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Archived Issues of Radiology Rounds
MGH Department of Radiology Website
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Evaluation of Renal Masses
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| Note: Updated information available (June 2007) |
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- Incidentally found simple renal cysts need no further imaging
- Most incidentally detected angiomyolipomas can be definitively diagnosed on imaging
- A renal mass protocol CT or MRI examination is indicated for all other suspected solid renal
masses and complex cysts
- Image-guided percutaneous biopsy is recommended for patients with small (≤4 cm) enhancing
renal masses, with suspicion of infection, or metastasis from a extra-renal cancer, or those who
are poor nephrectomy candidates and are being considered for ablative therapy
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The
vast majority of solid renal masses in patients with a history of
hematuria are primary renal cell carcinoma. Because this cancer is
relatively unresponsive to chemotherapy or radiotherapy, resection or
ablation of early stage disease is the only option with possibility of
cure. However, small renal masses are now commonly detected
incidentally during US, CT, or MRI examinations for non-urologic
indications. A significant proportion of these smaller masses are
benign (Table 1).
CT and MR imaging techniques can
differentiate between benign and malignant lesions in some cases, such
as angiomyolipomas containing fat. Until recently, percutaneous biopsy
was not considered accurate enough for diagnosis. Therefore, masses
that were not definitively benign on imaging were routinely resected or
ablated without a confirmed diagnosis of malignancy because of the high
likelihood of renal carcinoma.
Recent advances in radiological and pathologic techniques have
increased the accuracy of image-guided percutaneous biopsy and its use
has been shown to decrease the likelihood of finding a benign lesion
after nephrectomy. Therefore, percutaneous biopsy has a role to play in
the diagnosis and management of small renal masses, and has the
potential to spare many unnecessary and potentially morbid surgical
procedures.
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Figure 1. Angiomyolipoma.
Intravenous contrast enhanced CT shows a 2 cm fat-containing mass
(arrow), characteristic of angiomyolipoma, in the upper pole of the
right kidney.
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Incidentally Detected Lesions
Simple
renal cysts are common in the general population and if these are
detected incidentally by ultrasound, CT, or MRI, no further diagnostic
imaging is necessary. The presence of fat in a renal mass, which can be
detected by ultrasound, CT or MRI, implies that the lesion is an
angiomyolipoma (Figure 1). Further diagnostic imaging is recommended
for all other solid-appearing renal masses and complex cystic masses.
| Table 1. Fraction of Solid Renal Masses that are Benign1 |
| All sizes |
12.8% |
| < 1 cm |
46.3% |
| 1 - < 2 cm |
22.4% |
| 2 - < 3 cm |
22% |
| 3 - < 4 cm |
19.9% |
| 4 - < 5 cm |
9.9% |
| 5 - < 6 cm |
13.0% |
| 1Data from Frank et al., 2003 |
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| Figure 2.
Renal mass protocol CT. CT image prior to intravenous contrast
administration (A) demonstrates a 3.5 cm mass (arrow) in the left
kidney. This measures 39 Hounsfield units corresponding to
soft-tissue density. After administration of intravenous contrast
(B), the mass (arrow) demonstrates enhancement increasing to 68
Hounsfield units. Percutaneous needle biopsy revealed that this
lesion was a benign oncocytoma and the patient was spared surgery. |
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CT
A
renal protocol multidetector CT scan (Figure 2) is recommended for
further diagnostic imaging, unless the patient cannot tolerate
iodinated contrast agents. The renal protocol scan acquires three sets
of images: a non-contrast image followed by those acquired 40 and 100
seconds after the injection of contrast agent during the
corticomedullary (arterial) and nephrographic phases of enhancement,
respectively. Three-dimensional reconstruction of the corticomedullary
enhancement phase shows the vasculature, which can be useful for
surgical planning. However, small renal masses and renal cancers with
certain histologies (e.g. papillary cancer) can be difficult to detect
in this early phase. Detection of these masses is optimal during the
nephrographic phase.
Tumors that enhance may be
malignant but can also represent benign lesions such as adenoma,
oncocytoma, and leiomyoma. These need further evaluation, either with
long-term follow-up imaging or biopsy.
MRI
If
the patient cannot tolerate iodinated intravenous contrast, MRI is an
alternative modality for renal mass characterization. Non-contrast
images are acquired first, followed by gadolinium contrast-enhanced MR
angiography, MR venography, and MR urography at a series of time
intervals after the injection of contrast agent. Any mass that shows
enhancement is suspect for malignancy.
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Figure 3. CT-
guided percutaneous biopsy. A left lateral approach has been used to
insert a percutaneous core biopsy needle through a 3 cm left renal mass
(arrow). Pathologic diagnosis revealed papillary renal cell
carcinoma. Because of medical contraindications to nephrectomy,
the mass was treated with radiofrequency ablation.
