DOI: 10.1148/rg.274065135
RadioGraphics 2007;27:1109-1130
© RSNA, 2007
Interventional Radiologic Management of Renal Transplant Dysfunction: Indications, Limitations, and Technical Considerations1
Katsuhiro Kobayashi, MD,
Michael L. Censullo, MD, MA,
Lucho L. Rossman, MD,
Polina N. Kyriakides, MD,
Barry D. Kahan, MD, and
Alan M. Cohen, MD
1 From the Department of Diagnostic and Interventional Imaging (K.K., M.L.C., L.L.R., P.N.K., A.M.C.), and the Division of Immunology and Organ Transplantation, Department of Surgery (B.D.K.), University of Texas Medical School at Houston, 6431 Fannin St, Houston, TX 77030. Presented as an education exhibit at the 2005 RSNA Annual Meeting. Received July 13, 2006; revision requested September 1 and received October 17; accepted October 19. All authors have no financial relationships to disclose.
Address correspondence to K.K. (e-mail: Katsuhiro.Kobayashi{at}di.mdacc.tmc.edu).
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Abstract
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Renal transplantation is the treatment of choice for most patients with end-stage renal disease. However, in spite of continuous progress in surgical techniques and immunosuppressive therapy, a wide variety of vascular and nonvascular complications can arise postoperatively. Vascular complications include transplant renal artery stenosis, arteriovenous fistulas or intrarenal pseudoaneurysms following renal transplant biopsy, extrarenal pseudoaneurysms, and graft thrombosis. Nonvascular complications include urologic complications (eg, ureteral obstruction, urine leak) and perigraft fluid collections (eg, lymphocele, abscess, hematoma, urinoma). These postoperative complications can be diagnosed and managed with minimally invasive techniques; however, an understanding of renal transplant anatomy and the risks of posttransplantation immunosuppressive therapy unique to this patient population is essential to their successful application. In addition, familiarity with the indications for and limitations of these techniques as well as collaboration between the radiologist and the transplantation surgeon are vital for maximizing the chances of renal allograft survival.
© RSNA, 2007
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LEARNING OBJECTIVES
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After reading this article and taking the test, the reader will be able to:
- Identify renal transplant anatomy pertinent to the interventional radiologic management of transplant dysfunction.
- Describe various postoperative complications of renal transplantation, including their underlying causes and diagnostic work-up.
- Discuss minimally invasive techniques and their role in the management of renal transplant dysfunction.
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Introduction
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Renal transplantation was first performed successfully in the early 1950s and since that time has become the treatment of choice for most patients with end-stage renal disease. Renal transplantation confers longer-term survival and a better quality of life than does either hemodialysis or continuous ambulatory peritoneal dialysis (1). However, the success of transplantation depends on the preservation of renal graft function. Although there has been continuous progress in surgical techniques, immunosuppressive regimens, and supportive therapy to help preserve renal transplant function, many challenges remain, including the vascular and nonvascular complications that can arise postoperatively.
Postoperative complications occur in approximately 12%–20% of patients with renal transplants (2). Vascular complications include transplant renal artery stenosis (RAS), arteriovenous fistulas (AVFs) or intrarenal pseudoaneurysms following renal transplant biopsy, extrarenal pseudoaneurysms, and graft thrombosis. Nonvascular complications include urologic complications (eg, ureteral obstruction, urine leak) and perigraft fluid collections (eg, lymphocele, abscess, hematoma, urinoma). A delay in treating any of these complications may lead to the loss of renal graft function or even to the patient’s death.
Interventional radiologists can play a pivotal role in the prompt diagnosis and percutaneous treatment of postoperative complications by performing endovascular treatment, percutaneous urinary intervention, and abscess or fluid drainage. These minimally invasive procedures can either obviate open surgery or stabilize the patient’s condition prior to open surgical reintervention.
In this article, we comprehensively review renal transplant anatomy, the underlying causes of postoperative complications, and the diagnostic work-up that should be performed in these patients. We also discuss and illustrate current approaches to the interventional radiologic management of renal transplant dysfunction, with emphasis on the indications for and limitations and technical aspects of these minimally invasive procedures.
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Renal Transplant Anatomy
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A comprehensive knowledge of transplant anatomy is essential when performing interventional radiologic procedures for the management of postoperative complications. Generally, the transplanted kidney is placed heterotopically in an extraperitoneal space in the pelvis; that is, a right kidney is placed in the left iliac fossa and vice versa (3). The right iliac fossa is usually preferred, since the right iliac vein runs a more superficial and horizontal course on this side of the pelvis, making the creation of vascular anastomoses easier.
Arterial Anastomosis
In patients who receive cadaveric transplants, the donor renal artery along with a portion of the aorta (Carrel patch) is anastomosed end-to-side to the external iliac artery. In patients who receive living donor kidneys that were harvested with only the main renal artery, the donor renal artery is anastomosed either end-to-end to the internal iliac artery or end-to-side to the recipient external iliac artery (Fig 1). Special techniques are used to accommodate anatomic variations in donor kidneys. For example, in the case of multiple renal arteries (seen in approximately 15%–20% of all kidneys) (3), one long Carrel patch containing both branches or two smaller patches are created. Alternatively, an aortic segment can be excised to reshape a Carrel patch for anastomosis, after which two aortic segments, each containing one renal branch, are joined into a single Carrel patch for anastomosis (Fig 2). For two similar-sized renal arteries, a side-to-side conjoined anastomosis can be made to create a common ostium (Fig 3). For different-sized renal arteries, three types of anastomosis can be used: (a) the larger artery can be anastomosed end-to-end to the internal iliac artery and the smaller artery anastomosed end-to-side to the common or external iliac artery; (b) each renal artery can be anastomosed to a separate branch of the internal iliac artery; or (c) a smaller polar artery can be reimplanted end-to-side into the main renal artery. An autogenous vein bypass graft or a synthetic graft can be used to make up for a renal artery of insufficient length.
