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Radiology of Perinephric Fluid Collections
Clinical Radiology (2002) 57: 339±346 doi:10.1053/crad.2001.0854, available online at http://www.idealibrary.com on
Pictorial Review Radiology of Perinephric Fluid Collections M A U R IC E C . H A DD A D, M A H M O UD M. H AWA RY, N A B I L J . KHO URY, FAY S A L S . A B I - FA K H E R , NA B I L F. A M M O U R I , A G H I A D O . A L - K U TO U B I Department of Diagnostic Radiology, *American University of Beirut Medical Center, Beirut, Lebanon and {Department of Diagnostic Radiology, Tel Chiha Hospital, Zahleh, Lebanon Received: 24 January 2001
Revised: 11 June 2001 Accepted: 13 July 2001
The perinephric spaces consist of the subcapsular, perirenal, anterior and posterior pararenal spaces. Fluid may collect in one or more of these compartments; this can be readily demonstrated by crosssectional imaging, particularly computed tomography (CT). This pictorial review illustrates the radiological manifestations of perinephric ¯uid collections with their dierential diagnosis including perinephric abscess, perirenal urine collection, subcapsular and perirenal hematoma, renal lymphangiomatosis, pancreatic pararenal ¯uid collections and transudate ¯uid associated with nephropathies. Haddad, M. C. et al. (2002). Clinical Radiology 57, 339±346. # 2002 The Royal College of Radiologists Key words: kidney diseases, kidney US, kidney CT.
Lesions involving the perinephric spaces include primary or secondary solid neoplasms and ¯uid collections [1]. The perinephric ¯uid may be pus, urine, blood, lymph, exudate or transudate ¯uid resulting from abnormalities that arise within the kidney or adjacent retroperitoneal structures. In this pictorial review, we display various examples of these conditions and brie¯y discuss the anatomy of the retroperitoneal spaces and communications, the radiological appearances of ¯uid collections, the role of interventional procedures and the dierential diagnosis of perinephric ¯uid collections.
ANATOMIC-PATHOLOGIC CONSIDERATIONS
Basic knowledge of retroperitoneal anatomical spaces and their communications is essential for understanding pathways of ¯uid collections. Fluid can collect into one or more of the following retroperitoneal compartments: the subcapsular space, the perirenal space, the anterior and posterior pararenal spaces (Fig. 1a,b). Author for correspondence and guarantor of study: Dr Maurice C. Haddad, American University of Beirut Medical Center, Department of Diagnostic Radiology, P.O. Box 11-0236, Beirut, Lebanon. Fax: 00961-1-744464; E-mail: [email protected] 0009-9260/02/$ - see front matter
Subcapsular space. The subcapsular area is a potential space where ¯uid can accumulate causing compression of the renal parenchyma with secondary ischemia and renovascular hypertension ± so-called Page kidney, a rare but recognized phenomenon. Perirenal space. The perirenal space is formed by the anterior (Gerota's) and posterior (Zuckerkandl's) renal fascia. There is much controversy concerning the communications of the perirenal spaces. The traditional conception is that the perirenal spaces are open and have the potential for intercommunication across the midline [2,3], and may also communicate through open upper and lower ends with the mediastinum and bare area of the liver superiorly and pelvic extraperitoneal spaces inferiorly [4,5]. However, recent cadaveric studies by Raptopoulos et al. [6,7] suggest that the renal fascia is closed and fused medially, superiorly and inferiorly forming a cone that creates a barrier to spread of disease and ¯uid beyond the perirenal space. The perirenal space contains bridging septa (Kunin's septa) that extend from the renal capsule to the renal fascia [8]. Some of these septa may be arranged more or less parallel to the renal surface, the so-called posterior renorenal septum (Figs 1 and 15), seen in 10% of abdominal CT examinations as a structure running in the perirenal space from the anterolateral to the posteromedial aspect of the renal capsule [8,9]. # 2002 The Royal College of Radiologists
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Fig. 1 ± CT section at the renal hilum (a), with its corresponding schematic diagram (b). K kidney; S spine; A aorta; I inferior vena cava; D duodenum; AC ascending colon; DC descending colon; L liver. 1 perirenal space; 2 anterior renal fascia; 3 posterior renal fascia; 4 renorenal septum; 5 anterior pararenal space; 6 posterior pararenal space; 7 lateroconal fascia. Sagittal (c) and coronal (d) diagrams of boundaries and intercompartmental communications of the perirenal and pararenal spaces. K kidney; A adrenal gland; L liver; B bladder; P pancreas; PS perirenal space; APS anterior pararenal space; PPS posterior pararenal space; PES pelvic extraperitoneal space; 1 parietal peritoneum; 2 bare area of liver; 3 prevertebral retrocrural space and mediastinum; 4 transversalis fascia; 5 properitoneal space; 6 iliac crest; 7 diaphragm; 8 psoas muscle.
