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Experimental Studies |
1 From the Departments of Radiology (F.J.T., M.J.L.) and Anatomy (S.S.K., W.S.M.), Beaumont Hospital and Royal College of Surgeons in Ireland, Beaumont Rd, Dublin 9, Ireland. Received March 20, 2000; revision requested May 12; revision received July 6; accepted July 25. Address correspondence to M.J.L. (e-mail: leebeau@iol.ie).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Helical CT was used to guide the sequential injection of 100-mL intravenous boluses of dilute contrast medium, up to 300 mL, into the perirenal space of eight embalmed cadavers (three male, five female; mean age at death, 82 years; range, 72–93 years), with four left-sided and four right-sided injections. All images were acquired after the final injection (300 mL total) to facilitate coronal and sagittal reconstruction of relevant images. All images were reviewed to assess the flow pathways of contrast medium from the perirenal space to other retroperitoneal spaces.
RESULTS: In three cadavers that received left perirenal space injections and in two cadavers that received right perirenal space injections, communication was seen with the contralateral perirenal space through an area anterior to the aorta and inferior vena cava. In three cadavers that received right perirenal space injections, contrast material flowed from the right perirenal space to outline the bare area of the liver. Communication between the perirenal and pelvic extraperitoneal spaces was seen in all eight cadavers; contrast material extended into the pelvic extraperitoneal and presacral spaces.
CONCLUSION: These findings show that the perirenal spaces communicate with each other across the midline and with the pelvic extraperitoneal spaces. Clinical implications are that perinephric collections can potentially flow into the pelvis or across the midline.
Index terms: Abdomen, anatomy, 87.92 • Computed tomography (CT), contrast enhancement, 872.12112 • Computed tomography (CT), helical, 872.12115 • Retroperitoneal space, CT, 87.92
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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The current trend toward interventional radiology as a therapeutic modality in the treatment of intraabdominal disease, in particular the drainage of intraabdominal collections, requires definition of the anatomy of the retroperitoneum and its subcompartments (5). The many recent advances in imaging technology enable us to visualize the retroperitoneal compartments, and knowledge of retroperitoneal space communications might influence catheter placement.
Elucidation of the retroperitoneal anatomy until now has been achieved with observation of various clinical conditions (6). Findings of hematoma or urinoma secondary to trauma, abscess formation in diverticular disease, and fluid collections arising from acute pancreatitis have, with their distribution and natural evolution in the retroperitoneum, partially answered our questions (7,8). Experimental studies range from cadaveric dissection alone (9) to cadaveric dissection after the injection of latex or barium into the perirenal spaces and the correlation of findings with those of cross-sectional cadaveric imaging (10).
Another recent experimental model involves the injection of contrast medium into the retroperitoneum in cadavers and the performance of transverse imaging through the retroperitoneum (2). We favor this model since it is more accurately reproducible. By using this model, we sought (a) to determine, with the aid of helical computed tomography (CT), the anatomic communications of the perirenal space in cadavers; (b) to clarify contradictions in the literature regarding communication between the perirenal space and other retroperitoneal compartments; and (c) to provide information that assists in the clinical-radiologic assessment and treatment of various retroperitoneal diseases.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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The cadavers were selected according to size, with a bias toward large cadavers, which facilitated easier needle placement in the perirenal spaces and which provided better tissue plane definition at transverse imaging. Preparation of cadavers was performed by infusing a mixture of phenol, formaldehyde, alcohol, and glycerine via the femoral artery, with simultaneous fluid drainage from the adjacent femoral vein. All patients had died of conditions unrelated to the abdominal cavity, and in all patients, there was no history of abdominal or pelvic surgery or pathologic conditions.
All cadavers were imaged in the supine position with a helical CT scanner (Somatom Plus 4; Siemens, Erlangen, Germany). Initial localizing helical CT was performed (8-mm section thickness, pitch of 1:1.5, 120 kV, 200 mA, no gantry tilt, and standard reconstruction algorithm) to aid needle placement in the perirenal space. A 22-gauge, 20-cm Chiba needle (Cook, Bloomington, Ind) was directed into the perirenal space adjacent to the renal hilum, the anatomic location that best allowed correct siting of the needle tip in the perirenal space (Fig 1). In all but one cadaver, needle placement was achieved in one pass to minimize leakage of contrast medium through excess needle tracks.
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Review of each image was performed by two radiologists (F.J.T., M.J.L.) specializing in body imaging. Images were observed for clear delineation of the perirenal space, flow of contrast medium to the contralateral perirenal space across the midline, and flow to other named anatomic spaces. The effect of the injection of increasing volume was also observed. Finally, the presence of retrograde leakage of contrast medium along the needle track was also documented. All results were documented by consensus.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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The perirenal space was clearly delineated in all cadavers as a thin rim of contrast medium surrounding the kidney after the first injection of 100 mL of contrast medium (Fig 2). Contrast material tracked across the midline, anterior to the aorta and inferior vena cava and below the level of the renal hilum, in three of the cadavers after the initial bolus injection of 100 mL of contrast medium (Fig 3). The additional two injections, up to a total of 300 mL, served only to enhance the aesthetic character of the images and did not demonstrate any additional communication pathways between the retroperitoneal spaces. Contrast medium outlined the contralateral perirenal space in the case of the right ptotic kidney after the initial 100-mL contrast medium injection. In another cadaver, contrast medium crossed the midline as far as the inferior vena cava but failed to enter the right perirenal space even after the total 300 mL of contrast medium had been injected.
