DOI: 10.1148/rg.24si045503
RadioGraphics 2004;24:S117-S131
© RSNA, 2004
The Renal Sinus: Pathologic Spectrum and Multimodality Imaging Approach1
Sung Eun Rha, MD,
Jae Young Byun, MD,
Seung Eun Jung, MD,
Soon Nam Oh, MD,
Yeong-Jin Choi, MD,
Ahwon Lee, MD and
Jae Mun Lee, MD
1 From the Departments of Radiology (S.E.R., J.Y.B., S.E.J., S.N.O., J.M.L.) and Pathology (Y.J.C., A.L.), College of Medicine, Catholic University of Korea, 505 Banpo-Dong, Seocho-Ku, Seoul 137-040, South Korea. Recipient of a Cum Laude award for an education exhibit at the 2003 RSNA scientific assembly. Received February 4, 2004; revision requested April 2 and received May 7; accepted May 12. All authors have no financial relationships to disclose. Address correspondence to J.Y.B. (e-mail: jybyun@catholic.ac.kr).
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Abstract
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Various pathologic conditions can occur in the renal sinus, primarily originating in the constituents of the renal sinus, and the renal sinus can be secondarily involved by surrounding renal parenchymal and adjacent retroperitoneal lesions. Lipomatosis and cysts are common renal sinus lesions with little clinical significance, but differentiation from other pathologic conditions is important. Renal vascular lesions such as renal artery aneurysm or arteriovenous fistula can mimic other parapelvic or peripelvic lesions at excretory urography, but their vascular nature is evident at color Doppler ultrasonography, contrast material–enhanced computed tomography (CT), and magnetic resonance (MR) imaging. Although most tumors originating in the renal pelvis are transitional cell carcinoma or squamous cell carcinoma, renal parenchymal tumors such as renal cell carcinoma or benign multilocular cystic nephroma have a tendency to grow into the renal sinus. Rare tumors of mesenchymal origin can develop in the renal sinus, but their imaging findings are nonspecific. The observation of renal sinus fat is important for detecting a small tumor located in that area and determining the exact tumor stage. Multiplanar CT or MR images can allow exact evaluation of the extent of complex renal sinus disease.
© RSNA, 2004
Index Terms: Aneurysm, renal, 814.73 • Arteriovenous malformations, renal, 814.1494, 814.494 • Kidney, cysts, 814.311 • Kidney, hemorrhage, 814.4132, 814.64 • Kidney neoplasms, diagnosis, 814.30 • Lipoma and lipomatosis, 814.894 • Nephritis, 814.212 • Urinoma, 814.3116, 814.415
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LEARNING OBJECTIVES FOR TEST 3
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After reading this article and taking the test, the reader will be able to:
- Describe the normal anatomy and constituents of the renal sinus.
- List a broad spectrum of lesions that affect the renal sinus.
- Identify the multimodality imaging features of various pathologic processes of the renal sinus.
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Introduction
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The renal sinus is a central spacious cavity formed by the extension of the perinephric space into the deep recess located at the medial border of the kidney (Figs 1, 2). The renal sinus is surrounded by the kidney parenchyma laterally. The major branches of the renal artery and vein along with the major and minor calices of the collecting system are located within the renal sinus. The remainder of the sinus is filled with adipose tissue, lymphatic channels, nerve fibers of the autonomic nervous system, and varying quantities of fibrous tissue (1–4). Therefore, various pathologic conditions can occur in the renal sinus from any of its constituents. In addition, the renal sinus can be secondarily involved by surrounding renal parenchymal and adjacent retroperitoneal lesions.
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Figure 2. Normal computed tomographic (CT) anatomy of the renal sinus. Coronal contrast material-enhanced CT scan obtained during the excretory phase shows the extent of the renal sinus (arrowheads).
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As with any anatomic region, renal sinus lesions can be classified as nontumorous or tumorous. Nontumorous lesions include renal sinus lipomatosis, renal sinus cysts, vascular lesions, and fluid collections. Tumors involving the renal sinus can be classified according to their origins into four subgroups: (a) tumors of the renal pelvis, (b) primary tumors of mesenchymal origin, (c) tumors of the renal parenchyma that project into the renal sinus, and (d) retroperitoneal tumors that extend to the renal sinus.
The diagnosis of renal sinus lesions relies on a multimodality imaging approach including excretory urography, ultrasonography (US), CT, magnetic resonance (MR) imaging, and angiography. This article illustrates a broad spectrum of pathologic lesions affecting the renal sinus with emphasis on multimodality imaging findings.
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Imaging Modalities for Renal Sinus Lesions
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Various imaging modalities can be used for the evaluation of pathologic conditions affecting the renal sinus. These include excretory urography, US, CT, MR imaging, and angiography. Each modality can provide useful information about the detection, characterization, and extent of disease.
Excretory urography is useful for evaluating the involvement of the renal collecting system. Most abnormalities of the renal sinus are focal and termed parapelvic; the prefix "para" means "alongside" or "beside." These abnormalities cause focal displacement and compression of the pelvicaliceal system at excretory urography and a circumscribed mass on cross-sectional images. An irregular pelvicaliceal deformity suggests direct invasion by malignant tumors or unusual inflammatory conditions. Conversely, disorders that diffusely surround the pelvicaliceal system are termed peripelvic; the prefix "peri" means "around." The common peripelvic pathologic conditions are renal sinus lipomatosis and renal sinus cysts, both of which cause generalized effacement and stretching of the pelvicaliceal system at excretory urography (2). The uncommon peripelvic lesions include arteriovenous communications, renal sinus hemorrhage, urine extravasation into the renal sinus, and lymphoma infiltrating the renal sinus.
