This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Surgery
Which one of the following is not a CT feature of Adrenal adenoma? 
Select and explain. 
A. Low attenuation, B. Homogeneous density and well defined borders, C. Enhances rapidly, contrast stays in it for relatively longer time and washes out late, D. Calcification is rare
C: Enhances rapidly, contrast stays in it for relatively longer time and washes out late
Answer: C: Enhances rapidly, contrast stays in it for relatively longer time and washes out late 
Explanation: Enhances rapidly, contrast stays in it for relatively longer time and washes out late Adrenal adenomas show rapid contrast enhancement and rapid subsequent washout; whereas nonadenomas (adrenal ca, mets and pheochromocytomas) show slower washout. Characterstics of adenomas (which help differentiate it from nonadenomas) Homogenous well defined rounded tumor; usually smaller than 4 cm Low attenuation on CT Signal loss on MR chemical shift imaging Contrast enhancement pattern (adenomas show rapid enhancement and rapid washout whereas nonadenomas show delayed washout) Findings s/o malignancy in an incidentally discovered adrenal mass (Harrison 17/e p2258) - large size >4 cm - tumor inhomogenesity and irregular margins - calcifications - high attenuation of CT - no loss of signal on Chemical shift MR