Teaching Case

A 3-year-old female patient presented with complains of cough and cold for 1 month. She had suffered from many similar episodes in the past.

Contrast-enhanced CT showed an absence of the right lung, right pulmonary artery and right main bronchus. There was a compensatory hyperinflation of the left lung and marked mediastinal shift was seen towards the right side with the heart located in the right hemithorax. The left main bronchus as well as the left lung appeared normal. These imaging findings are diagnostic for a complete agenesis of the right lung.

Dysmorphic pulmonary abnormalities, defined as the absence of a whole lung or lobes are classified into three categories:

Type 1 (Agenesis): Complete absence of lung bronchus and no vascular supply to the affected side.
Type 2 (Aplasia): Rudimentary bronchus with complete absence of pulmonary parenchyma.
Type 3 (Hypoplasia): Presence of variable amounts of bronchial tree, pulmonary parenchyma and supporting vasculature [3].

It has been hypothesized that abnormal blood flow in the dorsal aortic arch during the 4th week of gestation (embryonic phase) causes pulmonary agenesis [2]. Its incidence is nearly the same in men and women. Left-sided agenesis is more common and those patients live longer than patients with right-sided agenesis [3]. Pulmonary agenesis and aplasia are frequently observed in association with other malformations such as diaphragmatic defects, kidney anomalies, extrapulmonary sequestration, musculoskeletal defects or congenital heart disease [1].

Pulmonary hypoplasia can be primary or secondary. Primary pulmonary hypoplasia, in which a cause cannot be elucidated, is much less common than secondary hypoplasia. The majority of cases of secondary hypoplasia are due to a process limiting the thoracic space for lung development, which can be intrathoracic or extrathoracic. The most common intrathoracic cause is a congenital diaphragmatic hernia, which can be left-sided (75%–90%), right-sided (10%) or bilateral (5%). The most common extrathoracic cause is severe oligohydramnios, occurring secondary to either fetal genitourinary anomalies (renal agenesis, cystic renal dysplasia, and urinary tract obstruction) or prolonged rupture of membranes. A hypoplastic thorax occurs in skeletal dysplasias (thanatophoric dysplasia) in which a small and rigid thoracic cage causes pulmonary hypoplasia [2].

Patients with dysmorphic pulmonary abnormalities are usually asymptomatic. Recurrent infections can increase the breathing distress [1].

Normograms have been published that illustrate the relationship between thoracic circumference and gestational age. A thoracic circumference below the 5th percentile for gestational age indicates pulmonary hypoplasia. Other parameters indicating pulmonary hypoplasia are a chest-trunk length ratio under 0.32 and a femur length–abdominal circumference ratio under 0.16 [2].

Diagnosis of dysmorphic pulmonary abnormalities can be made using CT, bronchoscopy, pulmonary angiography, and MRI [1]. Imaging findings in pulmonary aplasia and agenesis are similar, except for the presence of a short blind-ending bronchus in aplasia. Postnatal radiography demonstrates diffuse opacification of the involved hemithorax with ipsilateral mediastinal shift. CT helps to confirm the absence of the lung parenchyma, bronchi, and pulmonary artery on the involved side [2].

Overall prognosis in dysmorphic pulmonary abnormalities depends on the affected side, functional integrity of the remaining lung tissue as well as the presence of associated anomalies [3].