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Neoplastic and proliferative disorders of the perinephric space
Clinical Radiology 67 (2012) e31ee41
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Neoplastic and proliferative disorders of the perinephric space M.T. Heller*, K.A. Haarer, E. Thomas, F.L. Thaete Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
art icl e i nformat ion Article history: Received 18 December 2011 Received in revised form 27 March 2012 Accepted 28 March 2012
The perinephric space is a well-marginated central compartment of the retroperitoneum, located between the anterior and posterior pararenal spaces. Various neoplastic and proliferative disorders can affect the perinephric space, and there is a wide array of imaging findings. Although many perinephric lesions may extend directly from the kidney and adrenal gland, other lesions occur in the perinephric space due to haematogenous spread, as part of a systemic disease, or by extension from an adjacent retroperitoneal compartment. Imaging plays a pivotal role in the diagnosis of perinephric diseases, as many of the disease processes affecting this space will not result in clinical signs or symptoms until the disease is at an advanced stage. Despite the often shared non-specific clinical and imaging findings among these disease processes, application of a categorical differential diagnosis based on the imaging characteristics will serve to narrow the differential diagnosis and direct further evaluation and treatment. In this article, the lesions have been categorized as soft-tissue rind [nephroblastomatosis, fibrosis, ErdheimeChester disease (ECD), extramedullary haematopoiesis, lymphoma, infiltrating metastases], focal solid lesions (extension of renal or adrenal malignancies, melanoma metastases, treated lymphoma), fat-containing lesions (angiomyolipoma, liposarcoma, myelolipoma), and cystic lesions (lymphangiomas, abscesses). The aim of this article is to demonstrate and describe the key imaging features of several neoplastic and proliferative disorders that affect the perinephric space. Ó 2012 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
Introduction The perinephric space is a well-defined, retroperitoneal compartment located centrally between the anterior and posterior pararenal spaces (Fig 1). The main contents of the perinephric space are the kidney, proximal ureter, and adrenal gland while fat, bridging connective tissue, and vessels are found in varying amounts. The perinephric space is bounded primarily by the anterior and posterior renal * Guarantor and correspondent: M.T. Heller, Department of Radiology, University of Pittsburgh Medical Center, 200 Lothrop St, Suite 3950 PUH S. Tower, Pittsburgh, PA 15213, USA. Tel.: þ1 412 647 3550; fax: þ1 412 647 7795. E-mail address: [email protected] (M.T. Heller).
fasciae, also known eponymously as Gerota’s and Zuckerkandl’s fascia, respectively. The anatomic boundaries act to contain disease within the perinephric space, but also provide potential avenues for local spread to and from other retroperitoneal compartments. Additionally, disease processes may affect the perinephric space via haematogenous and lymphatic routes. The imaging findings associated with neoplastic and proliferative disorders affecting the perinephric space can generally be separated into the following categories to yield a more concise differential diagnosis: soft-tissue rind, focal solid masses, fatcontaining lesions, and cystic lesions. The aim of this article is to demonstrate and describe the general differential categories, and key imaging features, of neoplastic and proliferative disorders of the perinephric space.
0009-9260/$ e see front matter Ó 2012 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2012.03.015
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only discovered by imaging during screening of a syndromic patient. At computed tomography (CT), perinephric nephroblastomatosis appears as a homogeneous, low-attenuation rind of subcapsular soft tissue with minimal enhancement following contrast medium administration.5 The rind of soft tissue typically has a lobulate or undulating border and may occasionally mimic leukaemia, lymphoma, or polycystic kidney disease.6 At ultrasound, nephroblastomatosis may manifest with loss of corticomedullary differentiation, diffusely increased or decreased renal echogenicity, or variable sized cystic lesions.7 At magnetic resonance imaging (MRI), nephroblastomatosis is isointense to the normal kidney on T1-weighted imaging and isointense to slightly hyperintense relative to normal renal parenchyma on T2-weighted imaging. Malignant transformation to Wilms’ tumour occurs in approximately 35% of patients with nephroblastomatosis is suggested by development of a heterogeneous, soft-tissue mass, which may invade the vena cava and renal vein (Fig 2).4,8 Figure 1 Perinephric space anatomy. The perinephric space (PNS) is located in the retroperitoneum between the anterior pararenal space (APS) and the posterior pararenal space (PPS). The PNS is bound by Gerota’s fascia anteriorly and Zuckerkandl’s fascia posteriorly; these fascia fuse laterally to form the lateral conal fascia. The perinephric space contains the kidney, adrenal gland, fat, arteries (red lines), veins (blue lines), lymphatics (green lines), and septa (black wavy lines).
Differential diagnosis and imaging findings Soft-tissue rind Nephroblastomatosis The kidneys develop from a ureteric bud and surrounding metanephric blastema, which ultimately matures into normal renal parenchyma. Metanephric blastema that fails to mature during nephrogenesis persists into childhood as nephrogenic rests.1 Nephrogenic rests may be single, multiple, mixed, or diffuse; the presence of multiple macroscopic or diffuse nephrogenic rests is referred to as nephroblastomatosis. The distribution of nephrogenic rests and nephroblastomatosis can generally be classified as intralobar or perilobar: intralobar refers to random occurrence within the renal lobe while perilobar refers to occurrence in the cortex covering the lobe or at the corticomedullary junction. Perilobar distribution is more common and has a higher association with BeckwitheWiedemann syndrome and hemihypertrophy while intralobar nephroblastomatosis has a higher association with Drash syndrome, sporadic aniridia, and WAGR syndrome (Wilm’s tumour, aniridia, genito-urinary anomalies, and mental retardation).2,3 As nephroblastomatosis is a precursor for Wilms’ tumour and these syndromes are associated with abnormalities of the Wilms’ tumour suppressor genes on chromosome11, patients are screened regularly for the development of Wilms’ tumour.3,4 Clinically, nephroblastomatosis may be detected as unilateral or bilateral flank masses during physical examination. Alternatively, nephroblastomatosis may be clinically silent and
Fibrosis Retroperitoneal fibrosis (RPF) is a fibrotic reaction resulting in encasement of the abdominal aorta, inferior vena cava, or ureters, which may extend into the perinephric space. Clinically, the initial symptoms are typically non-specific, but often manifest with lumbar or flank pain, lower extremity swelling, or decreased urinary excretion.9 RPF is two to three times more common in men and occurs in patients ranging in age from 40 to 60 years.10 RPF may be secondary to inflammatory disorders, malignancy, or medications, but is idiopathic in 70% of cases, postulated to be secondary to an autoimmune response; additionally, it may be isolated or occur as part of multifocal fibrosclerosis along with autoimmune pancreatitis, sclerosing cholangitis, Riedel’s thyroiditis, and scleroderma (Fig 3).11,12 Perirenal fibrosis that occurs as part of retroperitoneal fibrosis or as a part of multifocal fibrosclerosis is usually not difficult to identify at imaging. However, the imaging findings of isolated perirenal fibrosis, such as can be seen in the setting of advanced systemic lupus erythromatosis, are non-specific and histopathological analysis may be needed to establish diagnosis. Management of RPF consists of removal of the offending agent when identified. Corticosteroids have proven effective in reducing symptoms and the size of the retroperitoneal fibrotic mass.13 Supplementation with immunosuppressive drugs, anti-rheumatic agents, and surgery can be used in refractory cases.12,14 At CT, RPF typically manifests as a homogeneous paraspinal mass, which is isodense to muscle and does not displace the aorta and inferior vena cava away from the spine (Fig 3). Imaging features and enhancement following contrast medium administration depends on the maturity of the fibrotic tissue; avid enhancement may be evident in the acute phases, while minimal to absent enhancement can be seen in chronic phases.15 With MRI, active fibrosis may show early enhancement and increased intensity on T2-weighted images while more advanced or chronic disease may show delayed enhancement and low signal
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Figure 2 Nephroblastomatosis. A 2-year-old female patient presented with an abdominal mass. (a) Contrast-enhanced CT shows a rind of soft tissue (arrowheads) surrounding both kidneys. A heterogeneously enhancing central mass (W) is part of an upper pole Wilms’ tumour. (b) Coronal, contrast-enhanced, T1-weighted image shows the Wilms’ tumour (W) in the upper pole of the right kidney and the low-signal rim of perinephric soft tissue (arrowheads). Surgical specimen confirmed Wilms’ tumour.
