Anatomical anomalies involving the craniovertebral junction are clinically important as they give rise to potentially serious neurological deficits due to atlantoaxial instability and dislocation. Potential adverse outcomes include persistent neck pain, headaches, and transient or permanent paresis.

Anomalies involving the odontoid process are exceptionally rare, and are due to one of three etiologies: trauma, osteolysis, or congenital malformation. Congenital anomalies of the odontoid are classified into four types depending on the extent of involvement: os odontoideum, ossiculum terminale, aplasia-hypoplasia, and duplication of the dens. Of these, aplasia is the least common and only a few cases have been reported in the literature.

Our patient with no history of trauma and radiographic evidence of a small ossicle without an odontoid process likely has os odontoideum. Dynamic flexion and extension imaging studies were recommended for further risk assessment and management.

This case was submitted with supervision and input from:

Thomas Zung, M.D.
Staff Radiologist
Department of Radiological Sciences
Olive View - UCLA Medical Center

Soni C. Chawla, M.D.
Associate Professor
Department of Radiological Sciences
David Geffen School of Medicine at UCLA
Olive View - UCLA Medical Center