Pulmonary agenesis is among the rarest congenital malformations of the respiratory system. It arises when the lung bud, the embryonic outgrowth of the foregut that normally branches into the airways and lung parenchyma, fails to develop on one side. The result is a complete absence of the affected lung tissue, airway, and vascular supply, rather than an underdeveloped lung that is merely small. The condition can affect either lung, and its reported incidence varies widely across older case series, in part because many affected infants die before a diagnosis is ever made. When one lung is missing, the remaining lung must carry the entire burden of gas exchange, and the cardiovascular system must adapt to a shifted distribution of blood flow. Survival is possible, particularly with unilateral agenesis and no other major anomalies, but the condition is frequently complicated by recurrent infections and, as in this case, pulmonary vascular disease.

The clinical course of the infant described in the report illustrates why the diagnosis is so often delayed. Shortly after birth she developed severe respiratory distress, a presentation that in a neonate is far more commonly explained by pneumonia, sepsis, transient tachypnea, or aspiration than by a missing lung. At the first facility she encountered, clinicians treated her for presumed pneumonia. When she failed to improve, she was referred onward to Tikur Anbessa Specialized Hospital, the tertiary referral center affiliated with Addis Ababa University, where the team led by pediatrician Beniam Tadewos Lamboro took a closer look at what her body was actually doing.

On admission, the physical examination offered the first decisive clues. The baby showed severe intercostal and subcostal retractions, the visible sinking of the chest wall between and beneath the ribs as she struggled to move air. More tellingly, auscultation revealed completely absent air entry on the left side of her chest. A silent hemithorax in a newborn is an alarming finding that demands an immediate explanation, whether that explanation is fluid, collapse, a diaphragmatic hernia, or the absence of lung tissue itself. The examining team recognized that a simple infection could not account for everything they were hearing and seeing.

Chest radiography then sharpened the picture considerably. The X-ray showed opacities in the right middle and lower lobes with air bronchograms, findings consistent with pneumonia, confirming that the infection was real. But it also showed complete opacification of the left hemithorax, together with two features that pointed away from infection and toward a structural problem: crowding of the ribs on the left side and a shift of the mediastinum, the central compartment of the chest containing the heart and great vessels, toward the left. These are classic signs of volume loss. When lung tissue is absent or collapsed, the structures around it fill the void, and the chest wall and mediastinum migrate toward the affected side. In pneumonia, by contrast, the affected side tends to hold its volume or even expand. The combination of infection on one side and volume loss on the other raised the suspicion of a congenital lung anomaly coexisting with pneumonia.

To settle the question, the team performed contrast-enhanced computed tomography of the chest. The CT scan delivered an unambiguous answer: the left main bronchus, the left lung, and the left pulmonary artery were completely absent. There was no vestige of left-sided pulmonary architecture at all. The scan also measured the ratio of the main pulmonary artery diameter to the aortic diameter, which exceeded 1, a radiographic marker associated with elevated pulmonary vascular resistance and pulmonary hypertension. This finding mattered enormously for prognosis and management, because it signaled that the single right lung was not only doing all the oxygenation work but was also facing abnormally high pressures in its circulation.

Echocardiography completed the hemodynamic assessment and revealed the downstream consequences of the missing lung. The right side of the heart, which pumps blood into the pulmonary arteries, was enlarged, a predictable consequence of pumping against increased resistance. The baby had a patent ductus arteriosus, a persistent fetal blood vessel connecting the aorta and the pulmonary artery, measuring 2.5 millimeters with bidirectional shunting, meaning blood was flowing back and forth across it rather than in a single direction. She also had severe tricuspid regurgitation, a leak of the valve between the right atrium and right ventricle, with a peak pressure gradient of 62 millimeters of mercury, a value that indicated severe pulmonary hypertension. In essence, the vascular bed of the lone right lung could not accommodate the entire cardiac output at normal pressures, and the heart was straining against that limitation.

Management proceeded along two parallel tracks. The team supported the infant’s breathing with continuous positive airway pressure, or CPAP, which keeps the airways and air sacs propped open and reduces the work of breathing without requiring invasive ventilation. At the same time, she received medical therapy aimed at lowering pulmonary vascular resistance and supporting cardiac function. This combination reflects the modern understanding of pulmonary agenesis as a cardiopulmonary condition rather than a purely anatomical one: the missing lung is fixed, but the pressures in the pulmonary circulation and the strain on the right heart are potentially modifiable with drugs. Notably, the infant survived the neonatal period, a stage at which many cases of pulmonary agenesis historically proved fatal.

Follow-up over the first nine months of life told a nuanced story. At six months, the child remained dependent on supplemental oxygen but had achieved age-appropriate growth and developmental milestones, an outcome the authors emphasize as meaningful given the severity of her initial presentation. Repeat echocardiography, however, showed that the patent ductus arteriosus had enlarged to 6 to 7 millimeters with persistent bidirectional shunting, indicating that the pulmonary vascular disease had not resolved and may have progressed. By nine months of age she was still on home oxygen and continuing medical therapy, but she had required no further hospitalizations. The report thus documents both the resilience of a child living with a single lung and the chronic, evolving nature of the pulmonary hypertension that accompanies it.

The authors draw a clear practical conclusion from this single case. Congenital lung agenesis can coexist with ordinary respiratory infections, and those infections can mask the underlying anomaly, delaying diagnosis and appropriate counseling. They argue that clinicians in resource-limited settings, where advanced imaging is not always available at first contact, should suspect congenital lung anomalies whenever a neonate or infant presents with persistent respiratory distress accompanied by radiographic signs of volume loss, specifically mediastinal shift and rib crowding on chest radiography. In such circumstances, they recommend considering CT imaging for confirmation. The case is also a broader argument for the value of publishing detailed clinical observations from settings where rare diseases are underreported: every documented case sharpens the pattern recognition of clinicians who may otherwise encounter such a presentation only once in a career, and for the family in this report, that sharpened recognition is what transformed a treatment-resistant pneumonia into a defined, manageable diagnosis.

Subject of Research: A rare case of neonatal left lung agenesis initially misdiagnosed as pneumonia in a resource-limited setting

Article Title: Neonatal left lung agenesis presenting as pneumonia in a resource-limited setting: a case report

Article References: Lamboro, B. T., Girma, S. M., Temesgen, N. E., Mengistu, A. G., & Mamo, Z. B. (2026). Neonatal left lung agenesis presenting as pneumonia in a resource-limited setting: a case report. BMC Pediatrics. https://doi.org/10.1186/s12887-026-07723-4

Image Credits: AI Generated

DOI: 10.1186/s12887-026-07723-4

Keywords: lung agenesis, neonatal respiratory distress, congenital anomalies, pulmonary hypertension, pneumonia, patent ductus arteriosus, chest CT, echocardiography, resource-limited settings, neonatology, case report, BMC Pediatrics