Intrapiriformis lipoma: an unusual cause of piriformis syndrome

We report on a patient with an unusual cause of non-discogenic sciatica.

A 48-year-old woman presented with a 10-day history of gradually worsening left buttock pain radiating to the ipsilateral posterior thigh and calf. She had a similar episode of less intense pain 8 months before which lasted about 2 months. She denied any history of antecedent trauma or back pain. MRI scan revealed a well-defined, fat-containing lesion of the left piriformis muscle similar to a lipoma displacing the sciatic nerve but not invading it. The sciatica was relieved after excision of the lesion. The patient remained asymptomatic after the operation.

The present case suggested that an intrapiriformis lipoma can cause secondary piriformis syndrome and medical practitioners should be aware of this condition and consider lipomas and other occupying lesions of the pelvic muscles as a differential diagnosis in patients presenting with radicular pain.