Merck Manual

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Occipitoatlantoaxial malformation, radiograph, dog
Occipitoatlantoaxial malformation, radiograph, dog

Occipitoatlantoaxial malformation and agenesis of the dens in a dog (lateral projection). Note the rounded appearance to the hypoplastic dens and displacement of C2 dorsally and caudally relative to C1.

Courtesy of Dr. Ronald Green.