RENAL VEIN THROMBOSIS DOPPLER

Renal vein thrombosis
This can occur when chronic renal disease is already present or in cases of a coagulation disorder with increased tendency to thrombose, for example polycythaemia. It is frequently associated with nephrotic syndrome. Other associated factors include the oral contraceptive pill and the use of steroids. Tumour thrombus from RCC is also prone to invade the ipsilateral renal vein, and sometimes may extend into the IVC and even renal artery. Thrombus in the renal vein, whether secondary to a malignancy or thrombocythaemia can travel up the IVC forming a source of emboli. If nonmalignant, the thrombus may be successfully treated medically and the renal function can be preserved even if the vein is totally occluded.

Ultrasound appearances
It is often possible to see echo-poor thrombus within a dilated renal vein, running beside the renal artery in an axial section through the renal hilum. Colour Doppler confirms absent venous flow. Perfusion within the kidney itself is reduced and there may be a highly pulsatile arterial waveform with reversed diastolic flow, although this is not commonly seen in the native kidney. If the thrombus produces a total and sudden occlusion, the kidney becomes oedematous and swollen within the first 24 h. Eventually it will shrink and become hyperechoic. Partially occluding thrombus is more difficult to diagnose as the changes in the kidney may not be apparent. However, a non-dilated renal vein with good colour Doppler displayed throughout has a high negative predictive value. Incomplete thrombosis may still demonstrate venous flow within the kidney, although the arterial waveforms are of lower velocity than normal, with a marked reduction in the systolic peak. Forward diastolic flow may be preserved at this stage.

Arteriovenous fistula
These lesions can occur at the site of a biopsy and are recognized on colour and spectral Doppler by localized vessel enlargement with turbulent, sometimes high-velocity flow. A ‘pool’ of colour flow is often present. The vein may show a regular, pulsatile pattern and be dilated. These iatrogenic fistulae usually resolve spontaneously and are clinically insignificant. If bleeding is a clinical problem and is ongoing, recurrent and/or severe then embolization is the treatment of choice.

Ultrasound in dialysis
Patients with chronic renal failure may undergo either haemodialysis (in which a subcutaneous arteriovenous shunt is created, often in the wrist) or continuous ambulatory peritoneal dialysis (CAPD), in which a catheter is inserted through the abdominal wall. Ultrasound may be used to assess the patency of the shunt or catheter, and may identify localized areas of infection along the CAPD tract which can be drained under ultrasound guidance if necessary. Ultrasound may also be used to diagnose acquired cystic kidney disease in long-term dialysis patients.