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Evaluation of Cystic Renal Masses: Comparison of CT and MR Imaging by Using the Bosniak Classification System¹

¹ From the Department of Radiology, NYU Medical Center, 560 First Ave, Suite HW 202, New York, NY 10016. Received June 30, 2003; revision requested September 10; revision received September 20; accepted October 21. Address correspondence to G.M.I. (e-mail: gary.israel@med.nyu.edu).

View larger version (154K): [in a new window]   Figure 1a. Transverse images in a 56-year-old woman (patient 11) with a Bosniak category IV cystic lesion in the left kidney. (a) Contrast-enhanced CT scan shows a complex cystic mass that contains a grossly thickened and enhancing wall (straight arrow) and enhancing soft-tissue components (curved arrow). (b) Gadolinium-enhanced fat-suppressed T1-weighted MR image (3.4/1.4; 12° flip angle) demonstrates similar findings when compared with the CT image. However, more septa are apparent within the mass at MR imaging. This lesion was surgically removed and determined to be a renal cell carcinoma.

View larger version (143K): [in a new window]   Figure 1b. Transverse images in a 56-year-old woman (patient 11) with a Bosniak category IV cystic lesion in the left kidney. (a) Contrast-enhanced CT scan shows a complex cystic mass that contains a grossly thickened and enhancing wall (straight arrow) and enhancing soft-tissue components (curved arrow). (b) Gadolinium-enhanced fat-suppressed T1-weighted MR image (3.4/1.4; 12° flip angle) demonstrates similar findings when compared with the CT image. However, more septa are apparent within the mass at MR imaging. This lesion was surgically removed and determined to be a renal cell carcinoma.

View larger version (196K): [in a new window]   Figure 2a. Images in a 70-year-old man (patient 1) with a cystic mass at the upper pole of the right kidney. (a) Transverse contrast-enhanced CT scan demonstrates a minimally complex cystic mass that contains a few hairline-thin septa (arrows) consistent with a Bosniak category II cyst. (b) Coronal T2-weighted MR image (/64; 150° flip angle) demonstrates more septa (arrows) within the lesion than are depicted on the CT scan. Note that while septa are hairline-thin at CT, they appear minimally thickened at MR imaging. The increased number and thickness of septa depicted on the MR image caused the lesion to be upgraded to category IIF. The lesion in this patient has been followed up for 4 years and is unchanged.

View larger version (185K): [in a new window]   Figure 2b. Images in a 70-year-old man (patient 1) with a cystic mass at the upper pole of the right kidney. (a) Transverse contrast-enhanced CT scan demonstrates a minimally complex cystic mass that contains a few hairline-thin septa (arrows) consistent with a Bosniak category II cyst. (b) Coronal T2-weighted MR image (/64; 150° flip angle) demonstrates more septa (arrows) within the lesion than are depicted on the CT scan. Note that while septa are hairline-thin at CT, they appear minimally thickened at MR imaging. The increased number and thickness of septa depicted on the MR image caused the lesion to be upgraded to category IIF. The lesion in this patient has been followed up for 4 years and is unchanged.

View larger version (179K): [in a new window]   Figure 3a. Transverse images in a 75-year-old man (patient 3) with a complex cystic mass in the right kidney. (a) Contrast-enhanced CT scan demonstrates a lobulated cystic mass that contains numerous hairline-thin septa (arrows) that are barely visible; findings are consistent with a Bosniak category IIF cyst. (b) T2-weighted MR image (/64; 160° flip angle) shows many more septa than are seen on the CT scan. Some of the septa are minimally thickened (straight arrow) and others are confluent (curved arrow) and have the gross thickening typical of category III lesions. Because of the lesion’s complexity at MR imaging, surgery was suggested as a treatment option; the patient refused surgery, and this lesion has remained unchanged for 1 year.

View larger version (178K): [in a new window]   Figure 3b. Transverse images in a 75-year-old man (patient 3) with a complex cystic mass in the right kidney. (a) Contrast-enhanced CT scan demonstrates a lobulated cystic mass that contains numerous hairline-thin septa (arrows) that are barely visible; findings are consistent with a Bosniak category IIF cyst. (b) T2-weighted MR image (/64; 160° flip angle) shows many more septa than are seen on the CT scan. Some of the septa are minimally thickened (straight arrow) and others are confluent (curved arrow) and have the gross thickening typical of category III lesions. Because of the lesion’s complexity at MR imaging, surgery was suggested as a treatment option; the patient refused surgery, and this lesion has remained unchanged for 1 year.

