Neuroblastoma

An 18-month-old infant presents with a firm, irregular abdominal mass that crosses the midline, periorbital ecchymoses ("raccoon eyes"), proptosis, and painful bone lesions. The child is irritable, losing weight, and demonstrates paroxysmal opsoclonus-myoclonus ("dancing eyes, dancing feet"). Laboratory studies show markedly elevated urinary VMA and HVA, and high serum LDH and neuron-specific enolase. Contrast-enhanced CT of the abdomen reveals a large heterogeneous suprarenal mass with coarse stippled calcifications. The structure marked **B** in the diagram shows the tumor's relationship to the major abdominal vessels. Which of the following best describes the key radiological distinction of the structure marked **B** compared to Wilms tumor?