An Uncommon Diagnosis in a Common Presentation: Renal Vein Thrombosis in a Young Adult

Renal vein thrombosis (RVT) is a condition primarily associated with nephrotic syndrome and malignancy, with a mean age of occurrence at 55 years. There are a few documented cases of RVT in the setting of a complicated urinary tract infection (UTI), especially in younger patients. We aim to examine the case of a 21-year-old female who presents with RVT in the setting of multiple risk factors and review relevant literature. A 21-year-old female with a history of vaping nicotine, cannabis use, and oral contraceptive pill (OCP) use presented with shortness of breath, left flank pain, and diarrhea. An initial evaluation suggested pyelonephritis, as supported by flank pain, pyuria, and bacteriuria on urinalysis, and a positive culture for <i>Escherichia coli</i>. Imaging of the abdomen and pelvis with non-contrast computed tomography (CT) revealed perinephric fluid with stranding of the left kidney and engorgement of the left renal vein. A follow-up contrast CT revealed a filling defect of the left renal vein. A CT angiogram was performed, showing a left renal vein thrombus. Initial management consisted of broad-spectrum antibiotics (ceftriaxone) for suspected pyelonephritis and a multimodal pain regimen. Following the discovery of the renal vein thrombus, a multidisciplinary team, including vascular surgery, interventional radiology, hematology, and nephrology, initiated anticoagulation. They planned for thrombectomy if renal function deteriorated, as no acute kidney injury was evident through quantification of serum creatinine on initial presentation. Full-dose low molecular weight heparin was initiated and later switched to unfractionated heparin in preparation for thrombectomy. The patient experienced symptomatic improvement on anticoagulation, and renal function remained stable. A decision to cancel the thrombectomy and plan for outpatient oral anticoagulation with apixaban was made, given clinical improvement and stable serum creatinine concentration. Apixaban was continued for three months, and the patient experienced complete symptom resolution without recurrence at six-month follow-up. This report focuses on an atypical case of RVT in the setting of a complicated UTI and multiple risk factors. Multiple explanations exist for thrombus formation, with a major driver being local endothelial damage secondary to infection. Another predisposing factor for RVT is nephrotic syndrome, which may have been secondary to infection or the renal thrombus itself. Additionally, OCPs and habitual nicotine use may have contributed to a hypercoagulable state and eventual thrombosis. Oral anticoagulation remains a safe, effective, and less invasive treatment of isolated renal vein thrombus without renal compromise.