Chronic expanding hematoma of the left erector spinae muscle after stereotactic body radiotherapy for renal cell carcinoma: a case report

BACKGROUND: Hematomas that slowly increase in size for more than 1 month after the initial hemorrhage are referred to as chronic expanding hematomas. Chronic expanding hematoma can also occur after radiosurgery; however, there have been no reports about chronic expanding hematoma in the trunk after stereotactic body radiotherapy. We report a case of chronic expanding hematoma of the left erector spinae muscle after stereotactic body radiotherapy for renal cell carcinoma. CASE PRESENTATION: A 74-year-old Japanese male complained of back pain 7 years after stereotactic body radiotherapy for renal cell carcinoma of the left kidney. There was no history of surgery or trauma to his back. After stereotactic body radiotherapy, there was no acute or late complication of more than grade 2. The renal cell carcinoma did not show shrinkage or progression, and he was diagnosed with stable disease on computed tomography. The patient remains in a stable disease condition 7 years after treatment without surgery or chemotherapy; however, he came to the hospital with gradually worsening back pain for several months. Computed tomography revealed the left erector spinae muscle to be swollen compared with the contralateral side at the third lumbar level. Ultrasonography showed a tumor of 30 mm in size without blood flow in the left paraspinal muscle. Positron emission tomography–computed tomography revealed uptake in the left paraspinal muscle. Pathological examination showed radiation-induced chronic expanding hematoma. CONCLUSIONS: We present the first case report of chronic expanding hematoma of the left erector spinae muscle after stereotactic body radiotherapy for renal cell carcinoma. Usually, stereotactic body radiotherapy for renal cell carcinoma would be considered unlikely to cause chronic expanding hematoma, but the introduction of dialysis and antiplatelet drugs may have increased the risk.