Renal venous thrombosis (RVT) is a condition in which a thrombus forms in the venous drainage system of one or both kidneys. The thrombus can extend from the arcuate renal vessels through the renal vein and as far as the vena cava¹ (Figure 117-1). The condition is also referred to as renal vein thrombosis, but because the thrombus often extends beyond the anatomic boundaries of the renal vein both proximally and distally, the term renal venous thrombosis is preferred.²

PATHOPHYSIOLOGY

In the pediatric population, the majority of cases of RVT occur in the neonatal period and RVT is the most common spontaneous thromboembolic event in this population.² Newborns are at risk for elements of Virchow’s triad (hypercoagulability, stasis, and vessel wall injury), which can lead to venous thrombosis. Newborns have increased renal vascular resistance and therefore relatively diminished renal blood flow.^1,2 Polycythemia, either idiopathic or associated with maternal diabetes mellitus or congenital heart disease, leads to sludging and stasis in the small vessels.³ Similarly, acute blood loss, shock, asphyxia, or sepsis can result in hypovolemia and vessel wall injury.⁴ Infants with traumatic delivery are at higher risk for RVT than are those delivered uneventfully.¹ In addition, central venous catheters, which are frequently needed in the neonatal period, are a well-documented risk factor for venous thrombosis.³

RVT occurs less commonly in older infants and children. When it does, there is likely a predisposing condition, and RVT is often triggered by a hyperosmolar state.⁴ For example, patients with severe dehydration (e.g. gastroenteritis) have decreased renal blood flow and hemoconcentration, which can increase the risk of thrombus formation.⁵ Similarly, radiologic procedures using hyperosmolar intravenous contrast agents can lead to RVT.² Healthcare providers should have a high index of suspicion for RVT in patients with hypercoagulability due to an underlying condition (e.g. cancer, trauma, burns, surgery, congenital heart disease, nephrotic syndrome, pregnancy, lupus) or inherited thrombophilia (e.g. factor V Leiden, homocystinuria, prothrombin mutation).^1,4,5 In patients with nephrotic syndrome, a hypercoagulable state is induced due to proteinuria. The loss of protein leads to a decrease in osmotic pressure, which triggers increasing platelet number and aggregation as well as a reduction in coagulation inhibitors. Certain medications, such as oral contraceptives and steroids, can also cause hypercoagulability.⁵ Rarely, trauma can lead to RVT, which may be associated with concurrent renal arterial thrombosis.⁵ Children with renal transplants are at risk for RVT, particularly if they are treated with cyclosporine.⁵

RVT classically presents with macroscopic hematuria and enlargement of one or both kidneys.³ Older children often complain of lumbar or flank pain. If both kidneys are affected, the patient will have oliguria and renal insufficiency.⁵ If the thrombus extends to the inferior vena cava, it can affect venous return from the lower extremity, in which case the child’s leg will be edematous, cool, and cyanotic.^2,3

Owing to the presence of the clot, the affected kidney enlarges over the course of about 1 week. Depending on the degree of obstruction, the kidney may become completely or partially atrophic over the following months. Some patients then develop hypertension, renal impairment, and tubulopathy.^4,5 The prognosis depends on the extent of the initial thrombus, whether it was bilateral or unilateral, and the degree of spontaneous recanalization.¹