Final answer:
The severe flank pain radiating to the groin in a 52-year-old woman is most likely caused by a kidney stone, indicated by symptoms consistent with renal colic and the possible presence of hematuria.
Step-by-step explanation:
The MOST likely cause of the 52-year-old woman's severe flank pain that radiates into her groin is D. kidney stone. This condition is characterized by symptoms such as severe episodic pain most commonly felt in the flank, lower abdomen, and groin, known as renal colic. Renal colic may also be associated with nausea, vomiting, and hematuria (bloody urine), due to damage to the lining of the urinary tract as the stone passes. These symptoms do not align with cholecystitis, ileus, or appendicitis, making a kidney stone the most probable diagnosis given the location and nature of the pain.