Spinal disease is a very common cause of neck and back pain. Patients presenting with spinal pain form a very important group at the Pain Clinic. Hence, appropriate evaluation of spinal disease is essential to provide excellent care to the patients.

This chapter describes the different imaging modalities available for the evaluation of spinal disease and imaging appearance of different spinal abnormalities. Emphasis will be laid on degenerative disease and postoperative changes with a brief note on nondegenerative diseases of the spine and diseases of the spinal cord.

PLAIN RADIOGRAPH

Plain radiography (PXR) is easily available and less expensive. It can be used as a screening study in patients presenting with pain to identify gross osseous and soft-tissue abnormalities related to degenerative changes, and for evaluation of hardware. Flexion and extension views are helpful in assessing instability and intersegmental mobility. Composite views are helpful in the evaluation of scoliosis. However, plain radiographs are not ideal for detailed evaluation of the spine and spinal contents.

COMPUTED TOMOGRAPHY

Computed tomography (CT) provides very good anatomic and structural details of the spine, in particular, the osseous details related to degenerative changes, trauma, and tumors. The spatial resolution is very good; however, the contrast resolution is low. Hence, it is not ideal for the evaluation of cord, nerve, and soft-tissue abnormalities, although gross abnormalities can be identified based on the alteration of the normal outlines of the structures and natural contrast among fat, bone, and disk. Usually, noncontrast studies are performed for evaluation of osseous details. Intravenous iodinated contrast medium is used for obtaining postcontrast CT images for evaluation of infection and tumors if Magnetic Resonance Imaging (MRI) cannot be performed. MRI is a better modality for these indications.

With the advent of newer generation scanners with multiple detectors, studies can be performed very rapidly and can include larger segments of the spine. Postprocessing methods help obtain very good reformations in multiple planes and form part of the standard algorithm of spinal imaging.

CT does have certain disadvantages that include risk of ionizing radiation, allergic reaction to intravenous contrast (IV) agent, and low-contrast resolution for assessment of intrathecal and soft-tissue abnormalities.

MAGNETIC RESONANCE IMAGING

Magnetic resonance imaging studies are performed using radiofrequency waves and, hence, have no risk of ionizing radiation. MRI is mostly used for detailed assessment and characterization of spinal disease, including cord and neural structures. It provides excellent anatomical details with high-contrast resolution. Acquisition of images using different sequences and in different planes helps in better characterization and localization of abnormalities compared to CT studies. Intravenous contrast agents such as gadolinium-based agents are helpful in the characterization of infective, inflammatory, vascular, and neoplastic lesions. For the evaluation of traumatic, degenerative, and congenital abnormalities, there is no need for IV contrast agents. The usual sequences that are performed are sagittal and axial T1-weighted (T1W) and T2-weighted (T2W) sequences, gradient echo, and short-time inversion recovery (STIR) sequences, which help in better characterization of the abnormalities. Wider and open-bore scanners are very helpful with claustrophobic patients and are increasing in availability and popularity. Dynamic MRI scanners and techniques help in assessing the spine and cord in different physiologic positions of the spine. These techniques can help identify latent abnormalities and subtle signs of instability.

The presence of certain implants or foreign bodies such as certain pacemakers, brain/cord stimulators, metallic foreign bodies in orbits, certain prostheses, and the like is not considered safe for MRI and precludes patients from undergoing MRI scan. It is essential to assess the safety of these by obtaining details of the implants from the manufacturer and obtaining screening radiographs, if necessary, in order to identify types of implants and any foreign bodies near vital organs. There are online resources to determine the MRI safety of various implants, such as www.mrisafety.com, that can be used as quick references when needed, in addition to the product manuals.

CONTRAST AGENTS FOR CT AND MRI

Intravenous contrast agents used for CT are iodinated contrast agents. Due to the risk of allergic reactions and renal failure, these are either contraindicated or to be used with certain precautions in patients with history of allergy to these agents and those with renal failure.

The intravenous contrast agents used for MRI are gadolinium based. There have been reports of association between gadolinium administration in patients with renal failure and a systemic syndrome called nephrogenic systemic fibrosis (NSF) that can be fatal. Hence, gadolinium agents must be used with caution in patients with acute or significant chronic kidney disease (estimated glomerular filtration rate (eGFR) <30 mL/min/1.73 m²), recent significant decrease in eGFR, recent liver or renal biopsy, hepatorenal syndrome, and so on. If the benefits outweigh the risk in these patients, it is usually recommended that appropriate precautions be taken for immediate dialysis after injection of gadolinium agent.¹ Note, however, that the protective effects of dialysis for prevention of NSF are unknown. Gadolinium is also to be used with caution in pregnant patients to avoid any potential harm to the fetus.²

FLUOROSCOPY

Fluoroscopic guidance is commonly used for performing image-guided procedures such as epidural and facet joint injections, for performing lumbar puncture in difficult situations, for myelography, and in the operating room for guidance and confirmation of position of hardware.

