Heath and Edwards pathological classification of pulmonary artery hypertension

Panels A and C are from a 38-year-old woman with severe PAH associated with systemic sclerosis. Panels B and D are from a 40-year-old woman with a ventricular septal defect and Eisenmenger syndrome.
(A) Grade II lesion depicting intimal hyperplasia and medial hypertrophy.
(B) Grade III lesion depicting an "onion-skin" appearance and vessel occlusion.
(C) Grade IV depicting a plexiform lesion (asterisk).
(D) Grade VI lesion depicting a plexiform lesion with fibrinoid necrosis.