Hepatocellular Adenoma

A 32-year-old woman on combined oral contraceptive pills for 10 years presents with acute right upper quadrant pain and hypotension. CT imaging shows a 7 cm well-circumscribed right hepatic mass with intratumoral hemorrhage. Resection specimen shows sheets and cords of bland hepatocytes with low nuclear-to-cytoplasmic ratio, eosinophilic cytoplasm with steatosis, and thin-walled arteries coursing through the lesion unaccompanied by portal veins or bile ducts. The structure marked **A** is most consistent with which diagnosis, and what is the PRIMARY pathophysiologic mechanism underlying its development in this patient?