intensity on T2-weighted images.16 When seen on ultrasound, retroperitoneal fibrosis appears as a hypoechoic halo of soft tissue. Differentiation of benign disease from malignant disease based on imaging alone is difficult.17 Bulkier disease with peripheral nodularity and mass effect on adjacent structures including displacement of the aorta and inferior vena cava away from the spine suggest malignancy.12
ECD ECD is a rare, non-Langerhans, histiocytic disorder, which affects middle-aged adults (mean age of 53 years) and may involve numerous organs, including the long bones, lungs, skin, pituitary gland, kidneys, adrenal gland, and heart. Lower extremity bone pain is the most common symptom, although clinical manifestations are protean, ranging from asymptomatic to life-threatening conditions
Figure 3 Idiopathic RPF. A 53-year-old man presented with back pain and mildly elevated creatinine. (a) Excretory phase CT image shows mild bilateral hydronephrosis and abnormal soft tissue (arrowheads) in the left perinephric space at the level of the renal hilum. (b) More inferiorly, a mantle of soft tissue (arrowheads) encases the aorta and inferior vena cava and tethers the ureters medially (arrows), resulting in partial obstruction of their lumen. Biopsy confirmed RPF.
such as heart failure, tamponade, or renal failure.18 Most patients (60%) have osseous involvement at the time of presentation, such as enlarged femora, metadiaphyseal sclerosis, and trabecular coarsening; however, renal involvement is found in 29% of patients and may be an isolated site of disease (Fig 4).18 Progressive fibrous perinephritis can lead to renal failure. At cross-sectional imaging, perinephric involvement of ECD may manifest as a mass-like, infiltrative pattern or a soft-tissue rind in the
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on T1 and T2-weighted sequences and show slight homogeneous enhancement following gadolinium administration.19 Treatment consists of a combination of surgery, corticosteroids, cyclosporine, and interferon.20
Extramedullary haematopoiesis Extramedullary haematopoiesis is a physiological compensatory mechanism for failure of erythropoiesis; it commonly occurs in the liver and spleen but may also involve the kidneys, breast, skin, and adrenal glands.21 Renal extramedullary haematopoiesis may be parenchymal, intrapelvic, or perinephric; intrapelvic and perinephric disease is often bilateral but may be unilateral. Patients are usually asymptomatic, but may present with abdominal pain or renal failure due to parenchymal involvement or ureteral compression. Imaging features on CT with perinephric disease include a perinephric, softtissue mass showing mild, homogeneous enhancement (Fig 5).29 At MRI, signal intensity on T2-weighted images is typically low owing to the haemosiderin content, but can be variable due to inclusion of foci of macroscopic fat. At ultrasound, findings usually consist of a solid hypoechoic perinephric mass. Additional imaging findings of hepatosplenomegaly and paraspinal soft tissue can aid in the diagnosis of extramedullary haematopoiesis.22 Treatment for symptomatic cases consists of surgery and radiation.
Lymphoma Perinephric lymphoma is commonly due to extension of retroperitoneal or renal lymphoma and is most often associated with an intermediate to high-grade non-Hodgkin’s lymphoma of B-cell lineage.23 Tumour isolated to the perinephric space is rare, accounting for less than 10% of cases of perinephric lymphoma.24 Lymphoma involving the kidneys and perinephric space is typically clinically silent but may present with flank pain, haematuria, palpable mass, or weight loss, and rarely acute renal failure.23 Multiple radiographic patterns of renal lymphoma may be observed, which include a single mass, multiple masses, contiguous retroperitoneal extension, perirenal involvement, and diffuse infiltration. Unilateral disease versus bilateral disease depends on the mode of spread. With the Figure 4 ECD. A 39-year-old man presented with lower extremity bone pain. (a) Anteroposterior radiograph of the lower extremities shows enlarged femora and metadiaphyseal sclerosis/thickening (white arrows) and a coarsened trabecular pattern. Periostitis is shown as mild wavy contour abnormality (black arrowheads). (b) Contrast-enhanced CT shows a circumferential soft-tissue rind (arrows) surrounding each kidney, which caused narrowing of the ureteropelvic junctions and resulted in mild hydronephrosis. Biopsy proved ECD.
perinephric space. On unenhanced CT, homogeneous softtissue, isodense to muscle may be seen in the perinephric space bilaterally. Perirenal infiltration with extension into the anterior and posterior pararenal space produces a “hairy kidney” appearance. Enhancement is homogeneous and poor following contrast medium administration. On MRI, ECD involving the kidneys will appear isointense to muscle
Figure 5 Extramedullary haematopoiesis. A 51-year-old man presented with perinephric soft tissue during a CT examination. Contrast-enhanced CT image shows hypovascular perinephric softtissue attenuation bilaterally (arrowheads). Biopsy proved extramedullary haematopoiesis.
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pattern of perinephric involvement, the tumour is often homogeneous, hypovascular, and mildly enhancing at cross-sectional imaging (Fig 6). Sonography shows a solid, hypoechoic perinephric mass. Renal lymphoma is typically hypointense on T1 and slightly hypo to isointense on T2 relative to the kidneys on MRI. Enhancement is homogeneous but less than the adjacent renal parenchyma following gadolinium administration.23 Treatment consists
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of chemotherapy; ureteral stenting can be used in cases of obstruction.
Metastases The perinephric space is an unusual site for identification of remote malignancies, but has been reported in melanoma, prostate, breast, and gastrointestinal tumour metastases due to haematogenous means, and in lung cancer metastases due to lymphatic spread.25,26 Additionally, metastases to the kidneys can infiltrate the perinephric space.27 Radiological features often depend on the type of primary tumour; for example, melanoma and breast metastases often show enhancement during the arterial phase followed by portal phase wash-out due to their hypervascular nature, while lung and prostate metastases typically do not show significant arterial enhancement. Although most perinephric metastases present as multiple, discrete, soft-tissue masses, some metastases, such as those secondary to breast cancer, can be infiltrative lesions (Fig 7).26,28 In these cases, the cross-sectional imaging findings are non-specific and often confusing due to overlap with lymphoma and other perinephric processes, although breast cancer metastases typically enhance much more briskly than lymphoma and rarely occur in isolation. However, in most cases of an infiltrative or nodular perinephric process, the imaging findings can be used to select the optimal site and approach for biopsy for definitive characterization.25
Focal solid lesions Focal solid masses in the perinephric space are most commonly due to malignancy. Differential considerations include extension from renal, adrenal, or retroperitoneal tumours and metastases (Fig 8). Identification of tumour in
Figure 6 Lymphoma (non-Hodgkin’s). Contrast-enhanced CT images from two patients with biopsy-proven non-Hodgkin’s lymphoma. (a) A rind of soft tissue (white arrows) surrounds the kidneys; note outer edge of renal cortex (black arrowheads). More inferiorly, ureteral compression from retroperitoneal adenopathy resulted in mild hydronephrosis. (b) (Different patient.) The soft-tissue rind (arrows) is more nodular and extensive. Note the necrotic appearing node near the renal hilum (arrowhead).
