What is the likely diagnosis?
Renal cell carcinoma is most likely. A renal oncocytoma or benign adenoma may have similar appearances.
Other than an obvious vascular solid mass, what other sonographic finding specifically demarcates a renal tumour?
A thin hypoechoic halo seen at the upper margin of mass (tumour pseudocapsule), is relatively specific for renal tumour. Its seen usually in renal cell carcinoma, oncocytoma and rarer adenomas.
A large soft tissue mass appears to arise from / involve the lower pole of the left kidney. On colour Doppler examination the mass demonstrates extensive internal vascularity. Additionally an anechoic 2cm lesion is present in the upper pole, without solid component.