In adults, vertebral osteomyelitis is the result of hematogenous seeding of the subchondral bone of the vertebral body (43). Patients with urinary tract infections, intravenous drug use, spinal surgery, dental infections, and abdominal and pelvic surgery are at increased risk of bacteremia. Presumably this results in septic emboli lodging in the end-arteriole in the vertebral body metaphysics (44). The areas of the vertebral metaphysis supplied by the end-arterioles undergo septic infarction with subsequent osteomyelitis. There is no direct route of communication with the intervertebral disc which becomes involved following the destruction of bone (43).
Disc space infections are associated with direct inoculation of bacteria into the disc space. Disc space infections are seen most often following surgical removal of the nucleous pulposus but can also be associated with spinal tap, myelography, and discography. Although disc space infection and vertebral osteomyelitis differ in route of infection, their clinical course and findings are similar (43).
Indium-111-leukocyte scanning is neither sensitive nor specific in the diagnosis of osteomyelitis (45,46). Palestro et al. performed 76 indium-111-leukocyte scans in 71 patients with suspected vertebral osteomyelitis (46). When increased activity of the vertebral body was seen it was highly specific for osteomyelitis (98%). Unfortunately, increased activity was seen infrequently (sensitivity of 39%). More than half (54%) of the patients with vertebral osteomyelitis had a photopenic defect on the indium-111-leukocyte scan. Photopenic defects were neither sensitive (54%) nor specific (52%) for infection. The cause of the failure of indium-111-leukocyte migration is uncertain, but has been postulated to be due to infection-induced occlusion of the microcirculation (47)
and death of the reticuloendothelial cells that normally accumulate leukocytes (40).
Gallium scintigraphy is the preferred radionuclide study in the evaluation of patients for either vertebral osteomyelitis or disc space infections. Bruschwein et al. evaluated planar gallium scanning in 100 consecutive patients with suspected disc-space infection. Planar gallium scintigraphy was sensitive (89%), specific (85%), and accurate (86%) in detecting disc-space infection (48). Modic et al. compared MRI with combined gallium and bone scanning and found that the sensitivity (96% vs 90%), specificity (92% vs 100%), and accuracy (94% vs 94%) were similar (49). MRI, however, provided additional information regarding the neural structure, the discs, and the paravertebral regions (49). Love et al. compared bone and gallium scintigraphy and MRI in the diagnosis of vertebral osteomyelitis in 22 patients (50). Gallium SPECT imaging was more accurate than planar gallium scintigraphy, planar bone scintigraphy, and SPECT bone scintigraphy. SPECT gallium scintigraphy was as sensitive for vertebral osteomyelitis as MRI (91% vs 91%). It was slightly, but not significantly, more spe cific (92% vs 77%). The authors concluded that, although MRI is the procedure of choice, SPECT gallium is an excellent alternative exam to use in patients with pacemakers or orthopedic hardware. It is also a useful complementary test for patients in whom the diagnosis is uncertain (Figs. 4 and 5).
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