(Radiographics. 2001;21:1103-1117.)
© RSNA, 2001
Helical CT in Renal Transplantation: Normal Findings and Early and Late Complications1
Carmen Sebastià, MD,
Sergi Quiroga, MD,
Rosa Boyé, MD,
Carmen Cantarell, MD,
Maite Fernandez-Planas, MD and
Agustí Alvarez, MD
1 From the Institute for Diagnostic Imaging (C.S., S.Q.) and the Departments of Radiology (R.B., M.F.P., A.A.) and Nephrology (C.C.), Hospital General Universitari Vall d’Hebron, Passeig Vall d’Hebron 119-129, Barcelona 08035, Spain. Presented as an education exhibit at the 2000 RSNA scientific assembly. Received March 15, 2001; revision requested April 17 and received May 21; accepted May 25. Address correspondence to C.S. (e-mail: sebastia@hg.vhebron.es).
 |
Abstract
|
|---|
Over a 5-year period, 346 helical computed tomographic (CT) studies were performed in renal transplant recipients. Helical CT proved useful in this context by depicting parenchymal, perirenal, renal sinus, pyeloureteral, and vascular complications in great detail. CT often delineates fluid collections and their anatomic relationship to adjacent structures better than ultrasonography (US), particularly in obese patients. CT-guided puncture and drainage can be performed in cases in which US is deemed inadequate. CT angiography can depict arterial diseases such as stenosis, thrombosis, arteriovenous fistulas, aneurysms, and pseudoaneurysms in the graft artery and in the recipient iliac arterial system, thereby obviating conventional angiography in some cases. Helical CT with three-dimensional image reformatting allows accurate imaging of the entire course of ureteral and periureteral diseases (eg, hydronephrosis, ureteral leak and stricture, pyeloureteral obstruction). CT can be used in the confirmation and staging of malignancies of the renal parenchyma and urothelium. It is also helpful in evaluating associated disease in the native kidneys, acute and chronic rejection, graft embolization, and end-stage disease. Although US and nuclear medicine examination are the imaging modalities of choice in renal transplantation, helical CT is a valuable alternative when these techniques are inconclusive.
Index Terms: Kidney, CT, 81.12115, 81.12116, 81.12117 • Kidney, diseases, 81.455 • Kidney, transplantation, 81.455 • Renal angiography, 81.12116
|
LEARNING OBJECTIVES
|
|---|
After reading this article and taking the test, the reader will be able to:
- Discuss the normal vascular and parenchymal helical CT findings in renal transplantation.
- Recognize early and late complications of renal transplantation as diagnosed with helical CT.
- Interpret CT urograms and multiplanar and 3D reformatted images of the graft renal artery and vein and the recipient iliac vasculature.
|
Introduction
|
|---|
Noninvasive imaging techniques have developed considerably in recent years, allowing improved detection of vascular and nonvascular diseases in renal transplantation. Ultrasonography (US) and nuclear medicine examinations make up the vast majority of radiologic procedures used to study these diseases. The new helical computed tomographic (CT) techniques and less nephrotoxic nonionic iodine contrast material allow low-risk, accurate evaluation of renal transplantation diseases at a lower cost and with greater availability than is possible with magnetic resonance (MR) imaging; thus, they are useful in cases in which US or nuclear medicine examinations yield nondiagnostic findings.
Helical CT can depict parenchymal, perirenal, renal sinus, pyeloureteral, and vascular diseases in renal transplantation in great detail.
Posttransplantation complications are characterized as either early or late. Early complications appear in the first weeks after transplantation and are usually attributable to surgical difficulties. Late complications appear some weeks after the procedure and are usually due to medical problems such as those related to immunosuppression and toxicity. Early complications include acute rejection, acute tubular necrosis, hematoma, pyelonephritis, abscess, urinoma, ureteral obstruction, vascular complications (eg, arterial stenosis and thrombosis, arteriovenous fistula and arterial pseudoaneurysm, renal vein thrombosis, graft torsion). Late complications include chronic rejection, other causes of ureteral obstruction, lymphocele, cyst, renal cell carcinoma and transitional cell carcinoma of the graft, complications due to immunosuppression (eg, lymphoma, Kaposi sarcoma, opportunistic infections involving the transplanted kidney).
