Infections of the Cervical Spine

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30 Infections of the Cervical Spine

Kamal R.M. Woods, Samer Ghostine, Terrance Kim, J. Patrick Johnson

KEY POINTS

• Early diagnosis and treatment is pivotal to the management of cervical spine infections, given their propensity to cause rapid and severe neurological decline.
• Most patients with cervical spine infections complain only of vague neck pain, although fevers, radiculopathy, neck rigidity, and dysphagia may also be present.
• The diagnosis of cervical spine infection is typically made based on elevated erythrocyte sedimentation rate (ESR) and confirmatory imaging.
• In the absence of acute neurological deficit or spinal instability, pyogenic cervical osteomyelitis, and cervical discitis are usually treated with 4 to 8 weeks of intravenous antibiotics.
• Surgical treatment is recommended for cervical epidural abscesses, subdural empyemas, and intramedullary abscesses.

Introduction

Evidence from Egyptian mummies suggests that infections of the spine predate the era of written history. In his textbook On the Articulations, Hippocrates (400 bc) included reports of vertebral deformity that likely resulted from what was later described by Pott as tuberculous spondylitis. Today, infections of the spine are relatively rare clinicopathologic entities. When they do occur, however, these infections still pose both diagnostic and therapeutic challenges to clinicians.

Spine infections predominate in the lumbar region, followed by the thoracic and then the cervical regions. Nonetheless, cervical infections are particularly problematic because of their propensity to cause more rapid and severe neurological deficits. The discussion that follows will examine the most surgically relevant cervical spine infections: pyogenic vertebral osteomyelitis, spinal epidural abscess, discitis, subdural empyema, and intramedullary abscess.

Basic Science

Cervical infections may be viewed from the perspective of the infectious organism: bacterial, viral, fungal, or parasitic. Alternatively, they may be approached based on the response of the host to the inciting organism: pyogenic (“pus-forming”), or granulomatous. The classic example of a granulomatous infection is tuberculous spondylitis (Pott disease), in which the histology shows caseating central necrosis surrounded by Langhans giant cells. Granulomatous infections may also be caused by fungi, such as aspergillosis, coccidiomycosis, blastomycosis, and cryptococcosis. Parasitic infections of the cervical spine, including cysticercosis, schistosomiasis, and echinococcosis, are extremely rare, and data on their management are limited to case reports.

Overall, the most common causative agent for spinal infections in the United States is Staphylococcus aureus, which is present in more than 50% of cases. When the spine infection is associated with a genitourinary or gastrointestinal infection, Escherichia coli, Proteus, and other gram-negative bacteria are frequently responsible. Patients who have a recent history of intravenous drug abuse are more likely to be infected with Pseudomonas aeruginosaStreptococcus is a significant cause of intramedullary cervical abscesses, as it can spread through the lymphatic system from the retropharyngeal space.

There are several potential routes for the dissemination of infections to the cervical spine, including direct extension from contiguous structures, open spinal trauma or surgery, hematogenous, or lymphatic. Both venous and arterial mechanisms have been implicated in hematogenous spread. The Batson venous plexus was proposed as a valveless conduit through which infections of the pelvis, such as urinary tract infections, may spread to the spine. This venous mechanism has been largely refuted, and an alternative arterial route postulated.1 In the case of vertebral pyogenic osteomyelitis, infection is thought to seed the metaphyseal (subchondral) bone near to the anterior longitudinal ligament via a rich arterial network. The posterior spinal arteries that branch off the dorsal artery entering the intervertebral foramen are probably responsible for cervical epidural abscesses. Infections of the retropharyngeal space can enter the lymphatics and spread along the spinal nerves to communicate with the spinal subarachnoid space and Virchow-Robin space, thus leading to cervical subdural empyemas or cervical intramedullary abscesses.

Interestingly, discitis is seen in two distinct patient populations: pediatric and adult. While discitis in the pediatric population is usually caused by a hematogenous source, adult discitis occurs in patients who have undergone prior surgery involving the disc space. The reason for this clear distinction is that, as the spine ages, there are changes that take place in its vascularity. Histologic studies have shown that an end-arteriolar supply of the disc is present during infancy and childhood, and these end arteries are obliterated by the third decade of life.2

Clinical Practice Guidelines

The guidelines that govern the diagnosis and treatment of cervical spine infections may vary on a case-by-case basis. However, there are certain common themes which ought to be emphasized.

