Ultrasound imaging of liver and renal transplantation.
Most complications can be detected by ultrasound imaging, thus often making ultrasound the first-line method of diagnosis. Ultrasound is often the modality of choice for primary evaluation, 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 common complications, most notably those of vascular etiology. Computed tomography, magnetic resonance imaging magnetic resonance imaging (MRI), noninvasive diagnostic technique that uses nuclear magnetic resonance to produce cross-sectional images of organs and other internal body structures. , and angiography are often reserved for cases in which ultrasound is inconclusive or the extent of a finding cannot be fully appreciated by ultrasound alone. It is essential that the radiologist is able to recognize these complications so that proper management, including further diagnostic workup work·up
n. Abbr. w/u
A thorough medical examination for diagnostic purposes. or surgical/radiologic intervention, can ensue.
In this article, the basic postsurgical anatomy of liver and renal transplants is presented, as well as the sonographic appearance of several of the complications that can often be detected by ultrasound, with emphasis on vascular complications.
Various surgical techniques have been developed to increase the number of available organs for transplantation, including the use of living donor transplants or split cadaveric organ transplants. Liver splitting involves the division of a donor cadaveric liver in order to transplant the left lateral segment into a small child and the extended right segment into a larger child or adult. (2,3) The sonographer Sonographers are medical professionals who operate ultrasonic imaging devices to produce diagnostic images and scans, videos, or 3D volumes of anatomy and diagnostic data. Sonography requires specialized education and skills to view, analyze and modify the scan to optimize the must know the type of procedure that was performed in order to correctly identify and assess the involved vasculature vasculature /vas·cu·la·ture/ (vas´ku-lah-chur)
1. circulatory system.
2. any part of the circulatory system.
n. , particularly when variant or suboptimal anatomy is identified or when a premorbid premorbid /pre·mor·bid/ (-mor´bid) occurring before development of disease.
Preceding the occurrence of disease. condition necessitates alteration of the routine transplant procedure, as in the case of an interposition in·ter·pose
v. in·ter·posed, in·ter·pos·ing, in·ter·pos·es
a. To insert or introduce between parts.
b. To place (oneself) between others or things.
Basic whole-liver transplantation involves 1 biliary and 4 vascular anastomoses and routine cholecystectomy. The preferred biliary anastomosis anastomosis /anas·to·mo·sis/ (ah-nas?tah-mo´sis) pl. anastomo´ses [Gr.]
1. communication between vessels by collateral channels.
2. is end-to-end from the donor common bile duct common bile duct
The duct that is formed by the union of the hepatic and cystic ducts and discharges into the duodenum. Also called gall duct. to the recipient common hepatic duct common hepatic duct
The part of the biliary duct system that is formed by the confluence of the right and left hepatic ducts and is joined by the cystic duct to become the common bile duct. . However, if the recipient common hepatic duct is diseased, too short, or otherwise inadequate for anastomosis, a choledochojejunostomy or hepaticojejunostomy with a Roux-en-Y limb is constructed.
The hepatic arterial anastomosis is typically an end-to-end fish-mouth anastomosis where the donor common hepatic artery In anatomy, the common hepatic artery is a short blood vessel that supplies oxygenated blood to the liver, pylorus (a part of the stomach), duodenum (a part of the small intestine) and pancreas. and splenic artery branch point or the origin of the celiac artery with an aortic Carrel Car·rel , Alexis 1873-1944.
French-born American surgeon and biologist. He won a 1912 Nobel Prize for his work on vascular ligature and grafting of blood vessels and organs. patch (small portion of the adjacent aorta surrounding the celiac artery origin) is connected to the recipient right and left hepatic artery bifurcation Bifurcation
A term used in finance that refers to a splitting of something into two separate pieces.
