Bronchopulmonary dysplasia

Clinical History

A young boy presented with a failure to thrive. He had been born pre-term and required supplementary oxygen therapy for the first few months of life. At the age of six months, he developed Rous Sarcoma Virus (RSV) bronchiolitis.

Imaging Findings

The patient was born at 25 weeks gestation, and weighed 970 g. During the first week, he developed increasing respiratory problems and required ventilation for 10 days. Following extubation, he had a prolonged period of oxygen dependence. At six months, while still in the neonatal unit, he developed RSV bronchiolitis. He left the neonatal unit at the age of nine months and was recommended to undergo home oxygen therapy, which was required until he was three and half years. At the age of seven, he was referred for further assessment due to a failure to thrive. He weighed 15 kg, had a heart rate of 90 and a respiratory rate of 20. Respiratory and cardiovascular examinations done were otherwise found to be unremarkable. A CXR, echocardiogram, overnight saturation monitoring and blood tests were found to be normal. Due to his respiratory problems, at around the time of birth, a CT scan of the chest was performed. The CT scan found to be showed low attenuation areas throughout both lungs which were associated with decreased vessel markings. Only the middle lobe and lingula had a normal attenuation. The findings were consistent with a diagnosis of bronchopulmonary dysplasia. The differential diagnosis made suggested obliterative bronchiolitis, but there were no real bronchial abnormalities to support this.

Discussion

Bronchopulmonary dysplasia (BPD) was first described in 1967 in prematurely born infants with severe respiratory distress (RDS) and who were treated with intermittent positive pressure ventilation and oxygen supplementation. With advances in treatment, the clinical and radiological presentation has changed, and the condition is now commonly referred to as chronic lung disease of infancy (CLD). The condition affects 3000–7000 neonates in the United States each year of which only 4000 survive infancy. Most of these neonates live on to reach adult life. The incidence of BPD has decreased with the advent of modern therapy, although with an increasing number of survivors, the total number of cases has remained the same. The current criteria used for diagnosis are (1) Positive pressure ventilation during the first two weeks of life for a minimum of three days. (2) Clinical signs of respiratory compromise persisting for more than 28 days of age. (3) Requirements for supplemental oxygen for more than 28 days of age to maintain a PaO2 above 50 mmHg. (4) Chest X-ray examinations with findings consistent with BPD. The four major risk factors for the development of BPD are: (1) Premature birth, (2) Respiratory failure – of any cause, (3) Oxygen supplementation, (4) Mechanical ventilation. Although known to be very common in patients with BPD, RDS is not an absolute precursor to the disease. With the advances in neonatal care, the disorder now most frequently occurs in infants weighing <1 kg. The precise aetiology of BPD is unknown, although it is almost certainly multifactorial. The elevated oxygen concentrations lead to the production of oxygen free radicals and the release of chemotactic factors that attract polymorphonuclear leucocytes. This results in an inflammatory reaction and the release of proteolytic enzymes. Pre-term babies have lower levels of anti-oxidant enzymes, increasing the susceptibility to lung oxygen toxicity. Ventilation causing repeated stretching of the immature lung has also been strongly implicated, as has the arrest of normal lung development in very pre-term babies. Histological examinations revealed squamous metaplasia of the large and small airways, peri-bronchial and peri-bronchiolar fibrosis, obliterating fibroproliferative bronchiolitis and prominent hypertrophy of smooth muscle. A destruction of elastin fibres, which provide the structural support for the alveolar septal development, is seen. The radiological findings have changed over the last 30 years due to an improvement in the treatment. The plain film findings of progressive reticular and cyst-like shadowing with hyperexpansion are now rarely seen. Both radiographic and pulmonary functions tend to improve with age. The CT findings include areas of reduced lung attenuation and perfusion with a decrease in the size and number of vessels. Bronchial wall thickening, decreased diameter in the ratio of bronchus to pulmonary artery, linear opacities and bullae are also described. The areas of reduced attenuation may be due to small airway obstruction, decreased bronchial diameter and arrested acinar development. The treatment for BPD includes steroids, surfactant therapy, modified ventilatory techniques, fluid restriction, appropriate nutrition, diuretics, bronchodilators and RSV prophylaxis. Two recent long term studies indicate that the survivors of BPD were twice as likely to be hospitalised in the first 2 years of life as compared with pre-term infants without BPD. Pulmonary function was also worse but a study in 1990 of young adults with prior BPD showed the pulmonary dysfunction to be asymptomatic. However, since the introduction of new neonatal techniques no long term assessment has been possible.

Differential Diagnosis List

Final Diagnosis

Bronchopulmonary dysplasia.

URL:	https://www.eurorad.org/case/2944
DOI:	10.1594/EURORAD/CASE.2944
ISSN:	1563-4086