Magnetic Resonance Imaging of the Renal Mass

0022-534 7/86/1363-0566$02.00/0

Vol. 136, September Printed in U.S.A.

THE JOURNAL OF UROLOGY

Copyright © 1986 by The Williams & Wilkins Co.

MAGNETIC RESONANCE IMAGING OF THE RENAL MASS NOLAN KARSTAEDT,* DAVID L. McCULLOUGH, NEIL T. WOLFMAN

AND

RAYMOND B. DYER

From the Departments of Radiology and Urology, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina

ABSTRACT

To compare the effectiveness of magnetic resonance imaging with that of excretory urography, retrograde pyelography, ultrasound, computerized tomography, angiography and venography 34 patients with renal masses, including 25 renal cell carcinomas, were examined on a 0.15 Tesla Picker 1100 magnetic resonance imager with multiple pulse sequences. Pathological proof was available for all cases except renal cysts, for which ultrasound or computerized tomographic findings were accepted. Differentiation of solid from cystic lesions was seen with magnetic resonance imaging, ultrasound and computerized tomography but not excretory urography. Tumor invasion of the renal vein and inferior vena cava was visualized in 7 patients by magnetic resonance imaging, ultrasound, computerized tomography and venography but not by excretory urography. Magnetic resonance Tl contrast scans best characterized renal masses, with good resolution of metastatic lymphadenopathy and renal cysts. Scans showing T2 contrast were best for identification of pseudocapsules in renal carcinoma, venous invasion by tumors and papillary adenocarcinoma. Advantages of magnetic resonance imaging include differentiation of solid masses from benign cystic lesions, and identification of major blood vessels and vascular invasion without administration of contrast medium. Disadvantages of magnetic resonance imaging are long imaging times and motion artifacts. Advances by the manufacturer in solving these problems will strengthen the role of magnetic resonance imaging in renal evaluation. Magnetic resonance imaging is a unique imaging method that can be performed in any of the 3 orthogonal anatomical planes with contrast resolution exceeding that of computerized tomography (CT). In addition, magnetic resonance imaging can detect flow, allowing the major blood vessels to be delineated. There have been several reports on magnetic resonance imaging of the kidneys 1- 9 but only 1 experience with more than 10 renal cell carcinomas. 1 We report a comparative study of the use of magnetic resonance imaging and other imaging modalities to evaluate renal masses, including 25 renal cell carcinomas in a series of 34 patients. SUBJECTS AND METHODS

We examined 23 men and 11 women with renal masses using a Picker 1100, 0.15 Tesla resistive-magnet imager. Multiple pulse sequences were obtained unless claustrophobia or other discomfort limited patient tolerance. Inversion recovery scans with an inversion time of 400 msec. and a repetition time of 1,500 to 3,000 msec. were used to visualize Tl contrast in the image (31 patients). Spin-echo scans with an echo time of 60 msec. and a repetition time of 1,750 to 3,000 msec. were used to visualize T2 contrast (23 patients). Spin-echo scans with an echo time of 30 to 40 m:sec. and a repetition time of 500 to 1,000 msec. were used to visualize the blood vessels (26 patients). The coronal imaging plane was used primarily, with transverse or sagittal planes obtained when necessary to clarify an abnormality. Informed consent was obtained from all patients and they were allowed to terminate the procedure at any time. The results of the magnetic resonance imaging studies were correlated with results of excretory urography (IVP), retrograde pyelography, ultrasound, CT, angiography and venography, which were obtained as indicated clinically. Accepted for publication April 22, 1986. * Requests for reprints: Department of Radiology, Bowman Gray School of Medicine, 300 S. Hawthorne Rd., Winston-Salem, North Carolina 27103.

All diagnoses were proved pathologically except for renal cysts, for which ultrasound or CT findings were accepted as diagnostic. RESULTS

The diagnoses and correlative imaging tests are summarized in table 1, and a specific breakdown for renal cell carcinoma is shown in table 2. Abnormalities were detected by magnetic resonance imaging in all patients examined. However, in both cases of renal lymphoma and in 1 case of metastatic disease to the kidney magnetic resonance imaging detected only nonspecific enlargement of the affected kidneys (fig. 1). All renal cysts were identified as round, smooth lesions of uniform signal intensity (fig. 2). Compared to normal kidney tissue they appeared dark on scans showing Tl contrast (long Tl) and showed varying signal intensity on T2 contrast scans (long T2). All renal cell carcinomas appeared as lesions that deformed the renal contour and demonstrated varying signal intensity with respect to the normal kidney on Tl contrast scans (fig. 3). The tumors were uniformly high in signal intensity on T2 contrast scans (long T2), making them difficult to separate from the normal kidney and perirenal fat. Pseudocapsules were identified in 3 tumors on Tl and in 7 on T2 contrast scans. In 7 patients invasion of the tumor into the renal vein and inferior vena cava was seen clearly (fig. 4). In each case the extent of the tumor thrombus was delineated and in 1 case a blood clot in the inferior vena cava below the tumor thrombus was identified as a subtle change in signal intensity. Collateral venous pathways were identified in all patients with inferior vena cava thrombus. A false positive diagnosis of tumor extension into the inferior vena cava was made in 1 case. Metastatic lymphadenopathy was identified in 2 patients on Tl but it was difficult to identify on T2 contrast scans (fig. 5). The only case of papillary adenocarcinoma differed from the other renal cell carcinomas in showing no contrast from normal kidney on a Tl contrast scan and a shorter T2 than normal kidney on a T2 contrast scan (fig. 6).