PICTORIAL REVIEW
Fig. 2 ± Unenhanced CT showing a large perinephric abscess containing pockets of gas. It involves the posterior pararenal space and the posterior abdominal wall, and displaces the left kidney anteriorly in a diabetic patient. Note the presence of bilateral renal
Anterior and posterior pararenal spaces. The anterior and posterior pararenal spaces may communicate with the pelvic extraperitoneal spaces inferiorly, the mediastinum and bare area of the liver superiorly (Fig. 1c,d). The anterior pararenal space communicates across the midline; the anterior and posterior pararenal spaces may potentially communicate along their inferior margins (Fig. 1c,d). In most instances, ¯uid collections remain con®ned in their compartment or space of origin. However, a new concept has been recently suggested by several authors [10±12] who have emphasized that in some instances, when large volumes of ¯uid develop rapidly, the capacity of the retroperitoneal space of origin to accomodate the ¯uid may be overwhelmed, often causing the recruitment of laminated variably fused and potentially expansile retroperitoneal interfascial planes and bridging septa for decompression. A potential space may be created between the fused layers or surfaces of fascia. Fluid can dissect these fasical planes and cross the midline through the retromesenteric anterior interfascial planes; or it may dissect the leaves of Gerota's fascia and extend behind the kidney into Zuckerkandl's fascia to mimic ¯uid in the posterior pararenal space without directly involving it [9,13]; or it may even spread through bridging septa in the perirenal space which are ®brous lamella that may serve as a bidirectional conduit for the spread of ¯uid from the perirenal interfascial planes into the perirenal space [12]. This concept of recruitable planes surrounding the renal fascia can help resolve several con¯icting recently published cadaver studies [2±7] that have investigated the extension of retroperitoneal ¯uid into the pelvis and across the midline [12]. PERINEPHRIC FLUID COLLECTIONS
Pus. Predisposing factors for perinephric abscess include diabetes, urinary tract calculi, and immunosuppression.
341
Fig. 3 ± Longitudinal sonogram of the right kidney showing mild hydronephrosis and perirenal ¯uid (white arrows) secondary to acute urinary obstruction with forniceal rupture and leakage of urine into the perirenal space.
Fig. 4 ± Unenhanced CT demonstrating perirenal ¯uid (white arrow) and stranding of the perirenal fat associated with mild fullness of the pelvicalyceal system (arrowhead) of the right kidney due to a ureteral calculous obstruction with forniceal rupture. The ureteral calculus is not shown on this particular image.
The imaging ®ndings (Fig. 2) consist of thickening of renal fascia and perirenal ¯uid which may occasionally contain air secondary to gas-forming organisms [14]. Antibiotic therapy with percutaneous drainage under imaging guidance is the preferred method of treatment [15].
Urine. Urine collection into the perirenal space may be the result of forniceal rupture secondary to acute urinary obstruction (Figs 3 and 4) most commonly due to a ureteral calculus. Leakage of urine into the perirenal space may also occur following trauma [16] or diagnostic instrumentation, which can be demonstrated on the delayed excretory phase of contrast-enhanced CT (Figs 5 and 6). A urinoma is a
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Fig. 5 ± Delayed CT of the kidneys during excretory phase showing leakage of urine opaci®ed with contrast medium (small arrows) due to disruption of the collecting system following a blunt trauma. Note also the presence of perirenal space ¯uid collection, and laceration of the left kidney (arrowheads).
chronic encapsulated extravasation of urine that leaks slowly over weeks into the perirenal space and collects within the cone of the renal fascia [17]. Decompression of the urinary tract by percutaneous catheter drainage of the urinoma, coupled with a percutaneous nephrostomy and antegrade or retrograde ureteral stent placement, may be necessary for the treatment of urinary leakage.
Blood. A perirenal hematoma may result from trauma, leaking aortic aneurysm, renal, adrenal or retroperitoneal tumors, vasculitis, bleeding diathesis, renal infarction, renal cyst, or it may be idiopathic in rare instances. Ultrasound (US) ®ndings are usually non-speci®c, and CT is a better
investigation for the evaluation of a perinephric hemorrhage. Acute hematoma has a higher attenuation value than the renal parenchyma on the unenhanced scan, and a lower attenuation value than normal enhancing renal parenchyma on contrast-enhanced CT (Fig. 7). With time, there is liquefaction of the hematoma with a decrease in its attenuation value approaching the density of water. For patients with a spontaneous perirenal hematoma in whom a mass is not detected on the initial CT, a follow-up examination may reveal a kidney tumor when the hematoma has resolved [18,19]. If no underlying cause of hemorrhage is visible on CT, selective renal angiography may be helpful to provide the diagnosis. Angiography may demonstrate a renal cell carcinoma or an angiomyolipoma. However, angiography is generally more useful in the evaluation of vascular diseases that are associated with spontaneous renal hemorrhage, such as arteriovenous malformations, renal artery aneurysms and polyarteritis nodosa (Fig. 7). Diagnostic angiography can be followed by therapeutic embolization of the bleeding vessels in suitable cases during the same procedure.