Risk Factors

Numerous risk factors for the development of cervical spine infections have been identified, including diabetes, intravenous drug usage (especially via the jugular vein), alcohol abuse, urinary tract manipulation or infection, immunocompromised state, steroid therapy, prior spine surgery, advanced age, and male gender. In the setting of diabetes, steroids, or other immunocompromised state, the diagnosis is usually delayed because of an impaired inflammatory response.

Clinical Presentation

The most common chief complaint for all cervical spine infections is vague, nonspecific neck pain of a progressive nature. With pyogenic osteomyelitis and discitis, this pain is exacerbated by neck motion, and eventually becomes extremely debilitating. Radicular pain is frequently present in epidural abscesses, and results from either direct nerve root compression or inflammation.3 If a cervical epidural abscess spreads to the retropharyngeal space, then dysphagia or even airway compromise may result.

The time course to presentation for cervical spine infections varies from acute (less than 1 week), to subacute (1 to 6 weeks), to chronic (more than 6 weeks). In the case of pediatric discitis, this pain is usually so severe at an early stage that a diagnosis is made before the infection spreads to the adjacent vertebral bodies.4 For pyogenic vertebral osteomyelitis, the presentation tends to be subacute to chronic in 90% of cases, partly because of its more insidious onset. A definitive diagnosis of pyogenic vertebral osteomyelitis is made, on average, 8 weeks to 3 months after disease onset.5 Patients who present acutely (less than 1 week) are more likely to be febrile, and to have other constitutional signs and symptoms.

Infections that result in the formation of a mass-occupying abscess have a greater chance of presenting with neurological deficit. This may be seen in vertebral osteomyelitis that extends into the epidural space, or with a primary spinal epidural abscess. Likewise, subdural empyemas and intramedullary abscesses cause neurological deficit at an early stage. In some instances of vertebral osteomyelitis, the bony quality is compromised to the extent that bony collapse may occur, leading to spinal instability and secondary neurological deficit. Sometimes, spinal epidural abscesses and subdural empyemas may cause neurological compromise that is out of proportion with the degree of compression. This is thought to be secondary to vascular compromise from venous compression, thrombosis, or thrombophlebitis.6

On physical exam, some patients with cervical infections may have local tenderness at the level of the infection, or diffusely in the cervical region. Given the paucity of other physical exam findings, such spine tenderness may seem somewhat dramatic. When the adjacent soft tissue is affected, the skin may show the typical signs of infection: erythema, swelling, warmth, induration, or even fluctuance. Meningitis may be associated with epidural abscesses and subdural empyemas, resulting in rigidity of the neck with passive flexion.

Laboratory and Imaging Studies

Much like the physical exam findings, laboratory data for cervical spinal infections can be rather obscure. The peripheral white blood cell count is usually normal or just slightly elevated. For this reason, it is imperative to check the erythrocyte sedimentation rate (ESR) when cervical infection is under consideration. In the case of pyogenic osteomyelitis, the ESR may be elevated to 43 to 87 mm/hr (Westergren method).7 Apart from its diagnostic value, the ESR is an important marker to assess the degree of response to treatment.

The next important diagnostic step is appropriate imaging of the spine. This investigation should begin with plain x-rays. In the case of discitis or vertebral osteomyelitis, narrowing of the disc space may be seen as early as 2 to 3 weeks after infection onset. By 10 to 12 weeks, there is sclerosis of the adjacent vertebral body endplates, due to the bony deposition caused by inflammation. This is likely related to the fact that the subchondral bone is highly vascular and, therefore, is the initial nidus of infection in the vertebral body.8 With time, the sclerotic process gives way to lysis of the bone, and thus blurring of the endplates on x-ray. The infection eventually spreads to involve the remainder of the vertebral body. In approximately 5% of pyogenic spinal infections, the infection involves the dorsal elements. As the bone is progressively compromised, bony collapse can take place and lead to fracture and deformity of the spine. Plain x-rays are usually normal with spinal epidural abscesses, subdural empyemas, and intramedullary abscesses.

Computed tomography (CT) scans allow for examination of the bony details with greater clarity. For this reason, bone erosion and rarefaction may be detected earlier than on plain x-rays. CT is particularly useful in surveying the posterior elements for involvement by infection, and in assessing associated fractures. Additionally, CT may provide useful information when planning surgical instrumentation of an unstable cervical spine.

