Congenital defect of anterior arch of atlas
Female in her 40's presents for CT scan to investigate chronic sinusitis. No symptoms instability or history of trauma.
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There is a well-corticated defect seen in the mid-line of the anterior arch of the atlas.
Normal paravertebral soft tissues.
Given the well-corticated margins, normal paravertebral soft tissues and lack of traumatic history the defect is almost certainly due to a developmental anomaly. Also note that the arch is thicker than normal, a frequent finding when the atlas has an incomplete bony ring (either anterior or posterior).
Healed fracture of the left anterior maxillary antrum.
Malformations of the anterior arch of atlas are very rare and are significantly less frequently encountered than malformations of the posterior arch of the atlas.
Although congenital anomalies of the atlas are commonly only discovered incidentally, it may occasionally cause instability requiring further management
It is important to distinguish these congenital anomalies from fractures. On imaging congenital clefts will appear smooth with intact cortical margins and no surrounding soft tissue changes, whereas fractures will have irregular edges and associated soft tissue changes
CT imaging is the gold standard for differentiating between fractures and congenital anomalies of atlas