Calcium pyrophosphate dihydrate (CPPD) disease or pseudogout of the cervical spine.

A partially calcified "mass" is seen behind the odontoid process compressing the cervical cord, so-called periodontoid pseudotumor.

It is an often misrecognized cause of acute neck pain in the elderly. The pseudotumor behind the dens may cause cervicomedullary compression.

Typical radiographic manifestations of CPPD in the cervical spine:

Calcific deposits can be seen in:

• the annulus fibrosus and transverse ligament of the dens
• the supraspinous and interspinous ligaments
• the intervertebral discs
• the longitudinal ligaments (may cause spinal stenosis)
• capsular calcifications in the apophyseal facet joints
• pseudotumoral periodontoid mass of the foramen magnum ("crowned dens")

Pyrophosphate arthropathy (in long-standing disease) causing:

• narrowing of intervertebral discs
• bone sclerosis
• osteophyte formation
• depositions of crystals within the joints can lead to erosions, subchondral cysts and pathologic fractures
• erosions and cysts of the odontoid process

The differential for calcific deposits in the cervical spine is limited:

• hydroxyapatite deposition disease (HADD) - can be indistinguishable from CPPD on CT
• The inflammatory response to the crystal deposits in the disc space can be aggressive enough to mimic a discitis
• gout can cause similar findings

Clinical history and/or crystal analysis may be needed for the definitive diagnosis. In difficult cases, a biopsy may be needed.