Myositis ossificans - cervical spine

On the right at C4/5 is a well circumscribed heterogeneously calcified/ossified mass which measures 20 x 17 x 18 mm which appears to arise from and is continuous with the articular pillar, with involvement of the C4/5 facet joint which appears fused. Slight sclerosis is demonstrated along the right side at the C4 and C5 vertebral bodies. 

The superior aspect of the mass remodels the pedicle of C4, and anteriorly results in severe stenosis of the neural exit foramen. Surrounding this mass is stranding and displacement of adjacent fat, and low density changes in the adjacent muscles consistent with the florid edema seen on MRI. There is no convincing extension into the epidural space, and the cervical cord appears unremarkable and the canal capacious.

The remainder of the cervical spine is unremarkable.

Conclusion:

Calcified/ossified mass arising from the right C5 articular pillar, in the setting of previous trauma and probably a previous superior articular facet undisplaced fracture likely represents post-traumatic myositis ossificans. An underlying tumor is thought much less likely, but cannot categorically excluded. If clinical concern exists then a CT guided bone biopsy can be safely performed.

A triple phase bone scan of the neck was performed followed by whole-body study and SPECT/CT of the neck. 

Dynamic flow and blood pool images show focally increased perfusion and vascularity in the right side of the mid survival spine. 

Delayed SPECT/CT static images show a single focus of intense increase in tracer uptake located between the right lateral masses of the C4 and C5 vertebrae and invading the right C4-5 apophyseal joint from anteriorly. This corresponds to a definite calcified irregularity seen on the CT scan at the site.

No other significant abnormalities are seen in the neck or upon following whole-body bone scan..

Overall impression :

Appearances are suspicious of a bone tumor or osteomyelitis or (very unusually hence unlikely) still active myositis ossificans in the right C4-C5 inter lateral mass invading the right C4-5 apophyseal joint from anteriorly. This abnormality is scintigraphically too intense for osteoarthritic type apophysitis and a simple fracture or myositis ossificans/heterotopic calcification would be expected to scintigraphically heal after 3 years.

Abnormality is centered at C4/5 level, with bone marrow enhancement that  extends through the right articular pillar, pedicle and right side of  vertebral body at C4 and C5. CT confirms fusion of the right C4/5 facet  joint, with an irregular calcific focus at the posterior aspect of the  adjacent exit foramen, and lucency with cortical loss where the involved articular pillar forms the posterior margin of the exit foramen.

Gross soft tissue edema within the surrounding paravertebral muscles with extension towards the midline anteriorly and posteriorly. No rim enhancing paravertebral fluid collection.

The oldest imaging available for comparison, the MRI from 2011, suggests a fracture fragment at the C5 superior articular process, with no MR evidence of fusion across the C4/5 facet at that time.

The remainder of the cervical spine demonstrates normal marrow signal. No canal stenosis or cord signal abnormality.

Conclusion :
Evidence of previous trauma in the right C4/5 articular pillar. Focus of ossification in the posterior aspect of the right exit foramen with associated florid surrounding soft tissue and bone marrow enhancement which has an appearance consistent with inflammation rather than tumor. Given previous history, this is most likely represent myositis ossificans. A less likely possibility would be post-traumatic degeneration with chronic indolent infection.

Oblique vies demonstrate irregularity at the articular facet of C4/5 on the right, suggesting a small fracture. 

A 12 G Bonopty penetration needle was passed down to the soft tissue component of the lesion posterior to the right C4/5 facet joint. A single coaxial pass of an 14 G Achieve needle was made through the  soft tissue component. 

Unfortunately despite the IV sedation and local anesthesia, the lesion remained too sensitive for passage of the needle down to bone or for further sampling. A sample was only obtained from the soft tissue component, not the bony component. If further specimens are acquired, patient will need general anesthesia or IV sedation with the attendance of an anesthesiologist.