US is useful to distinguish cystic from solid space-occupying lesions when the lesion is detected with excretory urography and functions as the initial screening modality for noninvasive imaging of the kidney. The normal renal sinus is seen as an area of increased echoes with variable contours due to the fat-parenchyma interface. A collapsed renal pelvis may be indistinguishable from echogenic renal sinus fat (5). Despite good results with US, there are limitations, especially with small lesions when the renal sinus lesion is poorly defined or the echo pattern is similar to or the same as that of the adjacent renal sinus fat or adjacent renal parenchyma (5). Color Doppler US is useful for the evaluation of renal vascular lesions, such as renal artery aneurysm, arteriovenous fistula, and renal vein varix. Angiography is usually required prior to treatment of renal vascular lesions.
CT is the most sensitive, efficient, and comprehensive imaging modality for evaluating the kidneys and is the problem-solving technique for a wide variety of renal sinus lesions. The recent development of multidetector CT provides dramatically faster scan acquisition and improved spatial resolution by means of thinner collimation. Multiplanar reconstruction images can allow exact determination of the extent of complex renal sinus disease (6). In general, the coronal plane is the most useful for the evaluation of renal sinus lesions because it provides a comprehensive view of the kidney, including the renal sinus (7).
MR imaging is an alternative to CT for the evaluation of renal sinus lesions because it allows detailed tissue characterization of complicated renal sinus lesions and direct multiplanar images with the same image resolution in the coronal, sagittal, and axial planes. It can also be used in patients with renal failure or contrast material allergies (7).
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Nontumorous Lesions of the Renal Sinus
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Lipomatosis
The normal renal sinus contains fat that envelops the other structures within it. The quantity of fat in the renal sinus normally and gradually increases with age and obesity. Proliferation of sinus fat also occurs abnormally in association with processes causing destruction or atrophy of renal tissue and with increased exogenous or endogenous steroids (1,2). Renal sinus lipomatosis involves prominent fat proliferation that leads to mass effect on the intrarenal collecting system. However, mass effect from renal sinus lipomatosis rarely leads to symptoms because caliceal obstruction does not result from simple lipomatosis (1). Excretory urography shows a radiolucent sinus associated with attenuation and stretching of the infundibula. US demonstrates enlargement of the echogenic central sinus complex. CT and MR imaging directly reveal the fatty nature of the sinus lipomatosis (Fig 3) (2).
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Figure 3a. Bilateral renal sinus lipomatosis in a 76-year-old asymptomatic man. (a) Excretory urogram shows diffuse elongation and attenuation of the renal pelvis and infundibula of both kidneys. (b) Axial contrast-enhanced CT scan shows proliferation of fat (arrows) in both renal sinuses, a finding suggestive of renal sinus lipomatosis.
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Figure 3b. Bilateral renal sinus lipomatosis in a 76-year-old asymptomatic man. (a) Excretory urogram shows diffuse elongation and attenuation of the renal pelvis and infundibula of both kidneys. (b) Axial contrast-enhanced CT scan shows proliferation of fat (arrows) in both renal sinuses, a finding suggestive of renal sinus lipomatosis.
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Replacement lipomatosis of the kidney is an extreme form of renal sinus lipomatosis that usually occurs unilaterally (8). Replacement lipomatosis is a sequela of severe renal atrophy or destruction usually due to chronic calculus disease with resultant hydronephrosis and inflammation (9). Plain radiography usually shows a staghorn calculus. Excretory urography demonstrates a poorly functioning or nonfunctioning kidney. CT and MR imaging clearly demonstrate masslike proliferation of the renal sinus fat and markedly atrophied renal parenchyma (Fig 4). The CT and MR imaging findings of replacement lipomatosis of the kidney may mimic those of focal fat-containing neoplasms that originate in the renal sinus, such as angiomyolipoma, lipoma, or liposarcoma (9). However, these tumors cause a focal mass effect on the intrarenal collecting system and are not associated with renal parenchymal atrophy or staghorn calculus. Xanthogranulomatous pyelonephritis is another important differential diagnosis when excretory urography reveals a staghorn calculus in a nonfunctioning kidney. CT often reveals low-attenuation tissue replacing the renal parenchyma. Xanthogranulomatous pyelonephritis and replacement lipomatosis may coexist (10).
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Figure 4a. Replacement lipomatosis of the renal sinus and periureteral space in a 63-year-old man with chronic renal calculus disease. A percutaneous nephrostomy tube was inserted for stone extraction. CT was performed because procedure-related hemorrhage was suspected. (a) Axial contrast-enhanced CT scan shows a tumorlike mass of fat (arrows) that occupies the left renal sinus and surrounds the left ureter (u). The left renal parenchyma is markedly atrophied in association with a large stone (arrowhead), and a large amount of subcapsular hematoma (H) is also seen. Note the percutaneous nephrostomy tube. (b) Photograph of the surgical specimen shows the markedly atrophied kidney (arrows) containing several stones; the kidney is surrounded by fatty tissue (F).
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Figure 4b. Replacement lipomatosis of the renal sinus and periureteral space in a 63-year-old man with chronic renal calculus disease. A percutaneous nephrostomy tube was inserted for stone extraction. CT was performed because procedure-related hemorrhage was suspected. (a) Axial contrast-enhanced CT scan shows a tumorlike mass of fat (arrows) that occupies the left renal sinus and surrounds the left ureter (u). The left renal parenchyma is markedly atrophied in association with a large stone (arrowhead), and a large amount of subcapsular hematoma (H) is also seen. Note the percutaneous nephrostomy tube. (b) Photograph of the surgical specimen shows the markedly atrophied kidney (arrows) containing several stones; the kidney is surrounded by fatty tissue (F).
