[Partial aplasia of the atlas in a child].

Congenital anomalies of the atlas are rare but well documented. They can range from total agenesis to partial clefts of the posterior and/or anterior arches and are mostly incidental findings after a sustained trauma. It is essential to differentiate these congenital variants from fractures of the atlas to prevent the patient from unnecessary (neuro-) surgical intervention. In this article the case of a 10-year-old girl is described with an unusual finding of partial aplasia of the posterior arch. The clinical features and diagnostic and therapeutic procedures are discussed.