The relation of sacral nerve roots to the piriformis muscle

Li A L K1, Cancelliere L1, Sermer C1, Balica A2, Campian E C3, Morozov V4, Fernandes G L5, Girão M J B C6, Moretti-Marques R7, Shaubi M8, Peng P1, Lemos N9

Research Type

Pure and Applied Science / Translational

Abstract Category

Anatomy / Biomechanics

Abstract 550
Open Discussion ePosters
Scientific Open Discussion Session 28
Friday 31st August 2018
13:15 - 13:20 (ePoster Station 6)
Exhibition Hall
Anatomy Biomechanics Pain, other Pain, Pelvic/Perineal Urgency Urinary Incontinence
1. University of Toronto, 2. Rutgers Robert Wood Johnson Medical School, 3. Saint Louis University, 4. Georgetown University, 5. Federal University of Sao Paulo, Santa Casa of Sao Paulo School of Medical Sciences, 6. Federal Universi, 7. Federal unive, 8. Univer, 9. University of Toronto, Federal University of Sao Paulo

Adrienne L K Li




Hypothesis / aims of study
First described in 1937 (1), piriformis syndrome is caused by abnormal piriformis bundles compressing the sciatic nerve, leading to pain in the buttocks, hips, and/or lower limbs and lower urinary tract symptoms. Beaton and Anson reported six possible relations between the sciatic nerve and its subdivisions to the piriformis muscle. Cadaver studies have found that these anatomical variations range 6.4 – 15.8% (1,2). More recently, intrapelvic entrapment of sacral nerve roots by abnormal bundles of the piriformis muscles have been described as a possible cause of pudendal neuralgia, lower urinary tract symptoms and sciatica (3)(Figure). However, the intrapelvic portions of the lumbosacral plexus and sacral nerve roots involved in anatomic variations of the piriformis muscles have not yet been reported.
Study design, materials and methods
A study of 32 female cadavers donated to an academic institution for medical education was undertaken. Laparoscopic pelvic dissections were performed, using standard laparoscopic techniques including Veress entry with closed intraperitoneal insufflation. Lateral and suprapubic ports were placed. Retroperitoneal dissection was undertaken using sharp and vessel-sealing instruments. Dissection was performed by gynecology faculty, fellows, and residents, under the supervision of faculty selected for their experience in minimally invasive gynecologic surgery. The quality of visualization was similar to an intraoperative dissection.  
	Of 32 cadavers, 29 had bilateral dissections, thus providing 61 total sites for analysis. Data was collected in native pairs. After dissecting the presacral space, the piriformis muscle was identified and followed to determine if any sacral nerve roots were entrapped by abnormal muscles bundles. In particular, we identified the specific nerve roots affected.
Anatomical variations were seen in 12 of 32 cadavers (37.5%, 95% CI 
20.73, 54.27). None had bilateral variants. Of the twelve variations, five were on the left, and seven on the right. The nerve root most involved was S3 (9/12), followed by S2 (11/12), S1 (5/12), and S4 (2/12).
Interpretation of results
This cadaver study reveals that intrapelvic piriformis anatomical variations that could lead to piriformis syndrome exists in the general population at a prevalence of 37.5%, which is much higher than most reports. This may be due to limitations in the six types described by Beaton and Anson (1).
Concluding message
Knowledge of the possible anatomical variations can greatly aid diagnosis of sciatica and pudendal neuralgia, neurogenic pelvic floor dysfunction and lower urinary tract symptoms.
Figure 1
  1. Beaton LE and BJ Anson. The relation of the sciatic nerve and of its subdivisions to the piriformis muscle. The anatomical record. 1937(70): 1-5.
  2. Natsis K, Totlis T, Konstantinidis GA et al. Anatomical variations between the sciatic nerve and the piriformis muscle: a contribution to surgical anatomy in piriformis syndrome. Surg Radiol Anat. 2014(36): 273-80.
  3. Lemos N, Papillon-Smith J, Moretti-Marques R, Fernandes G, Girao M, Solnik J. Intrapelvic nerve entrapment as a cause of pelvic floor dysfuction and refractory pudendal pain: a review of 50 cases. IN: 47th Annual Meeting of the International Continence Society, 2017, Florence. Neurourology & Urodynamics. Wiley, 2017. v.36(S3). p.S212 – S213
Funding None Clinical Trial No Subjects Human Ethics not Req'd REB in the institution does not require previous authorization for cadaver studies. Helsinki Yes Informed Consent No
07/06/2024 20:04:15