Osteomyelitis of the Spine

Osteomyelitis of the spine (pyogenic spondyli-tis) typically affects adults. The main causative agents include S. aureus and streptococcus, and rarely gram-negative bacilli and salmonella. Pyogenic spondylitis may result from the direct implantation of organisms at the time of operation. However, in the vast majority the infection is blood-borne. The organisms are introduced through the arterial rather than venous pathway, and the early foci are located in the subchondral zone or the endplate of the vertebral body, the area richly supplied with nutrient endarteries (the equivalent of the long bone metaphysis). Clinically, the infection starts in the subchondral zone of one of the midlumbar vertebrae and rapidly spreads to the apposing vertebra above or below across the disk. In the course of the spreading the disk is inescapably involved, producing infective (pyogenic) diskitis. Pyogenic spondylitis almost always involves two neighboring vertebrae in a set, and in only less than 1% of cases is it confined to one vertebra and one disk.

Radiographically, acute infective spondylitis with diskitis is characterized by the osteolysis of apposing endplates with a narrowed intervertebral space (Fig. 6.27B). The early lytic focus in the anterior rim of the vertebral endzone may not be seen easily, and conventional or computed tomography is often required. Indeed, such a lesion is one of the most important indications for bone scintigraphy (see below). Later in the chronic or healed stage, osteosclerosis may ensue.

Ordinary scintigraphy shows simple blocklike uptake in infective spondylitis, not distinguishing the individual components of the disease. Pinhole scintigraphy, however, can localize the abnormal uptake to the endplates of the affected vertebrae with visualization of the disk space in between. In the acute and subacute stages, tracer distribution is typically unequal between the two apposing endplates (Fig. 6.27A). Thus, the classic hematogenous form of spinal infection may indicate the sequence of infection: a dominant tracer uptake in the initially affected upper endplate of a cau-dally situated vertebra and less extensive uptake in the subsequently affected lower endplate of a cranially situated vertebra. At this stage, the disk space is invariably narrowed due to diskitis. The sequence of infection may be reversed in the direct implantation type, yet the basic features including the dominant initial focus, narrowed disk space, and less dominant secondary focus may remain the same (Fig. 6.28). When spondylitis is established, tracer accumulates in the entire span of the apposing endplates, giving rise to the sandwichlike appearance (Bahk et al. 1987). Old or longstanding lesions develop spurs at the vertebral edge, manifesting as horizontally aligned "hot" beaking. One condition that may resemble chronic pyogenic spondylitis with endplate sclerosis is spondylosis. However, the latter disorder strongly tends to involve the lower-most lumbar vertebrae and the sacrum, manifesting parallel band-like or arcuate uptake in the end-

Upper Endplate Vertebra

Fig. 6.27A, B Asymmetrical endplate involvement in acute, hematogenous, pyogenic spondylitis. A Posterior pinhole scintigraph of L2 and L3 vertebrae in a 53-year-old man with back pain reveals extensive area of intense tracer uptake in the dominant, initial infection in the upper half of the L3 vertebra and less intense change in the recessive, secondary focus in the lower endplate of the L2 vertebra. The disk space is narrowed (arrows). B Conventional anteroposterior X-ray tomogram shows lysis in the initial infection site of the L3 vertebra (open arrows) and mild shagginess in the secondarily involved L2 vertebra (arrowheads)

Fig. 6.27A, B Asymmetrical endplate involvement in acute, hematogenous, pyogenic spondylitis. A Posterior pinhole scintigraph of L2 and L3 vertebrae in a 53-year-old man with back pain reveals extensive area of intense tracer uptake in the dominant, initial infection in the upper half of the L3 vertebra and less intense change in the recessive, secondary focus in the lower endplate of the L2 vertebra. The disk space is narrowed (arrows). B Conventional anteroposterior X-ray tomogram shows lysis in the initial infection site of the L3 vertebra (open arrows) and mild shagginess in the secondarily involved L2 vertebra (arrowheads)

Xray Spondylitis

Fig. 6.28 Reversed asymmetry of the endplate involvement in postoperative spondylitis. Lateral pinhole scan of the midlumbar spine in a 20-year-old man with gramnegative bacillary spondylitis that started after laminec-tomy shows intense, semilunar tracer uptake in the initial focus in the lower L3 vertebral body (arrows) and less intense uptake in the upper endplate of the secondarily affected L4 vertebra. The disk space is narrowed (arrowheads)

Fig. 6.28 Reversed asymmetry of the endplate involvement in postoperative spondylitis. Lateral pinhole scan of the midlumbar spine in a 20-year-old man with gramnegative bacillary spondylitis that started after laminec-tomy shows intense, semilunar tracer uptake in the initial focus in the lower L3 vertebral body (arrows) and less intense uptake in the upper endplate of the secondarily affected L4 vertebra. The disk space is narrowed (arrowheads)

What Vertebral Endplate

Fig. 6.29 Parallelism of the endplate involvement in spondylosis. Anterior pinhole scan of the lower lumbar spine in a 42-year-old woman with lumbago demonstrates parallel arcuate tracer uptake in the lower endplate of the L4 vertebra and the upper endplate of the L5 vertebra (arrows). The intervertebral disk space is narrowed due to disk degeneration

Fig. 6.29 Parallelism of the endplate involvement in spondylosis. Anterior pinhole scan of the lower lumbar spine in a 42-year-old woman with lumbago demonstrates parallel arcuate tracer uptake in the lower endplate of the L4 vertebra and the upper endplate of the L5 vertebra (arrows). The intervertebral disk space is narrowed due to disk degeneration

Compresion Fracture Picture

Fig. 6.30 (Uni)concave and biconcave endplate deformities in spinal compression fractures. Posterior pinhole scan of the lumbar spine in an elderly woman with marked osteoporosis shows biconcave deformity in the L2 vertebra (open arrows) and (uni)concave deformity in L4 due to compression fractures (arrow). The former fractures were older than the latter, and hence show less intense tracer uptake. Note that the disk spaces are not narrowed

Fig. 6.30 (Uni)concave and biconcave endplate deformities in spinal compression fractures. Posterior pinhole scan of the lumbar spine in an elderly woman with marked osteoporosis shows biconcave deformity in the L2 vertebra (open arrows) and (uni)concave deformity in L4 due to compression fractures (arrow). The former fractures were older than the latter, and hence show less intense tracer uptake. Note that the disk spaces are not narrowed plates with a narrowed disk space (Fig. 6.29). Another confusing condition is the "fish vertebra" deformity of porotic vertebrae, but the depressed or concave "hot" endplate with a widened disk space is pathognomonic (Fig. 6.30). The radiographic and scintigraphic manifestations of tuberculous spondylitis are essentially the same as those of acute pyogenic spondylitis except for a few minor differences, which are discussed in the following section.

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Responses

  • Alan Wallace
    What does intense tracer uptake in spinal endplates indicate?
    3 years ago

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