Routine thin slice MRI effectively demonstrates the lumbar pars interarticularis.

AIM: To confirm that routine thin slice sagittal magnetic resonance imaging (MRI) of the lumbar spine effectively demonstrates the lumbar pars interarticularis.
METHOD: A retrospective review of 100 MRI examinations was carried out and the appearance of the pars interarticularis at L4 and L5 bilaterally was assessed and classified as Type 1 - normal, Type 2 - sclerotic pars, Type 3 - not assessable and Type 4 - pars defect. A total of 400 pars were assessed. Those with known or obvious lytic spondylolysis were excluded from the study. All MRI examinations had both sagittal T1- and T2- weighted sequences and both were assessed. Sagittal T1 sequences were carried out with a 3 mm slice thickness and T2 image sequences with a 4 mm slice thickness.
RESULTS: The total number of pars assessed as normal (Type 1) was 299 (75%) of the T1-weighted images; 80 (20%) were classified Type 2. On T2-weighted imaging 290 (72.5%) were Type 1 and 66 (16.5%) were Type 2. Both of these types of appearances correlate well with the finding of a normal pars interarticularis. Thus, 379 (95%) of the pars appeared normal on T1-weighting and 356 (89%) on T2-weighting.
CONCLUSION: Contrary to previous findings with 5 mm thick slices, routine thin slice sagittal T1 and T2 images effectively demonstrate the pars interarticularis, with acceptable data acquisition times and image quality. We believe this is mainly due to the thinner slices obtained in our series.