Lymph. Renal lymphangiomatosis is a rare benign disorder of uncertain etiology. Lymphangiomas are cystic areas lined with endothelium of localized lymphatic stasis due to developmental obstruction of the regional lymphatic drainage [20]. Renal lymphangiomtosis can occur at any ages [21]. Patients present with abdominal pain or mass. Hematuria, hypertension due to a Page kidney phenomenon and proteinuria may be present. Renal function tests are usually normal. US and CT show characteristic ®ndings [21] consisting of bilateral multiple small peripelvic cysts splaying the renal hilum of the kidney without evidence of cortical cysts, and the presence of perinephric ¯uid in the perirenal space representing capsular cysts [22] separated by thin septations (Fig. 8). The condition may be exacerbated
Fig. 6 ± (a) Delayed image during excretory phase of a contrast-enhanced CT of the kidneys showing leakage of urine opaci®ed with contrast medium into the right posterior pararenal space tracking into the right chest wall due to avulsion injury at the ureteropelvic junction (arrow) following a road trac accident. Note the presence of associated soft tissue laceration, and subcutaneous emphysema. (b) Follow-up contrast-enhanced CT obtained after double-J ureteral stenting showing complete healing with cessation of urine leakage. Note persistent right paravertebral soft tissue hematoma.
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Fig. 7 ± (a) Contrast-enhanced CT showing a large subcapsular hematoma causing ¯attening of the right kidney contour. (b) Selective angiogram of the right kidney showing small intrarenal aneurysms (arrows) in this patient with suspected periarteritis nodosa.
Fig. 8 ± (a) Longitudinal sonogram of the right kidney showing perirenal ¯uid (thick white arrows) surrounding the kidney with multiple small peripelvic cysts compatible with renal lymphangiomatosis. (b) T2-weighted MR image showing high-signal intensity bilateral capsular and peripelvic cysts separated by thin septations (small black arrows), associated with thickened renal fascia.
by pregnancy [23]. In asymptomatic cases no treatment is necessary, while in symptomatic cases percutaneous drainage may be eective [20]. Surgery which consists of marsupialization of the cysts should be considered as the last therapeutic measure since it often results in nephrectomy.
Fluid exudate. Patients with acute pancreatitis may have extrapancreatic exudates that collect in the anterior
pararenal spaces. US and CT are capable of demonstrating ¯uid collections in the anterior pararenal spaces, but CT is superior to US in the detection of pancreatitis and its complications. Patients with diuse pancreatitis usually have bilateral pararenal exudates (Fig. 9), while those with in¯ammation con®ned either to the head and neck or to the tail of pancreas tend to have unilateral exudates (Fig. 10) [24]. Fluid collections may
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Fig. 9 ± Contrast-enhanced CT showing bilateral perirenal and pararenal spaces, extrapancreatic ¯uid collections (small white arrows) secondary to acute pancreatitis.
Fig. 11 ± Contrast-enhanced CT demonstrating left perirenal space ¯uid collection with a smaller pararenal component (small white arrows) in this patient with acute on top of chronic pancreatitis. Note the presence of punctate pancreatic calci®cations in the pancreatic head and uncinate process.
Fig. 10 ± Contrast-enhanced CT showing unilateral right perirenal, intraperitoneal, and parapancreatic ¯uid collections (arrows) due to localized pancreatitis of the pancreatic head. Note the presence of dilated common bile duct and intrahepatic biliary radicles (arrowheads).
Fig. 12 ± Longitudinal sonogram of the left kidney showing a small kidney with increased cortical echogenicity and loss of the corticomedullary dierentiation in this patient with amyloid nephropathy and renal failure. Note the presence of a thin layer of perirenal ¯uid (thick white arrows) and ascites (asterisk).
Fig. 13 ± (a) Longitudinal sonogram of the right kidney showing a sonolucent rim (arrowheads) surrounding an enlarged poorly dierentiated kidney. (b) Contrast-enhanced CT of the kidneys showing bilateral renal enlargement with nodular in®ltration (arrowhead) and thickened renal fascia, secondary to non-Hodgkin's lymphoma with probable perirenal in®ltration. Note the presence of retroperitoneal adenopathy (arrow) and thickened gastric walls (asterisk).
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which can extend into the perirenal space. The ¯uid accumulation is a sign of a sodium retention state with or without renal failure which has been described by several authors [26±29]. The perinephric ¯uid is usually bilateral; occasionally it may be unilateral. On US, the kidneys invariably show signs of renal parenchymal medical disease along with the presence of perirenal ¯uid (Fig. 12). CT and magnetic resonance imaging (MRI) are not necessary for the diagnosis. DIFFERENTIAL DIAGNOSIS
Fig. 14 ± Contrast-enhanced CT showing bilateral perirenal soft tissue rim with a CT attenuation value of 44 HU associated with bilateral hydronephrosis (arrowheads). Needle biopsy con®rmed retroperitoneal ®brosis.
become infected, forming abscesses which may bene®t from percutaneous catheter drainage [25]. Acute on top of chronic pancreatitis may also be complicated by pancreatic ¯uid leakage that may extend into the pararenal and perirenal spaces (Fig. 11).