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Figure 1a. Drawings illustrate arterial anastomosis of a renal transplant with one renal artery. The renal artery is anastomosed either end-to-side to the external iliac artery (a) or end-to-end to the internal iliac artery (b). Note that a portion of the aorta (Carrel patch) is harvested with the renal artery in the end-to-side procedure (arrow). Renal veins are anastomosed end-to-side to the external iliac vein.
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Figure 1b. Drawings illustrate arterial anastomosis of a renal transplant with one renal artery. The renal artery is anastomosed either end-to-side to the external iliac artery (a) or end-to-end to the internal iliac artery (b). Note that a portion of the aorta (Carrel patch) is harvested with the renal artery in the end-to-side procedure (arrow). Renal veins are anastomosed end-to-side to the external iliac vein.
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Figure 2. Drawings illustrate alternate methods of anastomosing multiple renal arteries: excision of two aortic segments and anastomosis as a neo-Carrel patch (2), or side-to-side anastomosis of same-sized renal arteries (3).
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Figure 3. Drawings illustrate alternate methods of anastomosing multiple renal arteries: excision of two aortic segments and anastomosis as a neo-Carrel patch (2), or side-to-side anastomosis of same-sized renal arteries (3).
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Venous Anastomosis
Venous anastomoses are almost always placed end-to-side to the external iliac vein. Multiple renal veins are a more common anatomic variant than are multiple renal arteries. Because multiple renal veins usually have internal collateral vessels (4), smaller veins are typically ligated, resulting in a single anastomosis of the largest vein.
Ureteral Anastomosis
For urinary tract reconstructions, preferences vary from one institution to another. The most common method is the creation of a ureteroneocystostomy, although some institutions prefer a ureteroureterostomy or ureteropyelostomy that connects the recipient native ureter to the donor renal pelvis. Various techniques have been used for ureteroneocystostomy, but the basic approach is to tunnel the transplant ureter through the bladder wall to prevent reflux. The Politano-Leadbetter technique and the Lich-Gregoir technique (multistitch extravesical technique) are the most commonly used techniques. In the Politano-Leadbetter technique, the ureteral anastomosis is created from inside the bladder following placement of the ureter within the tunnel (Fig 4). In the Lich-Gregoir technique, the mucosa-to-mucosa anastomosis is created extravesically, after which the muscle layers of the bladder are reapproximated over the ureter (Fig 5). In the case of a living donor with a unilateral ureteropelvic junction stenosis, the affected kidney is preferentially harvested and a ureteropyelostomy created for urinary drainage.
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Figure 4. Drawing illustrates the Politano-Leadbetter technique of ureteroneocystostomy. This technique involves making an incision into the serosal surface of the urinary bladder and creating a submucosal tunnel within the bladder wall. The ureteral anastomosis is created from inside the bladder.
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Figure 5. Drawing illustrates the Lich-Gregoir technique. After myotomy incision and the creation of a mucosal nick, the ureter is anastomosed to the bladder mucosa with continuous sutures from outside the bladder. A submucosal tunnel is created by reapproximation of the seromuscular layer.
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Pediatric Transplantation
In children weighing less than 20 kg, the iliac fossa is too small to accommodate a kidney from an adult donor. Consequently, the graft is placed in a more cephalic position, with the anastomosis made to the distal aorta and vena cava in an end-to-side manner (5).
Kidney transplants from pediatric cadaveric donors generally consist of both kidneys along with segments of the aorta and vena cava to provide sufficient kidney function reserve for the adult recipient. These transplants are transplanted en bloc through an anastomosis to the recipient iliac vessels, either in an end-to-side fashion or "in continuity" using end-to-end anastomoses, with the donor aorta and vena cava interposed between the divided ends of the recipient external iliac artery and vein (Fig 6).
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Figure 6. Drawing illustrates renal transplantation from a pediatric donor. A segment of the abdominal aorta (A.A.) is anastomosed to the transected external iliac artery (E.I.A.), and the vena cava (V.C.) to the transected external iliac vein (E.I.V.) using an in continuity interposition technique.
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Vascular Complications
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Vascular complications occur in approximately 3%–15% of renal transplant recipients (2) and may result in significant morbidity (6). Because renal transplant biopsy is an important cause of vascular complications, we include a description of biopsy techniques that can minimize vascular injuries. We also discuss allograft rejection, an important cause of renal transplant dysfunction that requires biopsy.
Renal Artery Stenosis
Transplant RAS is a potentially curable cause of treatment-refractory hypertension that accounts for approximately 1%–5% of cases of posttransplantation hypertension (7). Transplant RAS may develop early or late in the posttransplantation period. Patients often experience accelerated hypertension of either sudden or insidious onset that is refractory to multiple drug regimens and is associated with progressive renal insufficiency in the presence of excessive diuretic use or treatment with angiotensin-converting enzyme inhibitors. The presence of a bruit is nonspecific and may be seen in healthy transplant patients.
The cause of transplant RAS appears to be multifactorial; suture technique, renal artery trauma during transplantation, kinking or twisting of the renal artery, rejection, atherosclerosis in donor or recipient arteries, and cytomegalovirus infection have all been implicated (7,8). Transplant RAS usually arises at the surgical anastomosis, although it can also occur in the donor renal artery and in the recipient iliac artery due to surgical trauma (eg, clamp injury). Although transplant RAS can be detected with diagnostic imaging, measurement of the serum cyclosporine level or allograft biopsy is often required to exclude other possible causes of hypertension or renal dysfunction. An algorithm that can be used to guide the diagnostic work-up and management of transplant RAS is shown in Figure 7.