In this article, we discuss and illustrate the normal parenchymal, vascular, and pyeloureteral helical CT findings in renal transplantation and the CT features of related complications. We also present CT findings in renal graft dysfunction related to the recipient iliac arteries and features of associated disease in the native kidneys, end-stage renal graft failure, and graft embolization.
|
Helical CT Technique
|
|---|
Over the past 5 years, we performed 346 helical CT studies in renal transplant recipients at our institution. Multiplanar and three-dimensional (3D) maximum-intensity-projection (MIP), shaded-surface-display (SSD), and volume-rendered reformatted images of the graft vessels and the recipient iliac arterial system and CT urograms were obtained in all cases. All examinations were performed with a CT-Twin II scanner (Elscint, Haifa, Israel).
We obtained unenhanced, contiguous 10-mm images of the pelvis to help locate the kidney allograft and plan the helical CT study. The study was planned from the top of the graft to the upper margin of the pubic symphysis (3.2-mm collimation, pitch of 1, 50% overlap).
We subsequently injected 100 mL of nonionic contrast material at a rate of 3 mL/sec and began the helical study 20–25 seconds after the start of injection. Another study was performed 120 seconds after contrast material administration to visualize the renal venous phase and, when pyeloureteral complications were suspected, a third, similar helical CT study was performed 5 minutes after contrast material administration.
|
Normal Helical CT Findings
|
|---|
Parenchyma
In adults, most kidney allografts are placed heterotopically in an extraperitoneal location in the iliac fossa (1). At unenhanced CT, the renal parenchyma demonstrates homogeneous soft-tissue attenuation (Fig 1a). Contrast material–enhanced arterial-phase (cortical nephrogram–phase) CT is used to evaluate the renal graft artery and vein and the iliac arterial system. In this phase, the cortex appears hyperattenuating and the medulla remains hypoattenuating because contrast material has not yet reached it (Fig 1b). Venous-phase (tubular nephrogram–phase) CT, at which the normal parenchyma is uniformly enhanced, is useful for demonstrating parenchymal masses (Fig 1c). Late excretory-phase (pyelogram–phase) CT is used to evaluate the pyeloureteral system and demonstrates hypoattenuating, heterogeneous renal parenchyma and contrast material filling of the collecting system (2).
View larger version (115K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1a. Normal graft parenchyma. (a) Unenhanced CT scan of a graft shows a soft-tissue-attenuation structure in the right lower quadrant (arrows). (b) Contrast-enhanced arterial-phase (cortical nephrogram-phase) CT scan shows intense cortical enhancement (arrow). (c) Contrast-enhanced venous-phase (tubular nephrogram-phase) CT scan shows uniformly enhanced parenchyma.
|
|
View larger version (130K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1b. Normal graft parenchyma. (a) Unenhanced CT scan of a graft shows a soft-tissue-attenuation structure in the right lower quadrant (arrows). (b) Contrast-enhanced arterial-phase (cortical nephrogram-phase) CT scan shows intense cortical enhancement (arrow). (c) Contrast-enhanced venous-phase (tubular nephrogram-phase) CT scan shows uniformly enhanced parenchyma.
|
|
View larger version (119K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1c. Normal graft parenchyma. (a) Unenhanced CT scan of a graft shows a soft-tissue-attenuation structure in the right lower quadrant (arrows). (b) Contrast-enhanced arterial-phase (cortical nephrogram-phase) CT scan shows intense cortical enhancement (arrow). (c) Contrast-enhanced venous-phase (tubular nephrogram-phase) CT scan shows uniformly enhanced parenchyma.
|
|
Vasculature
The most common technique for anastomosing the renal graft arterial supply in adults is the end-to-side technique using the renal artery and the external or common iliac artery (Fig 2a). Some surgeons choose an end-to-end anastomosis involving the renal artery and the internal iliac artery (Fig 2b). Multiple renal arteries can be anastomosed together using an aortic patch (Carrel patch) or anastomosed separately (Fig 2c) (1).
