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Neuroradiology Case of the Week

Case 146

Alisa Johnson, Jeevak Almast, MD, and PL Westesson MD, DDS, PhD

Clinical Presentation: The patient is a 58-year-old male with a history of severe neck pain presenting with left arm weakness, difficulty speaking, changed reflexes, and increasing neck pain.

Radiological Findings:

CT: There is a soft tissue density mass with an enhancing rim involving the C1 and C2 vertebral bodies in the left side.  There is erosion of the adjacent left lateral mass. There is also some erosion of the dens. This extends inferiorly and involves the left aspect of the body of C2 vertebral bodies where it demonstrates a more lytic appearance.  Alignment is maintained.

MRI: Abnormal T2 high signal with bone destruction is noted in C1 and C2. Non-enhancing portion is noted at the apex of odontoid process extending into the skull base and epidural space anterior to the cranio-cervical junction. This lesion is close to the medulla and abnormal T2 signal is noted in cranio-cervical junction on the right side. Surrounding soft tissue swelling is noted including prevertebral space from skull base to C4-5 level. These findings are likely representing osteomyelitis with abscess formation. The lesion in the medulla might be edema or infarction.

Differential diagnosis:

• C1-C2 osteoarthritis
• Rheumatoid arthritis
• Chordoma
• Primary bone tumor or metastasis
• Nasopharyngeal carcinoma
• Extension of skull base osteomyelitis
• Degenerative endplate changes
• Odontoid fracture
• Hemodialysis spondyloarthropathy
• Gout

Diagnosis: Osteomyelitis with epidural abscess

Clinical Discussion: Vertebral osteomyelitis is estimated to occur in approximately one per 100,000 people annually [1,2]. It accounts for approximately 1-7% of all bone infections. The cervical vertebrae are least likely to be affected composing only 3-10% [3] of the vertebral osteomyelitis cases. Cervical vertebral osteomyelitis has multiple etiologies, which include spontaneous, postoperative, traumatic, and hematogenously spread. Some of the risk factors and comorbidities for cervical osteomyelitis include trauma, drug abuse, diabetes, and an infectious processes in the extraspinal areas. The most common mechanism for infection to spread to the cervical spine is through a hematogenous route and staphylococcus aureus is themost common organism (40-80%) in the United States [2]. However, Mycobacterium tuberculosis is the most common cause of osteomyelitis worldwide [4]. Vertebral osteomyelitis frequently is complicated by "epiduralabscess", with can result in cord compression potentially leading to permanent paralysis ordeath if not treated.
     Clinically it can be difficult to diagnose vertebral osteomyelitis; however, early diagnosis is essential to avoid permanent neurological damage.; Most patients with cervical vertebral osteomyelitis complain of neck pain and stiffness. The neck pain usually begins insidiously and progressively worsens over several weeks and sometimes over several months. A minority of patients will present with the triad of fever, neck pain, and neurologic deficits [4]. Though neurologic symptoms are less common, they can be the early symptom in cervical osteomyelitis because of the relatively small cross-sectional diameter of the bone of the spinal canal relative to the diameter of the cervical spinal cord. Thus, the spinal cord is more prone to compression by epidural abscess or other deformities caused by the osteomyelitis. Physical examination may reveal tenderness over the cervical spine, pain with passive neck movement, or sensory/motor deficit. If there is an epidural abscess spinal cord injury may cause bladder and bowel dysfunction. Imaging is a powerful diagnostic tool. MRI is the most helpful in diagnosing vertebral osteomyelitis [5]. Once diagnosed, I.V. antibiotics are started and followed by a long course of oral antibiotics. Surgical decompression and stabilization will be pursued if indicated.

Neuroimaging Discussion: The best diagnostic clues for cervical osteomyelitis are the finding of bone destruction at the C1-2 level and/or a prevertebral soft tissue mass.  The size of the infection is variable and can be associated with a large epidural abscess.  On plain films the early changes with osteomyelitis are indistinct anterior margin of C1 and prevertebral soft tissue swelling.  Late changes will demonstrate gross boney destruction with a sensitivity of 80% and specificity of 50-60% [4].
     On CT studies without contrast  demonstrate destruction involving the anterior arch of C1, odontoid, and body of C2 with a soft tissue mass adjacent to the bone lesions.  The lesion may have variable extension into epidural space.  While on a CT with contrast, there will be enhancement of soft tissue or non-enhancing abscess formation.  MRI findings on T1WI classically demonstrate a low signal mass centered at C1-C2 and prevertebral increased soft tissue and edema.  There may be an epidural mass with thecal sac and cord compression.  T2WI and STIR will show diffuse increase signal from vertebral bodies and the soft tissue mass.   Two important findings to look for on the brain diffusion study are posterior circulation infarcts if the vertebral artery is compromised by the evolving infection and C1-2 subluxation which may compress the medulla and cause motor or sensory deficits [4]. 
     If you are looking more specifically for epidural abscesses study the post contrast MRI for

• Enhancement of disc and adjacent bone
• Diffuse enhancement of disc/vertebra complex
• Peripheral enhancement around pus collection
• Dural enhancement
• Prominence of epidural venous plexus

     The sensitivity of MRI for epidural abscess is over 90% [6].

References:

1. Chelsom J, Solberg CO: Vertebral osteomyelitis at a Norwegian University hospital 1987–97: clinical features, laboratory findingsand outcome. Scand J Infect Dis. 1998;30(2):147-51. [Medline]
2. Jensen AG, Espersen F, Skinhoj P, Rosdahl VT, Frimodt-Moller N: Increasing frequency of vertebral osteomyelitis following Staphylococcus aureus bacteraemia in Denmark 1980–1990. J Infect. 1997 Mar;34(2):113-8. [Medline]
3. Schimmer RC, Jeanneret C, Nunley PD, Jeanneret B: Osteomyelitis of the cervical spine: a potentially dramatic disease. J Spinal Disord Tech. 2002 Apr;15(2):110-7. [Medline]
4. Ross J, Brant-Zawadzki M, Chen M, Moore K, Salzman K. Diagnostic Imaging: Spine, 1st ed. Amirsys Inc: Altona, 2004. III: 1-14 to 17.
5. Sexton DJ. Uptodate.com 2005.
6. Castillo M. The Core Curriculum: Neuroradiology.  Lippincott Williams & Wilkins, Philadelphia: 2002, 378-384.