The "nutcracker" phenomenon in combination with IgA nephropathy.

The "nutcracker" phenomenon results from compression of the left renal vein between the superior mesenteric artery and the aorta. The main features of this phenomenon are non-glomerular haematuria on urinalysis and stenosis of the left renal vein with dilatation of the vein distal to the stenosis. The characteristics of two patients with the "nutcracker" phenomenon complicated by immunoglobulin A nephropathy were compared with those of 10 patients showing only the "nutcracker" phenomenon. Patients with the "nutcracker" phenomenon complicated by immunoglobulin A nephropathy showed aggravation of haematuria after upper respiratory infections, urinary red cell morphology indicating haematuria of glomerular origin, elevation of serum IgA, persistence of proteinuria, and granular casts in the urine. The coexistence of immunoglobulin A nephropathy was suspected when these characteristics were observed in patients with the "nutcracker" phenomenon. In such cases, a renal biopsy is needed for a final diagnosis.