MRIs Are Less Accurate Tools for the Most Critically Worrisome Pedicles Compared to CT Scans

Retrospective review of magnetic resonance imaging (MRI) and computed tomographic (CT) scan imaging modalities.

To determine MRI's capability of identifying pedicle morphology.

Understanding pedicle morphology is important for accurate placement of pedicle screws. The gold standard modality to assess pedicle morphology is CT scan. However, CT scans carry the risk of radiation exposure. We have studied MRI as a potential alternative to CT scan.

Nine hundred seventy pedicles in 33 spinal deformity patients were reviewed. Pedicle morphology was classified as follows: Type A (normal pedicle): >4-mm cancellous channel; Type B: 2-4-mm channel; Type C: any size cortical channel; and Type D: <2-mm cortical or cancellous channel. Pedicles in the same patients were classified on both low-dose CT scan and MRI. Concordance and discordance rates of MRI relative to CT scan in classification of pedicles into types A, B, C, and D were calculated for the entire length of the thoracolumbar spine and subgrouped into spinal sections. All images were evaluated by a single fellowship-trained musculoskeletal radiologist.

CT scan had 809 Type A, 126 Type B, 29 Type C, and 6 Type D pedicles. Group II (MRI) had 735 Type A, 203 Type B, 30 Type C, and 2 Type D pedicles. Analysis of the entire spinal column showed a concordance rate of 86.7% in classification of the pedicles into the 4 types. In the upper thoracic region, the concordance rate was 77.1%, main thoracic 85.5%, thoracolumbar 96%, and lumbar 98.1%. MRI has a poor overall accuracy for detecting Type C pedicles, only a 44.8% concordance with CT scan. MRI overcalls Type B pedicles, often calling Type A pedicles Type B.

MRI is an inferior alternative to CT scan as it has poor accuracy to properly detect pedicle abnormalities. The more severe the pedicle abnormality, the less diagnostic value the MRI has.

Level III, diagnostic.