AJR 2004; 183:1697-1702
© American Roentgen Ray Society
Differential Diagnosis of Perinephric Masses on CT and MRI
Antonio Westphalen1,
Benjamin Yeh,
Aliya Qayyum,
Anil Hari and
Fergus V. Coakley
1 All authors: Department of Radiology, University of California–San
Francisco, 505 Parnassus Ave., Rm. M-372, Box 0628, San Francisco, CA
94143-0628.
Received October 10, 2003;
accepted after revision June 3, 2004.
Address correspondence to F. V. Coakley.
Introduction
Masses in the perinephric space, including the peripelvic space of the
renal hilum, may be due to tumor, fluid, inflammation, or various
proliferative diseases. More broadly, abnormal tissue at the periphery of the
kidney may be subcapsular or perinephric in origin, and these processes are
not always distinguishable, so the differential diagnosis for perinephric
masses includes subcapsular disease. Radiologic evaluation of renal and
perinephric masses is increasingly important; for example, more than half of
renal cell carcinomas are discovered incidentally during imaging performed for
unrelated reasons [1]. The
objective of this pictorial essay is to provide a timely review of those
diseases that may result in perinephric or subcapsular masses, with an
emphasis on key clinical or radiologic differentiating features.
Tumors
Renal Cell Carcinoma
Although renal cell carcinoma is common, a perinephric pattern of spread is
seen only occasionally, typically in bulky tumors
(Fig. 1).
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Fig. 1. —58-year-old man presenting with gross hematuria and left flank pain.
Contrast-enhanced axial portal phase CT image shows large heterogeneous and
necrotic renal cell carcinoma (asterisk) invading perinephric space.
Significant thickening of renal fascia also is seen.
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Lymphoma
Primary renal lymphoma is rare, and renal lymphoma usually is seen in
widespread disease. Renal involvement is found in 15–50% of patients
with lymphoma at autopsy but in only 3–8% of patients at CT staging
[2,
3]. Perinephric lymphoma is one
of the described patterns of renal involvement and typically is homogeneous,
hypovascular, mildly enhancing, and associated with non-obstructive encasement
of retroperitoneal vessels [3]
(Fig. 2).
Posttransplantation Lymphoproliferative Disorder
Posttransplantation lymphoproliferative disorder is a lymphomalike
condition associated with Epstein-Barr virus infection that occurs as a
complication in 2% of the recipients of solid-organ transplants. In kidney
transplant recipients, posttransplantation lymphoproliferative disorder has a
predilection for occurring in the renal hilum and typically is hypointense on
both T1- and T2-weighted images, with minimal contrast enhancement
[4] (Fig.
3A,
3B,
3C).
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Fig. 3A. —43-year-old male renal transplant recipient with
biopsy-confirmed posttransplantation lymphoproliferative disorder in hilum of
transplanted kidney. Axial T1-weighted image shows hypointense mass
(arrow) in hilum of allograft. Note small nonspecific pocket of fluid
(asterisk) adjacent to allograft.
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Fig. 3B. —43-year-old male renal transplant recipient with
biopsy-confirmed posttransplantation lymphoproliferative disorder in hilum of
transplanted kidney. Axial T2-weighted image obtained at same level as
A shows same lesion (arrow) as predominantly hypointense.
Small nonspecific pocket of fluid (asterisk) adjacent to allograft is
also seen on this image.
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Fig. 3C. —43-year-old male renal transplant recipient with
biopsy-confirmed posttransplantation lymphoproliferative disorder in hilum of
transplanted kidney. Gadolinium-enhanced axial gradient-echo T1-weighted image
obtained with fat suppression at same level as A and B shows
minimal enhancement in lesion (arrow) and fluid pocket
(asterisk).
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Metastases
Metastases to the kidney are common findings at autopsy, typically in the
setting of widely disseminated disease, but rarely are recognized on imaging
[3,
5]
(Fig. 4). In a study performed
at Georgetown University Medical Center, perinephric spread was seen in six of
27 patients with radiologically evident metastases to the kidney
[5].
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Fig. 4. —76-year-old man with history of malignant melanoma.
Contrast-enhanced axial CT image of abdomen shows nodular left perinephric
metastasis (arrow). Diagnosis was confirmed by concordant progression
of perinephric lesion and widespread metastases elsewhere.
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Retroperitoneal Tumors
Retroperitoneal tumors—particularly sarcomas
(Fig. 5), multiple myelomas,
Castleman's disease tumors, and bulky primary renal tumors—may involve
the perinephric space by direct contiguous extension
[2].
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Fig. 5. —77-year-old woman with right upper quadrant pain.
Contrast-enhanced axial portal phase CT image shows large heterogeneous mass
(arrows), predominantly composed of fat in right upper quadrant,
invading perinephric space and renal hilum. Surgical resection established
diagnosis of myxoid liposarcoma.