View larger version (134K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2a. Arterial anastomosis. (a) SSD reformatted image shows an end-to-side anastomosis between the graft artery and the common iliac artery (arrow). (b) SSD reformatted image demonstrates an end-to-end anastomosis between the graft artery and the internal iliac artery (arrow). (c) SSD reformatted image shows two graft pedicles (arrows) anastomosed to the external iliac artery with a common aortic patch (Carrel patch).
|
|
View larger version (102K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2b. Arterial anastomosis. (a) SSD reformatted image shows an end-to-side anastomosis between the graft artery and the common iliac artery (arrow). (b) SSD reformatted image demonstrates an end-to-end anastomosis between the graft artery and the internal iliac artery (arrow). (c) SSD reformatted image shows two graft pedicles (arrows) anastomosed to the external iliac artery with a common aortic patch (Carrel patch).
|
|
View larger version (190K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2c. Arterial anastomosis. (a) SSD reformatted image shows an end-to-side anastomosis between the graft artery and the common iliac artery (arrow). (b) SSD reformatted image demonstrates an end-to-end anastomosis between the graft artery and the internal iliac artery (arrow). (c) SSD reformatted image shows two graft pedicles (arrows) anastomosed to the external iliac artery with a common aortic patch (Carrel patch).
|
|
Venous anastomoses are almost always performed end to side to the recipient external iliac vein (Fig 3a). When there are no abnormalities, the left donor kidney is preferred because the longer left renal vein facilitates venous anastomosis (3). A venous patch may be used in cases involving a short right renal vein (Fig 3b).
View larger version (152K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3a. Venous anastomosis. (a) SSD reformatted image demonstrates an end-to-side anastomosis between the renal vein and the external iliac vein (arrow). (b) SSD reformatted image shows the renal vein of the graft (thin arrow) anastomosed to the external iliac vein with a saphena patch (thick arrow).
|
|
View larger version (148K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3b. Venous anastomosis. (a) SSD reformatted image demonstrates an end-to-side anastomosis between the renal vein and the external iliac vein (arrow). (b) SSD reformatted image shows the renal vein of the graft (thin arrow) anastomosed to the external iliac vein with a saphena patch (thick arrow).
|
|
Because of early venous graft return, venous helical CT reformatted images can usually be obtained with arterial-phase imaging. When venous reformatted images are specifically required, we begin the helical CT study 30 seconds after contrast material administration.
Pyeloureter
The most frequently used technique for ureteral anastomosis is the Politano-Ledbetter reformatting technique (intravesical anastomosis) (Fig 4), which involves creation of a submucosal vesical tunnel near the trigone to avoid reflux and of a nippled ureteral anastomosis through the inside of the bladder (1). Extravesical anastomosis, in which the ureter is anastomosed from outside the bladder, is also gaining popularity. Advantages of this extravesical technique include decreased bladder bleeding, use of a shorter ureteral segment, and decreased surgical time (4).
View larger version (135K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4a. Ureteral anastomosis. (a) Axial contrast-enhanced CT scan demonstrates the intramural portion of the ureter (arrows). (b) Three-dimensional reformatted image shows kinking of the ureter (arrows).
|
|
View larger version (171K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 4b. Ureteral anastomosis. (a) Axial contrast-enhanced CT scan demonstrates the intramural portion of the ureter (arrows). (b) Three-dimensional reformatted image shows kinking of the ureter (arrows).
|
|
The main objective of ureteral anastomosis is to preserve the maximum vascular supply, thereby preventing ureteral necrosis, which leads to stenosis and leakage. The ureter should be neither too long (and thus susceptible to kinking or twisting) nor too short (and therefore subject to tension).
|
Perirenal and Renal Fluid Collections
|
|---|
Postoperative fluid collections are common following transplantation and include hematomas, lymphoceles, seromas, abscesses, and urinomas (discussed later). The majority of these collections can be detected at US. However, CT often delineates fluid collections and their anatomic relationship to adjacent structures better than US, particularly in obese patients. In addition, puncture and drainage can be performed with CT guidance in cases in which US is inadequate for demonstrating access to the collection.
Perirenal Hematoma
At CT, acute hematoma appears as a fluid collection with hyperattenuating areas prior to intravenous contrast material administration, a finding that is consistent with fresh blood (Fig 5). Immediate postoperative hematoma can be secondary to graft rupture or injury to the vascular pedicle. Emergency surgery is mandatory in these cases. The presence of an asymptomatic, hyperattenuating perirenal collection after surgery is common and can be treated conservatively if it does not increase in size (5,6).