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Cysts
Renal sinus cysts are common, with a reported prevalence between 1.28% and 1.5% in autopsy cases (3). Peripelvic cysts, parapelvic lymphatic cysts, parapelvic lymphangiectasia, and parapelvic cysts are a variety of terms that have been used to describe single or multiple cysts confined to the renal sinus (3,4).
There are two distinctly different patterns of cyst manifestation within the renal sinus (2–4). In the first pattern, multiple, small, confluent cysts appear to arise in the sinus itself. These cysts are termed peripelvic cysts and are benign extraparenchymal cysts located in the renal sinus. They are thought to be lymphatic in origin and are rarely symptomatic. They are often bilateral. At excretory urography, peripelvic cysts may be indistinguishable from renal sinus lipomatosis. At US and unenhanced CT, these cysts may mimic hydronephrosis; however, peripelvic cysts are not interconnected, and the lesions cannot be traced to the ureter. At excretory urography and contrast-enhanced CT performed during the excretory phase, differentiation of peripelvic cysts and hydronephrosis is obvious (Fig 5). The enhanced collecting systems are displaced and attenuated by the water-attenuation sinus cysts. Peripelvic cysts do not require close functional and morphologic monitoring due to their absence of symptoms and their unchanged dimensions at long-term follow-up (11).
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Figure 5a. Renal sinus cysts in a 53-year-old asymptomatic man. (a) Axial contrast-enhanced CT scan obtained during the nephrographic phase shows low-attenuation cystic lesions (arrows) in the left renal sinus; this finding could be misinterpreted as hydronephrosis. (b) Axial contrast-enhanced CT scan obtained during the excretory phase shows the cysts (arrows) in the renal sinus, an appearance different from that of hydronephrosis. The enhanced calices are stretched and attenuated but not obstructed by the cysts.
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Figure 5b. Renal sinus cysts in a 53-year-old asymptomatic man. (a) Axial contrast-enhanced CT scan obtained during the nephrographic phase shows low-attenuation cystic lesions (arrows) in the left renal sinus; this finding could be misinterpreted as hydronephrosis. (b) Axial contrast-enhanced CT scan obtained during the excretory phase shows the cysts (arrows) in the renal sinus, an appearance different from that of hydronephrosis. The enhanced calices are stretched and attenuated but not obstructed by the cysts.
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The other pattern of renal sinus cysts is that of a single, larger cyst occurring in the sinus and most likely originating from the adjacent parenchyma. These are termed parapelvic cysts and are simple renal cysts originating in the medial renal parenchymal tissue and protruding into the renal sinus. Parapelvic cysts display the same imaging features as simple renal cortical cysts (Fig 6). They are usually solitary or few in number. Occasionally, symptoms such as hypertension, hematuria, and localized hydronephrosis have been reported in large parapelvic cysts compressing the renal vasculature and/or adjacent collecting system structures (2).
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Figure 6a. Renal sinus cyst in a 54-year-old asymptomatic man. (a) Excretory urogram shows splaying of the calices and compression of the right renal pelvis (arrows), findings suggestive of a focal lesion. (b) Axial contrast-enhanced CT scan shows a single, well-defined, water-attenuation cyst (arrows) protruding into the renal sinus. It has the same appearance as the more common renal cortical cyst (arrowhead).
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Figure 6b. Renal sinus cyst in a 54-year-old asymptomatic man. (a) Excretory urogram shows splaying of the calices and compression of the right renal pelvis (arrows), findings suggestive of a focal lesion. (b) Axial contrast-enhanced CT scan shows a single, well-defined, water-attenuation cyst (arrows) protruding into the renal sinus. It has the same appearance as the more common renal cortical cyst (arrowhead).
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However, neither type of renal sinus cyst is often of clinical importance or the subject of pathologic study (2). Therefore, in the absence of precise pathologic-radiologic correlative data, the term renal sinus cyst is recommended as a generic description of any fluid-filled cyst found in the renal sinus (3).
Vascular Lesions
Vascular lesions, such as renal artery aneurysm, arteriovenous communication, or renal vein varix, can involve the renal sinus and manifest as a parapelvic mass or peripelvic lesion. Their vascular nature is readily identifiable at color Doppler US, contrast-enhanced CT or MR imaging, and angiography (Fig 7).
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Figure 7. Renal artery aneurysm in a 47-year-old man with gross hematuria. Coronal reformatted CT scan obtained during the corticomedullary phase shows a small saccular aneurysm (arrow) in the right renal sinus.
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The most common cause of aneurysms of the renal artery is atherosclerosis. Because annular calcification occurs in more than 50% of atherosclerotic renal artery aneurysms, the differentiation between a calcified renal artery aneurysm and a renal calculus is especially important before undertaking extracorporeal shock wave lithotripsy (Fig 8) (2). A variable degree of contrast enhancement or opacification is seen according to the amount of thrombus within the aneurysm at contrast-enhanced CT or angiography (Fig 8). Color Doppler US shows a fluid mass with flow characteristics, and spectral Doppler US demonstrates turbulent flow in the aneurysm (12).
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Figure 8a. Partially thrombosed renal artery aneurysm with rim calcification in a 67-year-old man with hypertension. (a) Axial unenhanced CT scan shows a large, lobulated, masslike lesion with soft-tissue attenuation and rim calcifications (arrows) in the right renal sinus. (b) Axial contrast-enhanced CT scan shows that the lesion is vascular (arrows) with a nonenhancing area suggestive of thrombus (T). (c) Direct right renal arteriogram shows the large, saccular, bilobed aneurysm.
