Papillophlebitis in Young Adults

A 26-year-old otherwise healthy female medical student presents with subacute mild blurring of vision in the left eye for 5 days, described as a "slight haze." She denies pain with eye movements, headache, or neurological symptoms. Best-corrected visual acuity is 6/9 in the left eye. Fundoscopy reveals a hyperemic swollen optic disc with blurred margins, and the structures marked **B** in the diagram are noted. Fluorescein angiography shows delayed venous filling with late diffuse disc hyperfluorescence. Which of the following best explains the pathophysiology of the findings at **B** in this clinical context?