Generally, this term is used to refer to the splitting of a security into two separate pieces for the purpose of complex taxation advantages. or the proper hepaticgastroduodenal artery bifurcation. If the recipient has a dual blood supply to the native liver (for example, a replaced right hepatic artery from the superior mesenteric artery), then the larger of the arterial inflow vessels is used in the anastomosis. When the donor liver has a replaced right hepatic artery, the donor celiac artery with the Carrel patch is harvested and an anastomosis is created between the replaced right hepatic artery and the proximal stump of the donor splenic artery, thus essentially recreating a single origin for the hepatic arterial inflow. (4) At times, it may be necessary to use a donor iliac artery interposition graft attached directly to the supraceliac or infrarenal aorta to ensure adequate arterial inflow as in the case of stenosis or small caliber of the more distal native artery. (5)
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The portal vein anastomosis is also an end-to-end anastomosis. In the case of portal vein thrombosis Portal vein thrombosis
The development of a blood clot in the vein that brings blood into the liver. Untreated portal vein thrombosis causes portal hypertension.
Mentioned in: Angiography or previous portal vein surgery, a donor iliac vein jump graft may be interposed between the recipient superior mesenteric vein superior mesenteric vein
A vein that begins at the ileum in the right iliac fossa, ascends in the root of the mesentery, and unites behind the pancreas with the splenic vein to form the portal vein. or splenic vein and the donor portal vein. (6)
The donor inferior vena cava inferior vena cava
n. Abbr. IVC
A large vein formed by the union of the two common iliac veins that receives blood from the lower limbs and the pelvic and abdominal viscera and empties into the right atrium of the heart. (IVC IVC
inferior vena cava ) is typically transected immediately above and below the intrahepatic portions and the supra- and infrahepatic anastomoses are performed in an end-to-end fashion (Figure 1A). A variation of this procedure involves an end-to-side (piggyback technique) or side-to-side anastomosis, thereby leaving the recipient IVC intact (Figure 1B). (7)
Liver transplant complications
Complications after liver transplantation can be subdivided into vascular and nonvascular. For the purpose of this article, emphasis will be placed on vascular complications.
Nonvascular complications--Small perihepatic fluid collections are common immediately after surgery and typically represent small hematomas or seromas. These collections should resolve within a few days or weeks after surgery. Although ultrasound is sensitive to the presence of perihepatic fluid, the specificity is very low. Many of the common fluid collections, including blood, pus, ascites, bile, or lymph, can all have a similar appearance (Figure 2). The differential diagnosis will depend on the specific appearance and timing of its development related to surgery. The significance of a perihepatic fluid collection often depends on the size of the collection (whether or not there is resultant mass effect) and the clinical setting.
Posttransplant liver parenchymal pa·ren·chy·ma
1. Anatomy The tissue characteristic of an organ, as distinguished from associated connective or supporting tissues.
2. abnormalities may be focal or diffuse. Focal lesions may represent pre-existing donor disease (such as a hepatic cyst or hemangioma hemangioma
Congenital benign tumour made of blood vessels in the skin. Capillary hemangioma (nevus flammeus, port-wine stain), an abnormal mass of capillaries on the head, neck, or face, is pink to dark bluish-red and even with the skin. Size and shape vary. ), infarct, abscess, biloma, or metastatic disease. Particular attention should be paid to the hepatic artery when a liver abscess or infarct is suspected, as they may be the result of hepatic arterial thrombosis or stenosis. Evaluation of the liver parenchyma Parenchyma
A ground tissue of plants chiefly concerned with the manufacture and storage of food. The primary functions of plants, such as photosynthesis, assimilation, respiration, storage, secretion, and excretion—those associated with living may reveal recurrent hepatic disease, as has been well documented in cases of viral hepatitis, primary biliary cirrhosis Primary Biliary Cirrhosis Definition
Primary biliary cirrhosis is the gradual destruction of the biliary system for unknown reasons.
