Munazza Anis MD, Presenter: Nothing to Disclose

Nancy S. Curry MD, Abstract Co-Author: Nothing to Disclose

To investigate the incidence of RCC with low attenuation values (<20 HU) in our patient population on unenhanced CT  

  Retrospective, IRB approved study Search of pathology archives of 600+ nephrectomies performed at MUSC from 2008-2013 191 patients with renal cell carcinoma 91 patients with 97 tumors had unenhanced MDCT within 6 months (120 kVp and slice thickness 3-5 mm) The lesions were identified by pathology reports and compared with enhanced CT or MR   81/91 patients with unenhanced CT’s were excluded: Tumors smaller than 1.5 cm, >7 cm Signs of obvious solid renal tumor on unenhanced CT (e.g., lobulated margins, heterogeneity, internal calcification) Patients with > 2 masses/ resected kidney Polycystic kidneys Tumors > 20 HU   Study population of 10/91 (11%) pts with 11 homogeneous tumors with attenuation < 20 HU ROI measurements of the lesions (at PACS review station) from middle of lesion on axial scan and/or coronal scan, sampling at least half the lesion volume; soft tissue window settings (350 width, 50 level) Renal parenchymal ROI and water attenuation standards were also measured (gallbladder or urinary bladder) when possible.  

10/91 patients (11%) with 11 low attenuation (< 20 HU), homogeneous RCC: 10 clear cell RCC (9 Gr II, pT1a; 2 pT3a) 1 pap RCC Gr III Size: 1.7 - 3.9 cm (mean 2.9 cm, median 3.2 cm) ROI: 7 HU – 19 HU (mean 14.7, median 15 HU) 2 tumors w necrosis (1 ccRCC, 1 pap RCC) One showed adjacent calcified cyst Only two of the 10 showed avid hypervascularity  

Low attenuation tumors on unenhanced CT are uncommon but were found in 10/91 patients (11%) with RCC, averaging 15 HU. (Regional areas of minimum attenuation less than 20 HU and maximum attenuation greater than 70 HU were seen in 24.9% (48/193) and 2.1% (4/193) of RCCs, respectively) All but one were clear cell subtype, none were cystic tumors; only two showed necrosis.  

Short of continuous sampling which is not clinically applicable, it may be advisable to check tumor ROI against water attenuation standards and renal HU measurement. ? Revise the “safe” lower level to < 15 HU. Further study needed.  

Anis, M, Curry, N, Role of Unenhanced CT in Undiagnosed Renal Cell Carcinoma (RCC).  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14014950.html