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Piriformis Fossa Space

recessus piriformis

The piriformis fossa is the space within the greater sciatic foramen through which the piriformis muscle, the sciatic nerve, the superior and inferior gluteal vessels and nerves, the pudendal nerve, the posterior femoral cutaneous nerve, and the nerves to the obturator internus and quadratus femoris all exit the pelvis. The piriformis muscle exits through the upper part of the foramen; the sciatic nerve exits just below or through the piriformis in its various anatomical relationships.

Region: Pelvis & Hip

Clinical Relevance

Clinical Notes

The piriformis fossa and its neurovascular contents are relevant in deep gluteal syndrome and piriformis syndrome, where space-occupying lesions or muscle hypertrophy compress the sciatic nerve within the greater sciatic foramen. MRI of the piriformis fossa in prone position demonstrates the sciatic nerve relationship to the piriformis. Piriformis injection under CT or ultrasound guidance targets this space. The piriformis fossa is also relevant in posterior hip approaches for arthroplasty, where the piriformis tendon is the primary landmark identifying the sciatic nerve and the hip joint posterior capsule.

Pathology

Common Injuries & Conditions

Deep Gluteal Syndrome from Space Occupation in Piriformis Fossa

Piriformis hypertrophy, fibrovascular bands, or masses within the greater sciatic foramen space compress the sciatic nerve producing deep gluteal pain and sciatica indistinguishable from disc herniation; MRI in the prone position demonstrates nerve compression within the fossa and endoscopic piriformis release or decompression of the fossa space provides relief.