Lesser Sciatic Foramen

The lesser sciatic foramen serves as a conduit for vital structures transitioning between the perineum and the posterior aspect of the pelvic region.^[3]

Location

The lesser sciatic foramen is located in the posterior part of the pelvis, bordered by several pelvic bones and ligaments:

• Superiorly by the spine of the ischium.
• Inferiorly and anteriorly by the sacrospinous ligament.
• Posteriorly by the sacrotuberous ligament.^[1]

Structure

Shape: The foramen is an oval-shaped opening with its long axis directed anteroposteriorly. Borders: The lesser sciatic notch of the ischium forms its bony boundary, while the sacrotuberous and sacrospinous ligaments create the soft tissue margins.^[8]

Function

• Neurovascular Passage: The primary function of the lesser sciatic foramen is to serve as a passageway for neurovascular structures. ^[5]This includes the pudendal nerve and internal pudendal vessels which re-enter the pelvis through this foramen after exiting the greater sciatic foramen.
• Muscular Passage: The tendon of the obturator internus muscle and its associated nerve traverse through the lesser sciatic foramen as they move from the pelvis to the gluteal region.

Clinical significance

The lesser sciatic foramen, though smaller in size, is of significant clinical importance due to the essential structures it harbors. ^[2]Central to its relevance is the pudendal nerve, a primary sensory and motor nerve of the perineum. Compression or irritation of this nerve as it traverses the foramen can result in pudendal neuralgia, characterized by chronic pelvic pain, tingling, or numbness.^[4] Moreover, this foramen allows passage for the internal pudendal vessels, which supply blood to various structures of the perineum. In surgical procedures involving the perineum or posterior pelvis, inadvertent injury to these vessels can lead to hemorrhage or compromised blood supply. The foramen also facilitates the movement of the obturator internus muscle, and any anomaly or injury around the foramen can impact the muscle's function, affecting hip movements.^[7] For clinicians, especially gynecologists, urologists, and orthopedic surgeons, understanding the anatomy and potential pathologies related to the lesser sciatic foramen is crucial for accurate diagnosis and effective therapeutic interventions.^[6]