Chronic expanding haematoma in the kidney following long-term hydronephrosis.

Chronic expanding haematoma is defined as a haematoma that gradually increases in size for ≥1 month. It is mostly related to trauma or surgery and can develop at any location in the body. Herein, we describe a case of a chronic expanding haematoma in the left kidney in a patient with a history of long-term hydronephrosis. The patient was a man in his 70 s who had undergone surgery for seminoma with lymph node metastasis 40 years prior. Following the procedure, he had been in an extended state of hydronephrosis. Computed tomography performed during the follow-up period revealed nodules in his persistently dilated left renal pelvis. A left nephrectomy was performed because the possibility of another malignancy could not be ruled out. Pathological examination revealed that the mass was a haematoma that had originated from the left kidney. To the best of our knowledge, this is the first clinical report in the literature of chronic expanding haematoma in the kidney.