Trauma is the most common reason for spine MRI. CT, and now increasingly MRI, have supplanted plain radiography in the evaluation of spinal trauma. Currently, CT alone is considered sufficient in the evaluation of thoracic and lumbar skeletal injuries. This is not true for cervical spine injuries.18
Initially, use either the NEXUS or Canadian C-Spine Rule criteria to determine if a trauma patient needs any imaging. Then, consider whether CT or MRI or both will be required, while realizing that the literature on this thorny issue continues to evolve. CT is the current standard for detecting bony injuries. MRI is usually reserved for patient in whom a soft-tissue, particularly ligamentous, injury is suspected. MRI is also required for the evaluation of any patient suspected of having sustained spinal cord injury.18 The downside of our increased MRI usage in the evaluation of potentially spine-injured patients has been the detection of many clinically insignificant findings.
Acute cauda equina syndrome is a neurosurgical emergency requiring prompt recognition, imaging, and immediate neurosurgical consultation. Common findings include: recent onset or worsening severe low back pain; bowel and/or bladder dysfunction; neurological deficits; and saddle anesthesia. Many processes can lead to the syndrome, but the most common is disc herniation with resultant cauda equina compression. The American College of Radiology appropriateness criteria cite MRI as the correct imaging modality for the diagnosis of acute cauda equina syndrome.19 In patients who’ve undergone previous herniated disc surgery, MRI with and without contrast must be obtained to differentiate between contrast-enhancing granulation tissue at the site of the surgery and nonenhancing herniated disc tissue.18
Infection is an important item in the differential diagnosis of back pain, with or without radiculopathy, and particularly important to consider if the patient has infectious disease risk factors. These risk factors include: spinal instrumentation via injections or surgery; intravenous drug use; prosthetic heart valves; systemic infections; other infectious sources in the body; and immunocompromising conditions.18 All spinal elements, including the spinal cord, meninges, joints, discs, and vertebrae can be affected. Realize that infection can occur by direct inoculation or contiguous or hematogenous spread. An MRI with and without contrast is essential to confirm the diagnosis.19 Your neurosurgical consultant will likely recommend imaging the entire spinal axis, since infectious lesions may be present at multiple levels.18
Pregnant patients with abdominal pain - concern for appendicitis (see the Cautions and Limitations section above on MRI in pregnancy)
Appendicitis occurs commonly in pregnancy. Missing the diagnosis can lead to fetal loss and other untoward outcomes. The 2018 American College of Radiology guidelines list MRI and ultrasound as imaging studies of choice in gravid patients in whom appendicitis is a concern.20 Ultrasound is more commonly available and less expensive but is limited by high rates of appendiceal non-visualization, likely due to appendix displacement by the uterus, patient habitus, bowel gas, and discomfort during the exam.21