Perirenal Lymphocele
Lymphocele formation is a late complication of renal transplantation caused by lymphatic obstruction or leak. It is usually asymptomatic but sometimes compresses adjacent structures and may cause hydronephrosis. It can occur in up to 15% of renal transplantations. Treatment consists of percutaneous drainage or open surgery. At CT, lymphocele is seen as a round, hypoattenuating collection that appears similar to seroma (Fig 6). The key to differentiation is that seroma appears immediately after surgery and decreases spontaneously, whereas lymphocele develops later and tends to grow.
View larger version (122K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 6. Perirenal lymphocele. Contrast-enhanced CT scan shows a round, hypoattenuating collection (arrow) compressing a graft (arrowhead). The collection does not enhance after contrast material administration, a finding that is consistent with a fluid collection.
|
|
Perirenal Abscess
Perirenal abscess is an uncommon early complication of renal transplantation. When a patient presents with fever and CT demonstrates a hypoattenuating perirenal collection with air, the diagnosis of perirenal abscess is clear (Fig 7). In cases with noninfectious clinical findings and a perirenal collection without air, diagnostic puncture is required. Abscess is treated with percutaneous or surgical drainage.
View larger version (127K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7a. Perirenal abscess in a patient with fever and septicemia. Contrast-enhanced CT scans demonstrate a hypoattenuating perirenal collection (arrows in b) with air (arrowheads), findings that are consistent with a perirenal abscess.
|
|
View larger version (128K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 7b. Perirenal abscess in a patient with fever and septicemia. Contrast-enhanced CT scans demonstrate a hypoattenuating perirenal collection (arrows in b) with air (arrowheads), findings that are consistent with a perirenal abscess.
|
|
Parenchymal Abscess
Urinary tract infection, the most common infection in renal transplant recipients, has a benign course and usually improves with antibiotic therapy. However, bacterial pyelonephritis often accompanies renal failure. Graft kidneys are less responsive to antibiotic therapy for acute pyelonephritis than are native kidneys (7). Abdominal CT should be performed in patients who respond poorly to antibiotic therapy to detect acute focal bacterial nephritis or renal abscess. Abscess manifests as a nonenhancing, hypoattenuating collection in the kidney (Fig 8). CT is used in interventional procedures such as drainage and aspiration for microbiologic culture.
View larger version (144K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 8a. Intrarenal abscess. (a) Axial contrast-enhanced CT scan shows a hypoattenuating collection in the parenchyma (arrow). (b) Coronal reformatted image depicts a biloculated cortical collection (arrows). (c) CT scan shows fine-needle percutaneous puncture. Arrow indicates needle. The sample of purulent material was cultured, and the collection proved to be a bacterial abscess.
|
|
View larger version (182K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 8b. Intrarenal abscess. (a) Axial contrast-enhanced CT scan shows a hypoattenuating collection in the parenchyma (arrow). (b) Coronal reformatted image depicts a biloculated cortical collection (arrows). (c) CT scan shows fine-needle percutaneous puncture. Arrow indicates needle. The sample of purulent material was cultured, and the collection proved to be a bacterial abscess.
|
|
View larger version (148K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 8c. Intrarenal abscess. (a) Axial contrast-enhanced CT scan shows a hypoattenuating collection in the parenchyma (arrow). (b) Coronal reformatted image depicts a biloculated cortical collection (arrows). (c) CT scan shows fine-needle percutaneous puncture. Arrow indicates needle. The sample of purulent material was cultured, and the collection proved to be a bacterial abscess.
|
|
|
Vascular Diseases
|
|---|
CT angiography can depict arterial diseases such as stenosis, thrombosis, arteriovenous fistulas, aneurysms, and pseudoaneurysms in the graft artery and in the recipient iliac arterial system. Conventional angiography remains the standard procedure for diagnosis of arterial diseases, but in many cases it is rendered unnecessary by CT angiography, a lower-risk technique with less radiation exposure and the possibility of reformatting images from any angle while removing superfluous structures with postprocess editing. Helical CT also allows direct visualization of venous thrombosis, torsion, and stenosis when US studies are not diagnostic.
