PRIMARY PLEXOGENIC PULMONARY-HYPERTENSION SHOWS IMPERFECT FORMATION OF THE INTERNAL ELASTIC LAMINA OF THE PULMONARY-ARTERIES

Lung tissue from subjects dying from primary plexogenic pulmonary hype rtension (PPH) has shown defects of elastin formation of the lung arte ries. Lung vessels from 5 cases of PPH were compared with those of 9 a ge-matched normal subjects, and 24 individuals having secondary pulmon ary hypertension (2 degrees PH). PPH cases and those with 2 degrees PH due to congenital heart disease with left-to-right shunts (2 degrees PH, LRS), showed active proliferation of medial smooth muscle cells (S MC) through defects of the internal elastic lamina (IEL) into the arte rial lumen to form typical plexiform lesions. Larger arteries showed a ccelerated intimal thickening similar to normal aging. Plexiform lesio ns were not seen in normal subjects or in those developing high pulmon ary pressures later in life. The observations showed that the developm ent of discontinuities of the IEL of the pulmonary arteries and intima l thickening is accelerated in normal subjects by high pulmonary arter y pressure, especially when this is established at a very young age. T hey suggest that such discontinuities occur in PPH due to inherent abn ormality of the elastin of the arterial walls, with advanced early pro liferation of medial SMC and obstruction of the pulmonary arterial cir culation.