Fluid transudate. Children and adults suering from nephropathies may have a subcapsular transudate ¯uid
Fig. 15 ± (a) Transverse sonogram of the right kidney showing a hypoechoic rim (arrowheads) surrounding its lateral border. (b) Unenhanced CT demonstrating that the hypoechoic rim is due to prominent fat between the kidney and the renorenal septum (small white arrows) in the perirenal space.
There are certain conditions which may mimic or simulate perinephric ¯uid, causing diagnostic pitfalls. These include the sonolucent cortical rim at the periphery of infantile polycystic kidneys [30], perirenal nonHodgkin's lymphoma (Fig. 13) [31,32], the circumferential hypoechoic rim or band surrounding the kidneys in acute cortical necrosis [33], retroperitoneal ®brosis (Fig. 14), perirenal halo due to prominent perirenal fat or thickened renal fascia (Fig. 15), and breathing artifact on CT (Fig. 16). CONCLUSION
The anatomy of the retroperitoneal spaces is well known, however, the question of whether the perirenal space is open or closed remains debatable and controversial. It is
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Fig. 16 ± Contrast-enhanced CT of the left kidney of a comatose patient showing a breathing artifact simulating perirenal ¯uid.
important to remember that perinephric ¯uid may consist of pus, urine, blood, lymph, exudate or transudate. In most instances, and in the appropriate clinical context, the radiological diagnosis is usually easily established using cross-sectional imaging techniques. However, in a few doubtful cases the nature of the ¯uid may be con®rmed by a needle aspiration performed under imaging guidance. REFERENCES 1 Pummill C. Lesions involving the perirenal space. Seminars in Roentgenology 1981;16:237±238. 2 Kneeland J, Auh Y, Rubenstein W, et al. Perirenal spaces: CT evidence for communication across the midline. Radiology 1987;164:657±664. 3 Lim J, Kim B, Auh Y. Anatomical communications of the perirenal space. Br J Radiol 1998;71:450±456. 4 Mindell H, Mastromatteo J, Dickey K, et al. Anatomic communications between the three retroperitoneal spaces: determination by CT-guided injections of contrast material in cadavers. AJR 1995;164:1173±1178. 5 Mastromatteo J, Mindell H, Mastromatteo M, Magnant M, Sturtevant N, Shuman W. Communications of the pelvic extraperitoneal spaces: helical CT cadaver study with pelvic extraperitoneal injections. Radiology 1997;202:523±530. 6 Raptopoulos V, Lei Q, Touliopoulos P, Vrachliotis T, Marks S Jr. Why perirenal disease does not extend into the pelvis: the importance of closure of the cone of the renal fasciae. AJR 1995;164:1179±1184. 7 Raptopoulos V, Touliopoulos P, Lei Q, Vrachliotis T, Marks S Jr. Medial border of the perirenal space: CT and anatomic correlation. Radiology 1997;205:777±784. 8 Kunin M. Bridging septa of the perinephric space: anatomic, pathologic, and diagnostic considerations. Radiology 1986;158: 361±365. 9 Korobkin M, Silverman P, Quint L, Francis I. CT of the extraperitoneal space: normal anatomy and ¯uid collections. AJR 1992;159:933±941.
10 Molmenti E, Balfe D, Kanterman R, Bennett H. Anatomy of the retroperitoneum: observations of the distribution of pathologic ¯uid collections. Radiology 1996;200:95±103. 11 Aizenstein R, Wilbur A, O'Neil H. Interfascial and perinephric pathways in the spread of retroperitoneal disease: re®ned concepts based on CT observations. AJR 1997;168:639±643. 12 Gore R, Balfe D, Aizenstein I, Silverman M. The great escape: interfascial decompression planes of the retroperitoneum. AJR 2000;175:363±370. 13 Raptopoulos V, Kleinman P, Marks S, Snyder M, Silverman P. Renal fascial pathway: posterior extension of pancreatic eusions within the anterior pararenal space. Radiology 1986;158:367±374. 14 Bova J, Potter J, Arevalos E, Hopens T, Goldstein H, Radwin H. Renal and perirenal infection: the role of computerized tomography. J Urol 1985;133:375±378. 15 Paley M, Sidhu P, Evans R, Karani J. Retroperitoneal collections: etiology and radiological implications. Clin Radiol 1997;52: 290±294. 16 Kawashima A, Sandler C, Corriere J Jr, Rodgers B, Goldman S. Uretero-pelvic junction injuries secondary to blunt abdominal trauma. Radiology 1997;205:487±492. 