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NJ:AGNETIC RESONANCE IMAGING OF RENAL M'ASS TABLE

Diagnosis Renal cell Ca Transitional cell Ca Oncocytoma Renal lymphoma or metastases Cysts

L Diagnoses and imaging tests performed

IVP/ Retrograde Pyelography

Angiography

Venography

Ultrasound

CT

Magnetic Resonance Imaging

13 0 0 0

9

8

0 0 0

0 0

5

9 2 0 3

1

25 2 1 5

25 2 1 5

5

4

2

0

4

5

5

No. Diagnoses 25 2

1

Bilateral lesions are counted as 2 diagnoses.

TABLE 2.

Correct diagnosis in renal cell carcinoma patients Correct Diagnosis

Study

IVP Angiography Venography Ultrasound CT Magnetic resonance imaging Pathological/surgical confrontation

No. Cases Studied 9

13 9 8

25 25 25

Renal Mass

Renal Vein/ Inferior Vena Cava Invasion

8 12 Not evaluated 8 25 25 25

Not evaluated Not evaluated 7 3 7 7 7

FIG. 1. Tl contrast scan of left kidney shows enlargement of lower pole without significant signal difference between lymphomatous mass (arrowheads) and normal kidney.

Two transitional cell tumors were studied. The solid mass in the collecting system was identified in each case. All masses were identified by an IVP in cases when it was performed. However, differentiation of solid from cystic tumors was not possible. Neither lymphadenopathy nor venous invasion was identified by an IVP.

Retroperitoneal Nodes Not Not Not Not

evaluated evaluated evaluated evaluated 3 2 3

FIG. 2. Simple renal cyst of right kidney. Tl contrast scan demonstrates round, dark (indicating long Tl) mass with no wall evident (arrow).

Although ultrasound examinations were performed in few cases differentiation of solid from cystic masses was made in each. Vascular invasion, if present, was diagnosed correctly by ultrasound in the patients studied. A false positive diagnosis of renal vein invasion was made.

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FIG. 3. Tl contrast scans of 3 patients with renal cell carcinoma. A, tumor (arrow) in upper pole of left kidney is brighter in signal intensity (shorter Tl) than normal renal tissue. B, tumor (arrow) in upper pole of right kidney is similar in signal intensity to normal renal parenchyma. C, tumor (arrow) in lower pole of left kidney is lower in signal intensity (longer Tl) than renal tissue. Unlike renal cyst, thick wall surrounding lesion is evident.

Differentiation of all solid from cystic masses was made with CT, which also allowed for identification of all enlarged nodes. Correct diagnoses in the 7 patients with venous invasion were made by CT. A false positive diagnosis of renal vein invasion was made in 1 case in which nodes had compressed the vena cava. With angiography, all renal cell carcinomas were diagnosed correctly except for an avascular papillary cell carcinoma that did not deform the contour of the kidney. All cases of renal vein and inferior vena cava extension were identified correctly with venography, which was the only test to demonstrate 1 case of extension into the contralateral renal vein. In 1 patient with a blood clot extending below the tumor thrombus the venogram did not distinguish between the 2 types of thrombus. DISCUSSION

Evaluation of the renal mass must accomplish 2 objectives: 1) differentiation of benign from malignant lesions and 2) accurate staging of malignancy to allow precise surgical planning. This review of our early experience suggests that magnetic resonance imaging may have a significant role in these tasks. We and others have found that magnetic resonance imaging can differentiate successfully solid masses from benign cystic lesions. 3 •5 • 6 •8 • 9 Some investigators note that signal changes on different pulse sequences permit hemorrhagic cysts to be differentiated from simple cysts. 3 •5 • 6 We have not observed this finding in our study. A note of caution may be in order regarding the diagnosis of cystic lesions. The magnetic resonance imaging signal changes according to the chemical contents of the cyst. Therefore, it is possible that the signal intensity of the cyst may vary from the expected, making diagnosis less certain. All solid lesions in the study were identified correctly with magnetic resonance imaging. The papillary adenocarcinoma is of particular interest in this context, since it showed magnetic resonance imaging signal characteristics significantly different from those of the other renal cell carcinomas. Without further study it is a matter of speculation whether this is a characteristic of all papillary adenocarcinomas. The transitional cell tumors were identified with difficulty because of their small size and the limited spatial resolution of the technique. Only 3 patients with renal cell carcinoma and 1 with lymphoma had lymphadenopathy in this series. Lymph nodes may be difficult to identify but with pulse sequences showing Tl contrast they could be separated from vessels and fat.

