AUTHOR AND EDITOR INFORMATION

Section 1 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Background

Infective spondylitis is an infection that involves 1 or more of the extradural components of the spine. Although it affects a small proportion (2-7%) of all patients with osteomyelitis, it is important because of its potential morbidity and mortality. Infective spondylitis most commonly appears as spinal osteomyelitis and/or diskitis. Its complications include paraspinal and epidural abscess formation.

Pyogenic spinal infections most commonly are caused by Staphylococcus aureus (in 60% of patients) and Enterobacter species (in 30% of patients). Osteomyelitis caused by Salmonella is most often seen in patients with sickle cell disease. Pseudomonas aeruginosa, Serratia species, and Candida species most often affect patients with a history of intravenous drug abuse. Mycobacterium tuberculosis causes most nonpyogenic spinal infections; however, fungi (eg, Cryptococcus species, Aspergillus species, coccidioidomycosis) also may cause infections.

Pathophysiology

The 3 main routes of spinal infection are hematogenous spread, direct inoculation, and contiguous spread.

In adults, most cases of infective spondylitis result from direct inoculation after spinal instrumentation procedures, including surgery, discography, and epidural injections. S aureus and Staphylococcus epidermidis. Infections that spontaneously result from a hematogenous source (eg, bacteremia, intravenous drug abuse) usually begin in a lumbar or thoracic vertebral body subjacent to the vertebral endplate by seeding of septic emboli via small, penetrating end arteries. Hematogenous spread along Batson venous plexus is no longer considered a major route of infection.

In adults, infection enters the disk space by means of contiguous involvement and by neovascular proliferation.

Loss of disk height can occur as pyogenic organisms release enzymes that dissolve the nucleus pulposus.

Nonpyogenic organisms, such as those that cause tuberculosis (TB), lack proteolytic enzymes; therefore, they tend to spare the disk. However, infections by these infections are characterized by large paraspinal lesions disproportionate to the amount of local bone destruction. Infection may spread to the psoas muscle and result in paravertebral abscesses that tend to calcify (especially characteristic of nonpyogenic infections).

In children, most cases of infective spondylitis are spontaneous and related to hematogenously borne infective spondylitis infection of the intervertebral disk because since residual vascular channels lead directly into the disk. These channels typically regress by the age of 15 years.

Spread from an adjacent source, such as a psoas abscess (see Image 1) is an uncommon mechanism. CSF and lymphatic spread are also uncommon routes of infection.

Risk factors for infective spondylitis include age older than 50 years, diabetes, immunosuppression, paraplegia, previous spinal fracture, and urinary tract instrumentation.

Frequency

United States

Infective spondylitis represents approximately 2-7% of all cases of osteomyelitis in patients, and the disease is increasing in frequency.

International

Nonpyogenic (ie, granulomatous) infections of the spine occur more frequently internationally, where organisms such as TB and brucellosis are endemic, than in the United States.

TB of the spine (ie, Pott disease) is most prevalent in persons in the fifth decade of life. Paraspinal collection and multivertebral infections are more common in this form than in pyogenic infections.

Mortality/Morbidity

Because symptoms may be present for months before the diagnosis is confirmed, the local disease process may progress, and patients may present with hip contracture or paralysis resulting from abscess formation in the paraspinal or epidural spaces.

Acute deterioration from epidural abscess used to be a rare complication; however, this complication is increasing in frequency among patients with diabetes, immunosuppression and intravenous drug abuse.

• Patients with epidural abscess may present with back pain, fever, or neurologic deficit and/or obtundation.

• Less than 2% of patients with epidural infection are children.
• Acute deterioration from epidural abscess may result from mechanical compression of the spinal cord from mass effect of the phlegmonous tissues or from spinal instability or ischemic compromise.

• Subarachnoid puncture is not recommended in patients with epidural abscess in the region of the abscess, but can be performed remotely.
• The effects of epidural abscess are seen in the thoracic region in 50% of cases, in the cervical region in 25%, and in the lumbosacral region in 35%.

• Surgical decompression and drainage and prolonged antibiotic use are standard treatment methods, although some patients may be treated conservatively especially if the disease is extensive, involving many levels of the spine.

• The mortality rate from this entity can be as high as 30%.

Race

Infective spondylitis has no racial predisposition.

Sex

The male-to-female ratio is 1.5-3:1.

Age

All age groups are susceptible to infective spondylitis; however, adults older than 50 years are most often affected.

• Patients with a history of intravenous drug abuse or underlying conditions, such as end-stage renal disease, diabetes, and AIDS, present at a relatively young age.
• Childhood spinal infections are a distinct variety of infective spondylitis that begins within the disk.

Anatomy

The mechanism for initiation and spread of the hematogenous infection to the spine differs between children and adults.

