Imaging of the Spine in Multiple Sclerosis 

Magnetic resonance imaging (MRI) was first used to visualize multiple sclerosis (MS) in the upper cervical spine in the late 1980s.^[1] Spinal MS is often associated with concomitant brain lesions; however, as many as 20% of patients with spinal lesions do not have intracranial plaques. No strong correlation has been established between the extent of the plaques and the degree of clinical disability. (See the image below).

Careful review of the patient's medical history and an evaluation of the brain with MRI can prove helpful in the diagnosis, especially in young females. MS is considered to be the most common demyelinating process involving the central nervous system (CNS).^[2]

Preferred examination

Although nonspecific, MRI is presently considered to be the most sensitive diagnostic imaging modality for revealing demyelinating plaques. MRI shows abnormalities in 95% of patients with clinically definitive MS.^{[3, 4]}

On long TR sequences, MRI scans show areas of demyelination as high-signal areas. Lesions of other etiologies (eg, viral myelitis, acute disseminated encephalomyelitis [ADEM]) may resemble MS plaques and must be considered along with the clinical history and the patient's presenting signs and symptoms. For patient education information, see Multiple Sclerosis.

Because computed tomography (CT) scanning has poor sensitivity, the detection, evaluation, and characterization of MS lesions and enhancement patterns are limited with this modality. As a result, with the advancement of MRI, evaluation of the spinal cord using axial CT scanning was abandoned.

On CT scans, large, masslike lesions can occasionally mimic a neoplasm, and characterizing them can be difficult. Primary and secondary neoplasms of the spinal cord (astrocytomas, ependymomas), infection, transverse myelitis, acute infarction, sarcoidosis, and systemic lupus erythematosus may mimic demyelinating MS plaques on CT scans.

MRI far exceeds CT scanning in the ability to demonstrate intramedullary pathology; MRI is currently used for the first-line investigation of spinal MS.^[5] Depending on their age, MS plaques appear on unenhanced, T1-weighted images as areas of slightly low to low signal intensity. Spinal plaques may appear as nodules, rings, or arcs and generally are less than 2 vertebral bodies in length.^[6] Plaques usually demonstrate prompt enhancement after the administration of a gadolinium-based contrast agent, which most often indicates active disease.^[7] The enhancement may last 2-8 weeks. Steroids typically do not suppress the enhancement of the active plaques. Classic chronic lesions do not demonstrate contrast enhancement. (See the image below.)

Most MS plaques appear hyperintense on T2-weighted images. The spinal cord may or may not be focally enlarged. Enlargement of the cord is usually seen with active disease. Larger active lesions may have extensive edema with associated cord expansion. Chronic lesions often demonstrate focal cord atrophy. Spinal lesions usually coexist with more severe concomitant brain plaques. As many as 20% of spinal MS lesions are isolated. Spinal cord narrowing due to atrophic changes is present in 10% of patients with spinal cord involvement.^[8] (See the images below.)

Tumefacient MS may mimic a neoplasm; a demyelinating process should always be considered if a masslike lesion is encountered. As is the case in the brain, a ring or arc of enhancement can often be found, as opposed to a more nodular or masslike enhancement. Follow-up studies are helpful.

Although not widely implemented, newer methods may be more specific in evaluating MS plaques.^[9] These methods include magnetization transfer and diffusion, as well as proton MR spectroscopy (MRS).^{[10, 11, 12]}

Typically, fast-FLAIR (fluid-attenuated inversion recovery) sequences have been shown to have a lower sensitivity than do fast spin-echo sequences (FSE) for depicting spinal cord MS lesions.^{[13, 14, 15]}

Studies have suggested that more cervical cord MS lesions can be revealed with magnetization transfer–prepared gradient-echo and fast-STIR (short TI inversion recovery) sequences than with FSE sequences, with fast-STIR demonstrating the greatest sensitivity.^{[14, 16, 17, 18, 19]}

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have been linked to the development of nephrogenic systemic fibrosis (NSF), also known as nephrogenic fibrosing dermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MR angiography (MRA) scans.

NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.

Differentials

The main differentials include, but are not limited to, the following:

• Primary or metastatic spinal cord neoplasms - Eg, astrocytomas, ependymomas
• ADEM
• Sarcoidosis
• Transverse myelitis
• Infarct
• Vasculitis
• Radiation myelitis
• Arteriovenous fistula

Neoplasms

The presence of cysts and hemorrhage support the diagnosis of neoplasm

ADEM

This may show enhancement. The concomitant presence of brain lesions is the rule. ADEM typically runs a monophasic course; therefore, it does not have the relapsing course of MS. A history of viral infection within the previous 3-4 weeks should alert the radiologist.

Sarcoidosis

This involves the CNS in approximately 5% of cases. Concomitant pial involvement is frequently encountered. Enhancement is usually the rule.

Transverse myelitis

This term is usually used for idiopathic inflammatory myelopathy. Cord swelling and enhancement may be present, often involving a longer segment than does MS. MRI of the brain may be helpful for showing additional lesions in case of MS or ADEM. Transverse myelitis usually responds to steroid therapy; therefore, a treatment trial is often considered before proceeding with biopsy. This process is typically monophasic.

Infarct

This is more common at the thoracic level. Usually, only a single lesion is present. Contrast may be present, although this is not the dominant feature. Signal alteration usually and initially involves the anterior gray matter (anterior spinal artery distribution). The patient's clinical presentation will be acute. Particularly consider the possibility of an infarct if the patient is older and/or has a history of aortic/vascular surgery.

Vasculitis

Processes such as systemic lupus erythematosus can result in spinal lesions that mimic MS. Often, multiple lesions are present. However, the clinical history is often known and can help to establish the correct diagnosis.

Radiation myelitis

Generally, doses higher than 4000cGy are required to cause this condition. The latency period is 1-3 years. Chemotherapy may be synergistic. Images may show some peripheral enhancement.

Arteriovenous fistula

Usually, this occurs at the thoracolumbar level, and patients are usually older than 50 years, with a long history of back pain. The cord signal abnormality can involve a very long segment. Look for a serpiginous flow void along the cord surface.

Degree of confidence

Although MRI is not specific, it is considered the most sensitive imaging modality for diagnosing spinal cord MS, for evaluating its extent, and for following up the response to treatment. MRI is more sensitive for identifying active plaques than is double-dose CT scanning or clinical examination.