Complications of renal transplantation: MR findings.

Because of its direct multiplanar capability, superb soft tissue contrast and ability to obtain dynamic three-dimensional angiograms using contrast agents without nephrotoxicity, magnetic resonance (MR) imaging and magnetic resonance angiography are ideal techniques for evaluating renal transplants. The following pictorial essay reviews the normal MR appearance of the transplant kidney as well as parenchymal, vascular, and peritransplant complications.     

Pancreatic transplantation using portal venous and enteric drainage: the postoperative appearance of a new surgical procedure

PURPOSE: To review the normal radiologic appearance of pancreatic transplants that use portal venous and enteric drainage, and to review the appearance of a variety of postoperative complications. METHOD: We retrospectively reviewed the computed tomographic (CT) scans, magnetic resonance (MR) images, and ultrasounds of patients who had undergone pancreatic transplantation using portal venous and enteric drainage. RESULTS: At CT, the normal pancreatic transplant appears as a heterogeneous mass composed of pancreatic parenchyma, vessels, and omental wrap. On MR imaging, a normal transplant demonstrates intermediate signal intensity on T1- and T2-weighted sequences. Sonographic evaluation of a normal transplant reveals a hypoechoic gland that contains readily detectable low-resistance arterial and venous Doppler waveforms. Acute postoperative complications include acute rejection, which has a nonspecific radiologic appearance, and transplant pancreatitis, which is often manifested on CT by stranding of the peritransplant fat. Chronic postoperative complications include small bowel obstructions, graft pancreatitis secondary to obstruction of the Roux loop, and chronic rejection. CONCLUSION: Knowledge of the radiologic appearance of the normal pancreatic transplant is required before transplant-related complications can be detected.     

Imaging the hepatic transplant

The radiologist plays a critical role in the preoperative assessment of possible hepatic transplant candidates. Any abnormality that would preclude transplantation or in some way alter the usual operative technique must be accurately documented and relayed to the surgeons. Computed tomography, duplex ultrasound, and MR imaging are the primary modalities used preoperatively. In some cases, CT performed during arterial portography is utilized to determine whether a liver transplant is necessary or whether a partial hepatic resection would suffice. Postoperatively, biliary obstruction or leakage, vascular thrombosis or stenosis, hemorrhage, and abscess formation are some of the most common potential complications seen in liver transplant patients. CT, duplex ultrasonography, and cholangiography are the mainstays in detecting post-transplant complications. The goal of the radiologist is to aid the clinician in recognizing these potential complications quickly so that operative or radiologic intervention may avoid irreversible graft dysfunction or even patient demise.     

Multi-Slice Spiral CT of Living-Related Liver Transplantation in Children: Pictorial Essay

In pediatric living-related liver transplantation, preoperative evaluation of the recipient is important for surgical planning, while the accurate diagnosis of postoperative complications is essential for graft salvage. Multiplanar and three-dimensional imaging using multi-slice spiral CT can be used for preoperative vascular imaging, as well as for evaluating postoperative complications. In this essay, we describe the usefulness of multi-slice CT, combined with a variety of different reconstruction techniques, for the preoperative evaluation of transplant recipients. In addition, we demonstrate the multi-slice CT findings of postoperative complications, including vascular stenosis or thrombosis, bile duct leak or stricture, and extrahepatic fluid collection.     

A review of sonographic evaluation of renal transplant complications

In this article, we present an overview of renal transplantation with its complications and discuss the abilities and limitations of ultrasound in evaluating these complications. We included renal transplants performed at our institution between 1993 and 2006 and gathered data on more than 1,000 patients who developed graft dysfunction. We analyzed the ultrasound findings in different posttransplant complications and compared our findings with those in published literature. We present this review article that elaborates and categorizes various transplant complications from an ultrasound perspective. Based on imaging evaluation, the complications of renal transplantation can be divided into four major categories: peri-renal, renal parenchymal, renal collecting system, and renal vascular complications. Common complications included acute tubular necrosis, graft rejection, drug nephrotoxicity, hematoma, lymphocele, urinoma, hydronephrosis, and vascular complications. Ultrasound has a key role in identification and management of most of these complications. However, some parenchymal complications may only be diagnosed on renal biopsy. Ultrasound is a very powerful screening tool to assess renal transplant dysfunction and has a primary role in early diagnosis and management of structural and vascular complications, which may need surgical intervention to save the graft.     