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Figure 7. Diagram illustrates an algorithm for the diagnostic work-up and management of transplant RAS. MRA = magnetic resonance angiography, PTA = percutaneous transluminal angioplasty.
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Color Doppler flow ultrasonography (US) is the most useful initial investigation in patients with suspected transplant RAS. It typically reveals an increase in the peak systolic velocity of the renal artery (>200 cm/sec), color aliasing at the stenotic segment, and a velocity gradient between the stenotic and prestenotic segments of the artery of more than 2:1. Gadolinium-enhanced magnetic resonance (MR) angiography is another useful noninvasive means of evaluating transplant RAS, especially in patients whose body habitus makes them unsuitable for US. Radionuclide imaging that includes the administration of an angiotensin-converting enzyme inhibitor (captopril scan) shows findings similar to those of renovascular hypertension in native kidneys (9).
Catheter-based angiography is the standard technique for diagnosing transplant RAS. The use of low- or isoosmolar contrast material is recommended to reduce the risk of contrast material–induced nephropathy (10). When renal insufficiency is present, carbon dioxide may be substituted for an iodinated contrast agent during preliminary angiography to minimize the use of iodinated agents. We do not favor the use of gadolinium because it may be more nephrotoxic than iodine-based contrast agents at equivalent radiopacities. Along with hydration, acetylcysteine, a thiol-containing antioxidant, may be administered in patients with renal insufficiency to minimize nephrotoxicity (11).
Before selective transplant renal arteriography is performed, it is essential to perform nonselective aortoiliac arteriography to exclude an inflow-preanastomotic stenosis in the recipient arteries, which can mimic transplant RAS clinically. This lesion can be managed well with percutaneous transluminal angioplasty (PTA) or stent placement (Fig 8).
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Figure 8a. Proximal right common iliac artery stenosis in a 51-year-old man with persistent hypertension and a rising serum creatinine level with a renal transplant in the right iliac fossa. (a) Digital subtraction angiogram of the distal aorta and common iliac arteries shows proximal right common iliac artery stenosis with a systolic pressure gradient of 50 mm Hg. PTA was performed with a 10-mm balloon catheter. (b) Angiogram obtained after PTA shows restoration of the normal luminal diameter of the right common iliac artery without a pressure gradient.
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Figure 8b. Proximal right common iliac artery stenosis in a 51-year-old man with persistent hypertension and a rising serum creatinine level with a renal transplant in the right iliac fossa. (a) Digital subtraction angiogram of the distal aorta and common iliac arteries shows proximal right common iliac artery stenosis with a systolic pressure gradient of 50 mm Hg. PTA was performed with a 10-mm balloon catheter. (b) Angiogram obtained after PTA shows restoration of the normal luminal diameter of the right common iliac artery without a pressure gradient.
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Knowledge of the type of anastomosis that was performed is essential to determining the optimal angiographic approach to the transplant renal artery. A contralateral approach is best for accessing an end-to-end anastomosis with the internal iliac artery, whereas an ipsilateral approach is usually best for accessing an end-to-side anastomosis with the external iliac artery. Multiple projections are often necessary to evaluate the stenosis in an ideal profile during angiography. Many end-to-side anastomoses are placed on the anterior external iliac artery and are usually best seen on a lateral view.
Once the stenosis has been optimally imaged and the degree of stenosis measured, the renal artery origin is selectively catheterized and a guide wire passed carefully through the stenosis. Some operators might not recross an obvious high-grade stenosis because of the potential technical difficulty or the risk of causing dissection. Pressure gradients are then measured across the stenosis both before and after angioplasty.
PTA is the initial treatment of choice for significant transplant RAS (Fig 9). Hemodynamically significant transplant RAS is indicated by narrowing of the luminal diameter by more than 50% or by pressure gradients more than 10% greater than the peak systolic blood pressure across the stenosis. Prior to PTA, heparin (3000–5000 U) should be administered to prevent thrombosis. Dilation is performed with an appropriate-sized balloon, normally equal to or 1 mm larger than a normal segment of the renal artery. The success rate of PTA, as shown by serum creatinine levels, ranges from 85% to 93%, with levels usually returning to baseline values within 3–5 days. Blood pressure is normalized in 63%–83% of patients with transplant RAS (12). Serious complications of PTA, such as arterial dissection, rupture, and thrombosis, occur in less than 4% of cases (13).
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Figure 9a. PTA of RAS in a 12-year-old girl with a rising serum creatinine level and hypertension. (a) Digital subtraction angiogram shows stenosis of the proximal main renal artery (arrow). Note the superior pole artery anastomosed end-to-side to the external iliac artery. PTA was performed with a 6-mm balloon. (b) Spot view of the anastomosis obtained during PTA shows a guide wire that was passed across the stenosis using an ipsilateral approach. Note the "waist" at the stenosis (arrow). (c) Postangioplasty angiogram shows a patent renal artery without residual stenosis.
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Figure 9b. PTA of RAS in a 12-year-old girl with a rising serum creatinine level and hypertension. (a) Digital subtraction angiogram shows stenosis of the proximal main renal artery (arrow). Note the superior pole artery anastomosed end-to-side to the external iliac artery. PTA was performed with a 6-mm balloon. (b) Spot view of the anastomosis obtained during PTA shows a guide wire that was passed across the stenosis using an ipsilateral approach. Note the "waist" at the stenosis (arrow). (c) Postangioplasty angiogram shows a patent renal artery without residual stenosis.
