Findings: A technetium 99m-MBP bone scan was performed with additional SPECT images through the lumbosacral spine. The planar images show a mild focal area of increased activity in the posterior process of the L5 vertebra bilaterally. The coronal and axial SPECT images show intense bilateral focal uptake in the pars interarticularis.

Diagnosis: Bilateral spondylolysis at L5.

Discussion: Discussion: Spondylolysis is defined as a defect in the pars articularis which is the weakest portion of the vertebra. The great majority (90%) of pars defects occur at the L5 level. Less common levels are L4 and L3. When the defects are bilateral, spondylolisthesis may subsequently occur. Spondylolisthesis occurs in roughly two-thirds of adults with bilateral pars defects. The etiology of spondylolysis is not fully known. However, common theories include that this may result from fatigue fracture related to repetitive trauma. The pars interarticularis may be hypoplastic making it prone to fractures. Pars defects are associated with athletes involved in contact sports. Also, more than 50% of individuals with pars defects have other family members with this disorder. This suggests that hereditary factors play a role in the pathogenesis as well as traumatic factors.

Radiographic evaluation of spondylolysis is best shown on oblique radiographs of the lumbar spine. However, this is the least sensitive examination. On a radionuclide bone imaging examination, planar images may show areas of increased radiopharmaceutical activity localized to the spine. However, planar imaging is significantly less sensitive than SPECT (emission tomographic images). This may be related to the overlap of multiple osseous structures on the planar imaging. Therefore, the scintigraphic evaluation of low back pain requires SPECT imaging. On the SPECT images, abnormal activity can be localized to the pars. This is related to increased osteoblastic activity.

Treatment of a pars defect in a child often requires a back-brace and follow-up imaging demonstrates resolution of the scinitigraphic abnormality, often with simultaneous resolution of symptoms. This usually occurs over a period one year.

References:
Murray JPC, Ell PJ. Nuclear Medicine and Clinical Diagnosis and
Treatment. Churchill-Livingstone; 1994:1019-1021.

Sty, Wells, Conway. Spine Pain in Children, Seminars in Nuclear Medicine, 1993.

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