Magnetic resonance imaging of the sacral plexus and piriformis muscles

J. Matthew Russell, Mark J. Kransdorf, Laura W. Bancroft, Jeffrey J. Peterson, Thomas H. Berquist, Mellena D. Bridges

Research output: Contribution to journalArticle

29 Scopus citations

Abstract

Objective: The objective was to evaluate the piriformis muscles and their relationship to the sacral nerve roots on T1-weighted MRI in patients with no history or clinical suspicion of piriformis syndrome. Patients and methods: Axial oblique and sagittal T1-weighted images of the sacrum were obtained in 100 sequential patients (200 pairs of sacral roots) undergoing routine MRI examinations. The relationship of the sacral nerve roots to the piriformis muscles and piriformis muscle size were evaluated, as were clinical symptoms via a questionnaire. Results: The S1 nerve roots were located above the piriformis muscle in 99.5% of cases (n=199). The S2 nerve roots were located above the piriformis muscle in 25% of cases (n=50), and traversed the muscle in 75% (n=150). The S3 nerve roots were located above the piriformis muscle in 0.5% of cases (n=1), below the muscle in 2.5% (n=5), and traversed the muscle in 97% (n=194). The S4 nerve roots were located below the muscle in 95% (n=190). The piriformis muscles ranged in size from 0.8-3.2 cm, with an average size of 1.9 cm. Nineteen percent of patients had greater than 3 mm of asymmetry in the size of the piriformis muscle, with a maximum asymmetry of 8 mm noted. Conclusion: The S1 nerve roots course above the piriformis muscle in more than 99% of patients. The S2 roots traverse the piriformis muscle in 75% of patients. The S3 nerve roots traverse the piriformis muscle in 97% of patients. Piriformis muscle size asymmetry is common, with muscle asymmetry of up to 8 mm identified.

Original languageEnglish (US)
Pages (from-to)709-713
Number of pages5
JournalSkeletal Radiology
Volume37
Issue number8
DOIs
StatePublished - Aug 1 2008

Keywords

  • Anatomy
  • MRI
  • Piriformis muscle
  • Piriformis syndrome
  • Sacral plexus
  • Sciatic nerve

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging

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    Russell, J. M., Kransdorf, M. J., Bancroft, L. W., Peterson, J. J., Berquist, T. H., & Bridges, M. D. (2008). Magnetic resonance imaging of the sacral plexus and piriformis muscles. Skeletal Radiology, 37(8), 709-713. https://doi.org/10.1007/s00256-008-0486-8