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Figure 9c. PTA of RAS in a 12-year-old girl with a rising serum creatinine level and hypertension. (a) Digital subtraction angiogram shows stenosis of the proximal main renal artery (arrow). Note the superior pole artery anastomosed end-to-side to the external iliac artery. PTA was performed with a 6-mm balloon. (b) Spot view of the anastomosis obtained during PTA shows a guide wire that was passed across the stenosis using an ipsilateral approach. Note the "waist" at the stenosis (arrow). (c) Postangioplasty angiogram shows a patent renal artery without residual stenosis.
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Restenosis occurs in 5%–30% of patients over a 6–8-month period (14) and can be treated with repeat PTA. Endovascular stent placement is now being used to treat restenosis, and the reported results have been favorable (Fig 10) (12,14). A stent may also be used in patients with (a) a persistent systolic pressure gradient that exceeds 10 mm Hg after angioplasty, (b) a flow-limiting dissection, and (c) a greater than 30% residual stenosis after angioplasty. Premounted balloon-expandable stents allow highly accurate stent placement, further improving technical success. The role of primary stent placement in this setting is still under investigation.
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Figure 10a. Stent placement for the management of recurrent proximal transplant RAS in a 46-year-old man. The patient had already undergone PTA three times. (a) Selective angiogram of the renal artery demonstrates recurrent proximal RAS (arrow). The pressure gradient measured 60 mm Hg. Following angioplasty with a 5-mm balloon, the pressure gradient decreased to 30 mm Hg but remained at that level. A 5 x 17-mm premounted balloon-expandable stent (Express SD; Boston Scientific, Natick, Mass) was deployed across the stenosis. (b) Angiogram obtained after further expansion of the stent with a 6-mm balloon shows good results. The pressure gradient decreased to 15 mm Hg.
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Figure 10b. Stent placement for the management of recurrent proximal transplant RAS in a 46-year-old man. The patient had already undergone PTA three times. (a) Selective angiogram of the renal artery demonstrates recurrent proximal RAS (arrow). The pressure gradient measured 60 mm Hg. Following angioplasty with a 5-mm balloon, the pressure gradient decreased to 30 mm Hg but remained at that level. A 5 x 17-mm premounted balloon-expandable stent (Express SD; Boston Scientific, Natick, Mass) was deployed across the stenosis. (b) Angiogram obtained after further expansion of the stent with a 6-mm balloon shows good results. The pressure gradient decreased to 15 mm Hg.
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Surgery is indicated for patients in whom PTA or stent placement is unsuccessful and for patients with very severe stenoses that are inaccessible with PTA. A surgical approach may also be preferable for treating stenoses at the anastomosis line (15). Surgical management includes resection and revision of the stenosis and placement of a patch graft or saphenous vein bypass graft at the stenotic segment. Surgery is reported to be successful in 63%–92% of patients, with transplant RAS recurring in 12% of patients after surgery (16).
Percutaneous Renal Transplant Biopsy
Despite advances in noninvasive diagnostic tests and techniques, core needle biopsy is still considered the standard technique for diagnosing renal transplant dysfunction. Although the procedure is relatively simple to perform, it carries a risk of complications, especially those related to bleeding and vascular injuries. Therefore, radiologists should be familiar with the proper biopsy technique to minimize these complications.
Before biopsy, coagulation profiles should be obtained to exclude bleeding disorders. An uncorrectable coagulopathy is an absolute contrain-dication to biopsy.
If the patient is scheduled for hemodialysis, we routinely postpone dialysis until at least 24 hours after biopsy to facilitate hemostasis. Little or no heparin should be used for the first postbiopsy dialysis treatment (17).
Real-time US guidance is most commonly used for these biopsies (Fig 11) because it allows precise localization of the allograft and the renal cortex, which contains the glomeruli to be targeted. A tangential approach at either the upper or lower pole of the allograft yields the largest biopsy area within the renal cortex and avoids major intra- or extrarenal vessels (17,18). The needle track within the kidney should traverse only the renal cortex. Major vessels can easily be identified with additional color Doppler flow US.
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Figure 11. Biopsy of a renal transplant under real-time US guidance in a 46-year-old man with decreasing renal function. An 18-gauge core biopsy needle (arrowheads) was advanced into the allograft cortex at the lower pole using a tangential approach.
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Although core needle biopsies performed with 16–18-gauge automated or semiautomated needles are most common, some centers also perform fine-needle biopsy, which can help detect the presence of rejection but not the degree or type (19). US is performed after biopsy to identify any acute bleeding complications.
The reported prevalence of complications including macroscopic hematuria ranges between 0.06% and 13% (18). Macroscopic hematuria is reported to occur in 5%–8% of patients (20,21). The wide variation in the complication rate may depend on multiple factors, including use of imaging guidance, gauge of the biopsy needle, and availability of follow-up imaging. Major complications of biopsy that lead to allograft loss are quite rare (19,22). Complications that potentially require intervention include perirenal hemorrhage, AVFs, pseudoaneurysms, and arteriocaliceal fistulas. These complications can be managed with transcatheter embolization techniques (described in the following section).
Biopsy-induced Vascular Injuries
AVFs and pseudoaneurysms are the two most common types of vascular injury resulting from percutaneous needle biopsy, occurring in conjunction with 1%–18% of renal allograft biopsies (23). An AVF occurs when an adjacent artery and vein are lacerated simultaneously; a pseudoaneurysm occurs when only the artery is lacerated. These vascular complications are easily detected with color Doppler flow and duplex Doppler US. Characteristic US findings in patients with AVFs include focal areas of disorganized color flow outside the borders of the normal renal vasculature (24). Spectral analysis may show increased arterial and venous flow, with high velocities and low impedance—the classic waveform of AVFs. A dilated draining vein may also be visible. Pseudoaneurysms appear as simple or complex renal cysts on gray-scale US images, but intracystic flow and alternating jets at the neck can be appreciated on color Doppler flow images. MR angiography can be a useful adjunct when US findings are inconclusive (25).
