A 62-year-old woman with a 10-year history of varicose veins presents with chronic bilateral lower-leg erythema, scaling, and pruritus. Examination reveals reddish-brown pigmentation over the medial malleoli bilaterally, mild pitting edema, and no systemic signs of infection. The structure marked **A** in the diagram shows the characteristic findings of stasis dermatitis. Which of the following best explains the pathophysiologic mechanism underlying the hemosiderin pigmentation seen in this patient?