A 58-year-old man presents with a 3-month history of dull flank and back pain, lower extremity edema, weight loss, and low-grade fever. He has a history of ergotamine use for migraine and smoking. Laboratory investigations show elevated ESR (85 mm/h), CRP (45 mg/L), mild anemia, and rising creatinine (2.4 mg/dL from baseline 1.0 mg/dL). Urinalysis is bland. Contrast-enhanced CT abdomen demonstrates a homogeneous soft-tissue plaque encasing the infrarenal abdominal aorta, IVC, and iliac vessels with **medial deviation of the ureters** and bilateral hydroureteronephrosis. The structure marked **A** in the diagram represents this periaortic soft-tissue rind. Which of the following best characterizes the pathophysiology of the fibrotic tissue marked **A** and its relationship to the ureters?