Presentation
Painful sensation in left buttocks while sitting.
Patient Data
The piriformis muscle of the patient are symmetrical in appearance without hypertrophy, fatty atrophy, muscle oedema or denervation. However, the left sciatic nerve demonstrates anterior and posterior divisions, passing above and below the left piriformis muscle which is a development variant. A normal sciatic nerve passes below the piriformis muscle, exiting the greater sciatic foramen as seen on the right.
The patient presented with piriformis syndrome symptoms, with this development variant being the only finding. This indicates possible compression while sitting due to the sciatic nerve passing through the piriformis muscle resulting in the left buttock pain.
Arrows point to difference in anatomical variance of sciatic nerve.
Case Discussion
The piriformis muscle is an oblique, flat muscle which runs from the lower spine to the top of the thigh. This muscle originates from the anterior (S2-S4) surface of the vertebrae and inserts on the hip bone's greater trochanter. It is adjacent to the sciatic nerve, and hypertrophy, inflammation or irritation of the muscle can cause it to irritate this sciatic nerve due to its proximity to the muscle. In piriformis syndrome, this sciatic nerve is entrapped or irritated by the piriformis muscle when sitting particularly, as the muscle presses against the sciatic nerve. In normal cases, this is due to hypertrophy or trauma but in rare cases, early division of the sciatic nerve as an anatomic variant can predispose people to piriformis syndrome 1.
In terms of anatomical variants, the main 3 that can predispose patients to piriformis syndrome, in order of most common to least, are: The sciatic nerve division passing through and below the piriformis muscle (case observed above), the sciatic nerve divisions passing above and below and the sciatic nerve emerging through the muscle. Patients with these anatomical variants can be asymptomatic until hypertrophy of the piriformis muscle causes the syndrome 2.
The symptoms include sciatica, chronic buttock and hip pain which worsens with hip movements or prolonged sitting 1.
The left sciatic nerve was scanned using a proprietary nerve view stir pulse allowing for greater clarity of the anatomical variant which suggests piriformis syndrome in line with the patient symptoms.
Case Courtesy of Dr. Zane Sherif and Mr. Ben Kennedy
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