24 - Bilateral High Bifurcation of the Sciatic Nerves That Passed Between Two Heads of the Piriformis Muscle in a 92 Year-Old White Female Donor Cadaver

Poster Board Number: 24
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Abstract Body : INTRODUCTION & OBJECTIVE
The sciatic nerve traditionally exits the pelvis deep to the piriformis muscle and tracks down as a single nerve until it reaches the popliteal fossa, wherein it bifurcates into the common fibular (peroneal) nerve and the tibial nerve. We hereby present findings of a bilateral high sciatic nerve bifurcation, the branches of which pass through the two heads of the piriformis muscle (split nerve / split muscle configuration). These findings have diagnostic (chronic pelvic pain syndromes), procedural (sciatic nerve block), and surgical (entrapment neuropathy) implications.

MATERIAL AND METHODS
We encountered a donor cadaver with bilateral sciatic nerve high bifurcation passing through the two heads of the piriformis muscles (split nerve/split muscle configuration) during routine anatomical dissection in the 2022 first-year medical student musculoskeletal anatomy course at the Uniformed Services University of the Health Sciences. The bifurcation occurred immediately above the greater sciatic foramen. One faculty member completed the dissection as a prosection for the musculoskeletal course. We conducted an additional literature review in an effort to further characterize the incidence, prevalence, and clinical implications of sciatic nerve anatomical variations.

RESULTS
Based on our case study, we will be evaluating a cohort of 48 cadavers (43 student-dissected plus 5 faculty-dissected prosections) plus 23 hemisected or complete- dissected pelvises (during the Reproductive Endocrinology module). We will describe and quantify the prevalence of high bifurcation sciatic nerve variations and the involvement of the piriformis muscle.

CONCLUSION
This case report highlights the clinical relevance of early or high sciatic nerve bifurcation above its usual location in the popliteal fossa. Our findings have potentially important clinical diagnostic, procedural and treatment implications for chronic pelvic pain syndrome, including, but not limited to, piriformis syndrome.

SIGNIFICANCE/IMPLICATION
Variations in the location of the sciatic nerve bifurcation into the common fibular (peroneal) nerve and tibial nerve can have both surgical and pathological implications. Popliteal sciatic nerve blocks involve placing a catheter within the sciatic nerve sheath in the popliteal fossa to anesthetize the sciatic nerve. The location of the sciatic nerve division into the tibial and common fibular nerves can be variable, ranging from the upper gluteal region down to the popliteal fossa. Pathologically, a high sciatic nerve bifurcation can result in nerve fibers piercing the piriformis muscle, producing symptoms of buttock and leg pain seen in piriformis syndrome. A deeper understanding of this high bifurcation and its consequences is crucial for anesthetists to safely and successfully perform the popliteal sciatic nerve block. This understanding is also important to aid in accurate diagnosis and effective treatment of piriformis syndrome.