Magnetic resonance imaging (MRI) remains key to the diagnosis of cervical infections. For pyogenic osteomyelitis, the sensitivity and specificity rates of MRI are 96% and 93%, respectively.9 MRI allows the spinal cord, nerve roots, and paraspinal soft tissue to be visualized to determine the extent of their involvement by the infection. Pyogenic osteomyelitis, discitis, epidural abscesses, subdural empyemas, and intramedullary abscesses all usually appear hypointense on T1-weighted MRI, and hyperintense on T2-weighted MRI. T1-weighted MRI with contrast enhancement is also useful to delineate the margins of an abscess. Another important feature of infections that is clearly demonstrated by MRI is their tendency to span from one vertebral body to the other, through the intervening disc space. Tumors, on the other hand, usually involve the anterior vertebral bodies and skip the disc spaces.

In certain circumstances, myelography via lateral C1-2 punctures may be valuable in making a diagnosis of cervical spine infection. An advantage of myelography is that cerebrospinal fluid can be obtained in the same procedure for laboratory studies. At the same time, myelography carries a risk of introducing an extradural infection into the intradural spaces. Nuclear scans may be beneficial in detecting an infection in the early stages; however, with advances in MRI technology, the role of nuclear studies is diminished.

Treatment

Patients with pyogenic cervical osteomyelitis and/or cervical discitis who lack acute (less than 72 hrs) neurological deficit or spinal instability are usually treated conservatively with 4 to 8 weeks of IV antibiotics. The commencement of antibiotics for these patients should be delayed until the causative agent has been identified, as prior treatment with antibiotics decreases the yield of subsequent cultures. In many cases, the infectious organism can be implied based on positive blood, urine, or sputum cultures. Blood cultures are most sensitive during the acute febrile stage of the infection. As the disease becomes more chronic, fever is less common and the sensitivity of blood cultures decreases.

When the extraspinal cultures are all negative, tissue culture is recommended before starting antibiotics. In the cervical spine, CT-guided needle biopsy is discouraged because of the close proximity of vital structures that are at risk of injury during percutaneous biopsy. Therefore, an open biopsy is usually required to obtain a tissue specimen in the cervical spine. Once tissue is obtained, broad-spectrum antibiotics may be started until final tissue cultures and sensitivities are available to fine-tune the antibiotic regimen. If the tissue culture is also negative, then the infection is treated with empirical broad-spectrum antibiotics.

Serial ESR and MRI are used to analyze the response to treatment. The ESR is expected to decrease by 50% by the end of antibiotic therapy. Failure to achieve this expected decrease in ESR is considered failure of medical management, and is an indication for surgical intervention. Other indications for surgical intervention in pyogenic cervical osteomyelitis and cervical discitis are acute (less than 72 hrs) neurological deficit at the initial presentation or at any point during medical therapy, and bony collapse leading to deformity or spinal instability.

Surgery for pyogenic cervical osteomyelitis and cervical discitis is usually done through the anterior triangle of the neck. Most cases of pyogenic osteomyelitis involve at least two adjacent vertebral bodies and the intervening disc space. Some authors recommend treating such an infection with a two-level corpectomy, three-level discectomy, and a strut graft between the remaining healthy endplates. However, it is important to evaluate surgical candidates on a case-by-case basis. If there is concern for the integrity of the posterior elements based on the CT, then posterior instrumentation may be indicated. For isolated cervical discitis without involvement of the adjacent endplates, anterior cervical discectomy and fusion is sufficient.

Surgical intervention should be regarded as the first-line treatment for cervical epidural abscesses, subdural empyemas, and intramedullary abscesses. Cervical epidural abscesses tend to be ventral, unlike in the thoracic and lumbar spines where they are more often dorsal. This allows such epidural abscesses to be drained after an anterior cervical discectomy, with or without corpectomy, depending on the extent of the abscess. When an epidural abscess extends into the retropharyngeal posterior triangle, such as commonly occurs with tuberculous infections, a posterior triangle exposure is needed. Rarely, an abscess at C1-C2 may require drainage using the retropharyngeal or transoral approach.

Posterior cervical laminectomy is used to treat cervical subdural empyemas and intramedullary abscesses. After durotomy, debridement or drainage of suppurative material is performed for subdural empyemas. For intramedullary abscesses, intraoperative ultrasound may be useful to localize the abscess. A midline myelotomy is then performed to access the abscess cavity. One must bear in mind that posterior cervical laminectomy has the potential to cause subsequent kyphotic deformity, especially in cases where the infection has also eroded the vertebral bodies anteriorly.