Figure 7 Breast cancer metastasis. A 41-year-old woman with a history of breast cancer presented with a lung nodule and infiltrating perinephric soft tissue. Contrast-enhanced CT shows an enhancing rind of soft tissue surrounding the kidney and extending around the aorta. Biopsy confirmed metastatic breast cancer.
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perinephric lymphoma from bulkly circumferential soft tissue to a focal lesion in the perinephric space (Fig 10).
Fatty lesions Angiomyolipoma Angiomyolipomas (AMLs) are common benign, fatcontaining renal lesions. Small AMLs tend to be homogeneous, fatty lesions at imaging, while larger lesions are often heterogeneous due to variable amounts of macroscopic fat,
Figure 8 Nodular metastases. A 21-year-old presented with multiple soft-tissue lesions. (a) Contrast-enhanced CT image shows multiple soft-tissue nodules (arrows) in the inferior perinephric spaces and subcutaneous fat (arrowhead). Biopsy of a palpable subcutaneous nodule revealed melanoma.
the perinephric space is important in staging and predicting survival in renal cell carcinoma (Fig 9); extension into the perinephric space signifies a T3 lesion indicating at least stage III disease. Other neoplasms, such as multiple myeloma, plasmacytoma, malignant fibrous histiocytoma, leukaemia, gastrointestinal stromal tumours, haemangiomas, leiomyomas and haemangiopericytomas infrequently occur in the perinephric space, but typically lack specific imaging findings to allow differentiation. Castleman’s disease, a rare systemic lymphoproliferative disorder with unicentric and multicentric forms, has also been reported to occur in the perinephric space; when it does affect the perinephric space, Castleman’s disease is more commonly multicentric.28 While the imaging appearances of lymphoma are protean, treatment may cause regression of extensive
Figure 9 Renal cell carcinoma. A 66-year-old presented with right flank pain and haematuria. Contrast-enhanced CT image shows a massive tumour (arrows) nearly replacing the right kidney (arrowhead) and filling the anteromedial aspect of the perinephric space. Pathology specimens confirmed renal cell carcinoma.
Figure 10 Treated lymphoma. A 72-year-old presented for follow-up after a history of treated lymphoma. (a) A non-enhancing soft-tissue nodule (arrow) in the posterior aspect of the perinephric space abuts the kidney. This finding had been stable for over 6 years. (b) Initial contrast-enhanced CT image from 7 years prior shows extensive perinephric soft tissue (arrows) with heterogeneous enhancement consistent with lymphoma.
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soft tissue, and aneurysms. As large AMLs are often exophytic, they are the most common fat-containing mass in the perinephric space. However, it is important to distinguish an exophytic AML from other fat-containing perinephric lesions such as a retroperitoneal liposarcoma. An imaging feature that favours the diagnosis of AML is the presence of a renal parenchymal notch or defect in the renal parenchyma at the site of tumour origin (Fig 11).29 AMLs more commonly have intratumoural aneurysms and tend to have large, intralesional blood vessels; comparatively, well-differentiated liposarcomas are typically avascular or contain small vessels.28,29 Also, the presence of additional fat-containing lesions is an indicator that an indeterminate fat-containing lesion is an AML; while multiple AMLs are common in the setting of tuberous sclerosis, they are also not infrequently found in patients without this disease, an occurrence of up to 27% in one study.29
Liposarcoma Liposarcoma is the most common malignant primary retroperitoneal tumour and consists of five subtypes: welldifferentiated, myxoid, round cell, pleomorphic, and dedifferentiated. Well-differentiated liposarcomas are the least aggressive, contain variable amounts of macroscopic fat, and may mimic an AML (Fig 12). Round cell and pleomorphic subtypes manifest as enhancing soft-tissue masses at CT and MRI and are considered to be high-grade tumours, often complicated by local recurrence and metastases following resection.30 Myxoid tumours often contain a cystic component and show reticulated enhancement at CT and MRI after contrast medium injection.31
Figure 12 Liposarcoma. A 60-year-old woman presented with weight loss. (a) Contrast-enhanced CT image shows a bilobed mass in the retroperitoneum containing a briskly enhancing soft-tissue component (arrow) in the perinephric space and an intermediate attenuation component (arrowhead) with small foci of intratumoural fat in the anterior pararenal space. (b) More inferiorly, there are more conspicuous fat components (arrows) in the perinephric space and continuation of the solid component (arrowhead) in the anterior pararenal space. Resection specimen confirmed liposarcoma.
Figure 11 Angiomyolipoma. A 39 year-old woman presented for evaluation of abdominal pain and was found to have an incidental mass in the left perinephric space. Post-contrast CT shows a predominantly fat-containing mass (arrow) in the perinephric space; a large feeding vessel (arrowhead) traversing the mass originates from the kidney. Resection specimens were consistent with angiomyolipoma.
Myelolipoma Myelolipomas are rare, benign neoplasms composed of adipose tissue and haematopoietic elements. Most myelolipomas are adrenal in origin, but may also arise from the perinephric space and presacral region.32 Most myelolipomas are discovered incidentally by imaging, but they can present with pain due to spontaneous haemorrhage and mass effect.
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The cross-sectional imaging findings of myelolipoma are largely dependent on the relative amounts of adipose and haematopoietic tissue; the tumours are usually heterogeneous, containing both hypervascular soft tissue and macroscopic fat elements (Fig 13).33 At ultrasound, myelolipomas generally have heterogeneous echogenicity due to their nonuniform consistency. CT typically shows macroscopic fat with interspersed regions of soft-tissue attenuation. At MRI, areas of fat show high signal intensity on T1 and T2-weighted sequences, while marrow-like regions have intermediate signal intensity similar to that of spleen.34
Lymphangiomas are rare, benign mesenchymal neoplasms, which are characterized by numerous intercommunicating, endothelial-lined spaces containing lymph fluid.35 Lymphangiomas are congenital due to developmental obstruction of regional lymph drainage. Lymphangiomas may be focal and unilateral, bilateral or diffuse; when diffuse, the condition is referred to as lymphangiomatosis (Fig 14). The lesions are usually asymptomatic but can result in haematuria
Figure 13 Myelolipoma. A 46-year-old man was referred for evaluation of an incidental suprarenal mass reported on cardiac MRI (not shown). (aeb) Contrast-enhanced CT image shows the predominantly fatty mass (arrows) filling the superomedial perinephric space. Resection specimen confirmed myelolipoma.
Figure 14 Perinephric lymphangiomatosis. A 20-year-old man had an abnormal renal ultrasound. (a) Longitudinal ultrasound shows a multiseptated, cystic lesion surrounding the right kidney (arrows); there was a similar finding on the left (not shown). (b) T2-weighted image shows a multiseptated, cystic mass (arrows) surrounding both kidneys. Percutaneous aspiration revealed chylous fluid, which contained numerous lymphocytes.
