Skeletal Radiology

, Volume 46, Issue 6, pp 751–757 | Cite as

Detection and prevalence of variant sciatic nerve anatomy in relation to the piriformis muscle on MRI

  • Vanja VarenikaEmail author
  • Amelie M. Lutz
  • Christopher F. Beaulieu
  • Matthew D. Bucknor
Scientific Article



To determine whether known variant anatomical relationships between the sciatic nerve and piriformis muscle can be identified on routine MRI studies of the hip and to establish their imaging prevalence.


Hip MRI studies acquired over a period of 4 years at two medical centers underwent retrospective interpretation. Anatomical relationship between the sciatic nerve and the piriformis muscle was categorized according to the Beaton and Anson classification system. The presence of a split sciatic nerve at the level of the ischial tuberosity was also recorded.


A total of 755 consecutive scans were reviewed. Conventional anatomy (type I), in which an undivided sciatic nerve passes below the piriformis muscle, was identified in 87% of cases. The remaining 13% of cases demonstrated a type II pattern in which one division of the sciatic nerve passes through the piriformis whereas the second passes below. Only two other instances of variant anatomy were identified (both type III). Most variant cases were associated with a split sciatic nerve at the level of the ischial tuberosity (73 out of 111, 65.8%). By contrast, only 6% of cases demonstrated a split sciatic nerve at this level in the context of otherwise conventional anatomy.


Anatomical variations of the sciatic nerve course in relation to the piriformis muscle are frequently identified on routine MRI of the hips, occurring in 12–20% of scans reviewed. Almost all variants identified were type II. The ability to recognize variant sciatic nerve courses on MRI may prove useful in optimal treatment planning.


Sciatic nerve Variant anatomy Piriformis MRI 


Compliance with ethical standards

Conflicts of interest

The authors report that they have no conflicts of interest concerning the materials or methods used in this study or the findings specified in this paper.


  1. 1.
    Konstantinou K, Dunn KM. Sciatica: review of epidemiological studies and prevalence estimates. Spine. 2008;33(22):2464–72.CrossRefPubMedGoogle Scholar
  2. 2.
    Fishman LM, Schaefer MP. The piriformis syndrome is underdiagnosed. Muscle Nerve. 2003;28(5):646–9.CrossRefPubMedGoogle Scholar
  3. 3.
    Papadopoulos EC, Khan SN. Piriformis syndrome and low back pain: a new classification and review of the literature. Orthop Clin North Am. 2004;35(1):65–71.CrossRefPubMedGoogle Scholar
  4. 4.
    Hallin RP. Sciatic pain and the piriformis muscle. Postgrad Med. 1983;74(2):69–72.CrossRefPubMedGoogle Scholar
  5. 5.
    Kosukegawa I, Yoshimoto M, Isogai S, Nonaka S, Yamashita T. Piriformis syndrome resulting from a rare anatomic variation. Spine (Phila PA 1976). 2006;31(18):E664–6.CrossRefGoogle Scholar
  6. 6.
    Beaton LE, Anson BJ. The relation of the sciatic nerve and its subdivisions to the piriformis muscle. Anat Rec. 1937;70:1–5.CrossRefGoogle Scholar
  7. 7.
    Natsis K, Totlis T, Konstantinidis GA, Paraskevas G, Piagkou M, Koebke J. Anatomical variations between the sciatic nerve and the piriformis muscle: a contribution to surgical anatomy in piriformis syndrome. Surg Radiol Anat. 2014;36(3):273–80.CrossRefPubMedGoogle Scholar
  8. 8.
    Kraus E, Tenforde AS, Beaulieu CF, Ratliff J, Fredericson M. Piriformis syndrome with variant sciatic nerve anatomy: a case report. PM R. 2016;8(2):176–9.CrossRefPubMedGoogle Scholar
  9. 9.
    Cassidy L, Walters A, Bubb K, Shoja MM, Tubbs RS, Loukas M. Piriformis syndrome: implications of anatomical variations, diagnostic techniques, and treatment options. Surg Radiol Anat. 2012;34(6):479–86.CrossRefPubMedGoogle Scholar
  10. 10.
    Chhabra A, Chalian M, Soldatos T, Andreisek G, Faridian-Aragh N, Williams E, et al. 3-T high-resolution MR neurography of sciatic neuropathy. AJR Am J Roentgenol. 2012;198(4):W357–64.CrossRefPubMedGoogle Scholar

Copyright information

© ISS 2017

Authors and Affiliations

  • Vanja Varenika
    • 1
    Email author
  • Amelie M. Lutz
    • 2
  • Christopher F. Beaulieu
    • 2
  • Matthew D. Bucknor
    • 1
  1. 1.Department of Radiology and Biomedical ImagingUniversity of California, San FranciscoSan FranciscoUSA
  2. 2.Department of RadiologyStanford University School of MedicineStanfordUSA

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