Renal Vascular Thrombosis
Stuart L. Goldstein
L. Leighton Hill
Renal vascular thrombosis is a rare condition in children that affects primarily neonates or children with a few select underlying conditions, such as nephrotic syndrome, or in the immediate postoperative renal transplant period. The newborn infant appears to be particularly at risk for the development of renal vascular thromboses. The vessels are small, renal blood flow is relatively low, the neonate is relatively polycythemic, vascular resistance is high, and fibrinolytic mechanisms may be immature. More than two-thirds of the children with renal vascular thrombosis are younger than 1 month old. The male-to-female ratio in reported series has ranged from 1.4:1.0 to 1.9:1.0 in the neonatal period.
RENAL VENOUS THROMBOSIS
Renal venous thrombosis (RVT) may be unilateral (most common) or bilateral. It is a rare condition in children past the neonatal period.
In neonates and young infants, RVT is seen with dehydration, shock, increased tonicity of body fluids, and polycythemia. Infants with RVT frequently have experienced perinatal asphyxia, prenatal or postnatal stress, or septicemia. A high incidence of preceding diarrhea is present. Not uncommonly, these infants have been exposed to radiographic contrast media. Additional predisposing factors in the newborn period include congenital renal anomalies, congenital nephrosis, severe pyelonephritis, and maternal diabetes. RVT can be primary, first involving the veins of the kidney, or secondary, extending into the renal veins from a thrombus in the inferior vena cava.
RVT seen after infancy usually is associated with nephrotic syndrome or with cyanotic congenital heart disease (either spontaneously or after angiography). RVT does not cause nephrotic syndrome; rather, patients with active nephrotic syndrome have a predisposition for the development of RVT because they have low serum levels of proteins that counteract coagulation, including antithrombin III, protein C, and protein S, which are lost in the urine. RVT has been reported in 1% to 5% of patients in the immediate postoperative transplant period and seems to occur more frequently when kidneys from smaller cadaveric donors are used for transplantation or when patients are hypotensive in the recovery room.
During conditions of hypovolemia, hemoconcentration, hyperviscosity, hyperosmolarity, sepsis, and asphyxia, local microthrombi may occur peripherally in venous radicals, and the thrombus formation then may progress through the arcuate and interlobular veins toward the main renal vein. More rarely, the clotting process moves in the opposite direction. RVT causes renal congestion and occasionally infarction. For signs and symptoms of RVT, see Box 340.1.
Proteinuria occurs commonly, although in some instances it may be caused by the physical presence of gross blood in the urine. More than 50% of the infants with RVT demonstrate evidence of a microangiopathic hemolytic anemia with red blood cell fragmentation; thrombocytopenia; low levels of fibrinogen, factor V, and plasminogen; and an increase in fibrin degradation products. These findings may reflect the presence of active disseminated intravascular coagulation. Depending on the severity and whether the thrombosis is unilateral or bilateral, azotemia and other biochemical evidence of acute renal failure may be present.