[isolated Agenesis of the Posterior Arch of the Atlas].

INTRODUCTION Congenital abnormalities of the posterior arch of the atlas (C-1) are very uncommon and not widely known. Isolated partial agenesis of the posterior arch of the atlas was initially considered a benign variation without any clinical or pathological significance. There is, however, increasing evidence that neurological symptoms may occur after minor cervical trauma in patients with an isolated partial agenesis of the posterior arch of the atlas, specially the types 'C' and 'D' malformations described by Currarino et al. CLINICAL CASE A 63 year old woman with cervicalgia and 'seasickness', was study with a plain cervical spine radiographs and CT with three-dimensional reconstruction, who showed a bilateral partial absence of the posterior arch of C-1 with persistent posterior tubercle, corresponded to type 'D' in the classification descrites by Currarino et al. CONCLUSIONS The fact of this pathology can unchain an important neurological symptoms after minor cervical trauma, oblige to the physician (radiologist, neurologist, neurosurgeon, traumatologist, rehabilitation specialist) know this pathology, for to include this patients in a group of the risk, and indicate to them who should avoid contact sports and other strenuous athletic endeavors, and furthermore value the surgical treatment.