ElHassan et al. Journal of Medical Case Reports 2010, 4:284 http://www.jmedicalcasereports.com/content/4/1/284 Page 4 of 5 Figure 4 Three-dimensional view on computed tomography angiography showing collateral vessels originating from the aorta and supplying the left lung. were previously described with LPA thrombosis at birth and clinical evidence of PPHN [4,12]. No reported cases were found of infants with congenital LPA thrombosis and left pulmonary hypoplasia. The pathogenesis of pulmonary hypoplasia is not fully understood, but a normal thoracic cavity volume, ade- quate respiratory motion and appropriate amniotic fluid volume are all essential for a normal lung growth in utero [5,6]. Although congenital pulmonary hypopla- sia can sometimes be idiopathic, it typically occurs when any or a combination of these factors is absent or impaired. It has been described in babies with malfor- mations of the chest wall, oligohydramnios and abnorm- alities of the tracheobronchial tree, although it remains most commonly associated with conditions that reduce intrathoracic space, such as diaphragmatic hernia or pleural effusions [5-7]. Limited reports exist of babies with congenital pulmonary hypoplasia and no clear evidence of fetal lung compression or abnormalities in fetal breathing mechanism or amniotic fluid volume. In those instances, suggested underlying mechanisms are the possibility of a genetic component or a delay in the development of the lung [5,6]. We postulate that a vascular injury could be responsi- ble for the arrest of lung maturation in utero and might be the main reason for LPA thrombosis and left pul- monary hypoplasia in this baby. Review of the embryol- ogy of the pulmonary vessels indicates that, in this patient, a potential vascular injury and an ensuing pul- monary arterial maturational arrest might have occurred between weeks five and eight of gestation [13]. In the fifth intrauterine week of life, the primitive pulmonary vessels develop from the sixth aortic arch [13]. By week eight of gestation, as the true central pulmonary arteries develop from the aortopulmonary trunk, the primitive pulmonary arteries arising from the aorta involute [13].