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Figure 8b. Partially thrombosed renal artery aneurysm with rim calcification in a 67-year-old man with hypertension. (a) Axial unenhanced CT scan shows a large, lobulated, masslike lesion with soft-tissue attenuation and rim calcifications (arrows) in the right renal sinus. (b) Axial contrast-enhanced CT scan shows that the lesion is vascular (arrows) with a nonenhancing area suggestive of thrombus (T). (c) Direct right renal arteriogram shows the large, saccular, bilobed aneurysm.
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Figure 8c. Partially thrombosed renal artery aneurysm with rim calcification in a 67-year-old man with hypertension. (a) Axial unenhanced CT scan shows a large, lobulated, masslike lesion with soft-tissue attenuation and rim calcifications (arrows) in the right renal sinus. (b) Axial contrast-enhanced CT scan shows that the lesion is vascular (arrows) with a nonenhancing area suggestive of thrombus (T). (c) Direct right renal arteriogram shows the large, saccular, bilobed aneurysm.
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There are three types of renal arteriovenous communications: congenital arteriovenous malformations; acquired arteriovenous fistula associated with renal biopsy, other renal operations, trauma (usually penetrating), or malignant tumors (most commonly renal cell carcinoma); and idiopathic arteriovenous fistula (13). Acquired lesions account for 70%–80% of all renal arteriovenous communications, and biopsy-related lesions are the most common among them. Most renal arteriovenous fistulas are clinically silent, but they may manifest with at least one of the following signs: gross hematuria, abdominal bruit, high-output cardiac failure, hypertension, or abdominal pain. An arteriovenous fistula may cause only subtle extrinsic impressions on the pelvicaliceal system by collateral vessels at excretory urography and can be easily missed even at cross-sectional imaging, depending on the lesion size (Fig 9).
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Figure 9a. Renal arteriovenous fistula in a 48-year-old woman with sudden onset of hematuria and right flank pain. Excretory urography performed 3 days before retrograde pyelography showed nonopacification of the right kidney. (a) Retrograde pyelogram shows nonopacification of the lower pole calices and irregular tortuous filling defects in and around the interpolar calices and pelvis (arrows). The pelvicaliceal system is mildly dilated. (b) Axial contrast-enhanced CT scan obtained during the corticomedullary phase shows tortuous, dilated, enhancing vascular structures (arrow) in the right renal sinus. Note the mildly dilated right renal pelvis and the double-J catheter (arrowhead) in the renal pelvis. (c) Coronal contrast-enhanced T1-weighted MR image (repetition time msec/echo time msec = 111/4.1) shows the tortuous vascular structures with signal void (arrows) along the dilated collecting system. (d) Right renal arteriogram shows the entangled vessels of the arteriovenous communication (arrows), which is sometimes referred to as a cirsoid aneurysm, in the lower polar area of the right kidney.
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Figure 9b. Renal arteriovenous fistula in a 48-year-old woman with sudden onset of hematuria and right flank pain. Excretory urography performed 3 days before retrograde pyelography showed nonopacification of the right kidney. (a) Retrograde pyelogram shows nonopacification of the lower pole calices and irregular tortuous filling defects in and around the interpolar calices and pelvis (arrows). The pelvicaliceal system is mildly dilated. (b) Axial contrast-enhanced CT scan obtained during the corticomedullary phase shows tortuous, dilated, enhancing vascular structures (arrow) in the right renal sinus. Note the mildly dilated right renal pelvis and the double-J catheter (arrowhead) in the renal pelvis. (c) Coronal contrast-enhanced T1-weighted MR image (repetition time msec/echo time msec = 111/4.1) shows the tortuous vascular structures with signal void (arrows) along the dilated collecting system. (d) Right renal arteriogram shows the entangled vessels of the arteriovenous communication (arrows), which is sometimes referred to as a cirsoid aneurysm, in the lower polar area of the right kidney.
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Figure 9c. Renal arteriovenous fistula in a 48-year-old woman with sudden onset of hematuria and right flank pain. Excretory urography performed 3 days before retrograde pyelography showed nonopacification of the right kidney. (a) Retrograde pyelogram shows nonopacification of the lower pole calices and irregular tortuous filling defects in and around the interpolar calices and pelvis (arrows). The pelvicaliceal system is mildly dilated. (b) Axial contrast-enhanced CT scan obtained during the corticomedullary phase shows tortuous, dilated, enhancing vascular structures (arrow) in the right renal sinus. Note the mildly dilated right renal pelvis and the double-J catheter (arrowhead) in the renal pelvis. (c) Coronal contrast-enhanced T1-weighted MR image (repetition time msec/echo time msec = 111/4.1) shows the tortuous vascular structures with signal void (arrows) along the dilated collecting system. (d) Right renal arteriogram shows the entangled vessels of the arteriovenous communication (arrows), which is sometimes referred to as a cirsoid aneurysm, in the lower polar area of the right kidney.