It has been reported that 70% of all AVFs resolve within 1–2 years, but that 30% persist or become symptomatic (26). Persistent or symptomatic AVFs can result in persistent hematuria or transplant dysfunction as the result of marked arteriovenous shunting stemming from an intrarenal "steal" phenomenon (Fig 12). Enlarging pseudoaneurysms can rupture.
Transcatheter embolization is the treatment of choice for both symptomatic AVFs and enlarging pseudoaneurysms. Superselective embolization performed with a coaxial catheter and metallic coils minimizes the loss of functioning allograft tissue. It also allows the occlusion of targeted vessels in a precise and definitive manner, unlike embolization with particles that may reflux into non-targeted branches. Because of the end-arterial supply of the kidney, a proximal occlusion is adequate to exclude AVFs or pseudoaneurysms from the circulation (Fig 13) (27). In AVFs with high blood flow, temporary balloon occlusion of the draining vein may be necessary during coil embolization to prevent coils from making their way into the systemic circulation (28). Pseudoaneurysms with a narrow neck may be embolized with coils tightly packed within the sac itself (Fig 14). This technique allows preservation of flow in the distal renal artery. Surgery is the treatment of last resort because partial and total nephrectomy are the only two options (29).
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Figure 13a. Transcatheter embolization of pseudoaneurysms and an AVF in a 33-year-old man with renal transplant dysfunction. (a) Angiogram of the transplant renal artery shows pseudoaneurysms and an AVF supplied by an enlarged lower segmental artery. (b) Selective angiogram of the segmental artery obtained after proximal embolization of the artery with coils shows successful exclusion of the pseudoaneurysms and AVF. Note the preservation of flow in the upper and middle segmental branches.
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Figure 13b. Transcatheter embolization of pseudoaneurysms and an AVF in a 33-year-old man with renal transplant dysfunction. (a) Angiogram of the transplant renal artery shows pseudoaneurysms and an AVF supplied by an enlarged lower segmental artery. (b) Selective angiogram of the segmental artery obtained after proximal embolization of the artery with coils shows successful exclusion of the pseudoaneurysms and AVF. Note the preservation of flow in the upper and middle segmental branches.
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Figure 14a. Pseudoaneurysm following renal transplant biopsy in a 31-year-old woman. (a) Digital subtraction angiogram demonstrates a pseudoaneurysm at the lower pole of the renal transplant. Following superselective catheterization of the feeding artery with a micro-catheter, the pseudoaneurysm was packed with detachable coils. (b) Selective angiogram of the lobular artery shows successful exclusion of the aneurysm.
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Figure 14b. Pseudoaneurysm following renal transplant biopsy in a 31-year-old woman. (a) Digital subtraction angiogram demonstrates a pseudoaneurysm at the lower pole of the renal transplant. Following superselective catheterization of the feeding artery with a micro-catheter, the pseudoaneurysm was packed with detachable coils. (b) Selective angiogram of the lobular artery shows successful exclusion of the aneurysm.
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Extrarenal Pseudoaneurysms
Extrarenal pseudoaneurysms are extremely uncommon in patients with renal transplants (<1% of patients); when they do occur, however, they can be devastating because of their potential for rupture (30). Extrarenal pseudoaneurysms may result from surgical techniques or infection and usually occur at the site of the arterial anastomosis. These pseudoaneurysms may be asymptomatic or may manifest clinically as a large, pulsating mass accompanied by abdominal pain. Hypertension or allograft dysfunction may be seen owing to the extrinsic compression of renal vessels. Color Doppler flow and duplex Doppler US can easily depict the pseudoaneurysms, whose features are the same as those of their intrarenal counterparts (24).
Although a few cases of the successful salvage of allografts with coil embolization (31) or US-guided thrombin injection of the pseudoaneurysm (32) have been reported, transplant nephrectomy is generally performed to prevent rupture (5). The placement of an endovascular stent graft may be an option in patients with an iliac artery pseudoaneurysm following transplant nephrectomy (33).
Graft Thrombosis
Graft thrombosis, either arterial or venous, is a rare complication, with a reported prevalence of 0.5%–6.2% (34); however, it is a major cause of graft loss in the early (<1 week) posttransplantation period. Renal artery thrombosis usually stems from the surgical technique and results from torsion, kinking, or angulation of the anastomosis or dissection of the arterial wall. Endovascular techniques with stent placement may prevent thrombosis in such patients (Fig 15). External compression by a hematoma or lymphocele or propagation of a deep venous thrombosis from the ileofemoral vein may lead to a renal vein thrombosis. Other causes include a hypercoagulable state and acute rejection (35).
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Figure 15a. Dissection of the renal artery salvaged with stent placement in a 61-year-old man. The patient had experienced persistent renal dysfunction after undergoing cadaveric transplantation 1 month earlier. (a) Digital subtraction angiogram of the right external iliac artery (ipsilateral femoral approach) shows dissection of the renal artery, a potential precursor to thrombosis. A 5 x 18-mm stent was placed across the stenosis and further expanded to 6 mm with a balloon. (b) Angiogram obtained after stent placement shows improvement of distal flow to the renal transplant.
