Piriformis muscle syndrome: A cross-sectional imaging study in 116 patients and evaluation of therapeutic outcome.

OBJECTIVES: To increase the clinical awareness of piriformis muscle syndrome (PMs) by reporting cross-sectional imaging findings, the clinical impact of imaging studies and treatment outcome.

METHODS: Within a 10-year-period, 116 patients referred for radiological evaluation of clinically suspected PMs, with excluded lumbar pathology related to symptomatology, were prospectively studied with MRI and/or computed tomography (CT). Piriformis muscle (PM), sciatic nerve (SN), piriformis region and sacroiliac joints were evaluated. PMs was categorised into primary/secondary, according to a reported classification system. Treatment decisions were recorded. Outcome was categorised using a 3-point-scale.

RESULTS: Seventy-four patients (63.8%) exhibited pathologies related to PMs. Primary causes were detected in 12 and secondary in 62 patients. PM enlargement was found in 45.9% of patients, abnormal PM signal intensity/density in 40.5% and sciatic neuritis in 25.7%. Space-occupying lesions represented the most common related pathology. Treatment proved effective in 5/8 patients with primary and 34/51 patients with secondary PMs. In 34 patients, imaging revealed an unknown underlying medical condition and altered treatment planning.

CONCLUSIONS: Secondary PMs aetiologies appear to prevail. In suspected PMs, PM enlargement represented the most common imaging finding and space-occupying lesions the leading cause. Imaging had the potential to alter treatment decisions.

KEY POINTS: • In clinically suspected PMs cross-sectional imaging may reveal variable pathology. • Secondary PMs aetiologies appeared to be more common than primary. • PM enlargement represented the most common imaging finding in clinically suspected PMs. • Space-occupying lesions in the piriformis region represented the leading cause of PMs. • In clinically suspected PMs cross-sectional imaging may alter treatment planning.