Anatomical neuromuscular variations determined by magnetic resonance imaging in chronic pelvic pain

Abstract

Background: The diagnosis of neuromuscular pelvic pain is challenging. Despite the increasing use of magnetic resonance imaging (MRI) in the assessment of pudendal neuralgia, there are limited data describing radiological variations of the nerve. Additionally, the utility of MRI in the assessment of pelvic floor tension myalgia is unknown. Aims: To describe the anatomical variations of the pudendal nerve and dimensions of pelvic muscles in patients investigated for neuromuscular pelvic pain using a combined MRI protocol. Materials and methods: A retrospective audit of MRI reports for 136 patients referred to a single radiologist was conducted. Reported data included the appearances of the pudendal nerve and its perineural structures, and the maximal thicknesses of pelvic muscles. Results: Several anatomical variations were identified in the course of the pudendal nerve at or above the ischial spine. Likely/highly likely nerve compression at this level was present in 34.6% of hemipelves. Variations associated with compression included delayed separation of the sacrospinous and sacrotuberous ligaments ( p < 0.0001), close apposition of ligaments ( p < 0.0001), interligamentous bands ( p = 0.033), coccygeal muscle contributions to the sacrospinous ligament ( p = 0.014) and proximal ( p < 0.0001) and thickened falciform ligaments ( p < 0.0001). Variations below the ischial spine were uncommon. Conclusions: This study represents a quantitative and qualitative expansion to the radioanatomical basis of pudendal nerve entrapment on MRI, and highlights the limitations of MRI obtaining reproducible measurements of pelvic muscles. Images from asymptomatic controls and further prospective evaluation of treatment outcomes is required to determine the clinical significance of MRI findings in the assessment of pudendal neuralgia.