Clinical Case Example

DISCITIS/SPINAL EPIDURAL ABSCESS

A 49-year-old male heroin abuser presented to the emergency department with progressive neck pain for 2 to 3 months, and inability to ambulate for the past 12 hours. His ESR was elevated, prompting imaging of the neck with plain x-rays (Figure 30-1A) followed by MRI (Figure 30-1B). A diagnosis of cervical discitis with an associated ventral epidural abscess was made, for which he underwent emergent anterior cervical decompression and drainage of the spinal epidural abscess. His kyphotic deformity corrected with extension of the neck on the operating table, and anterior reconstruction was achieved with allograft and anterior cervical plating (Figure 30-1C). Over the next several weeks, the patient gradually regained strength in his lower extremities and walked into his follow-up clinic visit at 6 weeks.

image

FIGURE 30-1 A, Lateral cervical x-ray demonstrating reduction in the height of the C5-6 disc space, erosion of the adjacent superior and inferior endplates, and kyphotic deformity with splaying of the spinous processes. B, T2-weighted MRI revealing increased signal in the C5-6 disc space, and extension of the infection into the epidural space causing cord compression and edema. C, Postoperative x-ray showing correction of the kyphotic deformity and the anterior C4-7 plate.

External immobilization has long been regarded as an important component of the treatment for pyogenic cervical osteomyelitis and/or discitis. However, the method and duration of immobilization has not been studied prospectively, and the exact role of immobilization has not been determined. Nonetheless, immobilization potentially accomplishes two goals: improved pain control, and stabilization of the spine. The orthosis that is selected depends on the affected cervical level and the degree of instability. Possible methods of immobilization include halo fixation, sternal-occipital-mandibular immobilizer (SOMI) brace, and hard cervical collar.

When spinal instability is present, it is necessary to consider internal fixation, with or without arthrodesis. Gross purulence was once considered an absolute contraindication to bone graft and instrumentation because of concern about recurrent infection. However, there are few practical solutions for an unstable cervical spine. Fortunately, there is now an increasing body of evidence that instrumentation and fusion may be safely performed after all grossly infected material is removed.10

Conclusions/Discussion

Infections of the cervical spine have a propensity to cause catastrophic neurological deterioration, underlining the importance of prompt diagnosis and treatment. Often, the clinical presentation is vague and insidious, leading to untoward delays in diagnosis. Therefore, a high index of suspicion is necessary, and appropriate laboratory and imaging investigations should be performed when clinically indicated.

It is widely accepted that most cases of pyogenic cervical osteomyelitis and cervical discitis may be treated conservatively with antibiotics, although the route and duration of antibiotics are yet to be studied in a prospective, randomized fashion. Some authors advocate early surgical intervention for all cervical spine infections in an attempt to avoid later complications, such as neurological decline or bony collapse. Well-designed clinical trials are needed to clearly define the role and timing of surgical intervention for infections of the cervical spine.

References

1. Wiley A.M., Trueta J. The vascular anatomy of the spine and its relationship to pyogenic vertebral osteomyelitis. J. Bone Joint Surg. Br.. 1959;41:796-809.

2. Conventry M.B., Ghormley R.K., Kernohan J.W. The intervertebral disc, its microscopic anatomy and pathology: part I: anatomy, development and physiology. J. Bone Joint Surg. Am.. 1945;27:105-112.

3. Martin R.J., Yuan H.A. Neurosurgical care of spinal epidural, subdural, and intramedullary abscesses and arachnoiditis. Orthop. Clin. North Am.. 1996;27:125-136.

4. Kemp H.B., Jackson J.W., Jeremiah J.D., Hall A.J. Pyogenic infections occurring primarily in intervertebral discs. J. Bone Joint Surg. Br.. 1973;55:698-714.

5. Vincent K.A., Benson D.R., Voegeli T.L. Factors in the diagnosis of adult pyogenic vertebral osteomyelitis. Orthop. Trans.. 1988;12:523-524.

6. Russell N.A., Vaughan R., Morley T.P. Spinal epidural infection. Can. J. Neurol. Sci.. 1979;6:325-328.

7. Ross P.M., Fleming J.L. Vertebral body osteomyelitis. Clin. Orthop.. 1976;118:190-198.

8. Allen E.H., Cosgrove D., Millard F.J. The radiological changes in infection of the spine and their diagnostic value. Clin. Radiol.. 1978;29:31-40.

9. Modic M.T., Feiglin D.H., Piraino D.W., Boumphrey F., et al. Vertebral osteomyelitis: assessment using MRI. Radiology. 1985;157:157-166.

10. Fang D., Cheung K.M., Dos Remedios I.D., et al. Pyogenic vertebral osteomyelitis: treatment by anterior spinal debridement and fusion. J. Spinal Disorder. 1994;7:173-180.

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