MYELOGRAPHY, CT MYELOGRAPHY

In patients who cannot undergo MRI and MR myelography, assessment of the extent of spinal canal stenosis, deformity on the cord, and extent of obstruction to flow of cerebrospinal fluid (CSF) can be performed by myelography and CT myelography. Iodinated contrast medium is injected into the CSF space of the thecal sac under fluoroscopic guidance. After allowing the contrast medium and CSF to flow in the thecal sac by appropriate positioning if necessary, fluoroscopic spot images are taken. At the completion of myelography, CT scan images of spine are obtained in the area of interest. Early and delayed CT images can be obtained until adequate information about the level and extent of obstruction to CSF flow is obtained.

Myelographic images can be obtained with MRI without the use of intrathecal contrast. To date, there are limited data comparing non-contrast to contrast-enhanced MR myelography.

DISKOGRAPHY

In this procedure, iodinated contrast agent is injected directly into the nucleus of the disc under fluoroscopic guidance and plain radiographs or CT images are obtained soon after injection. Extension of the contrast agent into the annulus fibrosus or epidural space indicates annular tear. Diskography is not routinely performed and is of controversial significance. It may be useful in patients with pain and no definitive imaging findings or in patients with degenerated discs at multiple levels to identify the most symptomatic level.^3,4

In patients allergic to iodinated contrast material, dilute gadolinium (off-label use, not FDA-approved for this purpose) can be used, and postinjection MR images can be obtained for the evaluation of discs.^5,6

RADIONUCLIDE STUDIES

Various radionuclide agents can be used in the evaluation of spinal disease depending on the clinical scenario. The most commonly used are the 99 m technetium methylene diphosphonate (Tc MDP) bone scan for detection of osseous lesions related to osteolytic or osteoblastic primary and secondary neoplastic lesions, stress fracture, pars defects, degenerative changes with acute component of marrow edema, and so on. In the evaluation of spinal osteomyelitis, 99 m technetium MDP and gallium-67 scans can be useful in the evaluation of active osteomyelitis. Radionuclide-labeled whole blood cells (WBCs) can be used in the evaluation of complicating osteomyelitis.⁷ FDG-PET (fluoro-deoxy glucose positron emission tomography) is very useful in the evaluation of different types of bone lesions related to infective, neoplastic etiologies, and the like.

The advantages and disadvantages of different imaging modalities are shown in Table 10-1.

Routine imaging of the spine for nonspecific symptoms in low-risk patients does not improve outcome and can also have deleterious effects, such as exposure to radiation; it may also result in unnecessary invasive treatments. Hence, routine imaging of the spine is not necessary in these patients.⁸

According to the recommendations by different societies such as American College of Physicians, the American Pain Society, and the American College of Radiology, imaging is to be considered based on the clinical presentation, the risk factors for serious condition, and/or if intervention is contemplated.^9,10 These factors are shown in Table 10-2.

The criteria for evaluation of neck and thoracic spinal symptoms and signs can be less stringent due to the greater risk for cord compromise and its devastating consequences. Clinical discretion and consultation with spine specialists can help in decision making.

The different types of imaging modalities described here complement each other in the evaluation of spinal disease. Because each modality has its own advantages and disadvantages, it is necessary to use the most cost-effective and accurate modality based on the clinical need.

The indications for different types of studies are shown in Tables 10-3, 10-4, and 10-5.

A systematic approach to interpreting spine studies is very important for accurate assessment and to avoid mistakes.

CT STUDIES

It is better to start with sagittal reformations for an overall review and then review the coronal and axial images; appropriate windowing and cross-referencing on picture archiving and communication systems (PACS) are very helpful in accurate localization of abnormalities.

1. 
   

   Number the vertebrae: This can be one of the most important steps, particularly if there is transitional anatomy. Appropriate and corresponding numbering has to be used when planning any procedure or intervention. Counting from C2 downward is considered as the accurate way of numbering the vertebrae. However, if cervical spine images are not available, counting can be based on morphological identification of sacrum. The location of the ilio-lumbar ligament can be used to identify the level of lumbosacral junction, assuming five lumbar vertebral bodies, which can, however, be a limitation of this method.¹¹ Note that the ilio-lumbar ligament is not reliably found at the L5 level and cannot be used to help with accurate numbering always.

   
   
2. 
   

   Vertebral bodies: height; alignment by checking the anterior spinal, posterior spinal, and spinolaminar lines on the sagittal plane and C1–C2 alignment in multiple planes; focal lesions.

   
   
3. 
   

   Disc space: height; asymmetric widening; vacuum phenomenon.

   
   
4. 
   

   Uncovertebral processes: degenerative changes.

   
   
5. 
   

   Facet joints: width; alignment; degenerative changes.

   
   
6. 
   

   Posterior elements: focal lesions; degenerative changes.

   
   
7. 
   

   Neural foraminae: narrowing (from disc or osseous changes)/widening (from tumors).

   
   
8. 
   

   Spinal canal: narrowing; occasionally abnormal widening-congenital/tumor.

   
   
9. 
   

   Osseous lesions: fractures, degenerative changes, lytic/sclerotic.

   
   
10. 
    

    Pre- and paravertebral spaces.

    
    
11. 
    

    Vascular structures: stenosis; aneurysm; dissection.

    
    
12. 
    

    Soft-tissue structures and viscera.

MR STUDIES