Naoki Takahashi MD, Presenter: Nothing to Disclose

Kohei Sasaguri MD, Abstract Co-Author: Nothing to Disclose

Mitsuru Takeuchi MD, PhD, Abstract Co-Author: Nothing to Disclose

Akira Kawashima MD, Abstract Co-Author: Nothing to Disclose

To evaluate the frequency of minimally enhancing small RCC on contrast-enhanced CT.

130 patients 148 with pathologically proven small RCC (<4cm) (mean age 61; 78 male, 52 female; 98 cc-RCC, 36 pap-RCC, and 14 other subtypes of RCC, mean size 25 mm) who underwent both unenhanced (NC) and contrast-enhanced (CE)-CT were included. CT attenuation of renal mass was measured on NC and CE-CT by placing a largest possible ROI. Renal mass with enhancement <20 HU (attenuation difference between CE-CT and NC-CT) was categorized as minimally enhancing mass. CT and clinical history of these patients were reviewed by 2 radiologists. The difficulty of making prospective diagnosis of solid mass was categorized using 4-point scale based CT imaging features.

Of 148 RCC, 14 RCC (3 cc-RCC, 11 pap-RCC, mean size: 21 mm) were categorized as minimally enhancing (enhancement: 1-19 HU, mean 12 HU, mean unenhanced CT value: 32HU). Concomitant RCC (either minimally enhancing or enhancing (>20HU) mass) were common (9/14). 3 pap-RCC were categorized as difficult to diagnose; 2 were homogeneous and showed enhancement < 5HU but ultrasound confirmed solid nature, 1 lesion was difficult to detect but found at the time of surgery for other RCC. 3 pap-RCCs were categorized as somewhat difficult; all were minimally heterogeneous and showed enhancement >15 HU and ultrasound confirmed solid nature. 5 RCCs (1 cc, 4 pap) were categorized as somewhat easy to diagnose; all were mildly heterogeneous with enhancement between 5-19 HU. 3 RCCs (2 cc, 1 pap) were categorized as easy to diagnose; all were moderately heterogeneous with higher degree of enhancement at the periphery the mass.

Minimally enhancing RCC represented 14/130 of small RCC. 6/14 (all pap-RCC) were relatively difficult to diagnose by CT, and required ultrasound for confirmation. 8/14 could be diagnosed relatively easily by CT imaging features.

Minimally enhancing RCC is uncommon, but the diagnosis is challenging when the tumor is homogenous.

Takahashi, N, Sasaguri, K, Takeuchi, M, Kawashima, A, Frequency of Minimally Enhancing Small RCC on Contrast-enhanced CT.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14011400.html