17 Healy M, Teng S, Moss A. Uriniferous pseudocyst: computed tomographic ®ndings. Radiology 1984;153:757±762. 18 Belville J, Morgentaler A, Loughlin K, Tumeh S. Spontaneous perinephric and subcapsular renal hemorrhage: evaluation with CT, US and angiography. Radiology 1989;172:733±738. 19 Yip K, Peh W, Tan PC. Spontaneous rupture of renal tumors: the role of imaging in diagnosis and management. Br J Radiol 1998;71: 146±154. 20 OÈzmen M, Deren , Akata D, Akhan O, OÈzen H, Durukan T. Renal lymphangiomatosis during pregnancy: management with percutaneous drainage. Eur Radiol 2001;11:37±40. 21 Varela J, Bargiela A, Requejo I, Fernandez F, Darriba M, Pombo F. Bilateral renal lymphangiomatosis: US and CT ®ndings. Eur Radiol 1998;8:230±231. 22 Murray K, McLellan G. Renal peripelvic lymphangiectasia: appearance at CT. Radiology 1991;180:455±456. 23 Tom Meredith W, Levine E, Ahlstrom N, Grantham J. Exacerbation of familial renal lymphangiomatosis during pregnancy. AJR 1988;151:965±966. 24 Grin J, Sekiya T, Isherwood I. Computed tomography of pararenal ¯uid collections in acute pancreatitis. Clin Radiol 1984;35:181±184. 25 Lee M, Wittich G, Mueller P. Percutaneous intervention in acute pancreatitis. Radiographics 1998;18:711±724. 26 Oro®no L, Herrero J, Quereda C, et al. Perirenal subcapsular ¯uid collection in a patient with membranous nephropathy and renal vein thrombosis. J Urol 1986;136:1287±1289. 27 Yassa N, Peng M, Ralls P. Perirenal lucency (`Kidney sweat'): a new sign of renal failure. AJR 1999;173:1075±1077. 28 Paterson A, Frush D, Sweeny L, Thomas P. Elevated renal rind. J Ultrasound Med 2000;19:459±463. 29 Haddad M, Medawar W, Hawary M, Khoury N, Ammouri N, Shabb N. Perirenal ¯uid in renal parenchymal medical disease (`¯oating kidney'): clinical signi®cance and sonographic grading. Clin Radiol (In press). 30 Currarino G, Stannard M, Rutledge J. The sonolucent cortical rim in infantile polycystic kidneys: histologic correlation. J Ultrasound Med 1989;8:571±574. 31 GoÈrg C, Weide R, Schwerk W. Unusual perirenal sonographic pattern in malignant lymphoma of the kidney. Clin Radiol 1995;50: 720±724. 32 Jafri S, Bree R, Amendola M, et al. CT of renal and perirenal nonHodgkin lymphoma. AJR 1982;138:1101±1105. 33 Sefezek S, Beckman I, Lupetin A, Dash N. Sonography of acute renal cortical necrosis. AJR 1984;142:553±554.
Pictorial Review Radiology of Perinephric Fluid Collections M A U R IC E C . H A DD A D, M A H M O UD M. H AWA RY, N A B I L J . KHO URY, FAY S A L S . A B I - FA K H E R , NA B I L F. A M M O U R I , A G H I A D O . A L - K U TO U B I Department of Diagnostic Radiology, *American University of Beirut Medical Center, Beirut, Lebanon and {Department of Diagnostic Radiology, Tel Chiha Hospital, Zahleh, Lebanon Received: 24 January 2001
Revised: 11 June 2001 Accepted: 13 July 2001
The perinephric spaces consist of the subcapsular, perirenal, anterior and posterior pararenal spaces. Fluid may collect in one or more of these compartments; this can be readily demonstrated by crosssectional imaging, particularly computed tomography (CT). This pictorial review illustrates the radiological manifestations of perinephric ¯uid collections with their dierential diagnosis including perinephric abscess, perirenal urine collection, subcapsular and perirenal hematoma, renal lymphangiomatosis, pancreatic pararenal ¯uid collections and transudate ¯uid associated with nephropathies. Haddad, M. C. et al. (2002). Clinical Radiology 57, 339±346. # 2002 The Royal College of Radiologists Key words: kidney diseases, kidney US, kidney CT.
Lesions involving the perinephric spaces include primary or secondary solid neoplasms and ¯uid collections [1]. The perinephric ¯uid may be pus, urine, blood, lymph, exudate or transudate ¯uid resulting from abnormalities that arise within the kidney or adjacent retroperitoneal structures. In this pictorial review, we display various examples of these conditions and brie¯y discuss the anatomy of the retroperitoneal spaces and communications, the radiological appearances of ¯uid collections, the role of interventional procedures and the dierential diagnosis of perinephric ¯uid collections.
