Infection Inflammation

ANKYLOSING SPONDYLITIS (SERONEGATIVE SPONDYLOARTHROPATHY)

KEYFACTS

This disease occurs predominantly in young men and is associated with histocompatibility antigen B27.

Ankylosing spondylitis is found in 1.4% of the population (particularly white Europeans or individuals of European descent).

Sacroiliitis is often the first manifestation followed by ankylosis of the lumbar and thoracic spine and ligamentous laxity (atlantoaxial subluxation), fractures, and epidural hematoma.

Complications: fractures (“banana” type), spontaneous epidural hematoma, erosive arachnoiditis with cauda equine syndrome, spinal cord infarctions, destructive noninfectious process (amyloidosis).

Main differential diagnosis: DISH, juvenile rheumatoid arthritis, infectious sacroiliitis, retinoid-induced changes.

FIGURE 24-1. Lateral cervical spine radiograph shows fusion of vertebral bodies by anterior syn-desmophytes. The facet joints are also diffusely fused.

FIGURE 24-2. Mldsaglttal T2, In the same patient, shows vertebral body fusion and partia disc reabsorption.

FIGURE 24-3. Midsagittal T1, in a different patient, shows fusion of lumbar vertebra, disc obliteration, and widening of the canal.

FIGURE 24-4. Axial T2, in the same patient, shows erosive changes in bone and nerve root clumping secondary to arachnoiditis.

FIGURE 24-5. Midsagittal CT reformation, in a different patient, shows fracture through the C6-7 disc.

FIGURE 24-6. Midsagittal CT reformation, in a different patient, shows severely displaced C5 involving both of its disc spaces.

SUGGESTED READING

Wang Y-F, Teng MM-H, Chang CY, Wu HT, Wang ST. Imaging manifestations of spinal fractures in ankylosing spondylitis. Am J Neuroradiol 2005;26:2067–2076.

SPONDYUTIS AND DISCITIS, PYOGENIC

KEYFACTS

Most adult spinal infections are caused by Staphylococcus aureus (60%, even in patients with AIDS), Enterobacter spp. (30%), Escherichia coli, Pseudomonas, and KLebsietta organisms.

Most cases of discitis and osteomyelitis arise from hematogenous dissemination (e.g., drug users and immunodepressed patients), ascending route (genitourinary tract manipulations), and direct inoculation (traumatic injuries and postsurgical).

In adults, the infection begins in the vertebral end-plates, while in children, the infection begins in the disc.

Discitis and osteomyelitis are usually seen in men between the sixth and seventh decades of life; the presenting symptoms are nonspecific (e.g., fever, pain, and elevated erythrocyte sedimentation rate).

Plain films are not sensitive and remain normal 7 to 10 days after onset of symptoms; magnetic resonance imaging (MBI) is the most reliable modality.

One-level involvement: 60% to 70%; involvement of multiple adjacent levels: 20%; multiple scattered level involvement: 10%.

Main differential diagnosis: degenerative changes, Schmorl node, trauma, hemodialysis (amyloid) arthropathy, tuberculosis, brucellosis, fungus.

FIGURE 24-7. Sagittal T2 shows bright L1-L2 disc with erosion of end-plates and edema in bone marrow.

FIGURE 24-8. Corresponding postcontrast T1 shows disc enhancement and phlegmon in epidural space compressing the cauda equina.

FIGURE 24-9. Axial postcontrast T1, in the same patient, shows extensive patchy disc enhancement, thick and enhancing epidural space, and extension of inflammatory process to the perispinal region including the psoas muscles.