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1382 PULMONARY VASCULAR PATHOLOGY IN FATAL NEONATAL MECONIUM ASPIRATION

Although it is suggested that vasoconstriction is responsible for the pulmonary hypertension and persistent fetal circulation (PFC) associated with meconium aspiration(MA), this has not been proven. We therefore studied the pulmonary vascular bed(PVB)of 10 consecutive term newborns(NB)in whom MA was diagnosed in life and confirmed at autopsy. The pulmonary arteries were injected with barium-gelatin before inflation fixation. Morphometric analysis of three structural features of the PVB: 1)Extension of muscle(EM) into small arteries, 2) Percentage medial wall thickness(%WT),and 3) Arterial concentration(AC)was performed. The findings were compared to those of normal fetal and neonatal lungs. The case histories were also reviewed. In 9/10 NB,PFC was evident clinically-in 8/10 right-to-left shunting at atrial level was confirmed by contrast echocardiography and in 7/10 shunting at ductal level was detected by a decrement in PaO2 ≥ 20 torr from right radial artery to descending aorta.All 9 NB with PFC had EM and increased %WT of the intraacinar arteries with severe encroachment upon the arterial lumen. The NB without PFC had normal arteries. AC was normal in all.The high correlation between fatal MA and PFC was unexpected. The structurally abnormal PVB found in all NB with MA and PFC could not have been caused by vasoconstriction alone and was similar to that seen in PFC without MA. This suggests a common cause of in utero maldevelopment of the PVB and perinatal MA.