Current uses of CT and MR imaging in the staging of lung cancer

In 1986, Pearson reported on the lung cancer experience in Toronto over the past 25 years. The number of unresectable operations had decreased from 25 to 5%. Operative mortality was down from 10 to 3% and 5-year survival increased from 23 to 40%. The reason for these statistics, he stated, was not better surgery but better selection of surgical candidates, due to invasive and noninvasive techniques. CT and MR imaging are part of those noninvasive techniques and also play an important role in guiding the invasive techniques. Although controversy exists regarding the proper size criteria and axis length in nodal assessment, and the use of imaging in staging T1N0M0 lung cancer, most clinicians rely on CT scans to evaluate the patient with lung cancer. No other imaging test is as comprehensive in evaluating the patient with lung cancer. The main role of MR imaging at this time is as a problem-solving tool. Focused MR imaging examinations should be used to evaluate or to resolve specific questions related to invasion of the chest wall, vascular structures, or brachial plexus, and adrenal mass characterization. MR imaging is also useful in evaluating the hilum and mediastinum in patients who cannot receive intravenous contrast for CT evaluation. The overall accuracy of CT and MR imaging is disappointing, particularly in crucial areas of determining operability such as distinguishing between patients with Stage IIIA or IIIB disease. It is unlikely that CT diagnosis can significantly improve; however, there is substantial potential for improved diagnostic accuracy with MR imaging as continued research moves this technology forward. The future may bring improved tissue characterization and vascular evaluation. At present, CT remains the procedure of choice in the initial assessment of the patient with lung cancer. The radiologist must be prepared to interpret these imaging studies in light of the specific findings that determine the stage and thus potential resectability of lung cancer.     

Surgical and endovascular repair of aortic coarctation: normal findings and appearance of complications on CT angiography and MR angiography

OBJECTIVE: A variety of treatment options exist for aortic coarctation, both surgical and catheter-based. Knowledge of the normal radiologic appearance of these, as well as their typical complications, is essential for interpretation of CT and MR angiographic studies in these patients. CONCLUSION: CT and MR angiography are noninvasive techniques that are well suited to follow patients after coarctation repair.     

Evaluation of vascular complications of pancreas transplantation with high-spatial-resolution contrast-enhanced MR angiography

PURPOSE: To retrospectively evaluate high-spatial-resolution contrast material-enhanced three-dimensional (3D) magnetic resonance (MR) angiography for assessment of vascular complications of pancreas allografts. MATERIALS AND METHODS: The institutional review board approved the study and waived the requirement for informed patient consent owing to the retrospective nature of the study with use of an anonymous-subject database. The study was HIPAA compliant. The clinical and MR angiography findings in 11 patients (eight men, three women; mean age, 43 years; age range, 30-54 years) who had a history of pancreatic transplant dysfunction and underwent a total of 13 contrast-enhanced 3D MR angiography examinations were retrospectively reviewed. Comparison with conventional angiography findings was possible for four MR angiography examinations, comparison with surgical findings was possible for two examinations, and clinical follow-up was possible for all examinations. Two observers in consensus and blinded to the clinical results performed image analysis of the arterial and venous segments. Classification agreement was assessed with quadratic weighted kappa statistics. RESULTS: Ten MR angiography examinations revealed vascular complications or signs suggestive of rejection. Only three examinations were considered to have completely normal results. All major complications were detected and included complete or partial arterial graft occlusion, stenosis of the arterial Y-graft caused by a kink, complete venous thrombosis, and arteriovenous fistula with pseudoaneurysm formation. For 46 arterial segments and 15 venous segments with angiographic and/or surgical comparison, overall agreement with MR angiography findings was nearly perfect (mean kappa, 0.983; standard error of the mean, 0.128). CONCLUSION: High-spatial-resolution MR angiography of pancreas allografts enables assessment of the arterial and venous vascular anatomy and can be used to reliably identify clinically relevant vascular complications.     

