revealed absence of the odontoid process of the C2 vertebra [Figure 1], with resultant atlantoaxial dislocation [Figure 2]. There was reduced caliber of the spinal cord at the C1-C2 level, with T2 hyperintense signals, suggestive of myelomalacic changes [Figure 2]. Subsequent non-contrast CT scan of the cervical spine with sagittal and coronal reconstructions confirmed the absence of the dens; there was also a well-corticated depression involving the superior border of the body of C2 [Figure 3]. Also noted was fusion of the body and posterior elements of the C2 and C3 vertebrae and subtle anterior migration of the axis vertebra at the atlanto-occipital junction. Three-dimensional volume-rendered post-processed CT scan [Figure 4] depicted the anomaly elegantly.

   Discussion Top

Congenital anomalies involving the craniovertebral junction are clinically important because of their potential for producing serious neurological deficits. The clinical features are chiefly because of the associated atlantoaxial dislocation and include persistent neck pain, headache, and transient/permanent paresis. [1] Often, patients presenting for the evaluation of trauma are found to have such anomalies, incidentally.

Congenital anomalies involving the odontoid process are rare. They can be classified into os odontoideum, ossiculum terminale, aplasia-hypoplasia, [2] and duplication of the dens. [3] Of these, aplasia of dens is very rare, with only a few cases reported in the literature. [4]

The development of the axis is complex [Figure 5]. Four ossification centers are present at birth: one for each neural arch, one for the body, and one for the odontoid. In utero, the dens has two ossification centers in the midline, which fuse by the 7th month of intrauterine life. A secondary ossification center appears at the apex (the terminal ossicle) at 3-6 years of age and fuses with the rest of the dens by 12 years of age. The body of C2 normally fuses with the dens by 3-6 years, with obliteration of the subdental synchondrosis. Posteriorly, the neural arches fuse by 2-3 years of age, and fusion with the odontoid takes place between 3 and 6 years of age, with obliteration of the neurocentral and lateral dental synchondrosis [Figure 5]. [5],[6],[7],[8],[9],[10]

In our case, the dens itself, as well as the part of the dens assimilated by the body of C2, was absent [Figure 5], the latter being evident by the corticated depression in the upper part of the C2 body in the midline.

Anomalies of the odontoid can usually be diagnosed on a standard series of radiographs, plus flexion and extension lateral films. With the increasing importance of CT scan and MRI in the study of the craniovertebral junction, a detailed evaluation of such congenital anomalies is now possible, as demonstrated in our case.

The first case of odontoid hypoplasia was reported by Roberts in 1933. [11] Since then, hypoplasia has been reported a few times but aplasia is considered very rare. [12]

   References Top

1.Guille JT, Sherk HH. Congenital osseous anomalies of the upper and lower cervical spine in children. J Bone Joint Surg Am 2002; 84A:277-88.  Back to cited text no. 1      
2.Fielding JW, Heinsinger RN, Hawkins RJ. Os odontoideum. J Bone Joint Surg Am 1983:62A:376-83.  Back to cited text no. 2      
3.Garant M, Oudjhane K, Sinsky A, O'Gorman AM. Duplicated odontoid process: plain radiographic and CT appearance of a rare congenital anomaly of the cervical spine. AJNR Am J Neuroradiol 1997;18:1719-20.  Back to cited text no. 3  [PUBMED]  [FULLTEXT]  
4.Smoker WR. Craniovertebral junction: normal anatomy, craniometry, and congenital anomalies. Radiographics1994; 14:25577.  Back to cited text no. 4      
5.Cone RO, Flournoy J, Macpherson RI. The craniocervical junction; Radiographics 1981;1:2-3.  Back to cited text no. 5      
6.Henry Gray, Bannister LH, Berry MM, Williams PL. Gray's anatomy. 37 th ed. Philadelphia, Pa: Lea and Febiger; 1989.  Back to cited text no. 6      
7.Herman MJ, Pizzutillo PD. Cervical spine disorders in children. Orthop Clin North Am 1999;30:457-66, ix.  Back to cited text no. 7  [PUBMED]    
8.Harris JH Jr, Mirvis SE. The radiology of acute cervical spine trauma. 3rd ed. The normal cervical spine. In: Mitchell CW, editor.Baltimore, Md: Williams and Wilkins; 1996. p. ;173.  Back to cited text no. 8      
9.Swischuk LE. Emergency imaging of the acutely ill or injured child. 4 th ed. The spine and the spinal cord. Philadelphia, Pa: Lippincott Williams and Wilkins,; 2000. p. 532-87.   Back to cited text no. 9      
10.Ogden JA. Radiology of postnatal skeletal development. XII. The second cervical vertebra. Skeletal Radiol 1984;12:16977.  Back to cited text no. 10      
11. Roberts SM. Congenital Absence of the Odontoid Process Resulting in Dislocation of the Atlas on the Axis. J Bone Joint Surg Am 1933;15:988-9.  Back to cited text no. 11      
12.Gillman EL. Congenital absence of the odontoid process of the axis: report of a case. J Bone Joint Surg Am 1959;41:345-8.  Back to cited text no. 12  [PUBMED]    

Correspondence Address:
Manish Bajaj
79 Adinath nagar, Old Fatehpura, Udaipur - 313 001
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-3026.63050

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  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]


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