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Figure 15b. Dissection of the renal artery salvaged with stent placement in a 61-year-old man. The patient had experienced persistent renal dysfunction after undergoing cadaveric transplantation 1 month earlier. (a) Digital subtraction angiogram of the right external iliac artery (ipsilateral femoral approach) shows dissection of the renal artery, a potential precursor to thrombosis. A 5 x 18-mm stent was placed across the stenosis and further expanded to 6 mm with a balloon. (b) Angiogram obtained after stent placement shows improvement of distal flow to the renal transplant.
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In renal artery thrombosis, flow in both main and intrarenal arteries is completely absent at color Doppler flow US (36). Radionuclide imaging shows absent perfusion, as indicated by a photopenic image at the allograft site (37). In renal vein thrombosis, color Doppler flow US shows completely absent venous flow and an abnormal arterial signal with a plateaulike reversed diastolic flow (38). Radionuclide imaging does not show a photopenic image, although it may show a lack of allograft perfusion (37). Catheter-based angiography, MR angiography, or MR venography may be performed to help confirm these findings (39). Graft loss is inevitable if the diagnosis of graft thrombosis is delayed. In patients with renal vein thrombosis, thromboembolic and septic complications or graft rupture resulting from the high venous pressure may cause death.
Once graft thrombosis has occurred, surgical thrombectomy with arterial or venous repair is usually performed; however, nephrectomy is necessary in most cases. Although several successful cases of catheter-directed thrombolysis with or without percutaneous angioplasty or stent placement have been reported (5,40,41), the role of interventional management in graft thrombosis is not clearly defined. Catheter-directed thrombolytic therapy is not recommended during the first 10–14 days after transplantation because of the risk of vascular suture line leakage secondary to an immature anastomosis (40).
Allograft Rejection
Acute rejection is the most common type of allograft rejection, affecting up to 40% of patients with renal transplants. With the advent of cyclosporine and current antirejection drugs, acute rejection is now typically asymptomatic. However, it may be accompanied by fever, graft tenderness, oliguria, or proteinuria. Typical histologic features include interstitial inflammation with or without hemorrhage, tubulitis, and arterial or arteriolar endotheliitis (42). The characteristic radionuclide imaging finding in patients with acute rejection is diminished flow, which is also seen in acute tubular necrosis (9). The differential diagnosis in the setting of absent flow includes graft thrombosis. Although Doppler US shows no specific findings, acute rejection can be identified from a resistive index that exceeds 0.80 (24).
Chronic rejection, the leading cause of late graft loss, is histologically characterized by sclerosing vasculitis and extensive interstitial fibrosis (42). A graft affected by chronic rejection shows a thin cortex and mild hydronephrosis on both gray-scale US and radionuclide images (24). Allograft biopsy is usually required to correctly diagnose acute or chronic rejection and to determine prognosis.
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Urologic Complications
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A urologic complication rate of 3%–9% has been reported (43). The transplant ureter tends to be involved by complications because of its limited vascular supply, which originates only from the renal hilum. Urologic complications consist predominantly of urine leaks and ureteral obstructions. The Politano-Leadbetter technique is associated with a greater prevalence of ureterovesical obstruction than is the Lich-Gregoir technique. In contrast, the Lich-Gregoir technique is associated with a higher prevalence of urine leaks and reflux (37). An algorithm for use in the diagnostic work-up and management of urologic complications occurring in conjunction with perigraft fluid collections is shown in Figure 16.
Ureteral Obstruction
Ureteral obstruction is reported to occur in 2%–10% of all renal transplant recipients (44). The most common cause is ureteral ischemia, normally involving the terminal ureter at the ureterovesical junction. This area is particularly vulnerable to ischemia because of its anatomic location: It is farthest from the renal artery that supplies the ureteral branch (45). Other causes of obstruction include ureteral kinking, perigraft fibrosis, extrinsic compression from perinephric fluid collections or masses, intrinsic obstruction from edema or stricture at the ureteroneocystostomy, clots, calculi or tumors, and previously unrecognized ureteropelvic junction obstruction that becomes evident in the postoperative period (2,45,46).
Mild dilatation of the renal pelvis and the ureter is quite common due to denervation of the transplanted renal collecting system (39); however, a rising serum creatinine level or oliguria indicates a possible ureteral obstruction. The early diagnosis of a ureteral obstruction can be challenging because renal allograft rejection has similar presenting features (47). Urinary tract infection is another clinical scenario encountered in patients with a ureteral obstruction because of their immunosuppressed state. US or radionuclide imaging can help confirm hydronephrosis. Renography performed with radioisotopes is less sensitive, allowing detection of ureteral stenosis in only 18% of cases, probably because of impaired uptake in the obstructed allograft (37). Computed tomography (CT) and MR imaging are also useful in excluding possible extrinsic compression from perigraft fluid collections or calculi.
Antegrade nephrostography is very effective in diagnosing ureteral obstruction. It not only depicts the site and nature of the obstruction (Fig 17), but can also show an access route for urinary drainage, permitting recovery of renal function, which confirms the diagnosis. Careful caliceal puncture is crucial in performing antegrade nephrostography. Because this access route will be used in the subsequent intervention, caliceal puncture minimizes the risk of vascular injuries during intervention. The lateral calix is ideal for entry, since this route avoids a possible transperitoneal approach that is more painful for the patient and is associated with the risk of injury to organs and vessels that may overlie the allograft (48). The Whitaker test, a pressure flow examination, is rarely performed nowadays because it provides little additional information (49). Retrograde pyelography is ideal for patients with a ureteroureterostomy or ureteropyelostomy but is often challenging to perform in patients with a ureteroneocystostomy because of the difficulty in cannulating the ureter. Therefore, it is important to obtain the patient’s surgical history before undertaking the procedure.
