Non-formation of the main trunk of the sciatic nerve and unusual relationships to the piriformis muscle

Abstract

Background: The sciatic nerve is the largest branch of the sacral plexus. Variations of its origin, exit from the pelvis, emergence and branching in the posterior region of the thigh, especially in regards to the piriformis muscle, are an object of interest due to the possibility to be involved in the pathogenensis of clinically significant non-discogenic sciatica or piriformis syndrome. Case report: We present a case of variant anatomy of the sciatic nerve, discovered during routine dissection of the left gluteal region of an adult female cadaver. We observed a non-formation of the main trunk of the nerve; rather, the tibial nerve passed inferiorly to the piriformis muscle, while the common peroneal nerve went through the body of the bifid piriformis muscle, immediately next to its tendon. The two branches continued their course in the thigh without joining and forming a proper sciatic nerve. The medical records of the body donor did not reveal any neurological impairment which could be linked to this anatomical peculiarity. Conclusion: The anatomy of the sciatic nerve could be considered to be a factor of clinical significance. The high prevalence of similar anatomical variations should be kept in mind during the diagnostic process of clinical entities involving the sciatic nerve.

Keywords

• Sciatic nerve
• piriformis muscle
• variation