Compared with adults, children have numerous paravertebral and intraosseous collateral arteries, as well as a direct blood supply to the intervertebral disk, which may result in its direct inoculation. This supplementary system regresses by the age of 15 years and is absent in older patients.

Adult hematogenous infections typically begin through segmental arteries (ie, lumbar, intercostal) that feed small, end-artery metaphyseal branches, causing infarction and bacterial seeding. Because of their relatively rich supply of metaphyseal branches, infection preferentially begins in the anterior subchondral regions of the vertebral body.

Infective spondylitis most commonly involves the lumbar (45%), thoracic (35%), and cervical (10-20%) levels. Secondary epidural abscess formation occurs in the cervical spine, followed in frequency by the thoracic and lumbar spine. Multilevel or multifocal disease also can occur (most common with TB) and accounts for the remaining patients. Two vertebral bodies and the intervening disk are involved in 67% of patients.

Clinical Details

The clinical presentation of patients with infective spondylitis varies but generally commences with the insidious development of localized back pain combined with nonspecific symptoms, such as malaise, fever, or weight loss. Fever and leukocytosis often are absent, but the erythrocyte sedimentation rate is elevated in 95% of patients. Levels C-reactive protein is also commonly elevated.

Transient bacteremia, intravenous drug abuse, invasive spinal procedures, or infection of the genitourinary tract, skin and/or soft tissue, or respiratory tract predisposes patients to infective spondylitis; however, the etiology remains unknown in 37% of patients. A culture-specific diagnosis is critical in the optimal treatment of the infections. This diagnosis can be obtained by means of surgery or image-guided biopsy.

The virulence of the organism, the overall health of the patient with respect to chronic illness, and the interval before clinical presentation determine the extent of disease at the initial evaluation. Patients with acute illness are usually defined as those presenting within 1 week of symptom onset, while chronically ill patients may present months later.

Medical treatment is the first line of therapy in a patient with no neurologic complication. Usually, a 6-week course of culture-specific intravenous antibiotic, with or without an oral antibiotic, is recommended. External spinal immobilization and/or bracing is also recommended. Operative treatment may be required in patients with a neurologic deficit, spinal instability, or failed medical therapy.

Preferred Examination

Although plain images, radiographs, CT, or nuclear medicine studies can help establish the diagnosis, MRI is considered the modality of choice for evaluating the presence and severity of spinal infection. MRI is especially effective for evaluating the neural structures of the spine (ie, spinal cord, nerve roots) and extradural soft tissue.

Along with appropriate history taking, physical examination, and positive blood cultures, findings on MRI or radionuclide studies can confirm the diagnosis.

CT is most useful for characterizing vertebral osteomyelitis in patients with subacute or chronic illness. CT provides radiologic guidance for interventional procedures (ie, biopsy, drainage).

Conventional radiographs are insensitive to the acute changes of infective spondylitis but can be used on a limited basis to follow up on chronically ill patients.

Limitations of Techniques

MRI is relatively expensive, it is contraindicated in patients with certain implanted medical devices (eg, pacemakers), and it is not tolerated by all patients because of claustrophobia or morbid obesity. Good MRIs require patient cooperation and are degraded by patient motion. Use of a gadolinium-based intravenous contrast agent is strongly recommended.

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. 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 MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. 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

movingor straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

CT is quick and inexpensive, but it exposes the patient to ionizing radiation and to a low risk of a reaction to the intravenous contrast agent, though detection of bone destruction or paraspinal mass does not require the use of contrast material.

Radionuclide studies can be time consuming and can have low spatial resolution.

Plain radiographs often are normal or nonspecific in patients with acute spinal infection.

DIFFERENTIALS

Section 3 of 12  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Other Problems to be Considered

Degenerative endplate changes (most common mimic)
Neuropathic arthropathy
Postoperative changes (granulation tissue)
Neoplasia (metastasis)
Spondyloarthropathy of hemodialysis
Rheumatoid arthritis
Seronegative spondyloarthropathies (eg, ankylosing spondylitis, Reiter syndrome)

RADIOGRAPH

Section 4 of 12  

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• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

Findings

Conventional radiography is insensitive to the early changes of infective spondylitis. In the acute setting, radiographs are normal. In the subacute period (1-3 wk), reduced disk-space height and/or endplate erosion may be evident. In the chronic period (>10 wk), vertebral body sclerosis or collapse may be observed on either side of a narrowed disk space. Paraspinal soft-tissue opacity may develop. Gradual disk obliteration may occur with fusion (ie, osseous, fibrous). Partial restoration of disk height may be observed with successful treatment.

Degree of Confidence

Plain radiographic findings suggestive of subacute or chronic infective spondylitis (eg, disk-space loss, endplate erosion, vertebral sclerosis) should be correlated with the patient's clinical history.

False Positives/Negatives

Radiographic findings lag behind clinical response to treatment by approximately 1 month.