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Figure 17. Ureteral obstruction in a 37-year-old woman with a rising serum creatinine level. Antegrade pyelogram (right anterior oblique projection) reveals a distal ureteral stricture (arrow) associated with severe hydronephrosis. Note the 22-gauge needle that was placed in a superior and lateral calix to avoid taking a peritoneal approach.
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Once the diagnosis of ureteral obstruction is established, a nephrostomy catheter is placed to permit recovery of renal function and provide access for subsequent percutaneous intervention. In patients with an acute obstruction secondary to edema at the ureteroneocystostomy or ureteral blood clots, urinary diversion through the nephrostomy catheter often temporarily relieves the obstruction until the edema subsides or clots are passed spontaneously (50). In cases complicated by infection, it is essential to externally drain the infected urine through the nephrostomy catheter with appropriate antibiotic coverage (Fig 18). However, it is important not to overdistend the collecting system and to minimize the amount of manipulation necessary to place the catheter so as to prevent septicemia. Antegrade pyelography is performed once the infection subsides. We place an antegrade nephroureteral stent in patients with persistent obstructions after definitive nephrostomy drainage. Balloon ureteroplasty is performed when high-grade perianastomotic strictures are found. A 5–8-mm angioplasty balloon is typically used, depending on the size of the ureter adjacent to the narrowing. The balloon is left inflated with a high pressure of 10–12 atm for approximately 30–120 seconds. The balloon dilation is repeated, or the balloon is increased in size until balloon waisting disappears. The nephroureteral stent can subsequently be exchanged for an 8–9-F pediatric-length double-J stent with a temporary "safety" nephrostomy catheter that is removed 24–48 hours later (Fig 19). Although a nephroureteral catheter can be left in place for subsequent follow-up nephrostography or repeat dilation when necessary, we prefer to place a double-J stent to minimize discomfort to the patient and the risk of infection associated with the external catheter in this immunosuppressed patient population (39,46). The double-J stent is eventually removed at flexible cystoscopy when clinically appropriate, usually in 6–12 weeks.
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Figure 18a. Emphysematous pyelitis treated with percutaneous nephrostomy in a 67-year-old diabetic woman who had undergone living-related renal transplantation 10 years earlier. (a) CT scan demonstrates air-fluid levels within the renal collecting system. Note the presence of pyelocaliectasis, a finding that suggests ureteral obstruction. Percutaneous nephrostomy was performed for external drainage, and the patient was started on intravenous antibiotic treatment. Urine culture grew Pseudomonas aeruginosa. (b) Antegrade pyelogram obtained after the patient had recovered clinically shows a proximal ureteral stricture (arrow). Note the decompressed renal collecting system. Adhesion of the proximal ureter to the surrounding scar tissue was found at surgery, and ureterolysis was performed to free up the ureter.
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Figure 18b. Emphysematous pyelitis treated with percutaneous nephrostomy in a 67-year-old diabetic woman who had undergone living-related renal transplantation 10 years earlier. (a) CT scan demonstrates air-fluid levels within the renal collecting system. Note the presence of pyelocaliectasis, a finding that suggests ureteral obstruction. Percutaneous nephrostomy was performed for external drainage, and the patient was started on intravenous antibiotic treatment. Urine culture grew Pseudomonas aeruginosa. (b) Antegrade pyelogram obtained after the patient had recovered clinically shows a proximal ureteral stricture (arrow). Note the decompressed renal collecting system. Adhesion of the proximal ureter to the surrounding scar tissue was found at surgery, and ureterolysis was performed to free up the ureter.
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Figure 19a. Balloon dilation of a ureteral stenosis followed by double-J stent placement in a 27-year-old woman with a rising serum creatinine level. (a) US image of the renal transplant shows moderate hydronephrosis. (b) Antegrade nephrostogram demonstrates a distal ureteral stenosis (arrow) and ureteral dilatation. (c, d) Fluoroscopic images show balloon dilation of the stenosis (c) and a double-J stent that was subsequently placed across the stenosis (d).
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Figure 19b. Balloon dilation of a ureteral stenosis followed by double-J stent placement in a 27-year-old woman with a rising serum creatinine level. (a) US image of the renal transplant shows moderate hydronephrosis. (b) Antegrade nephrostogram demonstrates a distal ureteral stenosis (arrow) and ureteral dilatation. (c, d) Fluoroscopic images show balloon dilation of the stenosis (c) and a double-J stent that was subsequently placed across the stenosis (d).
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Figure 19c. Balloon dilation of a ureteral stenosis followed by double-J stent placement in a 27-year-old woman with a rising serum creatinine level. (a) US image of the renal transplant shows moderate hydronephrosis. (b) Antegrade nephrostogram demonstrates a distal ureteral stenosis (arrow) and ureteral dilatation. (c, d) Fluoroscopic images show balloon dilation of the stenosis (c) and a double-J stent that was subsequently placed across the stenosis (d).
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Figure 19d. Balloon dilation of a ureteral stenosis followed by double-J stent placement in a 27-year-old woman with a rising serum creatinine level. (a) US image of the renal transplant shows moderate hydronephrosis. (b) Antegrade nephrostogram demonstrates a distal ureteral stenosis (arrow) and ureteral dilatation. (c, d) Fluoroscopic images show balloon dilation of the stenosis (c) and a double-J stent that was subsequently placed across the stenosis (d).
