Rectourethral Fistula After External Beam Radiotherapy for Prostate Cancer in a Patient With Thromboangiitis Obliterans: a Case Report

Background: Thromboangiitis obliterans (TAO) is a rare disease of unknown cause that causes segmental vasculitis in peripheral blood vessels. It is uncertain whether its presence is a cause of serious adverse events in patient receiving external beam radiotherapy. Case presentation: A 73-year-old Japanese man with prostate cancer underwent external beam radiotherapy. After the completion of radiotherapy, pain in his fingertips occurred and led to the diagnosis of TAO. The patient was instructed to stop smoking but was unable to do so. Nine months after the completion of radiotherapy, fecaluria appeared, and a rectourethral fistula was diagnosed by contrast enema. The patient's TAO was poorly controlled, and the patient died from aspiration pneumonia at 33 months after the completion of the radiotherapy regimen. No tumor recurrence was observed during this process, and there were no risk factors which may form a rectourethral fistula other than TAO. Conclusion: This is the first report on rectourethral fistula caused by external beam radiotherapy for prostate cancer in which TAO was suspected to be involved. Although little is known about the relationship between TAO and radiotherapy, it should be noted that radiotherapy itself may increase the risk of normal tissue toxicity in patients with TAO.