MR imaging in the management of thoracic malignancies

CT remains the modality of choice for evaluating patients with a thoracic malignancy. In specific cases MR imaging can provide useful information that cannot be obtained with CT, and thus is useful as a problem solving tool. Advantages of MR imaging include superb demonstration of vessels and vessel/mass relationships, direct multiplanar imaging capability, and the potential for tissue characterization. MR imaging is useful in staging the patient with lung cancer when vascular or mediastinal invasion is in question. Its specific applications in surgical planning include the question of chest wall invasion, brachial plexus involvement, and transgression of the diaphragm, pericardium, or lung apex. Multiplanar imaging is useful in radiation therapy planning, displaying lesion extent in a coronal or sagittal format rather than on multiple axial images. Multiplanar capability also resolves problem areas for CT such as the aortopulmonic window, subcarinal region, and lesions at the cervicothoracic or thoracoabdominal junction. Structures such as the trachea and superior vena cava can be evaluated in their plane of anatomic orientation. Routine spin-echo and fast (GRASS) imaging of mediastinal vessels is useful in the evaluation of venous thrombosis as a result of catheters or tumors. The diagnosis and follow-up are obtained without the use of intravenous contrast material or radiation. When CT cannot evaluate vessels adequately because of surgical clip artifacts or postoperative distortion of anatomy, MR imaging is useful in the determination of vessel patency as well as identification of tumor recurrence. Cardiac masses are very well demonstrated by MR imaging. A unique feature of MR imaging is its potential for tissue characterization and ability to assess disease activity. Lymphoma evaluation is an active area of research. MR imaging can evaluate the radiated patient for tumor response and recurrence. Fibrous tissue remains of low signal intensity on T2-weighted images, whereas tumor has increased signal intensity. MR imaging may detect tumor recurrence before an increase in the size of a residual lymphoma mass and before clinical recurrence is evident. The area of increased signal can also serve as a guide to the appropriate site for biopsy to confirm recurrence. In addition, MR imaging can help characterize some adrenal and liver masses, potentially helping to avoid more invasive diagnostic procedures. At the current time MR spectroscopy does not have a clinical role in thoracic malignancies, but it may be a powerful tool in the future for diagnosis and management.     

Imaging of vascular complications after hepatic transplantation

Vascular complications after hepatic transplantation can compromise graft and patient survival. Angiography defines the need for revascularization or retransplantation, but the value of noninvasive imaging in this setting is not clear. To assess the relative merit of noninvasive imaging techniques (sonography, scintigraphy, CT, and MR), we retrospectively reviewed 19 major vascular complications that occurred in 15 of 98 hepatic recipients over a 3 1/2-year period. Portal venous thrombosis was seen in seven patients, donor aortic or hepatic arterial thrombosis in seven, and inferior vena caval thrombosis in five. Sonography provided the initial diagnosis of portal venous thrombosis in three, arterial compromise in five, and caval obstruction in four. CT was the first diagnostic examination to identify portal occlusion in two, donor aortic thrombosis in one, and inferior vena caval thrombosis in one. Scintigraphy and MR imaging provided complementary data. Both sonography and CT are useful in the evaluation of vascular complications that occur after hepatic transplantation; however, neither is sufficiently sensitive to obviate angiographic assessment.     

Complications of anterior cruciate ligament reconstruction: MR imaging

Arthroscopic reconstruction of the anterior cruciate ligament (ACL) using autografts or allografts is being performed with increasing frequency, particularly in young athletes. Although the procedure is generally well tolerated, with good success rates, early and late complications have been documented. As clinical manifestations of graft complications are often non-specific and plain radiographs cannot directly visualize the graft and the adjacent soft tissues, MR imaging has a definite role in the diagnosis of complications after ACL reconstruction and may direct subsequent therapeutic management. Our purpose is to review the normal MR imaging of the ACL graft and present the MR imaging findings of a wide spectrum of complications after ACL reconstruction, such as graft impingement, graft rupture, cystic degeneration of the graft, postoperative infection of the knee, diffuse and localized (i.e., cyclops lesion) arthrofibrosis, and associated donor site abnormalities. Awareness of the MR imaging findings of complications as well as the normal appearances of the normal ACL graft is essential for correct interpretation. Electronic Publication     

Imaging of hip arthroplasty

The imaging evaluation of the prosthetic hip begins with radiography, but arthrography, aspiration, scintigraphy, sonography, CT and MR imaging all have roles in the evaluation of the painful prosthesis. This article will review the appearance of normal hip arthroplasty including hemiarthroplasty, total arthroplasty, and hip resurfacing, as well as the appearances of potential complications such as aseptic loosening and osteolysis, dislocation, infection, periprosthetic fracture, hardware failure, and soft tissue abnormalities.     