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Figure 9d. Renal arteriovenous fistula in a 48-year-old woman with sudden onset of hematuria and right flank pain. Excretory urography performed 3 days before retrograde pyelography showed nonopacification of the right kidney. (a) Retrograde pyelogram shows nonopacification of the lower pole calices and irregular tortuous filling defects in and around the interpolar calices and pelvis (arrows). The pelvicaliceal system is mildly dilated. (b) Axial contrast-enhanced CT scan obtained during the corticomedullary phase shows tortuous, dilated, enhancing vascular structures (arrow) in the right renal sinus. Note the mildly dilated right renal pelvis and the double-J catheter (arrowhead) in the renal pelvis. (c) Coronal contrast-enhanced T1-weighted MR image (repetition time msec/echo time msec = 111/4.1) shows the tortuous vascular structures with signal void (arrows) along the dilated collecting system. (d) Right renal arteriogram shows the entangled vessels of the arteriovenous communication (arrows), which is sometimes referred to as a cirsoid aneurysm, in the lower polar area of the right kidney.
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Although the definitive diagnostic procedure for evaluating these vascular lesions is renal angiography, they can also be assessed with color Doppler US, contrast-enhanced CT, or MR imaging. Color Doppler US demonstrates aliasing or color saturation due to the high flow rates and tortuosity of the vessels in the arteriovenous fistula. Spectral analysis with pulsed Doppler interrogation shows increased flow velocity and decreased resistance in the feeding artery and arterial pulsations in the draining vein (14). Contrast-enhanced CT shows the hypervascular nature of the tangled vessels with the aneurysmal component (Fig 9). MR images can demonstrate flow voids caused by high-velocity signal loss (Fig 9). Arteriography demonstrates the detailed anatomy of the feeding and draining vessels (Fig 9). The exact localization of vascular anatomy is important in order to plan embolic occlusion treatment that spares the renal parenchymal perfusion (13).
Inflammatory Lesions
Although it is rare to encounter a primary inflammatory lesion involving primarily the renal sinus, extension of renal inflammatory lesions into the renal sinus and perinephric space is not uncommon in chronic or severe pyelonephritis. Conglomerated inflammatory cells can cause a pseudotumor within the renal sinus (Fig 10) (4).
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Figure 10a. Renal aspergillosis in an 18-year-old man with acute myeloid leukemia who presented with fever and left flank pain. (a) Axial unenhanced CT scan shows a lobulated masslike lesion (arrows) with focal internal high attenuation, a finding suggestive of intralesion hemorrhage. (b) Coronal reformatted contrast-enhanced CT scan obtained during the excretory phase shows the poorly enhancing, low-attenuation, masslike renal parenchymal lesion extending to the renal sinus (arrow). Analysis of the nephrectomy specimen demonstrated a hemorrhagic mass due to focal invasive aspergillosis. Aspergillosis causes vascular occlusion and multiple renal infarcts. However, as in this case, differentiation from a tumor is not always easy.
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Figure 10b. Renal aspergillosis in an 18-year-old man with acute myeloid leukemia who presented with fever and left flank pain. (a) Axial unenhanced CT scan shows a lobulated masslike lesion (arrows) with focal internal high attenuation, a finding suggestive of intralesion hemorrhage. (b) Coronal reformatted contrast-enhanced CT scan obtained during the excretory phase shows the poorly enhancing, low-attenuation, masslike renal parenchymal lesion extending to the renal sinus (arrow). Analysis of the nephrectomy specimen demonstrated a hemorrhagic mass due to focal invasive aspergillosis. Aspergillosis causes vascular occlusion and multiple renal infarcts. However, as in this case, differentiation from a tumor is not always easy.
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Other Nonneoplastic Lesions
Fluid collections such as urinoma or hematoma may be seen in the renal sinus. Urinomas are usually associated with ureteral obstruction secondary to stone disease, resulting in rupture of the collecting system; they are also occasionally associated with traumatic laceration of the collecting system (1). Hemorrhage may be secondary to trauma but is usually a complication of anticoagulant therapy (15). US findings of urinoma or hematoma are similar to those of renal sinus cysts, but CT can help make the differential diagnosis. Acute hemorrhage has a higher attenuation than normal fluid, and extravasation of contrast material can confirm the presence of a urinoma at CT (1).
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Tumorous Conditions of the Renal Sinus
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Various types of benign and malignant neoplasms can be found involving the renal sinus, either arising primarily from sinus structures or secondarily extending into the sinus from the adjacent cortex or retroperitoneum. Observation of renal sinus fat is important in detecting a small tumor and determining the tumor stage.
Tumors of the Renal Pelvis
Malignant tumors arising from the renal pelvis constitute only 5% of urinary tract neoplasms; approximately 90% of pelvicaliceal cancers are transitional cell carcinomas and the remaining 10% are squamous cell carcinomas. These tumors are centered in the renal pelvis and secondarily invade the renal sinus fat and renal parenchyma (16).
At excretory urography, renal pelvis origin tumors appear as intraluminal filling defects due to tumor or blood and amputated calices resulting from malignant strictures. US shows a poorly defined soft-tissue mass replacing the renal sinus fat (17).
At CT and MR imaging, early-stage transitional cell carcinoma of the kidney—stage I or II—is seen as a central solid mass in the renal pelvis that expands centrifugally with compression of the renal sinus fat and appears separated from the renal parenchyma by either renal sinus fat or excreted contrast material (18). Conversely, invasive transitional cell carcinoma—stage III or IV—obliterates the renal sinus fat and infiltrates into the surrounding parenchyma, typically not disturbing its reniform contour (Fig 11) (19).
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Figure 11a. Transitional cell carcinoma of the renal pelvis in a 65-year-old man with a 1-month history of left flank pain and intermittent gross hematuria. (a) Axial contrast-enhanced CT scan obtained during the nephrographic phase shows an ill-defined low-attenuation mass (arrow) in the central portion of the left kidney. (b) Coronal maximum intensity projection CT scan obtained during the excretory phase shows a large filling defect with an irregular margin (arrows) in the pelvicalices of the left kidney, thus clearly demonstrating the extent of the tumor.