Description , primary sclerosing cholangitis Primary sclerosing cholangitis
A chronic disease in which it is believed that the immune system fails to recognize the cells that compose the bile ducts as part of the same body, and attempts to destroy them. , and malignancy, such as hepatocellular carcinoma and cholangiocarcinoma. Other diffuse parenchymal abnormalities include rejection, ischemia, hepatitis, or cholangitis, but these may show only nonspecific heterogeneity of the liver parenchyma. The hepatic artery resistive index has been shown to be unreliable in the assessment of transplant rejection. (7-9)
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Posttransplantation lymphoproliferative disorder posttransplantation lymphoproliferative disorder A complication of 1-10% of organ transplant recipients, which may be poly- or monoclonal; most affected cells contain EBV, usually latent; post-transplantation Pts at risk for PTLD can be identified by detecting (PTLD) complicates 2% to 8.4% of adult liver transplants. (10) This disease process can involve the lymph nodes, lungs, bowel, and abdominal organs. Extrahepatic ex·tra·he·pat·ic
Originating or occurring outside the liver. disease appears as a poorly defined hypoechoic hilar hi·lar
Of or relating to a hilum. mass, while intrahepatic disease may appear as a focal solid hypoechoic mass or a diffuse infiltrative parenchymal process (11) (Figure 3).
[FIGURE 3 OMITTED]
Biliary complications are common and are seen in up to 25% of transplants. (12) The vast majority of these complications are made up of biliary leaks. Bile leaks may occur at the T-tube insertion site after its removal several months after surgery, and at the anastomosis. Anastomotic strictures may result from scarring secondary to surgical manipulation and can result in intrahepatic biliary ductal dilatation. The native duct will often be normal in caliber. Nonanastomotic leaks and strictures are often the result of ischemia secondary to hepatic artery compromise. (13) Intra- or extrahepatic bilomas can collect as a result of a bile leak, which can then become infected. (14)
Less common biliary complications include biliary sludge and stones. Generalized bile duct abnormalities in the absence of obstruction or leakage can be seen in cases of rejection, ischemia, or cholangitis.
Hepatic vasculature--Vascular complications from liver transplantation can result in significant compromise to the graft, often in the early postoperative period. (11) Gray-scale, color, and spectral Doppler is performed on all of the major vessels in order to exclude thrombosis or stenosis. The authors must emphasize the importance of knowing the exact postsurgical anatomy, as it is essential that all vascular anastomoses are evaluated. The majority of vascular complications occur at or adjacent to an anastomosis.
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Hepatic artery thrombosis is the most common and most devastating vascular complication, accounting for 60% of all vascular complications and occurring in 4% to 12% of adult transplants. (15,16) Hepatic artery thrombosis is the second leading cause of graft failure in the early postoperative period after acute rejection. 7 Patients with hepatic arterial thrombosis may present with fulminant ful·mi·nant
Occurring suddenly, rapidly, and with great severity or intensity, usually of pain.
ful liver necrosis, bile leak due to bile duct necrosis, or relapsing bacteremia. (17)
Ultrasound correctly identifies 92% of thrombosed thrombosed /throm·bosed/ (throm´bozd) affected with thrombosis.
2. Of, being, or characterizing a blood vessel that is the seat of thrombosis. hepatic arteries. (18) Spectral Doppler evaluation of a thrombosed hepatic artery shows absent extra- and intrahepatic arterial flow (Figure 4). False-positive findings of hepatic artery thrombosis are often attributed to technical factors such as large patient size or marked ascites. Occasionally, the arterial flow may be below the level of detection for the ultrasound probe because of hepatic edema, systemic hypotension or proximal stenosis. (5,19) In the acute postoperative period, impending im·pend
intr.v. im·pend·ed, im·pend·ing, im·pends
1. To be about to occur: Her retirement is impending.
2. thrombosis may present with a typical pattern of progression on serial Doppler examinations (Figure 4). Sonograms show normal hepatic arterial flow on day 1, then a progressive decrease of diastolic Diastolic
The phase of blood circulation in which the heart's pumping chambers (ventricles) are being filled with blood. During this phase, the ventricles are at their most relaxed, and the pressure against the walls of the arteries is at its lowest. flow, followed by a dampening of systolic Systolic
The phase of blood circulation in which the heart's pumping chambers (ventricles) are actively pumping blood. The ventricles are squeezing (contracting) forcefully, and the pressure against the walls of the arteries is at its highest. flow, and finally the total loss of the hepatic arterial waveform. (7)
Hepatic artery stenosis has been reported to occur in 11% of orthotopic liver transplant patients, most often at the anastomotic site. (19,20) Contributory factors may include faulty surgical technique, clamp injury, vessel ischemia due to disrupted vasa vasorum, or rejection. Doppler ultrasound of the hepatic artery in the region of the stenosis will show a focal increase in velocity greater than 2 to 3 m/sec with associated turbulence and spectral broadening distally (Figure 5A). Distal to the stenosis, a tardusparvus waveform may be seen, consisting of a prolonged systolic acceleration time (>0.08 seconds) and a resistive index <0.5 (normal 0.5 to 0.7) (Figure 5B). If technical factors do not allow direct visualization of the hepatic artery anastomosis, a tardus-parvus pattern alone in the more distal hepatic artery is approximately 75% sensitive and specific for hepatic arterial stenosis. (19)
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Less commonly, liver transplantation may be complicated by a pseudoaneurysm, most often mycotic mycotic /my·cot·ic/ (mi-kot´ik)
1. pertaining to mycosis.
