An 84-year-old male patie...

An 84-year-old male patient presents with upper abdominal discomfort and weakness. Ultrasound reveals sludge-like material in the stomach and an irregular common bile duct (CBD) with the first half appearing normal, while the middle half is covered with a hyperechoic solid. Furthermore, there are signs of hydronephrotic changes, including a dilated renal pelvis and calyces in the right kidney, suggesting a possible obstruction in the ureter. To further investigate the underlying cause, the patient is advised to undergo an X-ray of the kidneys, ureters, and bladder (KUB) along with biochemical and serological tests. Additionally, a CT scan of the abdomen and pelvis has been recommended, and the patient is currently awaiting the results. What could be the diagnosis suspected in this case?