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Figure 11b. Transitional cell carcinoma of the renal pelvis in a 65-year-old man with a 1-month history of left flank pain and intermittent gross hematuria. (a) Axial contrast-enhanced CT scan obtained during the nephrographic phase shows an ill-defined low-attenuation mass (arrow) in the central portion of the left kidney. (b) Coronal maximum intensity projection CT scan obtained during the excretory phase shows a large filling defect with an irregular margin (arrows) in the pelvicalices of the left kidney, thus clearly demonstrating the extent of the tumor.
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Imaging findings of squamous cell carcinomas are indistinguishable from those of transitional cell carcinomas. Squamous cell carcinomas are strongly associated with renal calculi, and chronic irritation of the urothelium appears to be an important etiologic factor in the development of squamous cell carcinoma (20). The presence of a renal stone in association with a geographic infiltrating renal lesion with a large renal sinus component is suggestive of squamous cell carcinoma (Fig 12) (21).
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Figure 12a. Squamous cell carcinoma in a 50-year-old man with chronic calculus disease and left flank pain. (a) Axial unenhanced CT scan shows a high-attenuation stone (arrow) in the left renal pelvis. A tiny amount of air (arrowhead) due to previously performed percutaneous nephrostomy is seen in the renal sinus. (b) Axial contrast-enhanced CT scan obtained during the excretory phase shows an infiltrative mass (arrows) in the renal pelvis that extends to the renal parenchyma. Note the metastatic lymph nodes (arrowhead) in the paraaortic space.
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Figure 12b. Squamous cell carcinoma in a 50-year-old man with chronic calculus disease and left flank pain. (a) Axial unenhanced CT scan shows a high-attenuation stone (arrow) in the left renal pelvis. A tiny amount of air (arrowhead) due to previously performed percutaneous nephrostomy is seen in the renal sinus. (b) Axial contrast-enhanced CT scan obtained during the excretory phase shows an infiltrative mass (arrows) in the renal pelvis that extends to the renal parenchyma. Note the metastatic lymph nodes (arrowhead) in the paraaortic space.
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Primary Tumors of Mesenchymal Origin
Primary mesenchymal origin tumors of the kidney are rare but may develop in the renal sinus space as well as in the renal capsule and renal parenchyma. The previously reported benign tumors include hemangioma (Fig 13), fibroma, leiomyoma (Fig 14), angiomyolipoma, neurogenic tumor, and teratoma (22–30). The malignant renal neoplasms of pure mesenchymal origin include leiomyosarcoma (Fig 15), fibrosarcoma, liposarcoma, hemangiopericytoma (Fig 16), and malignant fibrous histiocytoma (31,32). Leiomyosarcoma is the most common malignant tumor of primary mesenchymal origin neoplasms (32).
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Figure 13a. Venous hemangioma of the renal sinus in a 33-year-old man with gross hematuria and left flank pain. (a) Axial unenhanced CT scan shows a well-defined high-attenuation lesion (arrows) adjacent to the left renal pelvis. (b) Axial contrast-enhanced CT scan shows that the mass (arrows) has low attenuation and poor enhancement. Because of the possibility of malignancy, left nephrectomy was performed. At pathologic examination, the lesion was composed of multiple vascular channels of variable sizes beneath the pelvic mucosa. Renal hemangioma is seldom diagnosed preoperatively but should be included in the differential diagnosis when CT demonstrates poor enhancement of a renal mass located at the pelvicaliceal junction or in the inner medulla. (Reprinted, with permission, from reference 22.)
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Figure 13b. Venous hemangioma of the renal sinus in a 33-year-old man with gross hematuria and left flank pain. (a) Axial unenhanced CT scan shows a well-defined high-attenuation lesion (arrows) adjacent to the left renal pelvis. (b) Axial contrast-enhanced CT scan shows that the mass (arrows) has low attenuation and poor enhancement. Because of the possibility of malignancy, left nephrectomy was performed. At pathologic examination, the lesion was composed of multiple vascular channels of variable sizes beneath the pelvic mucosa. Renal hemangioma is seldom diagnosed preoperatively but should be included in the differential diagnosis when CT demonstrates poor enhancement of a renal mass located at the pelvicaliceal junction or in the inner medulla. (Reprinted, with permission, from reference 22.)
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Figure 14a. Leiomyoma of the renal sinus in a 28-year-old woman with gross hematuria. (a) Excretory urogram shows focal smooth mass effect on the pelvicalices of the right kidney (arrows). (b) Axial contrast-enhanced CT scan obtained during the nephrographic phase shows a small mass (arrow) with soft-tissue attenuation obliterating the fat in the right renal sinus along the posterior margin of the renal pelvis. (c) Coronal reformatted CT scan shows the round soft-tissue attenuation mass (arrow) in the right renal sinus and mild dilatation of the pelvicaliceal system. (d) Photograph of the surgical specimen shows the well-defined round mass (arrows) in the renal sinus. Microscopic examination demonstrated a renal leiomyoma.
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Figure 14b. Leiomyoma of the renal sinus in a 28-year-old woman with gross hematuria. (a) Excretory urogram shows focal smooth mass effect on the pelvicalices of the right kidney (arrows). (b) Axial contrast-enhanced CT scan obtained during the nephrographic phase shows a small mass (arrow) with soft-tissue attenuation obliterating the fat in the right renal sinus along the posterior margin of the renal pelvis. (c) Coronal reformatted CT scan shows the round soft-tissue attenuation mass (arrow) in the right renal sinus and mild dilatation of the pelvicaliceal system. (d) Photograph of the surgical specimen shows the well-defined round mass (arrows) in the renal sinus. Microscopic examination demonstrated a renal leiomyoma.