Cystic lesions Lymphangioma
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or proteinuria occasionally. In extremely rare instances of giant lymphangiomas or extensive lymphangiomatosis, sufficient compression of the kidney has been reported to alter the renineangiotensinealdosterone system and result in hypertension, referred to as a Page kidney36,37; however, Page kidney is much more commonly due to compression by a subcapsular haematoma. At CT or MRI, lymphangiomas typically appear as a perinephric cystic lesions with variable peripheral or septal enhancement associated with normal appearing kidneys.38 Ultrasound shows numerous anechoic cystic regions separated by thin septa. Percutaneous aspiration may reveal chylous fluid or fluid rich in lymphocytes.44,45 Symptomatic cases are typically treated with surgery.39,40
Abscess and infection Despite not being a true proliferative disorder, perinephric infection is common and abscess can mimic cystic neoplasms. Both acute bacterial pyelonephritis and xanthogranulomatous pyelonephritis can cause severe renal infection, which extends into the perinephric space. Acute pyelonephritis is due to bacterial or fungal infection of the renal parenchyma and collecting system, which usually occurs due to ascending infection from the lower urinary tract. Bacterial pyelonephritis is most common due to Gram-negative organisms such as Escherichia coil.41 Patients typically present with fever, flank pain, and leukocytosis. In the perinephric space, the CT and MRI findings of acute pyelonephritis are non-specific and include thickening of Gerota’s fascia, perinephric fat stranding, and obliteration of perinephric fat planes.42 Ultrasound is relatively insensitive in showing extension of inflammation into the perinephric
Figure 15 Abscess. A 31-year-old woman presented with pyuria, leukocytosis, and flank pain. Contrast-enhanced CT image shows focal phlegmon (arrows) in the medial aspect of the left kidney. An ovoid fluid collection (arrowhead) in the medial aspect of the left perinephric space is consistent with an abscess. Percutaneous aspiration yielded pus.
Figure 16 Emphysematous pyelonephritis. A 49-year-old diabetic woman presented with fever and flank pain. Unenhanced contrast CT shows extensive gas (arrowheads) in the right renal collecting system, which dissects posteriorly into the perinephric space. Note adjacent phlegmon (p).
space.43 However, ultrasound is useful in detecting perinephric abscess and in guiding percutaneous catheter drainage. With ultrasound, perinephric abscesses typically appear as multilocular fluid collections with internal
Figure 17 Xanthogranulomatous pyelonephritis. A 52-year-old diabetic woman presented with flank pain. Contrast-enhanced CT image shows a staghorn’s calculus (arrow) in the renal pelvis, renal enlargement and heterogeneity, and dilatation of portions of the renal collecting system. Infiltration of the perinephric fat and thickening of Zuckerkandl’s fascia are due to spread of infection into the perinephric space. Nephrectomy specimen confirmed xanthogranulomatous pyelonephritis.
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echoes. CT and MRI reveal a heterogeneously enhancing, complex cystic lesion with enhancing internal septa and a variable degree of infiltration of the perinephric space (Fig 15). In cases of emphysematous infections, CT readily shows gas extending from the kidney into the perinephric space (Fig 16), while MRI will show signal voids, which may be difficult to interpret.44 With ultrasound, the “dirty shadowing” caused by perinephric gas may obsure a fluid collection and the kidney. Additionally, xanthogranulomatous pyelonephritis (XGP), a rare form of chronic pyelonephritis characterized by progressive renal destruction and replacement by lipid-laden macrophages, has been documented to involve the perinephric space; CT and MRI findings can include infiltration of the perinephric fat, massive accumulation of perinephric fat, and abscesses (Fig 17).45 Treatment of perinephric infection generally consists of antibiotics for the underlying renal infection and percutaneous catheter drainage of abscesses.
Summary The perinephric space is a central retroperitoneal compartment, which can host numerous neoplastic and proliferative processes. These disease processes can originate in the perinephric space or gain access via regional, lymphatic, or haematogenous spread. Imaging plays a central role in the detection and characterization of perinephric neoplastic and proliferative disorders, as many of these conditions may be clinically silent until late in the disease process.
Acknowledgements The authors thank Chris Granville, MD, for his help in creating Fig 1.
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11. Meier P, Vogt B, Blanc E. Rethinking the triggering inflammatory processes of chronic periaortitis. Nephron Exp Nephrol 2007;105:e17e23. 12. Cronin CG, Lohan DG, Blake MA, et al. Retroperitoneal fibrosis: a review of clinical features and imaging findings. AJR Am J Roentgenol 2008;191:423e31. 13. Kardar AH, Kattan S, Lindstedt E, et al. Steroid therapy for idiopathic retroperitoneal fibrosis: dose and duration. J Urol 2002;168:550e5. 14. McDougal WS, MacDonell Jr RC. Treatment of idiopathic retroperitoneal fibrosis by immunosuppression. J Urol 1991;145:112e4. 15. Feinstein RS, Gatewood OM, Goldman SM, et al. Computerized tomography in the diagnosis of retroperitoneal fibrosis. J Urol 1981;126:255e9. 16. Dunnick NR, Korobkin M, Francis I. Adrenal radiology: distinguishing benign from malignant adrenal masses. AJR Am J Roentgenol 1996;167: 861e7. 17. Fagan CJ, Larrieu AJ, Amparo EG. Retroperitoneal fibrosis: ultrasound and CT features. AJR Am J Roentgenol 1979;133:239e43. 18. Veyssier-Belot C, Cacoub P, Caparros-Lefebvre D, et al. ErdheimeChester disease. Clinical and radiologic characteristics of 59 cases. Medicine (Baltimore) 1996;75:157e69. 19. Dion E, Graef C, Haroche J, et al. Imaging of thoracoabdominal involvement in ErdheimeChester disease. AJR Am J Roentgenol 2004;183: 1253e60. 20. Braiteh F, Boxrud C, Esmaeli B, et al. Successful treatment of ErdheimeChester disease, a non-Langerhans-cell histiocytosis, with interferon-alpha. Blood 2005;106:2992e4. 21. Gryspeerdt S, Oyen R, Van Hoe L, et al. Extramedullary hematopoiesis encasing the pelvicalyceal system: CT findings. Ann Hematol 1995;71:53e6. 22. Mesurolle B, Sayag E, Meingan P, et al. Retroperitoneal extramedullary hematopoiesis: sonographic, CT, and MR imaging appearance. AJR Am J Roentgenol 1996;167:1139e40. 23. Sheth S, Ali S, Fishman E. Imaging of renal lymphoma: patterns of disease with pathologic correlation. RadioGraphics 2006;26:1151e68. 24. Reznek RH, Mootoosamy I, Webb JA, et al. CT in renal and perirenal lymphoma: a further look. Clin Radiol 1990;42:233e8. 25. La Fianza A, Maccabelli G, Van Der Byl G, et al. Isolated nodular metastases in perirenal space: our experience of nine cases and review of the literature. Minerva Urol Nefrol 2011;63:281e6. 26. Wilbur AC, Turk JN, Capek V. Perirenal metastases from lung cancer: CT diagnosis. J Comput Assist Tomogr 1992;16:589e91. 27. Choyke PL, White EM, Zeman RK, et al. Renal metastases: clinicopathologic and radiologic correlation. Radiology 1987;162:359e63. 28. Surabhi VR, Menias C, Prasad SR, et al. Neoplastic and non-neoplastic proliferative disorders of the perirenal space: cross-sectional imaging findings. RadioGraphics 2008;28:1005e17. 29. Israel GM, Bosniak MA, Slywotzky CM, et al. CT differentiation of large exophytic renal angiomyolipomas and perirenal liposarcomas. AJR Am J Roentgenol 2002;179:769e73. 30. Song T, Shen J, Liang BL, et al. Retroperitoneal liposarcoma: MR characteristics and pathological correlative analysis. Abdom Imaging 2007;32:668e74. 31. Chouairy CJ, Abdul-Karim FW, MacLennan GT. Retroperitoneal liposarcoma. J Urol 2007;177:1145. 32. Wagner JR, Kleiner DE, Walther MM, et al. Perirenal myelolipoma. Urology 1997;49:128e30. 33. Kenney PJ, Wagner BJ, Rao P, et al. Myelolipoma: CT and pathologic features. Radiology 1998;208:87e95. 34. Rao P, Kenney PJ, Wagner BJ, et al. Imaging and pathologic features of myelolipoma. RadioGraphics 1997;17:1373e85. 35. Westphalen A, Yeh B, Qayyum A, et al. Differential diagnosis of perinephric masses on CT and MRI. AJR Am J Roentgenol 2004;183:1697e702. 36. Schwarz A, Lenz T, Klaen R, et al. Hygroma renale: pararenal lymphatic cysts associated with renin-dependent hypertension (Page kidney). Case report on bilateral cysts and successful therapy by marsupialization. J Urol 1993;150:953e7. 37. Savin H, Jutrin I, Ravid M. Reversible renal hypertension due to renal hygroma. Urology 1989;33:317e9. 38. Haddad MC, Hawary MM, Khoury NJ, et al. Radiology of perinephric fluid collections. Clin Radiol 2002;57:339e46. 39. Davidson AJ, Hartman DS. Lymphangioma of the retroperitoneum: CT and sonographic characteristic. Radiology 1990;175:507e10.
