Renal vein thrombosis is a condition characterized by renal dysfunction secondary to a clot blocking the renal vein, which drains blood from the kidney. It is typically seen in patients suffering from nephrotic syndrome, but may also be diagnosed in individuals with renal malignancies, and hypercoagulable states. Clinical symptoms are variable and may be often masked by underlying conditions. Therefore diagnosis is based on clinical suspicion and confirmed with the radiological identification of the blood clot.
Renal vein thrombosis (RVT) is a relatively rare condition in which a clot occludes the renal vein draining blood from the kidney and leads to renal vein infarction . The exact reason why there is a predilection of the renal vein for thrombosis in as yet unknown . It occurs most often in patients with nephrotic syndrome but can also affect patients with renal malignancies, anti-glomerular basement membrane disease , Behçet syndrome, hypercoagulable states like pregnancy , antiphospholipid antibody syndrome and following renal transplantation.
The clinical presentation of RVT in adults is usually insidious and asymptomatic. The first indication of the condition may be when the clot in the renal vein travels to the lungs causing pulmonary embolism with dyspnea and chest pain. Some cases may present with unilateral lower limb swelling. The onset is often sudden in children and some adults with fever, nausea, vomiting, flank pain, oliguria, gross hematuria, and proteinuria which progresses swiftly to renal failure especially in bilateral renal vein thrombosis or in patients with a single kidney . The first symptom is usually flank pain occurring posterior to the lower ribs and in the region of the hips. In patients with renal malignancies, anorexia and weight loss may be predominant while patients with nephrotic syndrome may have anasarca.
Diagnosis in patients with RVT is difficult as the clinical presentation is often overshadowed by anasarca or weight loss and anemia due to the predisposing conditions like nephrotic syndrome and renal malignancies respectively. Routine laboratory tests like complete blood count, urinalysis, serum blood urea nitrogen (BUN) and creatinine levels may reveal anemia, oliguria/proteinuria, and elevated BUN/ creatinine levels due to renal dysfunction.
The diagnosis of RVT is based on radiological tests. Ultrasonography in the acute stage may reveal renal enlargement with hyperechogenicity  and is the first radiological investigation to be performed although it cannot confirm the diagnosis. Computed tomogram with angiography (CTA) is the gold standard investigation with almost 100% sensitivity and specificity  as it can detect the occluding thrombus with abnormal renal perfusion . The radiologist can also deduce the presence of a thrombus on CTA indirectly due to signs of renal enlargement, renal vein dilatation, poor renal venous drainage on a nephrogram, delayed corticomedullary differentiation, and renal fascial thickening . Instead of a CTA, magnetic resonance imaging (MRI) is preferred in patients with renal impairment as it can be performed without using nephrotoxic contrast . However, it has a lower sensitivity and specificity as compared to CTA .