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Figure 14c. Leiomyoma of the renal sinus in a 28-year-old woman with gross hematuria. (a) Excretory urogram shows focal smooth mass effect on the pelvicalices of the right kidney (arrows). (b) Axial contrast-enhanced CT scan obtained during the nephrographic phase shows a small mass (arrow) with soft-tissue attenuation obliterating the fat in the right renal sinus along the posterior margin of the renal pelvis. (c) Coronal reformatted CT scan shows the round soft-tissue attenuation mass (arrow) in the right renal sinus and mild dilatation of the pelvicaliceal system. (d) Photograph of the surgical specimen shows the well-defined round mass (arrows) in the renal sinus. Microscopic examination demonstrated a renal leiomyoma.
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Figure 14d. Leiomyoma of the renal sinus in a 28-year-old woman with gross hematuria. (a) Excretory urogram shows focal smooth mass effect on the pelvicalices of the right kidney (arrows). (b) Axial contrast-enhanced CT scan obtained during the nephrographic phase shows a small mass (arrow) with soft-tissue attenuation obliterating the fat in the right renal sinus along the posterior margin of the renal pelvis. (c) Coronal reformatted CT scan shows the round soft-tissue attenuation mass (arrow) in the right renal sinus and mild dilatation of the pelvicaliceal system. (d) Photograph of the surgical specimen shows the well-defined round mass (arrows) in the renal sinus. Microscopic examination demonstrated a renal leiomyoma.
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Figure 15a. Leiomyosarcoma of the renal sinus in a 65-year-old woman with left flank pain and a palpable left abdominal mass. (a) Axial contrast-enhanced CT scan shows a large mass (arrows) with heterogeneous attenuation expanding the left renal sinus. The renal parenchyma (P) is markedly compressed and displaced laterally. (b) Coronal turbo spin-echo T2-weighted MR image (6,500/120) shows the location and extent of the tumor (arrows). P = renal parenchyma. (c) Photograph of the surgical specimen shows the relatively well-defined tumor (arrows) (13 x 9 x 8 cm) in the renal sinus. The tumor has a solid and compact cut surface with central hemorrhage and necrosis. It is confined to the sinus and does not invade the renal parenchyma (P) or pelvis. The adjacent renal parenchyma is compressed by the tumor.
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Figure 15b. Leiomyosarcoma of the renal sinus in a 65-year-old woman with left flank pain and a palpable left abdominal mass. (a) Axial contrast-enhanced CT scan shows a large mass (arrows) with heterogeneous attenuation expanding the left renal sinus. The renal parenchyma (P) is markedly compressed and displaced laterally. (b) Coronal turbo spin-echo T2-weighted MR image (6,500/120) shows the location and extent of the tumor (arrows). P = renal parenchyma. (c) Photograph of the surgical specimen shows the relatively well-defined tumor (arrows) (13 x 9 x 8 cm) in the renal sinus. The tumor has a solid and compact cut surface with central hemorrhage and necrosis. It is confined to the sinus and does not invade the renal parenchyma (P) or pelvis. The adjacent renal parenchyma is compressed by the tumor.
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Figure 15c. Leiomyosarcoma of the renal sinus in a 65-year-old woman with left flank pain and a palpable left abdominal mass. (a) Axial contrast-enhanced CT scan shows a large mass (arrows) with heterogeneous attenuation expanding the left renal sinus. The renal parenchyma (P) is markedly compressed and displaced laterally. (b) Coronal turbo spin-echo T2-weighted MR image (6,500/120) shows the location and extent of the tumor (arrows). P = renal parenchyma. (c) Photograph of the surgical specimen shows the relatively well-defined tumor (arrows) (13 x 9 x 8 cm) in the renal sinus. The tumor has a solid and compact cut surface with central hemorrhage and necrosis. It is confined to the sinus and does not invade the renal parenchyma (P) or pelvis. The adjacent renal parenchyma is compressed by the tumor.
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Figure 16. Hemangiopericytoma of the renal sinus in a 30-year-old woman with generalized weakness. Axial contrast-enhanced CT scan shows a large, well-defined mass (M) with soft-tissue attenuation occupying the central portion of the left renal sinus and compressing the enhanced pelvicaliceal system. (Reprinted, with permission, from reference 31.)
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Imaging findings of these rare tumors are usually nonspecific. However, the common imaging findings of primary mesenchymal origin tumors of the renal sinus are as follows: The mass is relatively well-circumscribed, the epicenter of the mass is located at the renal sinus, the mass is surrounded by attenuated renal parenchyma, and the renal pelvis is stretched over the tumor with or without hydronephrosis. A preoperative differential diagnosis is difficult to make, and these kinds of tumors are usually misdiagnosed preoperatively as the more common renal cell carcinomas or transitional cell carcinomas and consequently treated with nephroureterectomy or radical nephrectomy, even in the benign cases (25).
Tumors of the Renal Parenchyma That Project into the Renal Sinus
Most renal parenchymal origin tumors grow by expansion, manifesting as ball-like masses (1). The medially growing renal parenchymal mass may project into the renal sinus and compress or infiltrate the renal sinus fat. The representative tumors are renal cell carcinoma and benign multilocular cystic nephroma.
