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1
Department of Radiology, University of Vienna, Waehringer Guertel 18-20,
A-1090 Wien, Austria.
2
Department of Nephrology, University of Vienna, A-1090 Wien, Austria.
Received July 26, 1999;
accepted after revision September 21, 1999.
Presented at the annual meeting of the American Roentgen Ray Society, New
Orleans, May 1999.
Abstract
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SUBJECTS AND METHODS. Twenty consecutive patients treated with continuous ambulatory peritoneal dialysis who were clinically suspected of dialysis-related complications were prospectively studied with MR peritoneography. For MR peritoneography, 20 ml of gadodiamide was added to 2000-ml dialysate solution (1.36% glucose) that was instilled into the peritoneal cavity. MR peritoneography was performed with the peritoneal cavity filled (n = 12) and after complete drainage of the contrast material-dialysate mixture (n = 20) on a 1.5-T MR unit with a phased array coil. Imaging included axial T1-weighted fast low-angle shot (TR/TE, 174/4.2) with and without fat saturation and axial and coronal T2-weighted fat-saturated turbo spin-echo (3000/138) sequences. All studies were performed without IV contrast material. Images were reviewed for evidence of peritoneal leaks, hernias, loculated fluid collections, and adhesions.
RESULTS. Abnormal findings were detected in 13 (65%) of 20 patients and included retroperitoneal leaks (n = 6), diaphragmatic leaks (n = 2), catheter exit-site leaks (n = 2), inguinal hernias (n = 2), and peritoneal adhesions (n = 1).
CONCLUSION. MR peritoneography is useful for the evaluation of complications related to continuous ambulatory peritoneal dialysis, and it offers excellent tissue contrast and multiplanar imaging for assessment of complications.
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Abdominal CT in conjunction with intraperitoneal infusion of contrast material was used as early as 1979 to assess the dynamics of intraperitoneal fluid [4]. Because of the increased use of CAPD for renal replacement therapy, CT has been a useful diagnostic tool for the assessment of CAPD-related complications. CT of the abdomen and pelvis after intraperitoneal administration of a mixture of contrast material and dialysate (CT peritoneography) can be used to reveal certain complications of CAPD, including fluid leaks and adhesions that restrict the peritoneal space available for dialysis [5, 6]. However, CT peritoneography has several limitations involving multiplanar imaging capabilities, and in addition, iodinated contrast material is required.
To our knowledge, MR imaging has not been used for diagnosis of CAPD-related complications. The purpose of our study was to assess the value of MR peritoneography for diagnosis of CAPD-related complications.
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MR Imaging
Before MR peritoneography, the peritoneal cavity was completely drained of
dialysate. Next, 20 ml of gadodiamide (Omniscan; Nycomed Amersham, Oslo,
Norway) was added to a 2000-ml dialysate solution (1.36% glucose) to achieve a
contrast material concentration similar to that used for MR arthrography
[7]. The contrast
material-dialysate mixture was instilled into the peritoneal cavity. At our
institution, these procedures are performed by the dialysis nurse because
strict adherence to an aseptic technique is mandatory. The patients were
encouraged to walk, strain, and bend for 30 min to achieve good distribution
of the contrast material-dialysate mixture.
MR imaging using a phased array coil was performed on a 1.5-T unit (Vision; Siemens, Erlangen, Germany) with the patient in the supine position. Axial T1-weighted fast low-angle shot (TR/TE, 174/4.2; slice thickness, 8 mm; slice gap, 0.8 mm) and axial and coronal T2-weighted fatsaturated turbo spin-echo images (3000/138; slice thickness, 8 mm; slice gap, 0 mm) were obtained. Coronal, sagittal, or coronal and sagittal T1-weighted fast low-angle shot images with fat saturation were obtained to evaluate questionable findings. Overall, the imaging protocol took about 30 min per patient. Twelve patients underwent MR peritoneography with the peritoneal cavity filled with the contrast material-dialysate mixture. All 20 patients underwent MR peritoneography immediately after complete drainage of the contrast material-dialysate mixture, using the same imaging parameters. All studies were carried out without IV contrast material.
Image Analysis
All MR images were analyzed by two experienced radiologists, who reached
final decisions by consensus. The images were evaluated for loculated
extraperitoneal (i.e., pleural or retroperitoneal) fluid collections, hernias,
unopacified fluid collections, and adhesions. The volume of the fluid
collections was estimated by the following formula: transverse diameter
x anteroposterior diameter x craniocaudal diameter x 0.52
[8]. The collections were
graded as small (5-10 ml), medium (11-30 ml), or large (>30 ml).
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Retroperitoneal leaks were detected in six patients (46%). The fluid collections affecting the para- and perirenal spaces were graded small in two patients and medium in four patients (Fig. 1A,1B). All six patients presented with ultrafiltration problems at CAPD.
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In two patients (15%), diaphragmatic leaks resulting in a moderate right-sided pleural effusion and a large right-sided pleural effusion were found. The leak represented a small discontinuity in one of the two patients (Fig. 2A,2B,2C) and a large disruption in the other (Fig. 3A,3B). Both leaks were surgically confirmed and repaired.
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Abdominal wall leaks (Fig. 4) were discovered in two (15%) of the 13 patients. Fluid collections were found at the site of insertion of the dialysis catheter and were regarded as medium (Fig. 5). Both patients presented with localized abdominal swelling and extravasation of dialysate at the catheter exit site.