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The success rates for internal stent placement combined with balloon ureteroplasty vary depending on the location of the obstruction and the time elapsed since transplantation. The distal ureter, especially at the ureterovesical junction, is the most common location of a ureteral obstruction. Obstructions at this location are usually seen in the early posttransplantation period and respond most favorably to a percutaneous approach, with the reported success rate ranging from 73% to 100% (5,44,46,50–52). On the other hand, obstructions at sites other than the distal ureter usually occur later (>3 months after renal transplantation) and respond poorly to a percutaneous approach. The reported low success rates in late obstructions (16%–33%) are mostly the result of generalized or focal fibrosis associated with rejection (46,51). Nonetheless, percutaneous intervention can facilitate conservative treatment prior to surgical intervention. The complications associated with this approach are generally minor, with infection (including bacteremia) and hematuria being the most frequent complications. Severe complications leading to graft loss are quite rare (50,51).
Urine Leak
Urine leak occurs in approximately 1%–5% of renal transplant patients (50). Because of the risk of infection in these patients, who are in an immunosuppressed state, urine leak is a potentially life-threatening complication requiring prompt intervention. Most leaks occur(a) at the distal ureter, possibly as a result of necrosis due to ischemia or rejection; or (b) at the ureteroneocystostomy site, stemming from problems at the time of surgery. Leaks occur less frequently in the proximal ureter or pelvicaliceal system secondary to distal ureteral obstruction.
Patients with urine leaks may present with pain, swelling, discharge from the wound, or urinoma. US and CT can demonstrate a perigraft fluid collection (Fig 20a). The pelvicaliceal system may be dilated as a result of ureteral obstruction by the urinoma. Radionuclide imaging can suggest a urine leak by showing abnormal uptake around the transplant (Fig 20b). A definitive diagnosis can be made on the basis of the creatinine level in the fluid from the wound or in the peri-transplant fluid obtained with US- or CT-guided needle aspiration. The urinoma should be drained percutaneously to relieve the extrinsic compression (and hence the associated symptoms) and to prevent infection.
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Figure 20a. Urine leak from the distal ureter in a 44-year-old man who had undergone renal transplantation and presented with hematuria and decreased renal function. (a) CT scan shows a large fluid collection surrounding the renal transplant. Note the deformity of the transplant, which is compressed by the collection. (b) Three-hour-delayed radionuclide image obtained with technetium-99m diethylenetriaminepentaacetic acid demonstrates abnormal uptake around the allograft, a finding that was not seen on a 20-minute-delayed image (not shown). Note the dilated pelvicaliceal system. US-guided aspiration of the perigraft fluid collection helped confirm a urinoma. A drainage catheter was placed within the urinoma. (c, d) Antegrade nephrostograms demonstrate a leak from the distal ureter (c) and an 8-F nephrostomy catheter that was placed for urinary diversion (d). Arrowhead indicates the drainage catheter within the urinoma.
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Figure 20b. Urine leak from the distal ureter in a 44-year-old man who had undergone renal transplantation and presented with hematuria and decreased renal function. (a) CT scan shows a large fluid collection surrounding the renal transplant. Note the deformity of the transplant, which is compressed by the collection. (b) Three-hour-delayed radionuclide image obtained with technetium-99m diethylenetriaminepentaacetic acid demonstrates abnormal uptake around the allograft, a finding that was not seen on a 20-minute-delayed image (not shown). Note the dilated pelvicaliceal system. US-guided aspiration of the perigraft fluid collection helped confirm a urinoma. A drainage catheter was placed within the urinoma. (c, d) Antegrade nephrostograms demonstrate a leak from the distal ureter (c) and an 8-F nephrostomy catheter that was placed for urinary diversion (d). Arrowhead indicates the drainage catheter within the urinoma.
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Figure 20c. Urine leak from the distal ureter in a 44-year-old man who had undergone renal transplantation and presented with hematuria and decreased renal function. (a) CT scan shows a large fluid collection surrounding the renal transplant. Note the deformity of the transplant, which is compressed by the collection. (b) Three-hour-delayed radionuclide image obtained with technetium-99m diethylenetriaminepentaacetic acid demonstrates abnormal uptake around the allograft, a finding that was not seen on a 20-minute-delayed image (not shown). Note the dilated pelvicaliceal system. US-guided aspiration of the perigraft fluid collection helped confirm a urinoma. A drainage catheter was placed within the urinoma. (c, d) Antegrade nephrostograms demonstrate a leak from the distal ureter (c) and an 8-F nephrostomy catheter that was placed for urinary diversion (d). Arrowhead indicates the drainage catheter within the urinoma.
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Figure 20d. Urine leak from the distal ureter in a 44-year-old man who had undergone renal transplantation and presented with hematuria and decreased renal function. (a) CT scan shows a large fluid collection surrounding the renal transplant. Note the deformity of the transplant, which is compressed by the collection. (b) Three-hour-delayed radionuclide image obtained with technetium-99m diethylenetriaminepentaacetic acid demonstrates abnormal uptake around the allograft, a finding that was not seen on a 20-minute-delayed image (not shown). Note the dilated pelvicaliceal system. US-guided aspiration of the perigraft fluid collection helped confirm a urinoma. A drainage catheter was placed within the urinoma. (c, d) Antegrade nephrostograms demonstrate a leak from the distal ureter (c) and an 8-F nephrostomy catheter that was placed for urinary diversion (d). Arrowhead indicates the drainage catheter within the urinoma.
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Antegrade nephrostography can accurately demonstrate the site of a leak, and percutaneous nephrostomy can divert urinary flow, permitting ureteral healing (Fig 20c, 20d). In cases of a suspected urinary bladder leak, which usually develops at the site of the cystostomy or ureteroneocystostomy, the leak can be demonstrated at cystography (37). A Foley catheter is left in the bladder for urinary drainage.
Surgical revision is required in some cases; however, the placement of a nephroureteral stent, or of a double-J stent with a nephrostomy catheter for external drainage,
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Abstract
LEARNING OBJECTIVES