2. caused by a fungus.
1. Relating to mycosis.
2. and occurring at the anastomosis. An intrahepatic pseudoaneurysm may result from a focal infection or a percutaneous procedure. On ultrasound, the pseudoaneurysm typically appears as an intrahepatic or periportal cystic structure with disorganized dis·or·gan·ize
tr.v. dis·or·gan·ized, dis·or·gan·iz·ing, dis·or·gan·iz·es
To destroy the organization, systematic arrangement, or unity of. turbulent flow along the course of the hepatic artery. (7)
Portal vein thrombosis or stenosis is a less common complication, occurring in 1% to 2% of patients. (15,20) Possible risk factors include faulty surgical technique, hypercoagulable states, vessel size discrepancies that lead to increased turbulence, excessive vessel length or previous portal vein surgery. Ultrasound of portal vein thrombosis may show an echogenic or hypoechoic intraluminal thrombus (Figure 6A) and an absence of Doppler flow (Figure 6B). A focal area of narrowing at the portal venous anastomosis may be normal, particularly in cases of size discrepancy between donor and recipient; however, a greater than 3- to 4-fold increase in velocity at the stenosis relative to the prestenotic segment is compatible with a significant stenosis.
Inferior vena cava thrombosis and stenosis are the least common vascular complications (found in <1% of transplant cases) (15,20) and more frequently involve the anastomosis. (5) With gray-scale ultrasound, IVC thrombus appears as an intraluminal echogenic structure (Figure 7A). Absence of flow can be confirmed with color and spectral Doppler imaging (Figure 7B). Inferior vena cava stenosis may show a focal narrowing of the IVC with color aliasing on Doppler imaging (Figure 8A) that should be differentiated from potential donor-recipient size discrepancy. A greater than 3- or 4-fold velocity increase at the stenosis relative to the prestenotic IVC is considered significant (Figure 8B and C). With IVC thrombosis or severe stenosis, there may be a reversal of flow of the hepatic veins and a loss of the normal phasicity of the venous waveforms of the hepatic veins and IVC proximal to the thrombosis/stenosis (7) (Figure 8D).
The transplanted kidney is usually placed in an extraperitoneal location in the right or left iliac fossa. Kidney transplants are identified by the source of the donor organ, including a cadaveric renal transplant (CRT (1) (C RunTime) See runtime library.
(2) (Cathode Ray Tube) A vacuum tube used as a display screen in a computer monitor or TV. The viewing end of the tube is coated with phosphors, which emit light when struck by electrons. ) (with the donor organ from a cadaver), a "living" renal transplant (LRT) (with the donor organ from a living relative) or a living nonrelative renal transplant (LNRT) (with the donor organ from a living nonrelated person). With CRT, a Carrel patch (a small portion of surrounding aorta) is acquired and anastomosed to the recipient external iliac artery Noun 1. external iliac artery - the outer branch of the common iliac artery on either side of the body; becomes the femoral artery
arteria iliaca, iliac artery - one of the large arteries supplying blood to the pelvis and legs in an end-to-side fashion. Both LRT and LNRT procedures often involve an end-to-side anastomosis of the donor renal artery to the recipient external iliac artery or an end-to-end anastomosis of the donor renal artery to the recipient internal iliac artery internal iliac artery
See internal iliac artery. . Variant anatomy with multiple renal arteries can be anastomosed separately to the external iliac artery or with a Carrel patch that encompasses all of the origins. Alternatively, the individual arteries can be anastomosed to the largest so that there is essentially a single donor vessel supplying the entire graft. The renal vein is attached in an end-to-side anastomosis to the external iliac vein external iliac vein
A continuation of the femoral vein above the inguinal ligament, uniting with the internal iliac vein to form the common iliac vein. . Ureteral ureteral
pertaining to or emanating from the ureter.
