Retro-Odontoid Pseudotumor in a Patient with Atlanto-Occipital Assimilation

Abstract

A retro-odontoid pseudotumor is an uncommon non-neoplastic mass. They are mostly associated with rheumatoid arthritis and atlanto-axial subluxation. The pathogenesis is degeneration of the transverse ligament due to chronic mechanical stress. In this case report, an atlanto-occipital assimilation altered the biomechanics of the cervical spine, causing chronic mechanical stress on the transverse ligament and subsequently the development of a retro-odontoid pseudotumor. This is in accordance with previous studies that have attributed the development of retro-odontoid pseudotumor to a loss of mobility of the cervical spine, in cases without associated rheumatoid arthritis or atlanto-axial subluxation.

Keywords: Odontoid process; atlanto-axial subluxation; pseudotumor; rheumatoid arthritis; transverse ligament.

Figure 1

Axial T2-weighted image. The retro-odontoid pseudotumor is seen as a hyperintense mass (black arrow) which extrudes through the transverse ligament and compresses the myelum (white arrow).

Figure 2

(A) Sagittal T1-weighted image. The retro-odontoid pseudotumor is seen as a mass (black arrow) extruding through the transverse ligament and compressing the myelum (white arrow). It has an isointense signal compared to the myelum. (B) Sagittal T2-weighted image. The retro-odontoid pseudotumor has a hyperintense signal (black arrow) and compresses the myelum (white arrow).

Figure 3

A = lateral view of the cervical spine in flexion; B = lateral view of the cervical spine in extension. Plain radiograph showing a lateral view of the cervical spine in flexion and extension. Note widening of the atlantodental interval in flexion (white arrow).

Figure 4

Sagittal (A) and coronal (B) reconstructions of a CT scan of the cervical spine shows assimilation of the massa lateralis of C1 and the occipital condyle (white arrows).