During routine anatomical dissection of the right lower limb of a 68-year-old male cadaver, a rare muscle variation was revealed and identified as an accessory piriformis muscle. This variant muscle started from the anterior surface of the sacrum below the usual piriformis muscle and extended in a well-identifiable lateral tendon also inserting to the greater trochanter of the femur. In the case described, the accessory piriformis pierced through the proximal part of the sciatic nerve. The length of the additional small muscle was 85 mm with the broadest part of the muscle belly as 9 mm. The course of the variant muscle, especially its tendinous part, might irritate the sciatic nerve and cause piriformis syndrome and other sciatica-like symptoms. The neurologists who diagnose piriformis syndrome and surgeons performing nerve releasing surgery should be well aware of the described rare muscle variation.
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