M.T. Heller et al. / Clinical Radiology 67 (2012) e31ee41 40. Levy AD, Cantisani V, Miettinen M. Abdominal lymphangiomas: imaging features with pathologic correlation. AJR Am J Roentgenol 2004;182:1485e91. 41. Stamm WE, Hooton TM. Management of urinary tract infections in adults. N Engl J Med 1993;329:1328e34. 42. Stunell H, Buckley O, Feeney J, et al. Imaging of acute pyelonephritis in the adult. Eur Radiol 2007;17:1820e8. 43. Majd M, Nussbaum Blask AR, Markle BM, et al. Acute pyelonephritis: comparison of diagnosis with 99mTc-DMSA, SPECT, spiral CT, MR
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imaging, and power Doppler US in an experimental pig model. Radiology 2001;218:101e8. 44. Poustchi-Amin M, Leonidas JC, Palestro C, et al. Magnetic resonance imaging in acute pyelonephritis. Pediatr Nephrol 1998;12: 579e80. 45. Loffroy R, Guiu B, Watfa J, et al. Xanthogranulomatous pyelonephritis in adults: clinical and radiological findings in diffuse and focal forms. Clin Radiol 2007;62:884e90.
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Pictorial Review
Neoplastic and proliferative disorders of the perinephric space M.T. Heller*, K.A. Haarer, E. Thomas, F.L. Thaete Department of Radiology, University of Pittsburgh Medical Center, Pittsburgh, PA, USA
art icl e i nformat ion Article history: Received 18 December 2011 Received in revised form 27 March 2012 Accepted 28 March 2012
The perinephric space is a well-marginated central compartment of the retroperitoneum, located between the anterior and posterior pararenal spaces. Various neoplastic and proliferative disorders can affect the perinephric space, and there is a wide array of imaging findings. Although many perinephric lesions may extend directly from the kidney and adrenal gland, other lesions occur in the perinephric space due to haematogenous spread, as part of a systemic disease, or by extension from an adjacent retroperitoneal compartment. Imaging plays a pivotal role in the diagnosis of perinephric diseases, as many of the disease processes affecting this space will not result in clinical signs or symptoms until the disease is at an advanced stage. Despite the often shared non-specific clinical and imaging findings among these disease processes, application of a categorical differential diagnosis based on the imaging characteristics will serve to narrow the differential diagnosis and direct further evaluation and treatment. In this article, the lesions have been categorized as soft-tissue rind [nephroblastomatosis, fibrosis, ErdheimeChester disease (ECD), extramedullary haematopoiesis, lymphoma, infiltrating metastases], focal solid lesions (extension of renal or adrenal malignancies, melanoma metastases, treated lymphoma), fat-containing lesions (angiomyolipoma, liposarcoma, myelolipoma), and cystic lesions (lymphangiomas, abscesses). The aim of this article is to demonstrate and describe the key imaging features of several neoplastic and proliferative disorders that affect the perinephric space. Ó 2012 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.
Introduction The perinephric space is a well-defined, retroperitoneal compartment located centrally between the anterior and posterior pararenal spaces (Fig 1). The main contents of the perinephric space are the kidney, proximal ureter, and adrenal gland while fat, bridging connective tissue, and vessels are found in varying amounts. The perinephric space is bounded primarily by the anterior and posterior renal * Guarantor and correspondent: M.T. Heller, Department of Radiology, University of Pittsburgh Medical Center, 200 Lothrop St, Suite 3950 PUH S. Tower, Pittsburgh, PA 15213, USA. Tel.: þ1 412 647 3550; fax: þ1 412 647 7795. E-mail address: [email protected] (M.T. Heller).
fasciae, also known eponymously as Gerota’s and Zuckerkandl’s fascia, respectively. The anatomic boundaries act to contain disease within the perinephric space, but also provide potential avenues for local spread to and from other retroperitoneal compartments. Additionally, disease processes may affect the perinephric space via haematogenous and lymphatic routes. The imaging findings associated with neoplastic and proliferative disorders affecting the perinephric space can generally be separated into the following categories to yield a more concise differential diagnosis: soft-tissue rind, focal solid masses, fatcontaining lesions, and cystic lesions. The aim of this article is to demonstrate and describe the general differential categories, and key imaging features, of neoplastic and proliferative disorders of the perinephric space.
0009-9260/$ e see front matter Ó 2012 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.crad.2012.03.015
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only discovered by imaging during screening of a syndromic patient. At computed tomography (CT), perinephric nephroblastomatosis appears as a homogeneous, low-attenuation rind of subcapsular soft tissue with minimal enhancement following contrast medium administration.5 The rind of soft tissue typically has a lobulate or undulating border and may occasionally mimic leukaemia, lymphoma, or polycystic kidney disease.6 At ultrasound, nephroblastomatosis may manifest with loss of corticomedullary differentiation, diffusely increased or decreased renal echogenicity, or variable sized cystic lesions.7 At magnetic resonance imaging (MRI), nephroblastomatosis is isointense to the normal kidney on T1-weighted imaging and isointense to slightly hyperintense relative to normal renal parenchyma on T2-weighted imaging. Malignant transformation to Wilms’ tumour occurs in approximately 35% of patients with nephroblastomatosis is suggested by development of a heterogeneous, soft-tissue mass, which may invade the vena cava and renal vein (Fig 2).4,8 Figure 1 Perinephric space anatomy. The perinephric space (PNS) is located in the retroperitoneum between the anterior pararenal space (APS) and the posterior pararenal space (PPS). The PNS is bound by Gerota’s fascia anteriorly and Zuckerkandl’s fascia posteriorly; these fascia fuse laterally to form the lateral conal fascia. The perinephric space contains the kidney, adrenal gland, fat, arteries (red lines), veins (blue lines), lymphatics (green lines), and septa (black wavy lines).
