Anatomical variability and laterality of the levator ani nerve: A cadaveric study

The levator ani nerve (LAN) plays a key role in pelvic floor functions; however, following injury, it may contribute to postoperative dysfunction. This study aimed to clarify the detailed anatomy of the LAN and establish a comprehensive framework relevant to nerve-sparing pelvic surgery.

Eleven human cadavers (22 hemipelves; 2 males and 9 females; median age at death, 91 years [range: 78-97 years]) were subjected to transabdominal pelvic dissection with preservation of the parietal pelvic fascia. The LAN was defined as any nerve innervating the levator ani muscle identified through gross anatomical examination. For each hemipelvis, we assessed the (i) number of LANs, (ii) laterality, (iii) segmental origin and intrapelvic course, and (iv) termination sites within the levator ani muscle.

LANs were identified bilaterally in all specimens (37 in total); they originated from various S3-S5 combinations, predominantly involving S4. Multiple LANs were present in 54.5% of the hemipelves. A medially directed branch, defined as the branch terminating closer to the pelvic midline than to its origin, was observed in 16.2% of LANs. Marked laterality was also observed. Most LANs terminated in the iliococcygeus muscle, and all were covered by the parietal pelvic fascia.

The LAN is an inherently variable neural system, predominantly derived from S4, and is characterized by marked structural laterality and diverse intrapelvic branching patterns. These features provide a morphological basis for individual differences in pelvic floor function, as the LAN is potentially vulnerable to surgical injury and may influence postoperative bowel function.