For the first time pulmonary agenesis was classified by Schneider [
8] which later on was modified by Boyden [
9] into three groups according to development of their primitive lung bud. Type I which is called pulmonary agenesis is complete absence of unilateral lung parenchyma, its bronchus and vasculature. Type II is named pulmonary aplasia which is complete absence of unilateral lung with a rudimentary bronchus. Type III is pulmonary hypoplasia characterized by partial existence of branchial tree with some parts of unilateral pulmonary parenchyma and its vessels [
2]. Although the main etiology of the disease is unknown, lack of vitamin A during pregnancy, viral agents, genetic as well as iatrogenic factors [
10] have been mentioned as possible causes [
2]. The lungs normally develop from foregut during the 4th and 5th weeks of gestation. The failure of bronchial analogue to divide equally between two lungs with possible abnormal blood flow in dorsal aortic arch during this period may result in hypoplasia, aplasia and agenesis of unilateral pulmonary parenchyma. In the meantime the contra lateral lung produces almost twice alveoli in compensation [
11]. As during this period of time the migration of heart also occurs, therefore some cases may coexist with congenital heart anomalies [
10]. Pulmonary hypoplasia may occur due to secondary reasons as well such as chest wall deformity, diaphragmatic hernia, cystic adenomatoid malformations, and pleural effusion. Bilateral pulmonary hypoplasia can also happen due to thoracic dystrophies and oligohydramnios [
6]. For diagnosis of pulmonary agenesis different imaging techniques can be used. Plain chest shows unilateral opaque lung with mediastinal shift whereas for final diagnosis CT scan, MRI [
12], bronchography, bronchoscopy and pulmonary angiography are used. Sometimes the disease can be detected in prenatal life by help of prenatal ultrasound showing hyperechoic hemithorax however the definitive diagnosis is hard [
13] which can be confirmed by Fetal MRI [
12]. According to the literature, left side agenesis is more common comparing to the right side with longer life expectancy. However in our cases just one patient had left lung agenesis while the other five cases had right side agenesis. Right lung agenesis happens with more incidences of cardiovascular abnormalities and patient may have more severe symptoms due to pronounced carina malformation and cardiac and mediastinal shift [
10]. Treatment strategies contain medical management and surgical repair. Medical treatments comprise control of recurrent chest infection, bronchodilators and controlling other complications. Surgery is usually needed in associated congenital anomalies. The prognosis usually depends to functionality of the unilateral existed lung and associated anomalies [
2].
As this anomaly can occur at any age, the possibility of lung agenesis should be in differential diagnosis of patients having decrease to absent breath sounds with less or no movement of unilateral chest wall and opaque hemithorax in plain film. For confirmation, diagnostic imaging such as chest CT scan, MRI, bronchoscopy and chest angiography can be done. The early detection of the pulmonary agenesis is essential to reduce the development of fibrosis in patient’s unilateral lung which can occur as result of recurrent chest infection. The surgical procedures should also be in consideration in presence of other congenital anomalies or complications.