Oncology - Bladder, Renal, Test
Mid-Atlantic Section 76th Annual Meeting
Introduction & Objective : Renal cysts and masses are common incidental findings on computed tomography (CT). It is often proposed that a cutoff of 20 Hounsfield units (HU) be used for renal cystic lesions to undergo further workup. It has been recognized that the papillary subtype of renal cell carcinoma (RCC) often presents as a low attenuation tumor on noncontrast CT. The objectives of this study are to describe the CT characteristics of papillary RCC, to compare differences between type 1 and type 2 papillary RCC, and to determine the frequency with which papillary RCC is demonstrated as a low attenuation tumor on CT.
Methods : Data was reviewed on all partial and radical nephrectomies performed between July 2007 and July 2017 with pathology confirmed diagnosis of papillary RCC. Tumors with multiple RCC types were excluded. Preoperative CT scans were reviewed. The largest dimension of each tumor was recorded in millimeters. Each tumor had some combination of the four principle phases used to study renal pathology - noncontrast, corticomedullary (30 seconds), nephrographic (100 seconds), and pyelographic (10 minutes). Density was recorded for each phase, when available, as the average of 6 evenly spaced axial regions.
Results : A total of 124 pathologic specimens were identified to contain papillary RCC, 84 of which had CT imaging available for review. Mean age was 61 years (range 21 to 94). Median largest dimension was 39.5 mm (range 1.8 to 170). 27 of these were reported to be type 1; 17 were type 2; and 40 were unspecified. Noncontrast CT was available for 73 tumors of which 16 (22%) had HU measuring fewer than 20. 12 of these 16 low density tumors (75%) were clinical stage T1 or T2. 5 were papillary type 1; 4 were papillary type 2; and 7 were unspecified. Attenuation varied within each CT phase. (Table) Mean attenuation at 100 seconds was 44.5 for type 1 papillary tumors and 48.8 for type 2.
Conclusions : Pathologically proven papillary RCC is a heterogeneous entity in terms of size and density on preoperative CT imaging. A noncontrast CT scan with HU fewer than 20 may not be adequate evaluation for incidental renal masses, as over 1 in 5 papillary RCCs measure at lower attenuation than this cutoff. Further study is needed to identify the appropriate role of ancillary imaging in the workup of benign-appearing renal cysts.