Diagnostic ultrasound ( PDFDrive )

CHAPTER 18 Organ Transplantation 651
sign of potential dysfunction. Other gray-scale indings include
increased cortical thickness, increased or decreased cortical
echogenicity, reduction of the corticomedullary diferentiation,
loss of the renal sinus echoes, and prominence of the pyramids
(Fig. 18.34).
Color Doppler assessment may be normal or may occasionally
show difuse decreased blood low. he RI of the intraparenchymal
arteries is also nonspeciic in these conditions and may be normal
or elevated. In severe cases, there may be a complete lack of low
in diastole or a reversal of diastolic low 44 (Fig. 18.35). Despite
the lack of speciicity of gray-scale and Doppler ultrasound in
these acute conditions, serial spectral Doppler measurements,
in combination with clinical assessments and biochemical indings,
provide a useful guide to the clinician in terms of monitoring
the allograt function and in determining the need for percutaneous
biopsy.
FIG. 18.32 Normal Renal Transplant Doppler. Color Doppler shows
low throughout kidney (top). Intrarenal spectral traces of upper, middle,
and lower poles show a resistive index of less than 0.8 and continuous
low throughout diastole. The main renal artery shows continuous low
with peak velocities less than 200 cm/sec (bottom).
hypotension. It is most common in the early postoperative period
and is the major cause of delayed grat function (deined as the
need for dialysis within the irst week of transplantation). 45,55 In
patients requiring dialysis, recovery is usually in the irst 2 weeks
of transplantation but may be delayed by up to 3 months. ATN
occurs in most cadaveric grats and is observed infrequently in
living related renal transplants because of the relatively short
cold ischemic time of the donor kidney. 44
Transplants afected by hyperacute rejection are rarely imaged
because grat failure occurs immediately at the vascular anastomosis
during surgery. 45 Acute rejection occurs in up to 40% of
patients in the early transplant period, peaking at 1 to 3 weeks
ater surgery, and is an adverse long-term prognostic indicator.
Most patients with acute rejection are asymptomatic, but a small
proportion may have lulike symptoms, malaise, fever, and grat
tenderness. Provided that the diagnosis can be rapidly established,
acute rejection usually can be promptly reversed with high-dose
steroids or antibiotic therapy. 44,56
he imaging features of ATN and acute rejection are almost
identical on gray-scale and Doppler ultrasound. Both conditions
can produce increases in renal volume of the allograt.
However, precise volumetric comparisons between interval
studies can prove diicult; subtle changes in two-dimensional
(2-D) measurements have not been adopted as a strong clinical
Chronic Rejection
Chronic rejection is deined as a reduction in allograt function
starting at least 3 months ater transplantation in association
with ibrous intimal thickening, interstitial ibrosis, and tubular
atrophy on histology. It is the most common cause of late grat
loss. he most frequent predisposing risk factor for development
of chronic rejection is recurrent previous episodes
of acute rejection. 44,45 On ultrasound, there is progressive
thinning of the renal cortex, prominence of the central renal
sinus fat, and a reduction in the overall size of the transplant.
Dystrophic calciications may be seen scattered throughout
the residual parenchyma. In the end-stage renal transplant, the
entire renal cortex can become calciied, appearing as a sharp
echogenic interface associated with clean distal shadowing
(Fig. 18.36).
Infection
Over 80% of patients with renal allograts will experience an
episode of infection within the irst year ater transplant surgery. 57
Transplant pyelonephritis can result from an ascending infection,
hematologic seeding, or contiguous spread from an adjacent
infected luid collection. Ultrasound indings include a focal or
difusely granular, echogenic renal cortex associated with loss
of the corticomedullary junction; increased echogenicity and
thickening of the perirenal fat secondary to extension of inlammation
or infection into the surrounding tissue; and uroepithelial
thickening (Fig. 18.37).
Pyonephrosis may occur occasionally in a chronically
obstructed transplanted kidney. In the early stages, the lumen
of the dilated collecting system appears anechoic. Once the lumen
becomes illed with purulent material, low-level echoes develop
within the calyceal system and ureter, sometimes associated with
luid-debris levels. Echogenic material within the collecting system
may also result from intraluminal blood or other illing defects,
or it may be artifactual as a result of scatter or s1ide-lobe artifact
(see Fig. 18.37).
Abscesses can arise from infection of a previously sterile
collection. On ultrasound, abscesses appear as a complex cystic
structure and may be associated with luid-luid levels or intraluminal
air (Fig. 18.38).