What is the most common malignant kidney tumor and its typical clinical and sonographic features?

• A. Renal cell carcinoma (RCC) / Grawitz's tumor: hematuria, flank pain or palpable mass; iso- or hyperechoic, heterogeneous, halo/rim, calcifications.
• B. Transitional cell carcinoma: painless hematuria with papillary formations.
• C. Wilms tumor: pediatric age with large unilateral mass.
• D. Angiomyolipoma: benign fat-containing lesion.

Answer: (A)

Renal cell carcinoma (Grawitz tumor) is the most common malignant kidney tumor in adults. Clinically, it often presents with hematuria, flank pain, and a palpable renal mass, and may be associated with weight loss, fever, anemia, or paraneoplastic syndromes. On ultrasound, it typically appears as a solid intrarenal mass that is iso- to hyperechoic relative to the cortex and is heterogeneous due to necrosis or hemorrhage. A halo or pseudocapsule may surround the lesion, and calcifications can be seen. Doppler usually shows internal vascularity, reflecting its rich blood supply. These features together—adult presentation, the solid heterogeneous mass with a halo and possible calcifications, and vascularity on Doppler—best fit renal cell carcinoma.