CT SCAN

Section 5 of 12  

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• References

Findings

CT scans can appear normal early in the disease. Disk-space narrowing or decreased attenuation in the disk is often the earliest manifestation of disease. After the administration of iodinated contrast material, the abnormal disk space, vertebral marrow, or paravertebral soft tissues may enhance.

Destruction (eg, diffuse, permeative) of the vertebral body and fragmentation of vertebral endplates are then observed. The presence of paraspinal soft tissue lesions and/or collections aids the diagnosis of infective spondylitis. Extrusion of the vertebral body can be observed in children.

Degree of Confidence

Overall, CT is more sensitive (68%), more specific (97%), and more accurate (80%) than plain radiography in identifying areas of vertebral osteomyelitis in animal models.

Because of its ease and speed of use, lower cost, and availability, CT is an excellent method for evaluating the bony changes of infective spondylitis and for directing radiologic intervention (ie, aspiration or biopsy) in spinal infections. CT-guided percutaneous aspiration procedures can be up to 91% sensitive and 100% specific in diagnosing active bacterial disk space infections, but they are less reliable than this in diagnosing nonbacterial infections.

False Positives/Negatives

Gas in the disk space (ie, vacuum phenomenon) may be observed on occasional CT scans. Although this finding is most often associated with degenerative disk disease, it can also occur with infection.

CT is less sensitive than MRI to soft tissue structures, but its sensitivity can be improved with the use of intravenous contrast material.

MRI

Section 6 of 12  

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• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
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• Multimedia
• References

Findings

MRI is the modality of choice for evaluating spinal infections. In particular, MRI is useful in detecting abnormalities in the acute stage of spinal infection. At this stage, MRI can demonstrate increased signal intensity on T2-weighted images in the vertebral body or disk space caused by infarction, abscess, or edema (see Image 2), and/or decreased signal intensity on T1-weighted images (due to edema) in the disk and adjacent endplates with a loss of the margin between the disk and the endplate.

Paraspinal and epidural abscesses generally appear isointense to muscle on T1-weighted images and hyperintense on fat fat-saturated T2-weighted or short-tau inversion recovery (STIR) images.

Vertebral body abscesses may appear more conspicuous on diffusion-weighted images (DWIs) than on conventional T1- or T2-weighte images.

Contrast-enhanced MRI studies can show epidural abscess (peripheral enhancement around an area of fluid signal intensity, (see Image 3), and/or abnormal disk, vertebral marrow, or paraspinal soft tissue enhancement.

The multiplanar capability of MRI provides excellent anatomic localization of the extent of infection and allows full evaluation of the spinal cord and nerve roots. MRI is also useful for evaluating postoperative spinal infections or for the follow-up evaluation of treated spondylitis.

Routinely perform fat-suppression sequences with contrast-enhanced T1-weighted imaging.

Degree of Confidence

MRI is 96% sensitive, 92% specific, and 94% accurate in the evaluation of infective spondylitis.

False Positives/Negatives

Signal and enhancement changes can persist after clinical resolution of the infection, and these findings gradually decrease over weeks to months. This observation illustrates the fact that contrast enhancement does not always indicate active infection. These changes do not occur as rapidly as with gallium scanning.

False-negative findings may occur in patients whose infective spondylitis is caused by low-virulence organisms (eg, diphtheroids, coagulase-negative staphylococci).

ULTRASOUND

Section 7 of 12  

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Findings

The usefulness of ultrasound is limited in infective spondylitis. Occasionally, ultrasonography may be useful for localizing large paraspinal fluid collections for aspiration and/or drainage. Color Doppler sonography may show hyperemia surrounding abscesses.

NUCLEAR MEDICINE

Section 8 of 12  

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• Multimedia
• References

Findings

Radionuclide studies are useful for early detection (3-15 d) of spinal infection. However, establishing this diagnosis can be more difficult in the spine than in other areas of the skeleton because of the presence of active bone marrow.

On 3-phase technetium-99m (^99mTc) scintigraphy, osteomyelitis is characterized by nonspecific arterial hyperemia and the progressive focal skeletal uptake of tracer.

Bone scan specificity may be increased by combining ^99mTc with an indium-111–labeled WBC or gallium-67 (⁶⁷Ga) scans. ⁶⁷Ga functions as an acute-phase reactant, localizing in any inflammatory process. ¹¹¹In-labeled WBCs accumulate in areas of infection and inflammation. Areas of infection should appear hotter on the ⁶⁷Ga scan than on the accompanying ^99mTc scan. Infective lesions may appear hot or cold on ¹¹¹In WBC scans. ⁶⁷Ga scans can normalize after satisfactory treatment and can be used to monitor the treatment response.

The use of single-photon emission CT increases the 3-dimensional localization of infection.