Differential diagnosis and imaging findings Soft-tissue rind Nephroblastomatosis The kidneys develop from a ureteric bud and surrounding metanephric blastema, which ultimately matures into normal renal parenchyma. Metanephric blastema that fails to mature during nephrogenesis persists into childhood as nephrogenic rests.1 Nephrogenic rests may be single, multiple, mixed, or diffuse; the presence of multiple macroscopic or diffuse nephrogenic rests is referred to as nephroblastomatosis. The distribution of nephrogenic rests and nephroblastomatosis can generally be classified as intralobar or perilobar: intralobar refers to random occurrence within the renal lobe while perilobar refers to occurrence in the cortex covering the lobe or at the corticomedullary junction. Perilobar distribution is more common and has a higher association with BeckwitheWiedemann syndrome and hemihypertrophy while intralobar nephroblastomatosis has a higher association with Drash syndrome, sporadic aniridia, and WAGR syndrome (Wilm’s tumour, aniridia, genito-urinary anomalies, and mental retardation).2,3 As nephroblastomatosis is a precursor for Wilms’ tumour and these syndromes are associated with abnormalities of the Wilms’ tumour suppressor genes on chromosome11, patients are screened regularly for the development of Wilms’ tumour.3,4 Clinically, nephroblastomatosis may be detected as unilateral or bilateral flank masses during physical examination. Alternatively, nephroblastomatosis may be clinically silent and
Fibrosis Retroperitoneal fibrosis (RPF) is a fibrotic reaction resulting in encasement of the abdominal aorta, inferior vena cava, or ureters, which may extend into the perinephric space. Clinically, the initial symptoms are typically non-specific, but often manifest with lumbar or flank pain, lower extremity swelling, or decreased urinary excretion.9 RPF is two to three times more common in men and occurs in patients ranging in age from 40 to 60 years.10 RPF may be secondary to inflammatory disorders, malignancy, or medications, but is idiopathic in 70% of cases, postulated to be secondary to an autoimmune response; additionally, it may be isolated or occur as part of multifocal fibrosclerosis along with autoimmune pancreatitis, sclerosing cholangitis, Riedel’s thyroiditis, and scleroderma (Fig 3).11,12 Perirenal fibrosis that occurs as part of retroperitoneal fibrosis or as a part of multifocal fibrosclerosis is usually not difficult to identify at imaging. However, the imaging findings of isolated perirenal fibrosis, such as can be seen in the setting of advanced systemic lupus erythromatosis, are non-specific and histopathological analysis may be needed to establish diagnosis. Management of RPF consists of removal of the offending agent when identified. Corticosteroids have proven effective in reducing symptoms and the size of the retroperitoneal fibrotic mass.13 Supplementation with immunosuppressive drugs, anti-rheumatic agents, and surgery can be used in refractory cases.12,14 At CT, RPF typically manifests as a homogeneous paraspinal mass, which is isodense to muscle and does not displace the aorta and inferior vena cava away from the spine (Fig 3). Imaging features and enhancement following contrast medium administration depends on the maturity of the fibrotic tissue; avid enhancement may be evident in the acute phases, while minimal to absent enhancement can be seen in chronic phases.15 With MRI, active fibrosis may show early enhancement and increased intensity on T2-weighted images while more advanced or chronic disease may show delayed enhancement and low signal
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Figure 2 Nephroblastomatosis. A 2-year-old female patient presented with an abdominal mass. (a) Contrast-enhanced CT shows a rind of soft tissue (arrowheads) surrounding both kidneys. A heterogeneously enhancing central mass (W) is part of an upper pole Wilms’ tumour. (b) Coronal, contrast-enhanced, T1-weighted image shows the Wilms’ tumour (W) in the upper pole of the right kidney and the low-signal rim of perinephric soft tissue (arrowheads). Surgical specimen confirmed Wilms’ tumour.
intensity on T2-weighted images.16 When seen on ultrasound, retroperitoneal fibrosis appears as a hypoechoic halo of soft tissue. Differentiation of benign disease from malignant disease based on imaging alone is difficult.17 Bulkier disease with peripheral nodularity and mass effect on adjacent structures including displacement of the aorta and inferior vena cava away from the spine suggest malignancy.12
ECD ECD is a rare, non-Langerhans, histiocytic disorder, which affects middle-aged adults (mean age of 53 years) and may involve numerous organs, including the long bones, lungs, skin, pituitary gland, kidneys, adrenal gland, and heart. Lower extremity bone pain is the most common symptom, although clinical manifestations are protean, ranging from asymptomatic to life-threatening conditions
Figure 3 Idiopathic RPF. A 53-year-old man presented with back pain and mildly elevated creatinine. (a) Excretory phase CT image shows mild bilateral hydronephrosis and abnormal soft tissue (arrowheads) in the left perinephric space at the level of the renal hilum. (b) More inferiorly, a mantle of soft tissue (arrowheads) encases the aorta and inferior vena cava and tethers the ureters medially (arrows), resulting in partial obstruction of their lumen. Biopsy confirmed RPF.
such as heart failure, tamponade, or renal failure.18 Most patients (60%) have osseous involvement at the time of presentation, such as enlarged femora, metadiaphyseal sclerosis, and trabecular coarsening; however, renal involvement is found in 29% of patients and may be an isolated site of disease (Fig 4).18 Progressive fibrous perinephritis can lead to renal failure. At cross-sectional imaging, perinephric involvement of ECD may manifest as a mass-like, infiltrative pattern or a soft-tissue rind in the
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on T1 and T2-weighted sequences and show slight homogeneous enhancement following gadolinium administration.19 Treatment consists of a combination of surgery, corticosteroids, cyclosporine, and interferon.20
Extramedullary haematopoiesis Extramedullary haematopoiesis is a physiological compensatory mechanism for failure of erythropoiesis; it commonly occurs in the liver and spleen but may also involve the kidneys, breast, skin, and adrenal glands.21 Renal extramedullary haematopoiesis may be parenchymal, intrapelvic, or perinephric; intrapelvic and perinephric disease is often bilateral but may be unilateral. Patients are usually asymptomatic, but may present with abdominal pain or renal failure due to parenchymal involvement or ureteral compression. Imaging features on CT with perinephric disease include a perinephric, softtissue mass showing mild, homogeneous enhancement (Fig 5).29 At MRI, signal intensity on T2-weighted images is typically low owing to the haemosiderin content, but can be variable due to inclusion of foci of macroscopic fat. At ultrasound, findings usually consist of a solid hypoechoic perinephric mass. Additional imaging findings of hepatosplenomegaly and paraspinal soft tissue can aid in the diagnosis of extramedullary haematopoiesis.22 Treatment for symptomatic cases consists of surgery and radiation.
