We present a case of piriformis syndrome in a woman in her 30's following low energy trauma, presenting with unilateral lower limb weakness, altered sensation and urinary retention. CT imaging revealed a bulky piriformis muscle which was further clarified on MRI as an intramuscular haematoma within the left piriformis causing compression of the left lumbosacral plexus. Haematoma formation was exacerbated due to use of an antiplatelet medication the patient was taking for Moyamoya disease, which carries an increased risk of cerebrovascular accident. Surgical exploration of the piriformis and sciatic nerve was undertaken and confirmed a haematoma within the piriformis. A full release of the piriformis tendon was undertaken, and the sciatic nerve was inspected, no further abnormality was found. After review in clinic post-discharge, the patient reported normal sensation and normal muscle power in her feet.