Transcript Role of ultrasound in renal transplantation

Role of Ultrasound In Renal
Transplantation
Dr. Ahmed Refaey
Consultant Radiologist
Prince Sultan Military Medical City
• Ultrasound is often the initial diagnostic
modality as it is noninvasive, relatively
inexpensive, does not require intravenous
contrast, can be obtained at the bedside, and
can often rapidly and accurately depict many
of the common complications
Normal anatomy
• Knowledge of the exact renal transplant
procedure performed is essential for accurate
interpretation of both normal and abnormal
findings. Particularly important is knowledge
of the vascular anatomy, so that all vessels
and anastomoses can be evaluated for
patency, stenosis or other complications.
* Vascular supply from end-to-side
anastomosis of donor artery and vein
to external iliac artery and vein.
• If multiple arteries, usually joined with
single anastomosis to EIA or can be
anastomosed separately to the external
iliac artery
• Ureter anastomosed to
superolateral wall of
urinary bladder
• The transplanted kidney
is usually placed in an
extraperitoneal location
in the right or left iliac
fossa
• The superficial location
makes it ideal for US
evaluation.
•
• Normal color doppler findings :
- arteries : brisk upstroke, low resistance with
normal RI of 0.6 – 0.75
- normal velocity of main renal artery < 200
cm/s
- veins : may be monophasic with continous
flow, or demonstrate some pulsatility with
cardiac cycle.
Renal artery
Doppler flow
pattern
• The transplanted kidney is a solitary
functioning kidney, so there is usually a
physiological hypertrophy, 15% in first 2
weeks and may increase by 40% in first 6
months.
US Evaluation of Complications of
Renal Transplantation
• Classically, the complications affecting the
transplanted kidney can be categorized as:
- anatomic
- functional
- vascular.
Complications
Anatomic
- Perinephric fluid
collections
- hydronephrosis Vascular
- Renal artery thrombosis
- parenchymal
- Renal vein thrombosis
masses.
- Renal artery stenosis
- Renal vein stenosis
- Arteriovenous fistulas
- Pseudoaneurysms.
Functional
• Rejection
• Drug toxicity
• Acute tubular necrosis
Anatomic Complications
- Perinephric fluid collections
- hydronephrosis
- parenchymal masses.
Perinephric Fluid collections
•
•
•
•
Hematoma
Urinoma
Lymphocele
Abscess
• found in ≤50% of renal transplants.
• The clinical relevance of a fluid collection
depends on its composition, size, location and
whether or not it is exerting mass effect on the
transplant kidney, ureter or other adjacent
structures
• Mass effect from perinephric fluid can result in:
-hydronephrosis
-kinking of the vascular pedicle
-edema of the leg, abdominal wall, labia or
scrotum.
• Hematoma
- often present in the immediate postoperative
period ≤2 weeks after surgery
- usually located either in the subcutaneous
tissue , or around the transplant
- the sonographic characteristics vary with age
- acute and chronic hematoma : echogenic
- intermediate hematoma: fluid filled, internal
septations.
• Urinoma
- often present in the immediate postoperative
period ≤2 weeks after surgery
- serious complication, usually caused by a
defect in the uretrovesical anastmosis
- appear as well-defined anechoic collections
without septations, unless infected or mixed
with blood
• Lymphocele
- a more delayed complication, occurring 4 to 8
weeks after surgery
- usually located between the bladder and the
kidney
- cystic, but a majority tend to have septations
- due to disruption of the adjacent lymphatic
channels
• Abscess
• uncommon, but can occur in the early
postoperative period due to pyelonephritis or
bacterial seeding of a urinoma, hematoma or
lymphocele
• Suspected when the patients presents with
fever and increased WBCs
• Sonographically, can vary from an echo-free to
complex echopattern.
Anatomic Complications
- Perinephric fluid collections
- hydronephrosis
- parenchymal masses.
Hydronephrosis
• Either due to extrinsic compression ( perinephric fluid
collection )
• or due to renal calculi, clot, anastomotic edema and
ureteral stenosis .
• It should be noted that anastomotic edema often
results in transient hydronephrosis of the transplanted
kidney.
• Also, apparent hydronephrosis may be the result of an
increased hydrostatic pressure due to a full bladder;
evaluation after voiding can avoid diagnostic error in
this setting.
Parenchymal masses
• Focal parenchymal lesions in the renal transplant,
whether hypoechoic or hyperechoic, are non-specific
findings
• Differential considerations include:
- focal pyelonephritis
- hematoma
- abscess
- infarction
- renal cell or transitional cell carcinoma
- post-transplantation lymphoproliferative disorder
(PTLD)
Anatomic Complications
- Perinephric fluid collections
- hydronephrosis
- parenchymal masses.
Functional Complications
• Rejection
• Drug toxicity
• Acute tubular necrosis
• Ultrasound plays a more limited role in the
evaluation of functional complications.
• very difficult to distinguish from one another
by imaging criteria alone.
