Piriformis muscle syndrome: MR imaging findings and treatment outcome in 23 patients

Abstract

Purpose: To increase the clinical awareness of piriformis muscle syndrome (PMs) by reporting the magnetic resonance (MR) imaging findings and therapeutic outcome in a series of 23 patients with clinically suspected syndrome. Material and Methods: Within a four-year period, 23 pelvic magnetic resonance (MR) imaging studies from 23 patients with clinically suspected PMs were retrospectively reviewed. Patients were recruited in four health care centers in three countries. Piriformis muscle (PM) dimensions/signal intensity and the presence of sciatic neuritis were assessed. The piriformis region was examined for the presence of PMs related causes. The syndrome was categorised into primary and secondary, according to a widely used classification system. Treatment decisions were recorded and outcome was categorised as response (R) or no response (NR). Results: Fourteen patients (61%) showed abnormal signal within the PM, 11 (48%) enlargement of the muscle and 8 (35%) sciatic neuritis. Ten patients were classified in the primary causes and 13 into secondary. Space occupying lesions comprised the leading cause of PMs and imaging played a crucial role both in diagnosis and in treatment planning. Treatment decisions proved effective in 8/8 patients with primary and in 9/13 patients with secondary PMs. Conclusions: In suspected PMs, MR imaging may depict a spectrum of findings including PM signal alterations/enlargement and sciatic neuritis, related to either primary or secondary causes. Space occupying lesions represented the leading cause of PMs.