Renal Cell Carcinoma.—
Renal cell carcinomas are the most common malignant renal parenchymal neoplasms. Most renal cell carcinomas grow by expansion and commonly extend into the renal sinus, leading to focal hydronephrosis or caliceal displacement (Fig 17) (32). The clinical significance of a renal cell carcinoma extending into the renal sinus is that the imaging appearance may be similar to that of transitional cell carcinoma, and the tumor stage influences the surgical management. Unlike transitional cell carcinoma, renal cell carcinoma has a tendency to extend into the venous system. Although indications for partial nephrectomy are constantly changing, the most suitable indication for partial nephrectomy is a renal tumor smaller than 3 cm without invasion of the renal sinus fat, perinephric fat, or renal collecting system, particularly in patients with diminished renal function, a solitary kidney, or bilateral renal malignancy (33,34). Invasion of renal sinus fat is one of the imaging findings indicating that partial nephrectomy cannot successfully and completely remove the renal mass. Three-dimensional CT or MR imaging helps delineate the precise location of the renal mass and its relationship to the collecting system and renal vessels.
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Figure 17. Extension of renal cell carcinoma into the renal sinus in a 51-year-old man with gross hematuria. Coronal reformatted contrast-enhanced CT scan obtained during the excretory phase shows tumor involvement of the renal sinus and the extent of the renal cell carcinoma (arrows). The pathologic stage was T3b N0.
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Multilocular Cystic Nephroma.—
Multilocular cystic nephromas are benign, multiseptated cystic tumors originating from the renal parenchyma. These tumors demonstrate a biphasic age distribution, occurring predominantly in boys and middle-aged women. This lesion frequently herniates into the renal sinus, thus causing a filling defect in the renal pelvis and sometimes obstructive caliectasia (35). At imaging, multilocular cystic nephroma manifests as a well-defined encapsulated cystic mass containing numerous thick septa (Fig 18) (33).
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Figure 18a. Multilocular cystic nephroma in a 32-year-old man. (a) Excretory urogram shows marked splaying of the upper and lower caliceal systems (arrows) with mild dilatation of the upper pole calix. (b) Axial MR image obtained with true fast imaging with steady-state precession (6.3/3.0, 70° flip angle) shows a high-signal-intensity cystic mass in the left kidney. Note the numerous fine septations without solid components. (c) Coronal gadolinium-enhanced T1-weighted MR image (130/4.1) shows herniation of the cystic mass (arrow) into the renal sinus.
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Figure 18b. Multilocular cystic nephroma in a 32-year-old man. (a) Excretory urogram shows marked splaying of the upper and lower caliceal systems (arrows) with mild dilatation of the upper pole calix. (b) Axial MR image obtained with true fast imaging with steady-state precession (6.3/3.0, 70° flip angle) shows a high-signal-intensity cystic mass in the left kidney. Note the numerous fine septations without solid components. (c) Coronal gadolinium-enhanced T1-weighted MR image (130/4.1) shows herniation of the cystic mass (arrow) into the renal sinus.
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Figure 18c. Multilocular cystic nephroma in a 32-year-old man. (a) Excretory urogram shows marked splaying of the upper and lower caliceal systems (arrows) with mild dilatation of the upper pole calix. (b) Axial MR image obtained with true fast imaging with steady-state precession (6.3/3.0, 70° flip angle) shows a high-signal-intensity cystic mass in the left kidney. Note the numerous fine septations without solid components. (c) Coronal gadolinium-enhanced T1-weighted MR image (130/4.1) shows herniation of the cystic mass (arrow) into the renal sinus.
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Retroperitoneal Tumors That Extend to the Renal Sinus —
Because the renal sinus is a medial extension of the perinephric space, any retroperitoneal tumor can extend to the renal sinus. The representative example is a lymphoma. Retroperitoneal lymphoma with contiguous extension into the renal sinus is one of the common manifestations of lymphoma (36). These patients present with a large, bulky retroperitoneal mass that envelops and surrounds the normal constituents of the renal sinus, often with contiguous spread into the perinephric space (Fig 19). This situation is most common in patients with advanced non-Hodgkin lymphoma. The renal vessels remain patent despite tumor encasement, a finding that is characteristic for lymphoma. On the contrary, obstructive hydronephrosis is often caused by direct involvement of the renal collecting system (36,37).
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Figure 19. Lymphoma involving the renal parenchyma and renal sinus in a 56-year-old man with generalized weakness. Coronal reformatted CT scan obtained during the nephrographic phase shows a large, relatively homogeneous retroperitoneal mass (arrows) extending to the renal sinus and mild hydronephrosis of the right kidney.
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At CT and US, lymphomatous masses are characteristically homogeneous. At CT, the mass enhances less. Renal lymphoma is usually hypoechoic at US, a finding that reflects tissue homogeneity. At MR imaging, renal lymphoma tends to be hypointense relative to the renal cortex on T1-weighted images and heterogeneously hypointense or isointense on T2-weighted images. Minimal enhancement is generally detected, although renal lymphoma enhances considerably less than normal renal parenchyma.
Metastasis to the sinus lymph nodes occurs either as part of a generalized retroperitoneal process or as isolated involvement, as with primary gonadal tumors, because of the rich supply of perforating capsular vessels and lymphatic channels passing into the renal sinus (Fig 20) (2).
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Figure 20. Metastatic lymphadenopathy in the renal sinus from colon cancer in a 57-year-old man. Axial contrast-enhanced CT scan shows a soft-tissue attenuation mass (arrows) in the right renal sinus with obstructive hydronephrosis.
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Conclusions
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A broad spe
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Abstract
LEARNING OBJECTIVES FOR TEST...
