Spinal imaging
The spine consist of the vertebral column and the spinal cord. Ordinary X-ray technique is quite suitable to detect different pathological conditions regarding the vertebrae and the intervertebral discs and joints, and is widely used in a various clinical settings. Both CT and MRI are able to visualise nuclear disc protrusion or herniation where plain X-ray technique is inadequate. So-called myelography (X-ray examination after injection of iodine-containing contrast medium into the sub-arachnoid space) is, however, still in use and is a good technique to examine pinching of nerve-roots. Today this invasive examination is used mainly as a supplement to CT or MRI.
Intraspinal tumours
Myelography can detect intraspinal tumours, but only the margins are visualised. Contrast enhanced MRI is able to visualise all spinal content directly; not only the borders of a tumour, but the whole lesion. MRI can differentiate cystic from solid tumours. CT can also detect intraspinal tumours, especially those localised outside the dural sac. But the sensitivity is fairly low due to small differences in X-ray absorption between normal and pathological tissue.
Therefore MRI is, practically speaking, the only modality which can characterise intra-spinal disorders.
Ordinary X-ray examinations are not able to reliably rule out intraspinal disease.
Extraspinal tumours - Tumours/destruction in vertebrae
Metastases from different primary tumours frequently affect the vertebrae. To be able to detect them, they either have to destruct parts of the vertebrae (osteolytic metastasis), or induce new bone formation (osteoblastic metastasis).
X-ray has a fairly good sensitivity to detect osteoblastic metastases but there can be problems to distinguish these from benign lesions. On the other hand osteolytic lesions need to be of some size to be detectable.
CT is useful to detect smaller destructions, and can also give useful information about soft tissue involvement.
Nuclear scans can detect osteoblastic lesions at a very early stage, but it can be a problem to differentiate these from degenerative changes. Osteolytic metastases are, on the other hand, hard to detect due to lack of osteoblastic involvement (which is needed for the radioactive markers to be taken up).
Degenerative disk disorders
CT is widely used to detect disk protusions and herniations. In clinical situations dealing with sciatic pain, CT is the preferred modality, because it is fast and much used world-wide. CT can be combined with injection of contrast media into the subarachnoid space (CT-myelography) for improved detection of pathology.
MRI is in most cases equal to or better than ordinary CT (probably the same sensitivity as CT-myelography)
Ordinary X-ray and NM examinations cannot rule out degenerative disk disorder reliably.
Infection
MRI and nuclear scans including PET are able to detect early signs of osteomyelitis. MRI will also show the extent and possible affection within the spinal canal and outside the vertebrae. Especially with nuclear scans, there are problems with specificity because other conditions can mimic similar changes. CT can show early reactive bony changes and absorptions. Ordinary X-ray will usually not show any changes during the first 2 weeks.
Trauma
X-ray is widely used in order to rule out fractures and misalignments after trauma. X-ray is in many ways still the best examination to perform to rule out or characterise fractures of the vertebral column. NM is also well suited and is particularly sensitive for the detection of stress fractures. CT is often used in "problem-areas", like parts of the cervical region, or to determine if a fracture is affecting the spinal canal.
MRI can tell a lot about the status of neural tissue (bleeding, laceration) which the other modalities can not.
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