Renal Artery Stenosis
Stenosis, the most common vascular complication of renal transplantation, occurs in 1%–12% of transplanted renal arteries and represents a potentially curable cause of hypertension following transplantation (Fig 9). It can occur as early as 2 days or as late as several years after the procedure. CT angiography yields fewer false-positive results than US and is less prone to artifacts due to postoperative clips than MR imaging in the diagnosis of renal artery stenosis (6,8). The stenosis usually occurs near the anastomosis site and is related to the surgical technique used. Distal stenosis seems to be caused by perfusion alterations, although some authors have suggested that it is a sign of rejection.
View larger version (175K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 9a. Renal artery stenosis in a patient with hypertension. (a) Curved reformatted image reveals more than 90% stenosis adjacent to the anastomosis site (arrow). (b) SSD reformatted image also demonstrates the almost totally occlusive stenosis (arrow).
|
|
View larger version (184K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 9b. Renal artery stenosis in a patient with hypertension. (a) Curved reformatted image reveals more than 90% stenosis adjacent to the anastomosis site (arrow). (b) SSD reformatted image also demonstrates the almost totally occlusive stenosis (arrow).
|
|
Iliac Artery Stenosis
Iliac artery stenosis near the anastomosis site, whether related to the surgical technique or to native atherosclerotic disease, has been described as a cause of hypertension in renal transplant recipients (8). We always evaluate the iliac arterial system with CT angiography to detect these associated vascular diseases (Fig 10).
View larger version (173K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 10. Iliac artery stenosis. MIP reformatted image shows common iliac artery stenosis adjacent to the anastomosis site (arrow). Note the double-artery renal transplant pedicle (arrowheads).
|
|
Renal Artery Thrombosis
Renal artery thrombosis appears immediately after transplantation. It is most often caused by hyperacute or acute rejection but may also be caused by inadequate surgical technique, hypotension, hypercoagulable state, cyclosporine therapy, and atherosclerotic embolism (9). Helical CT can often directly depict renal artery thrombosis when US studies are inconclusive. Renal infarct appears as a nonenhancing kidney with an enhancing capsule (Fig 11). Thrombosis of the main renal artery usually results in loss of the renal allograft.
View larger version (148K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11a. Renal artery thrombosis. (a) Axial contrast-enhanced CT scan depicts graft infarct as a nonenhancing kidney with an enhancing capsule (arrows). (b) Curved coronal reformatted image demonstrates the iliac arterial system and an almost totally thrombosed renal artery (arrows).
|
|
View larger version (77K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 11b. Renal artery thrombosis. (a) Axial contrast-enhanced CT scan depicts graft infarct as a nonenhancing kidney with an enhancing capsule (arrows). (b) Curved coronal reformatted image demonstrates the iliac arterial system and an almost totally thrombosed renal artery (arrows).
|
|
Intrarenal Arteriovenous Fistula and Pseudoaneurysm
Intrarenal arteriovenous fistulas and pseudoaneurysms are caused by trauma during percutaneous needle biopsy. They occur in 1%–18% of renal biopsies (10). Arteriovenous fistulas may form when an artery and vein are lacerated; pseudoaneurysms result when only the artery is lacerated (5). Small lesions may resolve spontaneously; if they do not, they can be successfully treated with percutaneous transcatheter embolization. Seventy percent of all intrarenal arteriovenous fistulas and pseudoaneurysms close spontaneously within 1–18 months (11). They are usually asymptomatic but can manifest with hypertension, hematuria, and deterioration of renal function. Doppler US is the modality of choice for diagnosis. Helical CT is a good alternative when US cannot define the nature of the lesion. Visualization of a round abnormality in the renal parenchyma that enhances similar to the aorta at arterial-phase CT indicates the vascular nature of the lesion. If the 3D reformatted images show abnormal early venous drainage adjacent to the lesion, arteriovenous fistula can be confidently diagnosed (Fig 12).