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In all four cadavers, contrast medium passed freely from the inferomedial aspect of the perirenal space into the right and left pelvic extraperitoneal compartments, as described earlier with the contralateral injections. Again, this passage occurred after the initial 100-mL injection (Figs 5, 6).
In three of four cadavers, contrast material tracked from the upper right perirenal space along the posterior aspect of the liver to outline the bare area of the liver, which was situated extraperitoneally between the dorsal ends of the hepatorenal (Morison pouch) and subphrenic recesses of the peritoneal cavity (Fig 7). Contrast medium was seen outlining the bare area of the liver after the injection of 100 mL of contrast medium in two cadavers and after the injection of 200 mL in the third. In two of these cadavers, there was additional tracking of contrast medium along the undersurface of the right lobe of the liver that caused effacement of the hepatorenal recess, which was best seen after the injection of 300 mL of contrast medium (Figs 7, 8). In two cadavers, contrast medium tracked into the peritoneal cavity along the needle track but remained localized.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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Anatomists Congdon and Edson (9) inferred a potential conduit across the midline between the two perirenal spaces. Since then, Meyers (12) has refuted this finding, claiming that fusion of the Gerota fascia with the dense collagenous connective tissue over the great vessels precludes communication between the two spaces. Kneeland et al (11) and others (2,3) have since demonstrated continuity across the midline in both clinical circumstances and cadaveric models. Raptopoulos et al (10) reconciled both views with the pathway-barrier theory that describes a fenestrated multitier barrier of septa separating the perirenal space from the central retroperitoneum that either facilitates or prevents communication between the perirenal space and the retroperitoneum, depending on the acuteness of the pathologic process. Our findings confirm the presence of a conduit, the Kneeland channel (named after one of the authors [11] who described it), between the two perirenal spaces below the level of the renal hila. It has been postulated (4) that above this level the anatomic barrier of the celiac and superior mesenteric axes prevents communication across the midline.
The upper boundary of the perirenal spaces has also created controversy with advocates, once again, regarding both a closed and an open theory. Meyers (12) described a closed upper perirenal space, with fusion of the anterior and posterior fascia above the adrenal glands. Furthermore, he specified that the right anterior pararenal space extended cephalic to the bare area of the liver and that the posterior pararenal space was limited superiorly by the diaphragm. Raptopoulos et al (1) similarly described a closed superior perirenal space.
Our study findings that demonstrate communication between the upper perirenal space and the bare area of the liver are in concordance with those of other authors (11,13,14). However, two cadavers that received injections in the right perirenal space demonstrated contrast medium tracking along the undersurface of the right lobe of the liver. This appearance most probably represents flow of contrast medium extraperitoneally along the hepatic surface of the hepatorenal recess. Lim et al (4) described free communication with the subphrenic extraperitoneal space abutting the inferior aspect of the left hemidiaphragm. We could not confirm this communication in our model, since no passage of contrast medium was seen beyond the superior boundary of the left perirenal space.
Raptopoulos et al (1) advocated a multilaminar filter barrier theory and showed no inferior communication between the perirenal and anterior or posterior pararenal spaces. This theory was based on the discovery of a multilaminar fascia in which the anterior and posterior perirenal fascias meet inferiorly. The model used was cadaveric dissection with or without prior injection of latex into the perirenal space.
Our findings also suggest a degree of inferior fusion between the anterior and posterior fascias but with a definite inferomedial defect best seen on the coronal reconstructions on which contrast medium tracked consistently into the pelvic extraperitoneal space. In addition, the presence of contrast material tracking along the properitoneal fat plane on images of all our cadaveric subjects strongly suggests communication between the caudal extremity of the perirenal space and the inferior portion of the posterior pararenal space.
Despite the nondynamic nature of this study, we suggest that contrast medium passes in retrograde fashion into the posterior pararenal space and, from there, anteriorly along the properitoneal fat plane toward the prevesical space (2). Our cadavers were studied in only the supine position, as this position best simulated that of most sick patients. It is probable that communication would have been demonstrated between the inferior perirenal and anterior pararenal spaces if we had performed the studies with the cadavers in the prone position.
The argument persists as to whether an embalmed cadaver is appropriate for study of the fascial planes (2). We suggest that, since several authors have almost identically demonstrated the flow pathways between the retroperitoneal spaces, the pathways are probably real conduits rather than selective identically located defects caused by the embalming process in all cadavers studied. When anatomic issues are addressed, the possibility of natural variations must always be considered. The limited number of cadavers used in our study precludes us from commenting definitively on this issue. In our study, the cadavers in which flow was not seen between the perirenal spaces may represent such anatomic variation.
Practical applications: The findings of this study strengthen the argument in favor of free communication between the perirenal spaces across the midline and with the pelvic extraperitoneal spaces below and the upper abdominal extraperitoneal spaces on the right, namely, the bare area of the liver. This finding has direct clinical implications in the management of several clinical conditions, predominantly in the prediction of the behavior of fluid collections in the retroperitoneum and in their treatment, a role which is now in the domain of the interventional radiologist. On the basis of our description of intercommunications between the perirenal spaces and other abdominal and pelvic extraperitoneal compartments, we can now critically evaluate the implications of a collection in specific extraperitoneal sites, possible pathologic causes, and treatment options relating to such collections. Furthermore, by using our knowledge of the flow pathways in the retroperitoneum and with the aid of gravity, one can achieve successful drainage of these collections with interventional radiologic techniques and avoid the surgical alternative with its associated morbidity. This knowledge may, in the future, help in planning the delivery of therapeutic agents to the retroperitoneum in cases of primary and metastatic tumor, fibrosis, amyloidosis, and pseudotumor.
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FOOTNOTES |
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS DISCUSSIONREFERENCES |
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