移植肝排斥反应血管和胆管改变的MR表现

目的：探讨磁共振血管造影（MRA）和胰胆管成像（MRCP）对诊断肝移植术后排斥反应的价值。方法：6例原位肝移植术（OLT）后排斥反应患者均用磁共振（MR）快速自旋回波（TSE）序列及快速小角度激发梯度回波（FLASH）序列常规扫描、磁共振胆管成像（MRCP）、钆喷替酸葡甲胺（Gd-DTPA）动态增强3D MRA检查,分析各序列图像特点。结果：①形态和信号改变：6例患者均有肝脏体积增大,饱满。仅1例重度急性排斥反应患者肝实质信号异常;②血管异常表现：1例急性排斥反应肝左动脉串珠样改变及供体段门静脉明显变细。1例急性排斥反应肝静脉末梢分支杵状扩张而下腔静脉吻合口通畅。其余4例血管无明显异常表现;③胆管异常表现：4例急性排斥反应患者肝内胆管纤细稀疏,1例肝内胆管未显影,1例无明显异常表现。3例慢性排斥反应患者中2例肝内胆管分支稀疏并左肝管串珠样改变;1例胆总管胆泥形成而肝内胆管未见扩张。结论：肝移植术后排斥反应有一些特征性的血管和胆管MR表现。磁共振血管造影和胆管造影作为一种非侵袭性影像检查方法,可以辅助临床诊断肝移植术后排斥反应。     

Helical CT in renal transplantation: normal findings and early and late complications.

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.     

Vascular and extravascular complications of liver transplantation: comprehensive evaluation with three-dimensional contrast-enhanced volumetric MR imaging and MR cholangiopancreatography

OBJECTIVE: Our purpose was to evaluate a comprehensive MR imaging strategy for recipients of liver transplants that relies on dynamic interpolated three-dimensional (3D) MR imaging for simultaneous vascular, parenchymal, and extrahepatic imaging. MATERIALS AND METHODS: Twenty-three consecutive adult patients underwent 30 MR imaging examinations between 2 days and 99 months (mean, 15 months) after transplantation using a breath-hold 3D gradient-echo sequence (TR range/TE range, 3.7-4.7/1.8-1.9; flip angle, 12-30 degrees ) with an intermittent fat-saturation pulse and interpolation in the section-select direction to enable pixel size 3 mm or less in all dimensions. Unenhanced and triphasic contrast-enhanced 3D imaging (average dose, 0.13 mmol/kg of gadopentetate dimeglumine) was performed. A subset of patients (n = 13) also underwent MR cholangiopancreatography using half-Fourier single-shot turbo spin-echo imaging. MR imaging examinations were correlated with digital subtraction angiography (n = 8), contrast-enhanced cholangiography (n = 9), sonography (n = 13), and histopathology (n = 14). RESULTS: MR imaging revealed abnormal findings in 27 (90%) of 30 examinations, including vascular disease in nine, biliary complications in four, and evidence of intra- or extra-hepatic hepatocellular carcinoma recurrence in six. Digital subtraction angiography confirmed seven MR angiography examinations but suggested disease overestimation in one. Contrast-enhanced cholangiography confirmed findings of MR cholangiopancreatography in seven cases but suggested disease underestimation in two. CONCLUSION: Dynamic interpolated 3D MR imaging combined with dedicated MR cholangiopancreatography can provide a comprehensive assessment of vascular, biliary, parenchymal, and extrahepatic complications in most recipients of liver transplants.     

