9%20ECOGRAFIA%20ABDOMINAL%20COMO%20CUANDO%20DONDE

186
ABDOMINAL ULTRASOUND
A
B
Figure 7.25 (A) LS and (B) TS of a dilated transplant kidney, showing the measurements used to calculate the ratio
between the dilated PCS and the kidney. This kidney was dilated but not obstructed.
Pathologically, rejection can be either cellular
(98%) or vascular (now accounting for only 2% of
cases). Improved immunosuppressive therapy has
greatly reduced the problems of rejection.
Ultrasound appearances of rejection
These are varied and non-specific. In the majority
of cases the kidney appears normal; however, greyscale
findings include enlargement due to oedema
(this change is subtle in the early stages and not a
reliable ultrasonic indicator), increased corticomedullary
differentiation with prominent pyramids,
infundibular thickening (thickening of the PCS
walls) and decreased fat in the renal sinus 31 (Fig.
7.26). These findings are subjective, non-specific
and limited in the diagnosis of rejection.
In chronic rejection there may be an overall
increase in the echogenicity of the kidney with
reduced corticomedullary differentiation.
Eventually the kidney will shrink. The Doppler
resistance indices are increased in rejection but,
again, this finding is non-specific 32 (see Table 7.4)
(Fig. 7.26B). In general, the higher the RI or PI,
the more likely is the diagnosis of acute rejection.
The cause of renal dysfunction is established by
biopsy.
Fluid collections associated with
transplantation
Up to 50% of renal transplants will demonstrate
perirenal fluid. 33 The size of the collection should
be monitored with ultrasound, as significant
growth may require intervention.
Table 7.4 Causes of high-resistance Doppler (low
EDF) in renal transplants
Cause Characteristics
Acute rejection Does not occur in the first 48 hours
ATN
Always occurs in the first 48 hours
Obstruction Has a relatively slight increase in RI and is
accompanied by pelvicalyceal system
dilatation
Ciclosporin Has to be prolonged and
nephrotoxicity severe to affect the EDF and blood
levels.
Renal vein A late complication of renal transplants
thrombosis has a characteristic reversed EDF
pattern. The artery has a low-velocity
systolic peak in the early stages. No
venous flow identified
Perirenal fluid Compression of the kidney
collections causes an increase in intrarenal pressure
While it is not possible to classify the collection
on the ultrasound appearances alone, the clinical
picture, including the time interval following
transplantation, can often be helpful.
●
Lymphocoele The commonest perirenal fluid
collection, lymphocoeles usually occur several
weeks or months after the transplant. They may
resolve spontaneously but occasionally require
percutaneous drainage if large. They may
compress the kidney, causing an increase in
vascular resistance on spectral Doppler (Fig.
7.27). The collection is anechoic but may
contain loculations or septa. If treated, then