Case Report: An Infrequent Anatomical Variation of the Sciatic Nerve and its Potential Clinical Complications

Abstract

The sciatic nerve (SN) is the largest peripheral nerve of the human body, responsible for most of the motor innervation of the perineum and lower limb. Originating from L4‐S3 in the sacral plexus, the SN exits the pelvis through the inferior border of the piriformis and separates into the tibial nerve and the common peroneal nerve as it reaches the popliteal fossa. While separation occurs at the apex of the fossa in most, approximately 12% of people have a more proximal separation of the SN into the tibial and common peroneal nerves as it leaves the pelvis. Variations in the anatomy of the nerve with respect to the piriformis muscle have also been described in literature. Thus, an abnormal course of the SN and/or unusual bifurcations in the gluteal region might be directly associated with its embryological development. Nevertheless, none of the proposed theories explaining how the SN advances from the spinal cord to the target muscles have been confirmed.In this case report, we describe a bilateral B‐type variation of the SN, following the Beaton and Anson classification system. The proximal division of the SN resulted in the presence of two distinct nerves at the piriformis muscle. While the common peroneal division exited through the substance of the piriformis muscle, the tibial division emerged below the muscle. The inferior gluteal nerves were also observed in this area, originating from the common peroneal division on both the left and right side. Both divisions descended normally along the posterior compartment of the thigh, and no other variations were observed. However, in the left posterior compartment of the thigh, the sural nerve emerged uniquely from the tibial nerve without any contribution from the common peroneal nerve, as would be expected.This variation is of clinical relevance since various syndromes, such as piriformis syndrome, sciatica and coccydynia, may present as non‐typical cases. For instance, the entrapment of the common peroneal division within the substance of the piriformis muscle in the cases of piriformis syndrome may accentuate the pain suffered by individuals with this B‐type variation. Similar discomfort accompanied with tenderness and/or numbness might be felt in cases of sciatica and coccydynia. Moreover, despite the symptomatologic manifestations incurred by this variation, surgical implications are of importance. Surgeons need to be aware of the possible variations that might be encountered during interventions, predominantly concerning the SN. Severe nerve injuries may otherwise occur during procedures, resulting in the possible paralysis of the muscles found in the lower limbs. Thus, knowledge regarding the morphology, location, and variation of the SN is vital both for making appropriate diagnosis and for avoiding iatrogenic nerve injuries.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.