Imaging in whole organ pancreatic transplants and a multimodality review of its complications

This pictorial review will describe the normal anatomy of whole organ pancreatic transplants and the common surgical variants with which the radiologist should be familiar. Complications may be divided into (1) vascular: arterial occlusion and stenosis, venous thrombosis, pseudoaneurysms and arteriovenous fistulae, (2) parenchymal complications such as pancreatitis and the variety of peripancreatic collections, and (3) enteric complications including leak and fistula formation. The radiologist plays a crucial role in the initial assessment of graft anatomy and perfusion, prompt diagnosis, and increasingly, in the management of complications.     

Dural arteriovenous fistulas: evaluation with MR imaging

The preangiographic diagnosis of cerebral dural arteriovenous fistula (DAVF) can be difficult. The magnetic resonance (MR) images of 12 patients with angiographically proved DAVF were evaluated to characterize the appearance of these lesions and to identify those patients at increased risk for complications. Patients with DAVF demonstrating venous occlusive disease are at higher risk for complications from the arterialized collateral venous system. This venous occlusive disease is demonstrated best at arteriography. The MR imaging appearance of dilated cortical veins without a parenchymal nidus is suggestive of a DAVF with veno-occlusive disease. Eight of the 12 patients in our series demonstrated this finding at angiography. Complications, including infarction and hemorrhage, were identified at MR imaging in eight patients with MR imaging evidence of veno-occlusive disease. At angiography 42% of these complications were not apparent. In one patient with a DAVF draining into an unobstructed right sigmoid sinus, results of MR study were normal. Although patients with DAVF without veno-occlusive disease may have normal findings at MR imaging, DAVF associated with veno-occlusive disease and dilated pial venous drainage can be documented on MR images. This subset of DAVF patients, many of whom were identified only at MR imaging, is at higher risk for complications due to veno-occlusive disease. These patients are believed to require more urgent therapy. MR imaging is useful in the pretherapeutic planning for patients with DAVF.     

Contrast-enhanced MR angiography of abdominal vessels: Is there still a role for angiography?

The purpose of this review article is to describe recent advantages in contrast-enhanced (CE) three-dimensional (3D) magnetic resonance angiography (MRA) in comparison with other vascular imaging techniques, and to discuss their current clinical applications for the imaging of abdominal vessels. Principles and technical considerations are presented and clinical applications are reviewed for different vascular diseases. In ruptured aortic aneurysms and acute dissections CT is the method of first choice. Contrast-enhanced 3D MRA can be well used for therapeutic planning and follow-up in patients with stable disease. A comprehensive MR examination including CE 3D MRA, MR urography and MR nephrogram has the potential to replace the conventional studies for the evaluation of renal vascular disease. It is an accurate method for imaging the origins of coeliac and superior mesenteric arteries, although the image resolution is too low for reliable assessment of the inferior mesenteric artery. Contrast-enhanced 3D MRA has emerged as the method of choice for studying the portal venous system in liver transplant recipients, in patients with portal hypertension and in cases with abdominal tumours for preoperative evaluation. Additional non-invasive flow measurements are useful in monitoring portal hypertension. The abdominal veins can be well imaged using unenhanced MR techniques. Imaging may be facilitated with intravascular contrast media. Contrast-enhanced 3D MRA can replace intra-arterial DSA for diagnosis, therapy planning and follow-up in patients with abdominal vascular disease. Catheter-based arteriography will still be used for interventional procedures such as percutaneous transluminal angioplasty, stent placement and embolisation.     

MR imaging evaluation of the postoperative knee: ligaments, menisci, and articular cartilage

The surgical management of knee injuries has increased in recent years. Postoperative magnetic resonance (MR) imaging of the knee following surgical intervention serves an important role in the diagnostic evaluation of patients with recurrent or residual symptoms following surgical intervention. MR imaging additionally assists in the noninvasive documentation of temporal changes at the surgical site potentially reflective of procedural success, or failure. Background understanding of the common surgical procedures performed, their normal postoperative MR imaging appearance, and imaging features of potential procedural complications are essential in the accurate evaluation of patients following prior knee surgery. The focus of the following article is to review the clinical and MR imaging features of the postoperative knee following prior surgical treatment of ligamentous, meniscal, and articular cartilage injuries of the joint.