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THE RENAL TRACT 181
der 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. 24
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 (Fig. 7.9). 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 (Fig. 7.23), 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. 25
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
+7.8MM
NORMAL 1686 HZ
Figure 7.23 Renal vein thrombosis. Small shrunken
kidney (6 cm) demonstrating hardly any perfusion, apart
from a tiny interlobar artery with forward and reverse
flow.
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.