View larger version (135K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 12a. Intrarenal arteriovenous fistula. (a) Axial contrast-enhanced arterial-phase CT scan demonstrates a round, hyperattenuating mass (black arrow) with enhancement similar to that of the renal artery (white arrow), a finding that is consistent with an aneurysm in the graft parenchyma. (b) Vascular MIP reformatted image depicts the aneurysm (arrows) with early venous return (arrowhead), a finding that is consistent with an arteriovenous fistula.
|
|
View larger version (119K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 12b. Intrarenal arteriovenous fistula. (a) Axial contrast-enhanced arterial-phase CT scan demonstrates a round, hyperattenuating mass (black arrow) with enhancement similar to that of the renal artery (white arrow), a finding that is consistent with an aneurysm in the graft parenchyma. (b) Vascular MIP reformatted image depicts the aneurysm (arrows) with early venous return (arrowhead), a finding that is consistent with an arteriovenous fistula.
|
|
Extrarenal Pseudoaneurysm
The prevalence of extrarenal arterial pseudoaneurysm following renal transplantation is less than 1% (12). Extrarenal pseudoaneurysm is directly related to arterial anastomosis surgery and, rarely, to infectious causes. It is usually asymptomatic but can occasionally cause renal dysfunction or compression of adjacent structures (13). When these pseudoaneurysms become large, they must be surgically removed to avoid spontaneous rupture. On arterial-phase helical CT scans, a saccular dilatation that is isoattenuating relative to the renal artery can be seen at the anastomosis site, a finding that is consistent with a pseudoaneurysm (Fig 13).
View larger version (145K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 13a. Extrarenal pseudoaneurysm. (a) Axial contrast-enhanced arterial-phase CT scan demonstrates a saccular dilatation with mural calcification at the site of anastomosis (arrow). (b-d) MIP (b) and SSD (c, d) reformatted images show different views of the pseudoaneurysm (arrow).
|
|
View larger version (122K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 13b. Extrarenal pseudoaneurysm. (a) Axial contrast-enhanced arterial-phase CT scan demonstrates a saccular dilatation with mural calcification at the site of anastomosis (arrow). (b-d) MIP (b) and SSD (c, d) reformatted images show different views of the pseudoaneurysm (arrow).
|
|
View larger version (139K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 13c. Extrarenal pseudoaneurysm. (a) Axial contrast-enhanced arterial-phase CT scan demonstrates a saccular dilatation with mural calcification at the site of anastomosis (arrow). (b-d) MIP (b) and SSD (c, d) reformatted images show different views of the pseudoaneurysm (arrow).
|
|
View larger version (162K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 13d. Extrarenal pseudoaneurysm. (a) Axial contrast-enhanced arterial-phase CT scan demonstrates a saccular dilatation with mural calcification at the site of anastomosis (arrow). (b-d) MIP (b) and SSD (c, d) reformatted images show different views of the pseudoaneurysm (arrow).
|
|
Renal Graft Torsion
Torsion of the renal graft is a rare surgical complication that usually occurs in children with intraperitoneal transplants. Torsion occurs when the kidney rotates around the vascular pedicle, leading to vascular occlusion and parenchymal infarction (14). Renal torsion can be an early or late complication. Prompt diagnosis permits graft detorsion and possible salvage. The most suggestive imaging finding is a change in the axis of the transplanted kidney. CT and MR imaging can show changes in renal graft orientation and vascular pedicle kinking, or secondary changes such as swelling or abnormal enhancement of the graft, hydronephrosis, and sinusal and perirenal fat infiltration (Fig 14). Torsion may be incomplete and intermittent.
View larger version (151K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14a. Graft torsion in a patient with renal transplant dysfunction. Doppler US depicted flow alterations in the renal artery and vein of the graft. (a) Axial contrast-enhanced CT scan shows pelvic ectasia and perirenal and sinus fat infiltration (arrow). (b, c) Curved (b) and volume-rendered (c) reformatted images demonstrate alteration in the orientation of the graft, torsion of the renal artery (thick arrows), and stenosis in the distal third of the renal vein (thin arrows). The graft was properly repositioned, and renal function improved immediately after surgery.
|
|
View larger version (154K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14b. Graft torsion in a patient with renal transplant dysfunction. Doppler US depicted flow alterations in the renal artery and vein of the graft. (a) Axial contrast-enhanced CT scan shows pelvic ectasia and perirenal and sinus fat infiltration (arrow). (b, c) Curved (b) and volume-rendered (c) reformatted images demonstrate alteration in the orientation of the graft, torsion of the renal artery (thick arrows), and stenosis in the distal third of the renal vein (thin arrows). The graft was properly repositioned, and renal function improved immediately after surgery.
