Alar ligament calcification is rare. The alar ligaments arise bilaterally from the upper portion of the odontoid process and run obliquely cephalad and laterally to insert on the medial surface of the occipital condyles. They stabilize the head during rotatory movements.
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Epidemiology
Focal calcification of the alar ligament is very uncommon 1-5.
Clinical presentation
Calcification of the alar ligament may be associated with neck and/or nuchal pain 1-4.
Pathology
Calcium pyrophosphate dihydrate (CPPD) and calcium hydroxyapatite (HAP) deposits are likely components of the calcification 2.
Radiographic features
CT scanning of C1-2 is the best tool for the diagnosis of this condition 2.
Plain radiograph
Radiographs of the cervical spine can demonstrate a calcification in the periodontoid tip area 1.
CT
Calcifications of the alar ligaments are corticated structures located between the top sides of the odontoid process and the medial surface of the occipital condyles 1-5. These calcifications may disappear with time 1.
MRI
MRI is useful for defining the anatomic location of the alar ligament, also it may show a nodular fragment with low signal intensity in the alar ligament area 1.
Treatment and prognosis
The treatment is usually conservative with anti-inflammatory therapy, neck immobilization, and bedrest 1,2,4.
History and etymology
Ziza et al. reported calcified deposits in ligaments of C1-2 in 1982, but they did not specify which ligaments 2,4.
Bouvet in 1985, Yasukawa in 1990, and Yoshida in 1993 described cases with calcified deposits of the ligaments of the atlas and axis 4.
In 2001, Kobayashi et al. reported two cases of focal calcification in the alar ligament for the first time 1,2,4,5.
Differential diagnosis
crowned dens syndrome: the calcifications are in a crown distribution around the top of the odontoid process and usually, affect the alar and transverse ligaments. Unlike crowned dens syndrome, calcifications of the alar ligaments are focally located along the alar ligaments 1,3,5
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fractures of the craniovertebral junction:
fractures of the odontoid process and occipital condyles are differential diagnoses from alar ligament calcification 1,3,5
corticated and smooth surface of the calcified structure indicates that it represents alar ligament calcification rather than a fragment of bone 5
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