View larger version (189K): [in a new window]   Figure 4a. Transverse images in a 65-year-old man (patient 6) with pathologically proved renal cell carcinoma. (a) Contrast-enhanced CT scan shows a cystic mass in the right kidney that has an enhancing thickened and irregular wall (arrow), typical of a category III lesion. (b) Gadolinium-enhanced fat-suppressed T1-weighted MR image (3.6/1.6; 12° flip angle) shows enhancing soft tissue (arrow) associated with the wall of the cyst, a finding that led to upgrading of the lesion to category IV.

View larger version (176K): [in a new window]   Figure 4b. Transverse images in a 65-year-old man (patient 6) with pathologically proved renal cell carcinoma. (a) Contrast-enhanced CT scan shows a cystic mass in the right kidney that has an enhancing thickened and irregular wall (arrow), typical of a category III lesion. (b) Gadolinium-enhanced fat-suppressed T1-weighted MR image (3.6/1.6; 12° flip angle) shows enhancing soft tissue (arrow) associated with the wall of the cyst, a finding that led to upgrading of the lesion to category IV.

View larger version (183K): [in a new window]   Figure 5a. Transverse images in a 44-year-old man (patient 5) with a large peripherally calcified mass in the right kidney. (a) Contrast-enhanced CT scan shows a large cystic mass with thick irregular calcification (arrow) in its wall. This lesion did not enhance and is consistent with a category IIF cyst; however, a surgical option was advised because of the young age of the patient and large size of the lesion. (b) T2-weighted MR image (/64; 160° flip angle) shows gross thickening of the lesion wall (arrows), which cannot be appreciated on the CT scan. Note the calcification depicted on the CT scan cannot be appreciated on the MR image. (c) Subtracted multiplanar reformation from a coronal three-dimensional gadolinium-enhanced fat-suppressed T1-weighted MR image (4.5/1.9; 12° flip angle) data set shows enhancement (arrows) within the thickened wall of the cyst, which led to an upgrade of the lesion to category III at MR imaging. At surgery, a benign hemorrhagic cyst was found.

View larger version (181K): [in a new window]   Figure 5b. Transverse images in a 44-year-old man (patient 5) with a large peripherally calcified mass in the right kidney. (a) Contrast-enhanced CT scan shows a large cystic mass with thick irregular calcification (arrow) in its wall. This lesion did not enhance and is consistent with a category IIF cyst; however, a surgical option was advised because of the young age of the patient and large size of the lesion. (b) T2-weighted MR image (/64; 160° flip angle) shows gross thickening of the lesion wall (arrows), which cannot be appreciated on the CT scan. Note the calcification depicted on the CT scan cannot be appreciated on the MR image. (c) Subtracted multiplanar reformation from a coronal three-dimensional gadolinium-enhanced fat-suppressed T1-weighted MR image (4.5/1.9; 12° flip angle) data set shows enhancement (arrows) within the thickened wall of the cyst, which led to an upgrade of the lesion to category III at MR imaging. At surgery, a benign hemorrhagic cyst was found.

View larger version (131K): [in a new window]   Figure 5c. Transverse images in a 44-year-old man (patient 5) with a large peripherally calcified mass in the right kidney. (a) Contrast-enhanced CT scan shows a large cystic mass with thick irregular calcification (arrow) in its wall. This lesion did not enhance and is consistent with a category IIF cyst; however, a surgical option was advised because of the young age of the patient and large size of the lesion. (b) T2-weighted MR image (/64; 160° flip angle) shows gross thickening of the lesion wall (arrows), which cannot be appreciated on the CT scan. Note the calcification depicted on the CT scan cannot be appreciated on the MR image. (c) Subtracted multiplanar reformation from a coronal three-dimensional gadolinium-enhanced fat-suppressed T1-weighted MR image (4.5/1.9; 12° flip angle) data set shows enhancement (arrows) within the thickened wall of the cyst, which led to an upgrade of the lesion to category III at MR imaging. At surgery, a benign hemorrhagic cyst was found.