ureterectasis. drainage is restored, preferably by means of ureteroneocystostomy. Another procedure sometimes performed for kidneys obtained from donors <5 years of age involves the transplantation of both kidneys into a single recipient and using the donor aorta and vena cava for vascular anastomosis (an "en bloc" pediatric pediatric /pe·di·at·ric/ (pe?de-at´rik) pertaining to the health of children.
Of or relating to pediatrics. transplant). As with liver transplants, knowledge of the exact renal transplant procedure performed is essential for accurate interpretation of both normal and abnormal findings.
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Renal transplant complications
Complications after renal transplantation can also be subdivided into vascular and nonvascular complications.
Nonvascular complications--Perinephric fluid collections are a common occurrence, found in up to 50% of renal transplants. (21) These include urinomas, hematomas, seromas, lymphoceles, and abscesses. Although ultrasound is sensitive for their detection, the sonographic appearance of collections can overlap. The clinical relevance of a fluid collection depends on its composition, size, location, and whether or not it is getting larger or exerting significant mass effect.
The differential diagnosis can be narrowed based on the time of presentation. Urinomas and hematomas often present in the immediate postoperative period (up to 2 weeks after surgery), with hematomas evolving in appearance over time. Lymphoceles are usually delayed, occurring 4 to 8 weeks after surgery. Unless infected or mixed with blood, urinomas appear as well-defined anechoic anechoic /an·echo·ic/ (an-e-ko´ik)
1. without echoes; said of a chamber for measuring the effects of sound.
in ultrasonography, an absence of internal echoes. collections without septations. Perinephric perinephric /peri·neph·ric/ (-nef´rik) perirenal; surrounding the kidney.
around the kidney. abscesses are uncommon but can occur in the early postoperative period and are caused by pyelonephritis pyelonephritis: see nephritis.
Infection (usually bacterial) and inflammation of kidney tissue and the renal pelvis. Acute pyelonephritis is usually localized and may have no apparent cause. or bacterial seeding of a urinoma, hematoma hematoma /he·ma·to·ma/ (he?mah-to´mah) a localized collection of extravasated blood, usually clotted, in an organ, space, or tissue. , or lymphocele. The clinical presentation plays a significant role in establishing the diagnosis.
[FIGURE 9 OMITTED]
[FIGURE 10 OMITTED]
Renal parenchymal abnormalities can be divided into focal or diffuse processes. A focal area of increased or decreased echogenicity may represent focal pyelonephritis, infarct, or rejection (Figure 9).
Posttransplantation lymphoproliferative disorder complicates approximately 1% of renal transplant patients, with a spectrum of disease ranging from mild diffuse polyclonal lymphadenopathy lymphadenopathy /lym·phad·e·nop·a·thy/ (-op´ah-the) disease of the lymph nodes.
angioimmunoblastic lymphadenopathy , angioimmunoblastic lymphadenopathy with dysproteinemia to malignant monoclonal lymphoma. (22) The following can be involved in PTLD: any of the solid organs; hollow viscera viscera /vis·ce·ra/ (vis´er-ah) plural of viscus.
1. The soft internal organs of the body, especially those contained within the abdominal and thoracic cavities. ; abdominal, retroperitoneal retroperitoneal /ret·ro·peri·to·ne·al/ (-per?i-to-ne´al) posterior to the peritoneum.
Situated behind the peritoneum. , and iliac lymph nodes; retroperitoneal musculature; or peritoneum peritoneum (pĕrətənē`əm), multilayered membrane which lines the abdominal cavity, and supports and covers the organs within it. The part of the membrane that lines the abdominal cavity is called the parietal peritoneum. of the abdomen, with the extranodal disease predominating. Involvement of the transplant kidney appears as single or multiple hypoor mixed echogenic masses.