ANATOMIC-PATHOLOGIC CONSIDERATIONS
Basic knowledge of retroperitoneal anatomical spaces and their communications is essential for understanding pathways of ¯uid collections. Fluid can collect into one or more of the following retroperitoneal compartments: the subcapsular space, the perirenal space, the anterior and posterior pararenal spaces (Fig. 1a,b). Author for correspondence and guarantor of study: Dr Maurice C. Haddad, American University of Beirut Medical Center, Department of Diagnostic Radiology, P.O. Box 11-0236, Beirut, Lebanon. Fax: 00961-1-744464; E-mail: [email protected] 0009-9260/02/$ - see front matter
Subcapsular space. The subcapsular area is a potential space where ¯uid can accumulate causing compression of the renal parenchyma with secondary ischemia and renovascular hypertension ± so-called Page kidney, a rare but recognized phenomenon. Perirenal space. The perirenal space is formed by the anterior (Gerota's) and posterior (Zuckerkandl's) renal fascia. There is much controversy concerning the communications of the perirenal spaces. The traditional conception is that the perirenal spaces are open and have the potential for intercommunication across the midline [2,3], and may also communicate through open upper and lower ends with the mediastinum and bare area of the liver superiorly and pelvic extraperitoneal spaces inferiorly [4,5]. However, recent cadaveric studies by Raptopoulos et al. [6,7] suggest that the renal fascia is closed and fused medially, superiorly and inferiorly forming a cone that creates a barrier to spread of disease and ¯uid beyond the perirenal space. The perirenal space contains bridging septa (Kunin's septa) that extend from the renal capsule to the renal fascia [8]. Some of these septa may be arranged more or less parallel to the renal surface, the so-called posterior renorenal septum (Figs 1 and 15), seen in 10% of abdominal CT examinations as a structure running in the perirenal space from the anterolateral to the posteromedial aspect of the renal capsule [8,9]. # 2002 The Royal College of Radiologists
340
CLINICAL RADIOLOGY
Fig. 1 ± CT section at the renal hilum (a), with its corresponding schematic diagram (b). K kidney; S spine; A aorta; I inferior vena cava; D duodenum; AC ascending colon; DC descending colon; L liver. 1 perirenal space; 2 anterior renal fascia; 3 posterior renal fascia; 4 renorenal septum; 5 anterior pararenal space; 6 posterior pararenal space; 7 lateroconal fascia. Sagittal (c) and coronal (d) diagrams of boundaries and intercompartmental communications of the perirenal and pararenal spaces. K kidney; A adrenal gland; L liver; B bladder; P pancreas; PS perirenal space; APS anterior pararenal space; PPS posterior pararenal space; PES pelvic extraperitoneal space; 1 parietal peritoneum; 2 bare area of liver; 3 prevertebral retrocrural space and mediastinum; 4 transversalis fascia; 5 properitoneal space; 6 iliac crest; 7 diaphragm; 8 psoas muscle.
PICTORIAL REVIEW
Fig. 2 ± Unenhanced CT showing a large perinephric abscess containing pockets of gas. It involves the posterior pararenal space and the posterior abdominal wall, and displaces the left kidney anteriorly in a diabetic patient. Note the presence of bilateral renal
Anterior and posterior pararenal spaces. The anterior and posterior pararenal spaces may communicate with the pelvic extraperitoneal spaces inferiorly, the mediastinum and bare area of the liver superiorly (Fig. 1c,d). The anterior pararenal space communicates across the midline; the anterior and posterior pararenal spaces may potentially communicate along their inferior margins (Fig. 1c,d). In most instances, ¯uid collections remain con®ned in their compartment or space of origin. However, a new concept has been recently suggested by several authors [10±12] who have emphasized that in some instances, when large volumes of ¯uid develop rapidly, the capacity of the retroperitoneal space of origin to accomodate the ¯uid may be overwhelmed, often causing the recruitment of laminated variably fused and potentially expansile retroperitoneal interfascial planes and bridging septa for decompression. A potential space may be created between the fused layers or surfaces of fascia. Fluid can dissect these fasical planes and cross the midline through the retromesenteric anterior interfascial planes; or it may dissect the leaves of Gerota's fascia and extend behind the kidney into Zuckerkandl's fascia to mimic ¯uid in the posterior pararenal space without directly involving it [9,13]; or it may even spread through bridging septa in the perirenal space which are ®brous lamella that may serve as a bidirectional conduit for the spread of ¯uid from the perirenal interfascial planes into the perirenal space [12]. This concept of recruitable planes surrounding the renal fascia can help resolve several con¯icting recently published cadaver studies [2±7] that have investigated the extension of retroperitoneal ¯uid into the pelvis and across the midline [12]. PERINEPHRIC FLUID COLLECTIONS
Pus. Predisposing factors for perinephric abscess include diabetes, urinary tract calculi, and immunosuppression.
341
Fig. 3 ± Longitudinal sonogram of the right kidney showing mild hydronephrosis and perirenal ¯uid (white arrows) secondary to acute urinary obstruction with forniceal rupture and leakage of urine into the perirenal space.
Fig. 4 ± Unenhanced CT demonstrating perirenal ¯uid (white arrow) and stranding of the perirenal fat associated with mild fullness of the pelvicalyceal system (arrowhead) of the right kidney due to a ureteral calculous obstruction with forniceal rupture. The ureteral calculus is not shown on this particular image.
The imaging ®ndings (Fig. 2) consist of thickening of renal fascia and perirenal ¯uid which may occasionally contain air secondary to gas-forming organisms [14]. Antibiotic therapy with percutaneous drainage under imaging guidance is the preferred method of treatment [15].