Lymphoma Perinephric lymphoma is commonly due to extension of retroperitoneal or renal lymphoma and is most often associated with an intermediate to high-grade non-Hodgkin’s lymphoma of B-cell lineage.23 Tumour isolated to the perinephric space is rare, accounting for less than 10% of cases of perinephric lymphoma.24 Lymphoma involving the kidneys and perinephric space is typically clinically silent but may present with flank pain, haematuria, palpable mass, or weight loss, and rarely acute renal failure.23 Multiple radiographic patterns of renal lymphoma may be observed, which include a single mass, multiple masses, contiguous retroperitoneal extension, perirenal involvement, and diffuse infiltration. Unilateral disease versus bilateral disease depends on the mode of spread. With the Figure 4 ECD. A 39-year-old man presented with lower extremity bone pain. (a) Anteroposterior radiograph of the lower extremities shows enlarged femora and metadiaphyseal sclerosis/thickening (white arrows) and a coarsened trabecular pattern. Periostitis is shown as mild wavy contour abnormality (black arrowheads). (b) Contrast-enhanced CT shows a circumferential soft-tissue rind (arrows) surrounding each kidney, which caused narrowing of the ureteropelvic junctions and resulted in mild hydronephrosis. Biopsy proved ECD.
perinephric space. On unenhanced CT, homogeneous softtissue, isodense to muscle may be seen in the perinephric space bilaterally. Perirenal infiltration with extension into the anterior and posterior pararenal space produces a “hairy kidney” appearance. Enhancement is homogeneous and poor following contrast medium administration. On MRI, ECD involving the kidneys will appear isointense to muscle
Figure 5 Extramedullary haematopoiesis. A 51-year-old man presented with perinephric soft tissue during a CT examination. Contrast-enhanced CT image shows hypovascular perinephric softtissue attenuation bilaterally (arrowheads). Biopsy proved extramedullary haematopoiesis.
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pattern of perinephric involvement, the tumour is often homogeneous, hypovascular, and mildly enhancing at cross-sectional imaging (Fig 6). Sonography shows a solid, hypoechoic perinephric mass. Renal lymphoma is typically hypointense on T1 and slightly hypo to isointense on T2 relative to the kidneys on MRI. Enhancement is homogeneous but less than the adjacent renal parenchyma following gadolinium administration.23 Treatment consists
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of chemotherapy; ureteral stenting can be used in cases of obstruction.
Metastases The perinephric space is an unusual site for identification of remote malignancies, but has been reported in melanoma, prostate, breast, and gastrointestinal tumour metastases due to haematogenous means, and in lung cancer metastases due to lymphatic spread.25,26 Additionally, metastases to the kidneys can infiltrate the perinephric space.27 Radiological features often depend on the type of primary tumour; for example, melanoma and breast metastases often show enhancement during the arterial phase followed by portal phase wash-out due to their hypervascular nature, while lung and prostate metastases typically do not show significant arterial enhancement. Although most perinephric metastases present as multiple, discrete, soft-tissue masses, some metastases, such as those secondary to breast cancer, can be infiltrative lesions (Fig 7).26,28 In these cases, the cross-sectional imaging findings are non-specific and often confusing due to overlap with lymphoma and other perinephric processes, although breast cancer metastases typically enhance much more briskly than lymphoma and rarely occur in isolation. However, in most cases of an infiltrative or nodular perinephric process, the imaging findings can be used to select the optimal site and approach for biopsy for definitive characterization.25
Focal solid lesions Focal solid masses in the perinephric space are most commonly due to malignancy. Differential considerations include extension from renal, adrenal, or retroperitoneal tumours and metastases (Fig 8). Identification of tumour in
Figure 6 Lymphoma (non-Hodgkin’s). Contrast-enhanced CT images from two patients with biopsy-proven non-Hodgkin’s lymphoma. (a) A rind of soft tissue (white arrows) surrounds the kidneys; note outer edge of renal cortex (black arrowheads). More inferiorly, ureteral compression from retroperitoneal adenopathy resulted in mild hydronephrosis. (b) (Different patient.) The soft-tissue rind (arrows) is more nodular and extensive. Note the necrotic appearing node near the renal hilum (arrowhead).
Figure 7 Breast cancer metastasis. A 41-year-old woman with a history of breast cancer presented with a lung nodule and infiltrating perinephric soft tissue. Contrast-enhanced CT shows an enhancing rind of soft tissue surrounding the kidney and extending around the aorta. Biopsy confirmed metastatic breast cancer.
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perinephric lymphoma from bulkly circumferential soft tissue to a focal lesion in the perinephric space (Fig 10).
Fatty lesions Angiomyolipoma Angiomyolipomas (AMLs) are common benign, fatcontaining renal lesions. Small AMLs tend to be homogeneous, fatty lesions at imaging, while larger lesions are often heterogeneous due to variable amounts of macroscopic fat,
Figure 8 Nodular metastases. A 21-year-old presented with multiple soft-tissue lesions. (a) Contrast-enhanced CT image shows multiple soft-tissue nodules (arrows) in the inferior perinephric spaces and subcutaneous fat (arrowhead). Biopsy of a palpable subcutaneous nodule revealed melanoma.
the perinephric space is important in staging and predicting survival in renal cell carcinoma (Fig 9); extension into the perinephric space signifies a T3 lesion indicating at least stage III disease. Other neoplasms, such as multiple myeloma, plasmacytoma, malignant fibrous histiocytoma, leukaemia, gastrointestinal stromal tumours, haemangiomas, leiomyomas and haemangiopericytomas infrequently occur in the perinephric space, but typically lack specific imaging findings to allow differentiation. Castleman’s disease, a rare systemic lymphoproliferative disorder with unicentric and multicentric forms, has also been reported to occur in the perinephric space; when it does affect the perinephric space, Castleman’s disease is more commonly multicentric.28 While the imaging appearances of lymphoma are protean, treatment may cause regression of extensive
Figure 9 Renal cell carcinoma. A 66-year-old presented with right flank pain and haematuria. Contrast-enhanced CT image shows a massive tumour (arrows) nearly replacing the right kidney (arrowhead) and filling the anteromedial aspect of the perinephric space. Pathology specimens confirmed renal cell carcinoma.
Figure 10 Treated lymphoma. A 72-year-old presented for follow-up after a history of treated lymphoma. (a) A non-enhancing soft-tissue nodule (arrow) in the posterior aspect of the perinephric space abuts the kidney. This finding had been stable for over 6 years. (b) Initial contrast-enhanced CT image from 7 years prior shows extensive perinephric soft tissue (arrows) with heterogeneous enhancement consistent with lymphoma.
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soft tissue, and aneurysms. As large AMLs are often exophytic, they are the most common fat-containing mass in the perinephric space. However, it is important to distinguish an exophytic AML from other fat-containing perinephric lesions such as a retroperitoneal liposarcoma. An imaging feature that favours the diagnosis of AML is the presence of a renal parenchymal notch or defect in the renal parenchyma at the site of tumour origin (Fig 11).29 AMLs more commonly have intratumoural aneurysms and tend to have large, intralesional blood vessels; comparatively, well-differentiated liposarcomas are typically avascular or contain small vessels.28,29 Also, the presence of additional fat-containing lesions is an indicator that an indeterminate fat-containing lesion is an AML; while multiple AMLs are common in the setting of tuberous sclerosis, they are also not infrequently found in patients without this disease, an occurrence of up to 27% in one study.29
Liposarcoma Liposarcoma is the most common malignant primary retroperitoneal tumour and consists of five subtypes: welldifferentiated, myxoid, round cell, pleomorphic, and dedifferentiated. Well-differentiated liposarcomas are the least aggressive, contain variable amounts of macroscopic fat, and may mimic an AML (Fig 12). Round cell and pleomorphic subtypes manifest as enhancing soft-tissue masses at CT and MRI and are considered to be high-grade tumours, often complicated by local recurrence and metastases following resection.30 Myxoid tumours often contain a cystic component and show reticulated enhancement at CT and MRI after contrast medium injection.31
Figure 12 Liposarcoma. A 60-year-old woman presented with weight loss. (a) Contrast-enhanced CT image shows a bilobed mass in the retroperitoneum containing a briskly enhancing soft-tissue component (arrow) in the perinephric space and an intermediate attenuation component (arrowhead) with small foci of intratumoural fat in the anterior pararenal space. (b) More inferiorly, there are more conspicuous fat components (arrows) in the perinephric space and continuation of the solid component (arrowhead) in the anterior pararenal space. Resection specimen confirmed liposarcoma.