The sonographic appearances of many diffuse renal parenchymal abnormalities are nonspecific. Diffuse renal enlargement, cortical thickening, increased or decreased cortical echogenicity, loss of corticomedullary differentiation, prominent pyramids, and thickening of the collecting system can all be seen in the setting of diminished renal function. Although elevated resistive index obtained at the arcuate arteries was previously described as an accurate method of detecting acute rejection, (23) it has been subsequently shown that increases in the resistive index can be seen in various other conditions, including acute tubular necrosis acute tubular necrosis Nephrology A pathologic change of acute renal failure due to shock, crush injuries, hemoglobinuria, toxic nephrosis, sepsis, drugs-aminoglycosides, amphotericin B, cyclosporine, radiocontrast, ischemia in transplanted kidneys Predisposing , renal vein thrombosis Renal Vein Thrombosis Definition
Renal vein thrombosis develops when a blood clot forms in the renal vein, which carries blood from the kidneys back to the heart. The disorder is not common. , graft infection, compressive perinephric fluid collections, and obstructive hydronephrosis. (24) An elevated resistive index (>0.8) is now used as a nonspecific parameter of renal dysfunction (Figure 10). Ultimate differentiation between acute tubular necrosis (acute vasogenic nephropathy), acute or chronic rejection, or drug nephrotoxicity neph·ro·tox·ic·i·ty
The quality or state of being toxic to kidney cells.
nephrotoxicity(ne·fr requires a biopsy.
Urologic complications occur in 4% to 8% of patients, including urine leak/ urinoma, urinary obstruction, and urinary calculi Calculi (singular, calculus)
Mineral deposits that can form a blockage in the urinary system.
Mentioned in: Urinary Incontinence . (25) Urine leaks and urinomas often occur in the early postoperative period; the patient usually presents with pain and swelling at the surgical site and drainage from the wound. Urinomas appear as nonspecific, well-defined anechoic collections without septations.
Urinary tract obstruction urinary tract obstruction Urology A block in urine flow, often caused by a stone. See Kidney stone. occurs in approximately 2% of renal transplants, most often during the first 6 postoperative months. More than 90% occur at the distal third of the ureter ureter (yrē`tər), thick-walled tube that conveys urine from the kidney to the urinary bladder. It is approximately 10 in. (25. , most commonly at the ureterovesicle junction. (26) Causes of obstruction include edema at the anastomosis, ischemia or rejection leading to fibrosis and stenosis, technical error during the ureteroneocystostomy, and kinking of the ureter. Other, less common causes include calculi, papillary necrosis, fungus ball, hematoma, and extrinsic compression by perinephric fluid.
The patient with urinary obstruction may not complain of typical renal colic, as the transplant kidney is denervated denervated Neurology Nervelessness; loss of neural connections. See Chemical denervation. . Additionally, this denervation denervation /de·ner·va·tion/ (de?ner-va´shun) interruption of the nerve connection to an organ or part.
denervation prevents the transplanted kidney from maintaining any intrinsic tone, often resulting in a persistent appearance of mild dilatation. It should also be noted that edema and fibrosis associated with rejection may prevent the normal dilatation seen with hydronephrosis. (27) Thus, the clinical setting and the use of further imaging (eg, diuretic renography renography /re·nog·ra·phy/ (re-nog´rah-fe) radiography of the kidney.
Radiography of the kidney.
radiography of the kidney. ) may be necessary to determine the functional significance of the appearance of a dilated collecting system. Secondary infection or pyonephrosis should be suspected when complex-appearing urine is detected in a dilated collecting system (Figure 11).
[FIGURE 11 OMITTED]
[FIGURE 12 OMITTED]
Renal transplant recipients are at increased risk for developing renal calculi. (28) Renal stones typically appear as echogenic, strongly shadowing structures in the collecting system. Fungus balls should be suspected when a highly echogenic mass in the transplanted collecting system exhibits weak shadowing.