Rejection
• Hyperacute rejection
• Acute rejection
• Chronic rejection
Rejection
- Hyperacute rejection : no role since the
diagnosis is typically made immediately after
transplant while still in the operating room
• Acute rejection
- Acute rejection takes several days to develop
and peaks at 1 to 3 weeks after transplant
- findings have been shown to be unreliable in
its diagnosis. In cases of severe acute
rejection, the transplanted kidney becomes
edematous , globular, hypoechoic mass with
poor differentiation of the central renal sinus
fat with elevation of the resistive index
Acute transplant rejection
• Enlarged, globular,
hypoechoic renal
transplant with loss of
the normal
corticomedullary
differentiation and ill
definition of renal sinus
fat due to severe
edema
Acute rejection
• Spectral doppler
image of a
segmental artery
reveals a mildly
increased
resistive index
due to
parenchymal
edema
Chronic rejection
- most common cause of late graft loss
- begins 3 months after the transplantation.
- US: cortical thinning , mild hydronephrosis ,
prominent sinus fat, dystrophic calcification,
decreased color, normal or increased RI.
Acute tubular necrosis
• More common than rejection
• Little sonographic change in parenchyma
pattern.
• ATN occurs in the immediate post transplant
period as a result of ischemia, thus more
commonly seen in cadaveric transplants
Acute tubular necrosis
• In summary, most cases of functional
complications have non-specific imaging
findings consisting of parenchymal edema and
elevated resistive indices and require tissue
analysis with renal biopsy for diagnosis.
Complications
Anatomic
- Perinephric fluid
collections
- hydronephrosis Vascular
- Renal artery thrombosis
- parenchymal
- Renal vein thrombosis
masses.
- Renal artery stenosis
- Renal vein stenosis
- Arteriovenous fistulas
- Pseudoaneurysms.
Functional
• Rejection
• Drug toxicity
• Acute tubular necrosis
Vascular Complications
- Renal artery thrombosis
- Renal vein thrombosis
Early complications
- Renal artery stenosis
- Renal vein stenosis
Late complications
- Arteriovenous fistulas
- Pseudoaneurysms.
post biopsy complications
• Vascular complications occur in less than 10%
of transplant recipients
• Often correctable
• Ultrasound plays a pivotal role in identifying
and quantifying vascular complications of
renal transplants.
Early complications
• Renal artery thrombosis and renal vein
thrombosis are both devastating
complications seen in the early post operative
period that can rapidly lead to graft loss.
Renal artery thrombosis
• a rare early complication
• can be caused by severe rejection, acute
tubular necrosis or faulty surgical technique.
• Doppler US shows absent intrarenal arterial
and venous flow
Renal vein thrombosis
• more common than renal artery thrombosis
• typically occurs between the third and eighth
days post transplant
• Possible etiologies include poor surgical
technique, compression of the renal vein by a
fluid collection or hypovolemia
• On US, The kidney may appear enlarged and
hypoechoic with lack of Doppler signal in the
renal vein.
• The renal artery shows increased resistance,
often with a reversed diastolic flow.
Renal artery stenosis
• usually occurs during the first 3 years after
surgery and is the most common vascular
complication after renal transplantation,
occurring in ≤10% of patients
• Approximately half of stenoses occur at the
anastomosis
• Patients often present with severe hypertension,
audible bruit over the graft and graft dysfunction.
• Doppler US will show a focal area of color aliasing
with peak systolic velocities >200 cm/sec .
• A tardus-parvus waveform may be appreciated in
the arcuate and interlobar arteries of the renal
parenchyma
• Sharp rise systolic flow
• Delayed systolic
upstroke
• Rounding of the
systolic peak
• Decrease RI
Renal vein stenosis
• is less common and usually results from
extrinsic compression by fluid collections or
perivascular fibrosis.
• Doppler US shows focal aliasing with a threeto fourfold increase in velocity indicating a
significant stenosis
• Normal velocity in the
renal vein at the level
of hilum
• At the anastmosis,
there is focal color
aliasing and elevated
velocity
Arteriovenous fistulas and
pseudoaneurysms
• are possible complications from percutaneous
biopsy of the transplant kidney
• The majority of these lesions are small and
clinically insignificant. However, large shunts
may lead to renal ischemia, and rupture of
large arteriovenous fistulas and
pseudoaneurysms can cause hematuria or
perigraft hemorrhage
AVM
- focal area of mixed colors (
aliazing), with high velocity, and
increase diastolic flow, due to AV
fistula.
Pseudoaneurysm
- may appear as simple cyst on
gray scale imaging but with typical
swirling arterial flow on color
doppler
Complications
Anatomic
- Perinephric fluid
collections
- hydronephrosis Vascular
- Renal artery thrombosis
- parenchymal
- Renal vein thrombosis
masses.
- Renal artery stenosis
- Renal vein stenosis
- Arteriovenous fistulas
- Pseudoaneurysms.
Functional
• Rejection
• Drug toxicity
• Acute tubular necrosis
Summary of abnormal renal transplant
US findings
US findings
Differential Diagnosis
Increase size of the
graft
- rejection, infection, venous
Decrease size of the
graft
- Chronic ischemia, chronic rejection
High RI
- Severe
Low RI
- Arterial stenosis,
Hydronephrosis
- Obstruction
thrombosis
rejection, ATN, drug toxicity,
hydronphrosis, extrensic compreesion
AV fistula, advanced aortic or
iliac atherosclerosis
( stone, clot), anastmotic
stenosis/edema, neurogenic bladder, bladder
outlet obstruction.