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Image-Guided Percutaneous Biopsy
Percutaneous biopsy with CT (Figure 3) or ultrasound guidance is
indicated for patients with a small solid renal mass and known
extrarenal primary malignancy, patients who are not surgical candidates
because of medical co-morbidity or non-resectability, or patients with
a mass that may be caused by infection. New evidence suggests that
biopsy is also indicated for small (≤4 cm) enhancing renal masses.
Percutaneous CT-guided biopsy has been shown to be safe (Table 2) and
accurate. Needle-track seeding is extremely rare, occurring in
<0.01% of cases. Sensitivity for the diagnosis of malignancy is
reported to be 80-92% and specificity, 83-90%. At MGH, both core and
fine needle biopsies are performed, which is incrementally better than
either method alone. Diagnostic specimens are obtained in >95% of
cases. Histologic and immunocytochemical studies of biopsy
samples can definitively diagnose lipid-poor angiomyolipoma, which
cannot be diagnosed on imaging alone, and metanephric tumors.
Oncocytomas can be distinguished from oncocytic renal cell carcinomas
with a strong degree of confidence using appropriate staining and
ultrastructural studies. Consequently, at MGH, biopsy preceding
surgery has resulted in a decreased nephrectomy rate for benign lesions
from 20% to 4% of all ≤4 cm renal masses resected.
Patient Preparation and Care for CT-Guided
Percutaneous Biopsy
Patients must have normal coagulation studies and be taken off
anti-coagulant medication. Patients may drink clear fluids but must not
eat after midnight on the day of the procedure. Biopsy procedures are
generally performed under conscious sedation with local anesthesia.
After completion of the procedure, patients are observed for 3 hours
and can expect to go home that day. Hematuria may occur and last up to
10 days after the procedure.
| Table 2. Complication Rate of Percutaneous CT-Guided Biopsy at MGH (407 cases) |
| Complication |
% (n) |
| Minor* |
3% (13) |
| Overnight Admission |
2% (9) |
| Significant Bleeding† |
1% (3) |
| Death, blood transfusion, surgical intervention, intensive care admission |
0 |
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*e.g. small perinephric hematoma
† large perinephric hematoma (subjective)
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Follow-Up Imaging
Follow-up
imaging is usually performed for the majority of tumors found to be
benign on biopsy, especially onconcytomas. The timing of follow-up
examinations is individualized for each patient, depending on their
histopathology results.
Scheduling
Renal protocol CT can be performed at Mass General West Imaging in
Waltham, Mass General Imaging Chelsea, or the main MGH campus. MRI can
be performed at all these facilities as well as Mass General Imaging in
Charlestown. All these studies can be ordered online via the Radiology
Order Entry (http://mghroe
) or
by calling 4-XRAY (617-724-9729). Before a percutaneous image-guided
biopsy is performed, the patient should be evaluated by a urologist.
Biopsies are performed only on the main campus and can be scheduled by
calling 617-726-8396. A procedure request form is available on the MGH Radiology website, http://www.massgeneralimaging.org.
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Further Information
For
further questions on radiology examinations and procedures for renal
masses, please contact, Anthony Samir, M.D.
, Abdominal Imaging and
Intervention (617-726-8396).
We would like to thank Dr.
Samir and Francis J. McGovern, M.D., Department of Urology, for their
advice and assistance in the preparation of this article.
This article provided useful information about the appropriate use of imaging studies:
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References
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Cohen, HT and McGovern, FJ. (2005) Renal-cell carcinoma. N Engl J Med 353: 2477-90
Israel, GM and Bosniak, MA. (2005) How I do it: evaluating renal masses. Radiology 236: 441-50
Samir, AE, Eisner, BH, Hunter, SE, Eswara, JR, Hahn, PF, Maher, MM,
Gervais, DA, McGovern, FJ and Mueller, PR (2006). Preoperative image guided biopsy of small renal masses decreases nephrectomies performed for benign disease. SSA06-04 Radiological Society of North America Annual Meeting. Chicago, ILL.
Silverman, SG, Gan, YU, Mortele, KJ, Tuncali, K and Cibas, ES. (2006) Renal masses in the adult patient: the role of percutaneous biopsy. Radiology 240: 6-22
Tuncali, K, vanSonnenberg, E, Shankar, S, Mortele, KJ, Cibas, ES and Silverman, SG. (2004) Evaluation of patients referred for percutaneous ablation of renal tumors: importance of a preprocedural diagnosis. AJR Am J Roentgenol 183: 575-82
Zagoria, RJ and Dyer, RB. (1998) The small renal mass: detection, characterization, and management. Abdom Imaging 23: 256-65
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