Urine. Urine collection into the perirenal space may be the result of forniceal rupture secondary to acute urinary obstruction (Figs 3 and 4) most commonly due to a ureteral calculus. Leakage of urine into the perirenal space may also occur following trauma [16] or diagnostic instrumentation, which can be demonstrated on the delayed excretory phase of contrast-enhanced CT (Figs 5 and 6). A urinoma is a
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Fig. 5 ± Delayed CT of the kidneys during excretory phase showing leakage of urine opaci®ed with contrast medium (small arrows) due to disruption of the collecting system following a blunt trauma. Note also the presence of perirenal space ¯uid collection, and laceration of the left kidney (arrowheads).
chronic encapsulated extravasation of urine that leaks slowly over weeks into the perirenal space and collects within the cone of the renal fascia [17]. Decompression of the urinary tract by percutaneous catheter drainage of the urinoma, coupled with a percutaneous nephrostomy and antegrade or retrograde ureteral stent placement, may be necessary for the treatment of urinary leakage.
Blood. A perirenal hematoma may result from trauma, leaking aortic aneurysm, renal, adrenal or retroperitoneal tumors, vasculitis, bleeding diathesis, renal infarction, renal cyst, or it may be idiopathic in rare instances. Ultrasound (US) ®ndings are usually non-speci®c, and CT is a better
investigation for the evaluation of a perinephric hemorrhage. Acute hematoma has a higher attenuation value than the renal parenchyma on the unenhanced scan, and a lower attenuation value than normal enhancing renal parenchyma on contrast-enhanced CT (Fig. 7). With time, there is liquefaction of the hematoma with a decrease in its attenuation value approaching the density of water. For patients with a spontaneous perirenal hematoma in whom a mass is not detected on the initial CT, a follow-up examination may reveal a kidney tumor when the hematoma has resolved [18,19]. If no underlying cause of hemorrhage is visible on CT, selective renal angiography may be helpful to provide the diagnosis. Angiography may demonstrate a renal cell carcinoma or an angiomyolipoma. However, angiography is generally more useful in the evaluation of vascular diseases that are associated with spontaneous renal hemorrhage, such as arteriovenous malformations, renal artery aneurysms and polyarteritis nodosa (Fig. 7). Diagnostic angiography can be followed by therapeutic embolization of the bleeding vessels in suitable cases during the same procedure.
Lymph. Renal lymphangiomatosis is a rare benign disorder of uncertain etiology. Lymphangiomas are cystic areas lined with endothelium of localized lymphatic stasis due to developmental obstruction of the regional lymphatic drainage [20]. Renal lymphangiomtosis can occur at any ages [21]. Patients present with abdominal pain or mass. Hematuria, hypertension due to a Page kidney phenomenon and proteinuria may be present. Renal function tests are usually normal. US and CT show characteristic ®ndings [21] consisting of bilateral multiple small peripelvic cysts splaying the renal hilum of the kidney without evidence of cortical cysts, and the presence of perinephric ¯uid in the perirenal space representing capsular cysts [22] separated by thin septations (Fig. 8). The condition may be exacerbated
Fig. 6 ± (a) Delayed image during excretory phase of a contrast-enhanced CT of the kidneys showing leakage of urine opaci®ed with contrast medium into the right posterior pararenal space tracking into the right chest wall due to avulsion injury at the ureteropelvic junction (arrow) following a road trac accident. Note the presence of associated soft tissue laceration, and subcutaneous emphysema. (b) Follow-up contrast-enhanced CT obtained after double-J ureteral stenting showing complete healing with cessation of urine leakage. Note persistent right paravertebral soft tissue hematoma.
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Fig. 7 ± (a) Contrast-enhanced CT showing a large subcapsular hematoma causing ¯attening of the right kidney contour. (b) Selective angiogram of the right kidney showing small intrarenal aneurysms (arrows) in this patient with suspected periarteritis nodosa.
Fig. 8 ± (a) Longitudinal sonogram of the right kidney showing perirenal ¯uid (thick white arrows) surrounding the kidney with multiple small peripelvic cysts compatible with renal lymphangiomatosis. (b) T2-weighted MR image showing high-signal intensity bilateral capsular and peripelvic cysts separated by thin septations (small black arrows), associated with thickened renal fascia.
by pregnancy [23]. In asymptomatic cases no treatment is necessary, while in symptomatic cases percutaneous drainage may be eective [20]. Surgery which consists of marsupialization of the cysts should be considered as the last therapeutic measure since it often results in nephrectomy.
Fluid exudate. Patients with acute pancreatitis may have extrapancreatic exudates that collect in the anterior
pararenal spaces. US and CT are capable of demonstrating ¯uid collections in the anterior pararenal spaces, but CT is superior to US in the detection of pancreatitis and its complications. Patients with diuse pancreatitis usually have bilateral pararenal exudates (Fig. 9), while those with in¯ammation con®ned either to the head and neck or to the tail of pancreas tend to have unilateral exudates (Fig. 10) [24]. Fluid collections may
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Fig. 9 ± Contrast-enhanced CT showing bilateral perirenal and pararenal spaces, extrapancreatic ¯uid collections (small white arrows) secondary to acute pancreatitis.
Fig. 11 ± Contrast-enhanced CT demonstrating left perirenal space ¯uid collection with a smaller pararenal component (small white arrows) in this patient with acute on top of chronic pancreatitis. Note the presence of punctate pancreatic calci®cations in the pancreatic head and uncinate process.