Figure 11 Angiomyolipoma. A 39 year-old woman presented for evaluation of abdominal pain and was found to have an incidental mass in the left perinephric space. Post-contrast CT shows a predominantly fat-containing mass (arrow) in the perinephric space; a large feeding vessel (arrowhead) traversing the mass originates from the kidney. Resection specimens were consistent with angiomyolipoma.
Myelolipoma Myelolipomas are rare, benign neoplasms composed of adipose tissue and haematopoietic elements. Most myelolipomas are adrenal in origin, but may also arise from the perinephric space and presacral region.32 Most myelolipomas are discovered incidentally by imaging, but they can present with pain due to spontaneous haemorrhage and mass effect.
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The cross-sectional imaging findings of myelolipoma are largely dependent on the relative amounts of adipose and haematopoietic tissue; the tumours are usually heterogeneous, containing both hypervascular soft tissue and macroscopic fat elements (Fig 13).33 At ultrasound, myelolipomas generally have heterogeneous echogenicity due to their nonuniform consistency. CT typically shows macroscopic fat with interspersed regions of soft-tissue attenuation. At MRI, areas of fat show high signal intensity on T1 and T2-weighted sequences, while marrow-like regions have intermediate signal intensity similar to that of spleen.34
Lymphangiomas are rare, benign mesenchymal neoplasms, which are characterized by numerous intercommunicating, endothelial-lined spaces containing lymph fluid.35 Lymphangiomas are congenital due to developmental obstruction of regional lymph drainage. Lymphangiomas may be focal and unilateral, bilateral or diffuse; when diffuse, the condition is referred to as lymphangiomatosis (Fig 14). The lesions are usually asymptomatic but can result in haematuria
Figure 13 Myelolipoma. A 46-year-old man was referred for evaluation of an incidental suprarenal mass reported on cardiac MRI (not shown). (aeb) Contrast-enhanced CT image shows the predominantly fatty mass (arrows) filling the superomedial perinephric space. Resection specimen confirmed myelolipoma.
Figure 14 Perinephric lymphangiomatosis. A 20-year-old man had an abnormal renal ultrasound. (a) Longitudinal ultrasound shows a multiseptated, cystic lesion surrounding the right kidney (arrows); there was a similar finding on the left (not shown). (b) T2-weighted image shows a multiseptated, cystic mass (arrows) surrounding both kidneys. Percutaneous aspiration revealed chylous fluid, which contained numerous lymphocytes.
Cystic lesions Lymphangioma
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or proteinuria occasionally. In extremely rare instances of giant lymphangiomas or extensive lymphangiomatosis, sufficient compression of the kidney has been reported to alter the renineangiotensinealdosterone system and result in hypertension, referred to as a Page kidney36,37; however, Page kidney is much more commonly due to compression by a subcapsular haematoma. At CT or MRI, lymphangiomas typically appear as a perinephric cystic lesions with variable peripheral or septal enhancement associated with normal appearing kidneys.38 Ultrasound shows numerous anechoic cystic regions separated by thin septa. Percutaneous aspiration may reveal chylous fluid or fluid rich in lymphocytes.44,45 Symptomatic cases are typically treated with surgery.39,40
Abscess and infection Despite not being a true proliferative disorder, perinephric infection is common and abscess can mimic cystic neoplasms. Both acute bacterial pyelonephritis and xanthogranulomatous pyelonephritis can cause severe renal infection, which extends into the perinephric space. Acute pyelonephritis is due to bacterial or fungal infection of the renal parenchyma and collecting system, which usually occurs due to ascending infection from the lower urinary tract. Bacterial pyelonephritis is most common due to Gram-negative organisms such as Escherichia coil.41 Patients typically present with fever, flank pain, and leukocytosis. In the perinephric space, the CT and MRI findings of acute pyelonephritis are non-specific and include thickening of Gerota’s fascia, perinephric fat stranding, and obliteration of perinephric fat planes.42 Ultrasound is relatively insensitive in showing extension of inflammation into the perinephric
Figure 15 Abscess. A 31-year-old woman presented with pyuria, leukocytosis, and flank pain. Contrast-enhanced CT image shows focal phlegmon (arrows) in the medial aspect of the left kidney. An ovoid fluid collection (arrowhead) in the medial aspect of the left perinephric space is consistent with an abscess. Percutaneous aspiration yielded pus.
Figure 16 Emphysematous pyelonephritis. A 49-year-old diabetic woman presented with fever and flank pain. Unenhanced contrast CT shows extensive gas (arrowheads) in the right renal collecting system, which dissects posteriorly into the perinephric space. Note adjacent phlegmon (p).
space.43 However, ultrasound is useful in detecting perinephric abscess and in guiding percutaneous catheter drainage. With ultrasound, perinephric abscesses typically appear as multilocular fluid collections with internal
Figure 17 Xanthogranulomatous pyelonephritis. A 52-year-old diabetic woman presented with flank pain. Contrast-enhanced CT image shows a staghorn’s calculus (arrow) in the renal pelvis, renal enlargement and heterogeneity, and dilatation of portions of the renal collecting system. Infiltration of the perinephric fat and thickening of Zuckerkandl’s fascia are due to spread of infection into the perinephric space. Nephrectomy specimen confirmed xanthogranulomatous pyelonephritis.
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echoes. CT and MRI reveal a heterogeneously enhancing, complex cystic lesion with enhancing internal septa and a variable degree of infiltration of the perinephric space (Fig 15). In cases of emphysematous infections, CT readily shows gas extending from the kidney into the perinephric space (Fig 16), while MRI will show signal voids, which may be difficult to interpret.44 With ultrasound, the “dirty shadowing” caused by perinephric gas may obsure a fluid collection and the kidney. Additionally, xanthogranulomatous pyelonephritis (XGP), a rare form of chronic pyelonephritis characterized by progressive renal destruction and replacement by lipid-laden macrophages, has been documented to involve the perinephric space; CT and MRI findings can include infiltration of the perinephric fat, massive accumulation of perinephric fat, and abscesses (Fig 17).45 Treatment of perinephric infection generally consists of antibiotics for the underlying renal infection and percutaneous catheter drainage of abscesses.
Summary The perinephric space is a central retroperitoneal compartment, which can host numerous neoplastic and proliferative processes. These disease processes can originate in the perinephric space or gain access via regional, lymphatic, or haematogenous spread. Imaging plays a central role in the detection and characterization of perinephric neoplastic and proliferative disorders, as many of these conditions may be clinically silent until late in the disease process.
Acknowledgements The authors thank Chris Granville, MD, for his help in creating Fig 1.
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