90 Korean J Pain Vol. 23, No. 1, 2010 division among the sciatic nerves was different from the common piriformis syndrome. 　　It is known that radiotherapy may cause damage to the nerves. The brachial plexopathy after radiotherapy on the axillary glands for a breast cancer patient was firstly reported. Post-radiation complications of intrapelvic tumor including cervical cancer usually occur at the bladder, in- testinal tract, and ureter, but neuropathy is known to be very rare. However, lumbosacral plexopathy has been re- ported in the case where the radiotherapy of more than 70 cGy was performed on the pelvis, and plexopathy usu- ally has bilateral symptoms or signs of a weakened muscle at the proximal part [3,7]. The case where sciatic neuritis occurred after the radiotherapy on metastasis of liver cancer to ilium and the pain relieved by sciatic nerve blockade has been also reported [8]. Post-radiation dam- age on muscles is rarely found, but muscular dystrophy, edema, fibrosis, and contracture can occur with increased probability of complications when chemotherapy is con- ducted in parallel. The patient in this case report was given radiotherapy for ten years over the dose of 80 cGy, includ- ing external beam radiotherapy and concurrent che- mo-radiotherapy with brachytherapy and cisplatin. It has been reported that the damage on muscles occurs over several years and the probability of occurrence is in- creased as the total dose is larger or as the radiation dose per one time is larger even with the same total dose [3,9]. 　　We have found the right sciatic neuropathy by electro- myography and the fatty atrophy at the right piriformis muscle by conducting a lumbar spine MRI. The status of the piriformis muscle was reviewed based on the pelvic MRI, which had been performed on the patient to check the recurrence and metastasis of a tumor from the past. As a result, asymmetric piriformis muscle atrophy was also found in the pelvic MRI performed one year before the visit (Fig. 2A), and serious fatty atrophy and edema in the pir- Fig. 2. Magnetic resonance imaging of the pelvis. (A) Axial and coronal T2-weight- ed MR images show mild atrophy of the right piri- formis muscle (white arrow). (B) Two years later, axial and coronal T2-weighted MR images demonstrate marked atrophy of the right piri- formis muscle (open arrow), producing a ghost-like ap- pearance.