Comment to Question 3

 

1.- Plain film
Plain films may help in interpreting and choosing other studies. In uncomplicated acute infection, the triad of soft tissue swelling, bone destruction, and periosteal reaction is fairly specific for osteomyelitis and is sufficient to warrant a course of therapy. However, plain film is non-specific and spine infection cannot be excluded if plain film is negative.
2.- CT scan
The CT scan (with and without contrast) is very accurate in detecting cortical destruction, intraosseous gas, periosteal reaction and soft tissue extension. In addition, CT scan provides radiological guidance for interventional procedures (i.e., biopsy, drainage). However, CT depiction of soft tissue structures is less sensitive than MRI.
3.- Radio-nuclide imaging
There are different nuclear medicine imaging procedures available to evaluate bone lesions , including the three-phase bone scan, indium -labelled leukocyte scan, gallium scan and bone marrow scan. Bone scan specificity may be increased by combining Tc 99m with an indium-labelled white blood cell (In 111 WBC) scan or gallium 67 scan (Ga 67). However, indium scan has low sensitivity in the spine. Gallium imaging is the most sensitive and specific radio-nuclide scanning technique for vertebral osteomyelitis. A typical positive test reveals intense uptake in two adjacent vertebrae with loss of the intervening disc space.
4.- MRI
MRI is considered the best diagnostic tool to study osteomedullary inflammations and, particularly, to diagnose and follow-up spondylodiscitis. MRI provides specificity and in most cases allows differentiation from tumour and degenerative disease.
In vertebral osteomyelitis, findings on T1-weighted images include decreased signal intensity in the disc and adjacent vertebral bodies and loss of endplate definition. Findings on T2-weighted images include increased signal intensity in the disc and adjacent vertebral bodies.
With gadolinium, there is enhancement of the disc adjacent to the vertebrae, and of the involved paraspinal and epidural soft tissue.
However, MRI has several limitations: it is relatively expensive, is contraindicated in patients with implant devices (eg, pacemakers), and it is not tolerated by all patients because of claustrophobia or morbid obesity. Good MRI requires patient cooperation and is degraded by patient motion.
In summary, plain film and CT scan can help to establish the diagnosis. Radio-nuclide imaging and MRI permit early differentiation of spinal infection, but MRI provides greater anatomic information and easier differentiation of infection from degenerative changes and metastatic disease. For this reason MRI is considered the modality of choice for evaluating the presence and severity of spinal infection.