Fig. 10 ± Contrast-enhanced CT showing unilateral right perirenal, intraperitoneal, and parapancreatic ¯uid collections (arrows) due to localized pancreatitis of the pancreatic head. Note the presence of dilated common bile duct and intrahepatic biliary radicles (arrowheads).
Fig. 12 ± Longitudinal sonogram of the left kidney showing a small kidney with increased cortical echogenicity and loss of the corticomedullary dierentiation in this patient with amyloid nephropathy and renal failure. Note the presence of a thin layer of perirenal ¯uid (thick white arrows) and ascites (asterisk).
Fig. 13 ± (a) Longitudinal sonogram of the right kidney showing a sonolucent rim (arrowheads) surrounding an enlarged poorly dierentiated kidney. (b) Contrast-enhanced CT of the kidneys showing bilateral renal enlargement with nodular in®ltration (arrowhead) and thickened renal fascia, secondary to non-Hodgkin's lymphoma with probable perirenal in®ltration. Note the presence of retroperitoneal adenopathy (arrow) and thickened gastric walls (asterisk).
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which can extend into the perirenal space. The ¯uid accumulation is a sign of a sodium retention state with or without renal failure which has been described by several authors [26±29]. The perinephric ¯uid is usually bilateral; occasionally it may be unilateral. On US, the kidneys invariably show signs of renal parenchymal medical disease along with the presence of perirenal ¯uid (Fig. 12). CT and magnetic resonance imaging (MRI) are not necessary for the diagnosis. DIFFERENTIAL DIAGNOSIS
Fig. 14 ± Contrast-enhanced CT showing bilateral perirenal soft tissue rim with a CT attenuation value of 44 HU associated with bilateral hydronephrosis (arrowheads). Needle biopsy con®rmed retroperitoneal ®brosis.
become infected, forming abscesses which may bene®t from percutaneous catheter drainage [25]. Acute on top of chronic pancreatitis may also be complicated by pancreatic ¯uid leakage that may extend into the pararenal and perirenal spaces (Fig. 11).
Fluid transudate. Children and adults suering from nephropathies may have a subcapsular transudate ¯uid
Fig. 15 ± (a) Transverse sonogram of the right kidney showing a hypoechoic rim (arrowheads) surrounding its lateral border. (b) Unenhanced CT demonstrating that the hypoechoic rim is due to prominent fat between the kidney and the renorenal septum (small white arrows) in the perirenal space.
There are certain conditions which may mimic or simulate perinephric ¯uid, causing diagnostic pitfalls. These include the sonolucent cortical rim at the periphery of infantile polycystic kidneys [30], perirenal nonHodgkin's lymphoma (Fig. 13) [31,32], the circumferential hypoechoic rim or band surrounding the kidneys in acute cortical necrosis [33], retroperitoneal ®brosis (Fig. 14), perirenal halo due to prominent perirenal fat or thickened renal fascia (Fig. 15), and breathing artifact on CT (Fig. 16). CONCLUSION
The anatomy of the retroperitoneal spaces is well known, however, the question of whether the perirenal space is open or closed remains debatable and controversial. It is
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Fig. 16 ± Contrast-enhanced CT of the left kidney of a comatose patient showing a breathing artifact simulating perirenal ¯uid.
important to remember that perinephric ¯uid may consist of pus, urine, blood, lymph, exudate or transudate. In most instances, and in the appropriate clinical context, the radiological diagnosis is usually easily established using cross-sectional imaging techniques. However, in a few doubtful cases the nature of the ¯uid may be con®rmed by a needle aspiration performed under imaging guidance. REFERENCES 1 Pummill C. Lesions involving the perirenal space. Seminars in Roentgenology 1981;16:237±238. 2 Kneeland J, Auh Y, Rubenstein W, et al. Perirenal spaces: CT evidence for communication across the midline. Radiology 1987;164:657±664. 3 Lim J, Kim B, Auh Y. Anatomical communications of the perirenal space. Br J Radiol 1998;71:450±456. 4 Mindell H, Mastromatteo J, Dickey K, et al. Anatomic communications between the three retroperitoneal spaces: determination by CT-guided injections of contrast material in cadavers. AJR 1995;164:1173±1178. 5 Mastromatteo J, Mindell H, Mastromatteo M, Magnant M, Sturtevant N, Shuman W. Communications of the pelvic extraperitoneal spaces: helical CT cadaver study with pelvic extraperitoneal injections. Radiology 1997;202:523±530. 6 Raptopoulos V, Lei Q, Touliopoulos P, Vrachliotis T, Marks S Jr. Why perirenal disease does not extend into the pelvis: the importance of closure of the cone of the renal fasciae. AJR 1995;164:1179±1184. 7 Raptopoulos V, Touliopoulos P, Lei Q, Vrachliotis T, Marks S Jr. Medial border of the perirenal space: CT and anatomic correlation. Radiology 1997;205:777±784. 8 Kunin M. Bridging septa of the perinephric space: anatomic, pathologic, and diagnostic considerations. Radiology 1986;158: 361±365. 9 Korobkin M, Silverman P, Quint L, Francis I. CT of the extraperitoneal space: normal anatomy and ¯uid collections. AJR 1992;159:933±941.
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