Degree of Confidence

The degrees of confidence of the aforementioned scans is as follows:

False Positives/Negatives

Nuclear scintigraphy is sensitive for vertebral osteomyelitis; however, increased bone turnover from surgery, fracture, or degenerative changes decreases specificity.

False-negative results may occur when atherosclerosis or primary bone destruction compromises blood flow to a lesion.

¹¹¹In WBC scans can increase the specificity of a bone scan, but the images can appear false-negative in patients with chronic osteomyelitis or false-positive in inflammatory or reactive conditions such as rheumatoid arthritis and fractures.

ANGIOGRAPHY

Section 9 of 12  

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Findings

Angiography has no practical role in the diagnosis of spine infection.

INTERVENTION

Section 10 of 12  

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• Multimedia
• References

In the setting of an appropriate patient history, physical examination, and corroborative imaging, a positive blood culture may identify the causative organism and direct antibiotic therapy; however, blood cultures can be negative in 50% of patients with spinal infection.

Invasive methods may be required to establish the diagnosis. Spinal biopsy can be performed as an open surgical procedure or as an image-guided percutaneous procedure. Percutaneous image-guided biopsy (eg, with CT [see Image 4] or fluoroscopy [see Image 5]) has a lower morbidity rate than an open biopsy. This technique can be highly sensitive and specific. Obtain and submit multiple samples in appropriate containers for Gram staining, acid-fast bacillus smears, fungal staining, and cultures.

See Medical/Legal Pitfalls below for a discussion of the effect of concurrent antibiotic therapy.

Medical/Legal Pitfalls

• Failure to make the diagnosis after percutaneous spinal biopsy is a pitfall. The culture is most likely to be negative if the patient was recently or is currently treated with antibiotics. Therefore, if biopsy is considered for diagnosis, perform it as early in the clinical course as possible.
• Failure to detect infection at the site of recent spinal operations is problematic because normal granulation tissue or recurrent disc herniation can be difficult to differentiate from superimposed infection.
• Failure to differentiate nonpyogenic organisms from neoplasia is another pitfall. The skip nature of subligamentous spread, the indolent course, and lack of disk destruction may mimic findings of cancer.
• Failure to differentiate infective spondylitis from seronegative spondyloarthropathies (eg, ankylosing spondylitis, psoriatic arthritis, Reiter disease) is a pitfall. Patients with these conditions may present with some or all of the imaging abnormalities of infective spondylitis.
• Failure to distinguish the similar imaging characteristics of infective spondylitis from those of patients receiving long-term dialysis who may present with a noninfectious, rapidly progressive spondyloarthropathy.
• Failure to differentiate infective spondylitis from degenerative disk disease, which may mimic infective spondylitis in rare cases, is a pitfall. MRI results usually can differentiate the 2 conditions.

MULTIMEDIA

Section 11 of 12  

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• CT SCAN
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• Nuclear Medicine
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• Multimedia
• References

Media file 1:  T2-weighted MRI shows a large, right psoas abscess with epidural extension. Despite the large fluid collection, results of percutaneous biopsy were culture negative. The patient was treated with intravenous antibiotics before the procedure.
	View Full Size Image
Media type:  MRI

Media file 2:  Discitis/osteomyelitis is seen on this T2-weighted MRI of the lumbar spine, which demonstrates destruction of the L3-4 disk space with the adjacent endplate and/or vertebral body. L3 and L4 vertebral bodies show increased T2 signal, indicating edema and/or infarction. Also shown is a retropulsion of debris, which compresses the thecal sac.
	View Full Size Image
Media type:  MRI

Media file 3:  The epidural abscess on this contrast-enhanced T1-weighted MRI demonstrates the loss of disk-space height, which is most prominent at C4-5 and C5-6. A large, peripherally enhancing epidural abscess extends from C5-6 to the C2 level. The thecal sac and cord are compressed.
	View Full Size Image
Media type:  MRI

Media file 4:  This image of a CT-guided biopsy of discitis/osteomyelitis demonstrates extensive destruction and fragmentation of the vertebral body resulting from infective spondylitis. CT-guided percutaneous needle aspiration and biopsy was performed to obtain material for cultures to direct appropriate antibiotic therapy.
	View Full Size Image
Media type:  CT

Media file 5:  Fluoroscopy-guided radiograph shows how disk aspiration can be used to direct an image-guided procedure. Image also demonstrates the relatively subtle changes of infective spondylitis on radiography. Although early loss of the disk space may be present, no definite endplate erosion is seen. MRI findings were supportive of infection; the biopsy was culture positive for Staphylococcus aureus.
	View Full Size Image
Media type:  X-RAY

REFERENCES

Section 12 of 12

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• Mri
• Ultrasound
• Nuclear Medicine
• Angiography
• Intervention
• Multimedia
• References

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Article Last Updated: Mar 22, 2007