|
|
View larger version (182K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 14c. Graft torsion in a patient with renal transplant dysfunction. Doppler US depicted flow alterations in the renal artery and vein of the graft. (a) Axial contrast-enhanced CT scan shows pelvic ectasia and perirenal and sinus fat infiltration (arrow). (b, c) Curved (b) and volume-rendered (c) reformatted images demonstrate alteration in the orientation of the graft, torsion of the renal artery (thick arrows), and stenosis in the distal third of the renal vein (thin arrows). The graft was properly repositioned, and renal function improved immediately after surgery.
|
|
Renal Vein Thrombosis
Renal vein thrombosis is an early complication of renal transplantation and is usually related to inadequate surgical technique, hypovolemia, renal vein compression, and iliac vein thrombosis (10). Renal vein thrombosis occurs in up to 4% of transplant recipients (15). Doppler US is used for quick diagnosis because the pathologic condition must be treated with thrombectomy as soon as possible. Delayed renal and iliac vein thrombosis has been described in chronic rejection and treated successfully with anticoagulation therapy (16). When renal vein thrombosis occurs, the thrombus can be directly seen inside the vein at helical CT. Indirect signs include visualization of a delayed nephrogram and, on delayed images, the continued presence of contrast material. Helical CT can be useful for follow-up in cases of medically treated venous thrombosis. Stenosis of the renal vein is another infrequent venous complication secondary to inadequate surgical technique and perivenous diseases such as fibrosis or mass compression. Helical CT allows direct visualization of the stenosis and perivascular causes in these cases.
|
Urologic Diseases
|
|---|
Urinoma
The prevalence of urologic complications following renal transplantation is 2.6%–13% (17). Ureteral extravasation producing urinoma can be caused by graft rejection, ureteral necrosis due to ischemia, or inadequate surgical technique (17). Urine leaks usually occur in the 2nd or 3rd postoperative week and require surgical or percutaneous intervention (18). At unenhanced CT, urinoma manifests as a hypoattenuating collection; after contrast material administration, direct visualization of the passage of ureteral contrast material to the collection is the clue to diagnosis (Fig 15).
View larger version (161K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 15a. Urinoma due to ureteral necrosis. (a) Axial contrast-enhanced CT scan shows the distal ureter of the graft (black arrow) with ureteral extravasation (arrowhead) and urinoma (white arrows). (b) SSD reformatted image demonstrates ureteral leakage (arrow).
|
|
View larger version (166K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 15b. Urinoma due to ureteral necrosis. (a) Axial contrast-enhanced CT scan shows the distal ureter of the graft (black arrow) with ureteral extravasation (arrowhead) and urinoma (white arrows). (b) SSD reformatted image demonstrates ureteral leakage (arrow).
|
|
Ureteral Obstruction
Graft hydronephrosis due to complications involving the ureter is encountered in 3%–5% of renal transplant recipients. High-dose steroid use is a strong risk factor for urologic complications, particularly ureteral leak and stricture. With the introduction of cyclosporine therapy associated with low-dose steroid therapy, urologic complications have decreased. Pyeloureteral obstruction can be treated endoscopically with balloon dilation or stent placement (18). There are two kinds of ureteral obstruction: early-onset, which responds better to percutaneous treatment, and late-onset, which responds less well. Early obstruction of the ureter is secondary to kinks, clots, edema, inflammation, or a tight submucosal tunnel. Late-onset obstruction is caused by fibrosis, ischemia, or periureteral masses (Fig 16) or may be secondary to rejection. Helical CT with 3D image reformatting allows accurate imaging of the entire course of ureteral and periureteral diseases.
View larger version (130K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 16a. Pyeloureteral obstruction due to lymphocele. Axial contrast-enhanced excretory-phase CT scans depict graft hydronephrosis (arrow in a) secondary to lymphocele (arrowheads in b) and compressing the distal ureter (arrow in b).
|
|
View larger version (124K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 16b. Pyeloureteral obstruction due to lymphocele. Axial contrast-enhanced excretory-phase CT scans depict graft hydronephrosis (arrow in a) secondary to lymphocele (arrowheads in b) and compressing the distal ureter (arrow in b).
|
|
|
Posttransplantation Malignancies
|
|---|
Immunocompromised patients have a higher prevalence of malignant neoplasms, the most common of which are neoplasms of the skin, cervix, and rectum, Kaposi sarcoma, and lymphoma (19).
