A 71-year-old woman with a history of mitral valve replacement and atrial fibrillation (AF) who was on warfarin experienced right abrupt onset flank pain radiating to external genitalia, as well as nausea and vomiting. She declined to be visited in the clinic due to the COVID-19 outbreak and asked for a phone consultation instead. She had minor urination problems, but no gross hematuria, or fever. Considering her previous history of renal stones and the pattern of her pain, we prescribed painkillers and requested a renal ultrasound, and urinalysis with the impression of acute renal colic. After two days of follow-up, and phone calls, the patient's pain was aggravating and she felt a heavy sensation on her right flank. Urinalysis was positive for blood, and the renal ultrasound showed a hypoechoic structure with a maximum diameter of 140x54 mm, and inferomedial extension of 87x48 mm. These findings were highly suggestive of a partially small size right kidney with an extrinsic impression caused by a real mass or a similar lesion that covered the entire kidney. Due to the bizarre shape of the right kidney and non-conclusive ultrasonography, we requested the patient be referred to Shiraz Central Hospital for further evaluation. On the day of admission, the patient looked ill with pale conjunctivae. Her pulse rate was 120 beats per minute and irregular (AF), and her blood pressure (BP) was 100/60 mmHg. A tense and tender mass was palpated in the right flank and upper quadrant of the abdomen, extending to the lower quadrant. Her laboratory data demonstrated a drop in hemoglobin (Hb) to 6.6 g/dL (baseline was 12 g/dL). The platelet count was normal (239000/microl), but the prothrombin time (PT) was 56.0 seconds with an international normalized ratio (INR) of more than 6. The level of blood urea nitrogen (BUN) and creatinine were 40 mg/dL and 2.82 mg / dL, respectively. Urine microscopy revealed trace blood with 3-5 red blood cells per high-power field of the microscope. Due to warfarin toxicity, the patient was admitted with an impression of retroperitoneal hematoma. A non-enhanced computed tomography (CT) scan of the abdomen and pelvic cavity disclosed an inhomogeneous lesion along the superolateral border of the right kidney, which seemed to be engulfing the entire kidney with perinephric fat stranding. 
In the first days of admission, the Hb level was adjusted to 10 mg/dL by blood transfusion. Moreover, we administered the patient several bags of fresh frozen plasma (FFP) to treat the coagulopathy and prevent further bleeding. On the fifth day of hospitalization, the creatinine level dropped to 1.7 mg/dL, and an enhanced abdominopelvic CT scan was performed, which showed a partially enhancing small-size kidney engulfed by a heterogenous lesion causing mass effect surrounded by scattered non-enhancing septa (Figure 1). On the sixth day of hospitalization, the Hb level dropped to 8 mg/dL with aggravation of flank pain and flank fullness, which was in favor of rebleeding. Therefore, the patient was transferred to the operating room, and through a right incision, we entered the abdominal cavity. A massive hematoma in the retroperitoneum was detected, pushing the liver upward and the ascending and transverse colon anteriorly (Figure 2). The right colon was medialized and we entered the retroperitoneal space. The hematoma was confined to the Gerota's fascia with extension into the pelvic cavity but not pulsatile. After ligation of the renal pedicle, the right kidney, and Gerota's fascia was removed, the bleeders were controlled and a Jackson- Pratt surgical drain was inserted into the retroperitoneum. The postoperative course was rather uneventful, and the oozing from the retroperitoneum was not significant. A few days later, the patient was discharged in a good condition with a creatinine level of 1.8 mg/dL and INR of 2.5.
A gross evaluation of the kidney revealed extensive hemorrhage and blood clots in the renal parenchyma and perinephric fat (Figure 3). A microscopic examination was in favor of chronic pyelonephritis with hemorrhage and vascular congestion (Figure 4). Since renal cell carcinoma (RCC) is the most prevalent cause of spontaneous renal hemorrhage, we invited another pathologist to review the slides and utilized immunohistochemistry (IHC) markers to rule out renal malignancy; however, reevaluation of the case confirmed the initial diagnosis.