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Fluid
Hematomas
Described causes of spontaneous (nontraumatic) perinephric hematomas
include angiomyolipoma, renal cell carcinoma, polycystic kidney disease, and
bleeding diathesis [2,
6]. The underlying tumor may be
identifiable on imaging, even in cases of acute bleeding
(Fig. 6). Retroperitoneal
leakage from a ruptured abdominal aortic aneurysm also may result in
perinephric hematoma.
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Fig. 6. —67-year-old woman with angiomyolipoma of left kidney
presenting as acute left flank pain. Unenhanced axial CT image shows perirenal
hematoma (arrow) originating from ruptured angiomyolipoma
(asterisk).
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Urinomas
Perinephric urinomas may be due to an obstructive forniceal rupture or
trauma. The history of trauma or the finding of an obstructing stone usually
suggests the correct diagnosis. Delayed CT scans may show extravasation of
excreted contrast material [2,
6] (Fig.
7A,
7B).
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Fig. 7A. —67-year-old man with flank pain after aortic aneurysm repair.
Contrast-enhanced axial arterial phase CT image shows fluid collection in left
perirenal space (arrow) and adjacent to aorta. Appearance of aorta is
due to tortuosity and postoperative changes. Perinephric hematoma
(asterisk) also is evident.
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Fig. 7B. —67-year-old man with flank pain after aortic aneurysm repair.
Contrast-enhanced axial delayed CT image obtained at same level as A
shows excreted contrast material passing from left renal pelvis
(arrow) into perinephric fluid collection (asterisk),
confirming diagnosis of urinoma.
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Abscesses
A perinephric abscess may be the result of urinary tract infection or may
arise from infection of a preexisting perinephric hematoma or urinoma.
Clinical and radiologic clues include a history of diabetes mellitus or
immunosuppression therapy, clinical manifestations of sepsis, thick enhancing
wall, and intralesional gas [2,
6].
Lymphangiomatosis
Renal lymphangiomatosis is a rare benign malformation of the perinephric
lymphatic system resulting in characteristic unilocular or multilocular
thin-walled perinephric cysts. Pregnancy may exacerbate the condition (Fig.
8A,
8B,
8C). The diagnosis can be
confirmed by the aspiration of chyle
[6].
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Fig. 8A. —Pregnant 31-year-old woman with hereditary lymphangiomatosis.
Diagnosis was confirmed by aspiration of chyle from perinephric cystic
lesions. Longitudinal sonogram shows cystic structures around right renal
pelvis (asterisk) and kidney (arrow).
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Fig. 8B. —Pregnant 31-year-old woman with hereditary lymphangiomatosis.
Diagnosis was confirmed by aspiration of chyle from perinephric cystic
lesions. Axial fast spin-echo T2-weighted image shows multiple bilateral
perirenal (arrows) and peripelvic (asterisks) cystic
structures.
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Fig. 8C. —Pregnant 31-year-old woman with hereditary lymphangiomatosis.
Diagnosis was confirmed by aspiration of chyle from perinephric cystic
lesions. Coronal single-shot fast spin-echo T2-weighted image shows same
perirenal (arrows) and peripelvic (asterisks) cysts seen in
B.
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Inflammation
Xanthogranulomatous Pyelonephritis
Xanthogranulomatous pyelonephritis is a rare inflammatory and locally
aggressive tumorlike renal mass that usually arises in the setting of renal
stones or chronic infection by Proteus, Escherichia coli, or
Pseudomonas bacteria. The histopathologic finding of lipid-laden
foamy macrophages is diagnostic for this condition. The typical imaging
appearances are of an ill-defined renal mass with some combination of stones,
hydronephrosis, parenchymal renal abscesses, and perinephric extension
[2]
(Fig. 9).
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Fig. 9. —51-year-old woman with xanthogranulomatous pyelonephritis and
history of staghorn calculus and chronic urinary tract infection. Axial late
arterial phase contrast-enhanced CT image shows enlarged right kidney with
abscesslike low-density cavity (asterisk) in renal hilum. Staghorn
calculus is noted (arrowheads) and was also seen on unenhanced images
(not shown). Perirenal space extension of inflammatory process
(arrow) also is visible.
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Pancreatitis
Fluid dissecting between fascial planes in the perinephric space is seen in
patients with pancreatitis. The left or right kidney may be affected,
depending on whether the inflammatory fluid tracks from the tail or the head
and neck of the pancreas, respectively
[6].
Proliferative Diseases
Extramedullary Hematopoiesis
Extramedullary hematopoiesis may occur in chronic anemia, blood dyscrasias
such as leukemia, and replacement of the normal bone marrow by tumor or bone
overgrowth. Renal extramedullary hematopoiesis may be perinephric
(Fig. 10). It is typically
hypodense on CT and hypointense on T1-weighted and mildly hyperintense on
T2-weighted imaging. The patient's clinical history may indicate the correct
diagnosis.
