Anterior and posterior fusion defects of C1

Note the well corticated margins and absence of a discrete fracture line. Such fusion defects are congenital in nature, and are primarily incidental findings. Incomplete posterior fusion can be seen in normal children up to the age of 10, with bony fusion typically occurring by age 5. Clefts of the posterior arch occur in 5% of the population, whereas those of the anterior arch are much more rare, occurring in 0.1%.

Anterior and posterior fusion defect of C1
Part of the on-line supplement to Neuroradiology – The Essentials with MR and CT (© 2015)