A 58-year-old woman from Mumbai undergoes a routine abdominal ultrasound for abdominal pain. The radiologist reports a 4 cm complex cystic lesion in the left kidney with internal echoes and a thick, enhancing septum on contrast-enhanced CT. There is no hydronephrosis, renal function is normal (eGFR 72 mL/min), and the patient is asymptomatic regarding the lesion. What is the most appropriate next step in management?