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Fig. 10. —68-year-old man with extramedullary hematopoiesis due to
myelofibrosis. Contrast-enhanced axial CT image obtained during portal venous
phase shows large hypodense, hypovascular mass encasing right renal hilum,
distorting collecting system (asterisk). Lesion (arrows) is
also seen in perirenal space bilaterally. Note preservation of renal contours.
Appearance is nonspecific. Diagnosis was established by biopsy.
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Retroperitoneal Fibrosis
Retroperitoneal fibrosis usually is idiopathic. The typical appearance is
of a hypodense mass on CT or a hypointense mass on T1- and T2-weighted
imaging. The mass infiltrates the retroperitoneum and encases the major
vessels. Vascular occlusion is uncommon, although obstruction of the inferior
vena cava is a recognized complication. Contrast enhancement is minimal and is
more apparent on delayed images. Perinephric involvement is rarely seen in
isolation, so the diagnosis is usually straightforward
[2]
(Fig. 11).
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Fig. 11. —51-year-old man with retroperitoneal fibrosis.
Contrast-enhanced axial delayed CT image shows hypodense, nonenhancing mass
extending into right renal hilum (white arrow) with associated
hydronephrosis (asterisk) and renal atrophy. Subtle extension of
retroperitoneal process anterior to left kidney (black arrow) also is
present. Appearance is nonspecific, and differential includes malignancy such
as lymphoma. Diagnosis was confirmed by biopsy.
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Rosai-Dorfman Disease
Rosai-Dorfman disease (sinus histiocytosis with massive lymphadenopathy) is
a benign systemic histiocytic proliferative disorder presenting with
lymphadenopathy, fever, leukocytosis, elevated erythrocyte sedimentation rate,
and polyclonal hypergammaglobulinemia. Renal involvement is characterized on
CT by infiltrative hypodensity at the periphery of the kidney as a result of
the accumulation of histiocytes. The imaging findings are often more
suggestive of a subcapsular rather than a perinephric process
[7]
(Fig. 12).
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Fig. 12. —24-year-old woman with 2-year history of Rosai-Dorfman
disease. Contrast-enhanced axial delayed CT image shows that left renal hilum
is encased by large lobulated hypodense and hypovascular mass and that
pelvicaliceal system (asterisk) is compressed. Appearance is
nonspecific. Diagnosis was established by biopsy.
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Erdheim-Chester Disease
Erdheim-Chester disease (lipoid granulomatosis) is a relentlessly
progressive multisystem disorder characterized radiologically by bilateral
symmetric medullary osteosclerosis with cortical thickening of long tubular
bones, sparing the axial skeleton. Retroperitoneal and perinephric
infiltration may occur [8].
Long-bone abnormalities are crucial findings for recognition of this disease
(Fig. 13A,
13B).
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Fig. 13A. —48-year-old man with Erdheim-Chester disease presenting with
flank and extremity pain. Contrast-enhanced axial CT image shows left
perinephric hypovascular mass (arrow) associated with fat stranding.
Note moderate hydronephrosis (asterisk). Appearance is
nonspecific.
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Fig. 13B. —48-year-old man with Erdheim-Chester disease presenting with
flank and extremity pain. Conventional radiograph of right and left femurs
shows typical cortical and medullary sclerosis. Findings are bilateral and
symmetric. Erdheim-Chester disease was raised as possible diagnosis in view of
femoral abnormalities and was confirmed by biopsy of perinephric tissue.
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Subcapsular Disease
Renal Cortical Necrosis
Renal cortical necrosis is characterized by the destruction of the renal
cortex with sparing of the renal medulla and is the cause of approximately 2%
of cases of acute renal failure. Renal cortical necrosis is usually seen as a
complication of obstetric catastrophes. In the acute setting, CT shows
nonenhancement of the renal cortex, with the exception of a thin subcapsular
rim, and normal medullary enhancement
(Fig. 14). In chronic cases,
renal cortical eggshell calcification may occur
[9].
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Fig. 14. —33-year-old woman with acute renal failure from cortical
necrosis after severe antepartum hemorrhage. Contrast-enhanced axial CT image
shows lack of enhancement of renal cortex (arrow) with normal renal
medulla enhancement. Note slight enhancement of renal capsule
(arrowheads).
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Nephroblastomatosis
Nephroblastomatosis is the presence of multiple or diffuse nephrogenic
rests, embryonal tumors that result from abnormal renal histogenesis and are
precursors of Wilms' tumor. Nephroblastomatosis is characterized by the
presence of multiple well-defined round or ovoid foci in the periphery of the
renal cortex (Fig. 15).
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Fig. 15. —9-month-old boy with nephroblastomatosis. Axial
contrast-enhanced CT image shows that kidneys are bilaterally enlarged due to
cortical hypodense, non-enhancing, soft-tissue mass (arrows). Note
distorted renal parenchyma centrally.
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Conclusion
A variety of conditions may result in perinephric and subcapsular disease,
with potentially overlapping radiologic features; however, close attention to
and knowledge of the associated clinical and imaging features can facilitate a
confident and specific diagnosis in many cases.
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