Agenesis of the Odontoid Process

Abstract

Failure of ossification of the odontoid process of the second cervical vertebra is a rare developmental anomaly which may be asymptomatic for many years. As a result of more thorough roentgenologic examinations, the condition has been noted with increasing frequency since its original description by Roberts in 1933 (1). We have had the opportunity of observing such a case with severe neurological symptoms. A search of the world literature revealed 14 examples of this anomaly, listed in Table 1. In only a single instance were there persistent neurological findings. Associated congenital malformations have been observed in 2 cases: a partial fusion of the second and third vertebrae in 1 (7), and in the other a hemivertebra of the axis (8). Case Report G. S. H., a 29-year-old Indian male, was admitted to the University of Oklahoma Hospitals on Aug. 6, 1954, with a history of progressive weakness in all four extremities for four months. In July 1954, two months prior to admission, he became confined to bed because of weakness and spasticity in his legs. He denied any sensory disturbances or bladder or bowel symptoms. There was no history of trauma. Neurological examination revealed no abnormalities of the cranial nerves. Mobility of the neck was normal, with no tenderness over the cervical spine. A marked quadriparesis was present, in association with pronounced atrophy of the small muscles of the hands and peroneal group bilaterally. The deep tendon reflexes in all four extremities were extremely active, and there was a bilateral wrist and ankle clonus. Bilateral Babinski responses were elicited. Coordination and sensation were intact throughout. The clinical impression was amyotrophic lateral sclerosis. Routine laboratory studies, including a complete blood count and urinalysis, were negative. Spinal fluid examination, including the Queckenstedt sign, was normal. Routine x-ray examinations of the skull and cervical spine disclosed some deformity of the second cervical vertebra. The odontoid process could not be identified, and the atlas was displaced posteriorly on the axis. The posterior arch of the first cervical vertebra showed a marked degree of sclerosis, with narrowing of the space between this arch and the spinous process of the axis. In a mid-line lateral laminagram, these findings were more clearly visualized (Figs. 1 and 2). Anteroposterior open-mouth exposures demonstrated a subluxation of the atlas to either side of the axis (Fig. 3). Air myelography revealed encroachment on the spinal canal by the first cervical vertebra with flexion of the neck, which permitted anterior dislocation of that vertebra on the axis (Fig. 4). Following completion of these diagnostic studies, the neurosurgical consultant was called to see the patient and recommended exploratory laminectomy, which was performed on Aug. 26, 1954. A bony abnormality of the arch of C-1 was found.