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MR peritoneography revealed an inguinal hernia in two patients (15%) (Fig. 6). One patient presented with scrotal edema, and the other patient presented with localized swelling at the inguinal canal and a slight decrease of ultrafiltration. In one patient who presented with extensive peritoneal adhesions, unopacified fluid collections were found on MR peritoneography. In 12 patients, we performed MR peritoneography both with a filled peritoneal cavity and after complete drainage of the peritoneal cavity. MR peritoneography before drainage did not provide any additional information to the examination performed after drainage. No contrast agent-related side effects were seen in our study population.
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Several investigators have performed scintigraphy of the abdomen after the intraperitoneal instillation of a radioisotope and have succeeded in showing inguinal and umbilical hernias [13, 14]. This technique, however, has poor spatial resolution. Since 1979, CT peritoneography has been used to assess the dynamics of intraperitoneal fluid [4]. Twardowski et al. [3] reported that the CT examination of patients on CAPD could be improved by the application of a mixture of contrast material and dialysis fluid before scans were obtained. CT peritoneography has several advantages over standard CT. For example, loculated nonopacified fluid collections can be more readily distinguished from adjacent dialysate in the peritoneal cavity [14, 15]. In addition, the site and pathway of dialysis-fluid leakage can be detected [16, 17]. These advantages are important in abdominal swelling that may be caused by an inflammatory process, extravasation of leaked dialysate, or an abdominal wall hernia.
Patients on CAPD have a high incidence of abdominal hernias caused by chronically increased intraperitoneal pressure [18,19,20]. Leakage may result either in open extravasation of dialysate along the catheter tunnel or in abdominal wall edema from diffusion of the fluid into the subcutaneous tissue. Numerous catheter designs and surgical techniques have been used in attempts to reduce the prevalence of this problem [21,22,23,24]. Until now, CT peritoneography was the imaging technique of choice for CAPD-related complications. However, even in the era of helical CT imaging with thin overlapping slices, CT peritoneography has some limitations in multiplanar reconstructions of large imaging volumes. Moreover, the use of iodinated contrast material runs the risk of anaphylactic reactions. In the literature, data are sparse concerning gadolinium chelates and their excretion in patients with renal disease. Gadopentetate dimeglumine-DTPA (Magnevist; Schering, Berlin, Germany) has an excellent safety profile in terms of drug-related toxicity and the incidence of adverse events [25]. After IV injection, gadolinium chelates diffuse rapidly into the extracellular compartment of the body, and 99.9% are excreted through the kidney [26].
The renal tolerance of the drug is excellent, even in patients with preexisting impairment of renal function [27]. Dörsam et al. [28] showed that gadopentetate dimeglumine can be removed from the body by peritoneal dialysis at a peritoneal clearance rate of 5.13 ml/min.
With retroperitoneal leaks, MR peritoneography depicts a variety of CAPD-related complications with precise detail. Retroperitoneal leaks commonly located at the peri -and pararenal spaces are best seen on T1-weighted fast low-angle shot images, which provide high contrast between dialysate spiked with gadodiamide and the perirenal fat. Because surgery is not feasible in most of these patients, hemodialysis or referral for kidney transplantation is recommended if ultrafiltration failure is clinically significant.
Diaphragmatic leaks are rare complications and are more often seen on the right side (92%) than on the left side. However, even in series with large numbers of patients, no adequate explanation for the right-sided preference was found [29]. In patients with right-sided leaks, MR peritoneography with multiplanar imaging is useful to evaluate all parts of the diaphragm. Coronal and sagittal images may be obtained for assessment of the lateral and posterior recesses (Fig. 3A,3B). Surgical repair of diaphragmatic leaks can achieve a high success rate, and CAPD can be resumed.
Catheter exit-site leaks can be classified according to the anatomic compartment of the leak: subcutaneous, subfascial, or in the rectus sheath (Fig. 4). MR peritoneography may show extravasation of contrast material in these patients. However, in our experience, the precise anatomic compartment is difficult to define with MR peritoneography. Torso array coils placed on the abdomen are susceptible to near-field artifacts. To circumvent this problem, a surface coil placed on the suspected leakage site could be used instead.
Hernias most commonly occur at the site of peritoneal incision for catheter insertion, at the umbilicus, and at the inguinal canal. These sites represent potential areas of structural weakness. Umbilical and inguinal hernias can develop as a result of a sudden increase in intraabdominal pressure and can also cause abdominal wall and scrotal edema. MR peritoneography offers an excellent tissue contrast in patients with hernias. Hernias usually require surgical repair, which was performed successfully on one of our patients.
MR peritoneography was well tolerated by all our patients. Catheter manipulations performed by nurses at the dialysis department ensured adherence to strict aseptic technique. For evaluation of CAPD-related complications, MR peritoneography should only be performed after drainage of the contrast material-dialysate mixture. MR peritoneography with a filled peritoneal cavity did not provide any additional information and did not depict more extraperitoneal leaks.
Our study was limited because we did not compare MR peritoneography with CT peritoneography, which is the standard imaging technique in patients with suspected CAPD-related complications. However, we wanted to avoid the additional radiation burden of CT to chronically ill patients. The purpose of our study was to evaluate the new imaging technique, MR peritoneography. Moreover, we decided not to perform two peritoneographic studies on our patients for ethical reasons. In addition, the rate of false-negative diagnoses cannot be determined from this study because definitive surgical proof was obtained in only two patients with abnormal findings.
In conclusion, MR peritoneography seems to be useful for the evaluation of CAPD patients. It offers excellent tissue contrast and multiplanar imaging capability for evaluation of CAPD-related complications.
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