Renal vasculature--Vascular complications occur in 1% to 10% of patients. (25,29) Renal artery thrombosis renal artery thrombosis Acute renal arterial thrombosis, renal artery occlusion Nephrology Abrupt occlusion of RA which, if complete, may cause permanent renal failure; loss of function of one kidney may be asymptomatic as 2nd is a devastating complication and often leads to graft loss. Doppler ultrasound shows absent intrarenal arterial or venous flow. It should be noted that markedly diminished blood flow can be seen in severe rejection and may not be detected on color Doppler. (30)
Renal vein thrombosis is an early complication that can be secondary to surgical technique, compression of the renal vein by a fluid collection, or hypovolemia hypovolemia /hy·po·vo·le·mia/ (-vol-em´e-ah) diminished volume of circulating blood in the body.hypovole´mic
See oligemia. . The kidney may appear enlarged and hypoechoic with a lack of Doppler signal in the renal vein. The renal artery shows increased resistance, often with reversed, plateauing diastolic flow (31) (Figure 12). Reversal of diastolic flow can also be seen in the setting of severe rejection or acute tubular necrosis, but the additional finding of absent venous flow is essentially diagnostic for renal vein thrombosis.
Renal artery stenosis Renal Artery Stenosis Definition
Renal artery stenosis is a blockage or narrowing of the major arteries that supply blood to the kidneys.
Description usually occurs during the first year after surgery and is the most common vascular complication of renal transplantation. Approximately half of stenoses occur at the anastomosis due to perfusion cannula injury, faulty suture technique, or reaction to suture material, with end-to-end anastomoses having a higher risk of stenosis. Stenosis can occur proximal to the anastomosis (often due to atherosclerotic disease) or distal to the anastomosis, secondary to rejection or turbulent flow. Doppler ultrasound will show a focal area of color aliasing with velocities >2 m/sec, a velocity gradient between the stenotic and prestenotic segment of more than 2:1, and poststenotic spectral broadening (Figure 13A). A tardus-parvus waveform may be observed in the renal parenchyma (32) (Figure 13B).
Renal vein stenosis is less common and usually results from extrinsic compression by fluid collections or perivascular perivascular /peri·vas·cu·lar/ (-vas´ku-lar) near or around a vessel.
around a vessel.
perivascular cellulitis fibrosis. A focal aliasing with a 3- to 4-fold increase in velocity on color Doppler imaging indicates a significant stenosis. (33)
Arteriovenous fistulas and pseudoaneurysms may result from percutaneous biopsy of the transplant kidney. Most 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 hematuria
Blood in the urine. It usually indicates injury or disease of the kidney or another structure of the urinary system or possibly, in males, the reproductive system. It may result from infection, inflammation, tumours, kidney stones, or other disorders. or perigraft hemorrhage. Gray-scale ultrasound may show findings similar to simple or complex renal cysts, but with color Doppler, intense, disorganized flow is identified (Figure 14A). Larger arteriovenous fistulas may show a focal flurry of disorganized color flow thought to be caused by vibration of the tissue surrounding the fistula. The feeding artery will show a high-velocity, low-resistance waveform, and the draining vein may show pulsatile pulsatile /pul·sa·tile/ (pul´sah-til) characterized by a rhythmic pulsation.
characterized by a rhythmic pulsation. , arterialized flow (34) (Figure 14). Pseudoaneurysms with a narrow neck show a "to-and-fro" waveform (forward and reverse flow in the neck). Pseudoaneurysms can occur at vascular anastomoses or in association with infection.
[FIGURE 13 OMITTED]
Ultrasound is a useful tool in imaging both renal and hepatic transplants. Knowledge of the surgical anatomy and normal and abnormal appearances of the transplanted organ permits prompt recognition of complications.
[FIGURE 14 OMITTED]
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Dr. Piyasena is a 4th-year Radiology Resident and Dr. Allison is the Director of the Radiology Residency Program and the Director of Ultrasound, Department of Radiology, Georgetown University Hospital
Georgetown University Hospital was founded in 1898 as part of Georgetown University, a Catholic, Jesuit University in the Georgetown neighborhood of , Washington, DC.
Rohan V. Piyasena, MD, and Sandra J. Allison, MD