The ability of magnetic resonance imaging to identify the major blood vessels and vascular invasion by tumor without the administration of contrast medium or direct vascular access is a major advantage over CT, which requires intravenous contrast medium administration with precise injection techniques and fast CT scanners to achieve similar results. CT displays only transaxial images and some surgeons prefer the coronal or sagittal display of the magnetic resonance imaging scans, which demonstrate more clearly the relationship of the tumor thrombus to hepatic veins. Venography displayed the venous thrombosis most precisely but it required significant intervention, at times necessitating superior vena cava and right atrial catheterization to demonstrate the craniad extent of large tumor thrombi that could not be visualized from below. Angiography was the only technique that demonstrated with certainty the number and position of renal arteries. If preoperative arterial embolization is to be performed then obviously angiography is a requirement. However, we concluded that angiography did not supply new diagnostic information in any of our cases. Although magnetic resonance imaging demonstrates a remarkable ability to image the renal mass it is not without disadvantages. It does not detect calcification. The shape of the machine tends to produce claustrophobia, although we had few instances in this series. Imaging times are long and motion artifact is a major problem, especially in ill or anxious patients. Finally, the range of pulse sequences and imaging planes available increases the number of decisions involved in the imaging of each case. Multiple pulse sequences are necessary for accurate diagnosis and surveys of large anatomical areas are timeconsuming. In the relatively short period during which we have used magnetic resonance imaging the manufacturer has made significant advances toward solving these problems and we believe that magnetic resonance imaging will have a substantial role in the future evaluation of renal masses. REFERENCES 1. Hricak, H., Demas, B. E., Williams, R. D., McNamara, M. T.,

Hedgcock, M. W., Amparo, E. G. and Tanagho, E. A.: Magnetic resonance imaging in the diagnosis and staging of renal and perirenal neoplasms. Radiology, 154: 709, 1985. 2. Leung, A. W.-L., Bydder, G. M., Steiner, R. E., Bryant, D. J. and Young, I. R.: Magnetic resonance imaging of the kidneys. Amer. J. Roentgen., 143: 1215, 1984.

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FIG. 4. Patient with tumor thrombus in inferior vena cava. A, T2 contrast magnetic resonance imaging scan shows relationship of craniad extent of tumor thrombus (arrowhead) to hepatic veins ( V). B, magnetic resonance imaging scan shows relationship of caudad extent of tumor thrombus (arrowhead) to normal left renal vein (V). Vascular channels within thrombus are identified (arrows), as is entry of retroaortic component of left renal vein (open arrow) into inferior vena cava. C, venogram does not show superior extent of tumor, which can be identified only by superior vena cava catheterization and right atrial injection. D, scan from arterial phase of dynamic CT series. Vascular tumor (arrows) and vascular tumor thrombosis (T) are seen in enlarged inferior vena cava.

FIG. 5. Patient with metastatic adenopathy. Transverse scan through mid kidney (Tl contrast) shows node (arrow) immediately posterior to left renal vein. Tumor (arrowhead) in left kidney is just visible. Benign cyst is seen in right kidney.

3. Choyke, P. L., Kresse!, H. Y., Pollack, H. M., Arger, P. M., Axel, L. and Mamourian, A. C.: Focal renal masses: magnetic resonance imaging. Radiology, 152: 471, 1984. 4. te Strake, L., van der Hem, G. K., Hooijkaas, J. A. P., Poppema, S. and Brouwer-van Herwijnen, A. A.: Nuclear magnetic reso-

FIG. 6. Patient with papillary adenocarcinoma of right kidney. A, T2 contrast magnetic resonance imaging scan shows tumor (arrow) as darker (shorter T2) than kidney. Note that on T2 contrast scans kidney is not well differentiated from perinephric fat. B, arteriogram was considered normal. In retrospect, subtle area of avascularity is identified (arrowheads).

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nance imaging of the kidney. Diagn. Imaging Clin. Med,, 53: 198, 1984. 5. Hricak, H., Williams, R. D., Moon, K. L., Jr., Moss, A. A., Alpers, C., Crooks, L. E. and Kaufman, L.: Nuclear magnetic resonance imaging of the kidney: renal masses. Radiology, 147: 765, 1983. 6. LiPuma, J. P.: Magnetic resonance imaging of the kidney. Rad. Clin. N. Amer., 22: 925, 1984. 7. Fiegler, W., Felix, R., Nagel, R., Schomer, W. and Claussen, C.: Die Kernspintomographie bei raumfordernden Nierenprozessen.

ROFO, 141: 155, 1984. 8. Kulkarni, M. V., Shaff, M. I., Sandler, M. P., Tishler, J., Winfield, A. C., Patton, J. A., Wolfe, 0., Partain, C. L. and James, A. E., Jr.: Evaluation of renal masses by MR imaging. J. Comput. Assist. Tomogr., 8: 861, 1984. 9. Smith, F. W., Hutchison, J.M. S., Mallard, J. R., Reid, A., Johnson, G., Redpath, T. W. and Selbie, R. D.: Renal cyst or tumour? Differentiation by whole-body nuclear magnetic resonance imaging. Diagn. Imaging, 50: 61, 1981.