Lymphoma
Lymphomas that occur in transplant recipients exhibit aggressive atypical features not commonly seen in lymphomas occurring in the general population. Posttransplant lymphoproliferative disorder is associated with Epstein-Barr virus and occurs in approximately 1% of renal allograft recipients (20).
The most common radiographic appearance of posttransplant lymphoproliferative disorder is lymphadenopathy; however, this disorder can involve any of the solid organs or hollow viscera. It can even affect the graft itself, and its predilection for the renal hilum is noteworthy (21). CT findings are nonspecific and may include nonenhancing or peripherally enhancing, low-attenuation masses (Fig 17).
View larger version (117K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 17a. Lymphoma in a renal graft. (a) Axial contrast-enhanced CT scan shows a hypoattenuating lesion in the renal parenchyma (arrow). (b) Contrast-enhanced CT scan demonstrates pelvic adenopathy (arrow).
|
|
View larger version (147K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 17b. Lymphoma in a renal graft. (a) Axial contrast-enhanced CT scan shows a hypoattenuating lesion in the renal parenchyma (arrow). (b) Contrast-enhanced CT scan demonstrates pelvic adenopathy (arrow).
|
|
Renal Cell Carcinoma
Renal cell carcinoma in the allograft kidney can be inadvertently introduced by means of the transplanted organ or de novo tumor development enhanced by immunosuppression (22). Renal cell carcinoma is generally less aggressive in transplanted kidneys than in native kidneys. Treatment consists of partial or total transplant nephrectomy. The differential diagnosis includes metastasis to the breast or lung, primary renal cell carcinoma in the native kidneys, lymphoma, and abscess. The prevalence of urothelial malignancies is also greater in transplant recipients (23). CT can be used in the confirmation and staging of malignancies of the renal parenchyma (Fig 18) and urothelium.
View larger version (165K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 18a. Renal cell carcinoma in a renal graft. (a) Axial CT scan demonstrates two enhancing tumors in the graft (arrows). (b) SSD reformatted image (craniocaudal view) more clearly delineates the location of the tumors (arrows).
|
|
View larger version (168K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 18b. Renal cell carcinoma in a renal graft. (a) Axial CT scan demonstrates two enhancing tumors in the graft (arrows). (b) SSD reformatted image (craniocaudal view) more clearly delineates the location of the tumors (arrows).
|
|
Kaposi Sarcoma
Kaposi sarcoma accounts for 6% of tumors in patients who have undergone transplantation (24). Renal allograft involvement by Kaposi sarcoma is rare. The disease manifests as graft parenchymal involvement or sinus and hilum involvement (Fig 19). When CT demonstrates an infiltrating lesion in the sinus, the differential diagnosis should include lymphoma, sarcoma, transitional cell carcinoma, and postoperative fibrosis.
View larger version (160K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 19a. Kaposi sarcoma involving a renal transplant. (a) Axial contrast-enhanced CT scan reveals an infiltrating mass in the renal hilum (arrows). (b) Coronal reformatted image shows the mass surrounding the graft pedicle (arrows).
|
|
View larger version (163K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 19b. Kaposi sarcoma involving a renal transplant. (a) Axial contrast-enhanced CT scan reveals an infiltrating mass in the renal hilum (arrows). (b) Coronal reformatted image shows the mass surrounding the graft pedicle (arrows).
|
|
|
Associated Diseases in the Native Kidneys
|
|---|
Primary carcinomas of the kidney account for 4.6% of cancers in renal transplant recipients. Most develop in the native kidneys in cases of acquired renal cystic disease in end-stage renal failure (Fig 20). Native kidneys tend to bleed spontaneously due to the rupture of a cyst or tumor. When a renal transplant recipient has atypical lumbar pain and decreased hematocrit, spontaneous native renal bleeding should be suspected. The diagnosis is easily made with CT (Fig 21).
Top
Abstract
LEARNING OBJECTIVES
