Chest ImagingCystic fibrosis
(CF), complex inherited disorder of infants, children and young adults. It is the most common lethal hereditary disease in the white population and is inherited as an autosomal recessive trait. In the United States and European countries, the gene frequency in white people is approximately 1/25, resulting in a disease incidence of 1 in 2500 live birth. CF is a systemic illness affecting the sweat and salivary glands, pancreas, gastrointestinal tract, liver, male reproductive system, upper respiratory tract and lung. Manifestations of CF in the neonatal period result from gastrointestinal involvement; later, pancreatic and
pulmonary manifestations usually predominate. The course is highly variable and depends at least in part on the specific molecular abnormalities in the mutant gene.
Pulmonary complications account for the majority of morbidity and mortality. Owing to advances in therapy, the median survival is currently 29 years. It is estimated that one third of the population with this paediatric disease is now adult.
The lung is normal at birth but pulmonary changes with obstruction of the peripheral airways from retained secretions may be seen within weeks after birth. These changes induce hypoplasia of bronchial and mucous glands. Because of poor collateral ventilation due to poor function of the pores of Kohn and channels of Lambert in childhood, mucous plugging results in atelectasis if obstruction is complete or obstructive overinflation from a ball-valve effect. Over time, there is progressive involvement of larger airways, resulting in mucous plugging, bronchiectasis and infectious bronchitis. Diminished mucociliary clearance permits colonization of airways by bacteria. Initially the colonization organisms are Staphylococcus aureus and Haemophilus influenzae. As the disease progresses colonization with mucoid variants of pseudomonas species occurs. Pseudomonas aeruginosa is the most prevalent of the pathogens in CF, causing chronic infections in up to 80% of patients. Pseudomonas cepacia is an increasingly recognized virulent pulmonary pathogen, often coexisting with Pseudomonas aeruginosa in patients with severe pulmonary disease. Other pulmonary pathogens in CF include aspergillus, mycobacteria and respiratory viruses. The recurrent and persistent infections induce an intense inflammatory response. The abnormal airway secretions with the by-products of the organismneutrophil interactions, cause decreased ciliary effectiveness and stasis of infected secretions. This results in bronchiectasis, which prolongs the stasis and predisposes to abscess formation and haemoptysis. Sixty per cent of patients with CF present with at least one episode of haemoptysis over their lifetimes. There is a correlation between haemoptysis and the presence of bronchial artery hypertrophy and bronchopulmonary anastomoses within bronchial walls (see systemic hypervascularization pulmonary). The pulmonary function is characterized initially by airway obstruction and hyperinflation. In more advanced disease, the total lung capacity may decline as interstitial fibrosis and restrictive components are manifest. Ventilation and perfusion mismatch induce gas exchange abnormalities. Areas of mucous plugging are perfused and not ventilated. This results in hypoxaemia initially during sleep or exercise. Progression of hypoxaemia if untreated leads to pulmonary hypertension and cor pulmonale that are poor prognostic signs particularly in adulthood.
The spectrum of severity of CF is quite broad over a wide range of ages. The disease now may be recognized for the first time in adults. The rate of progression of disease is highly variable as well. In infants and children, the earliest radiographic sign is overinflation due to mucous plugging of small bronchi and bronchioles. Overinflation is readily identifie On the radiograph, linear shadows, tram-line opacities and ring shadows represent dilated thick-walled bronchi, and multiple nodular opacities represent mucous plugging. HRCT is more sensitive and specific in the evaluation of bronchiectasis (Fig.2). Cylindrical bronchiectasis is the most common pattern in CF, but varicose and cystic bronchiectasis may be seen as the disease progresses. An airfluid level within the dilated bronchi represents chronic airway suppuration. Lobar pneumonia is rare. The radiological changes of CF are most commonly seen in the right upper lobe. Mucoid impaction in dilated bronchi is frequently observed; lobar and segmental atelectasis may result (Fig.1). Large cystic air-spaces generally connected to dilated bronchi may be seen. The majority represent bronchiectatic cysts. Some, however, represent emphysematous spaces. Lung abscesses are difficult to differentiate from infected dilated bronchi. Pleural effusion is not common. Pleural thickening, better appreciated on CT scans, must be accurately identified in those patients in whom lung transplant is considered. Pneumothorax is a complication observed in 5-20% of patients, generally seen in more severe disease and associated with a worse prognosis. In the case of haemoptysis, chest radiographs generally fail to localize the source of pulmonary haemorrhage. If haemorrhage does not resolve under medical treatment, angiographic embolization of the bronchial or nonbronchial systemic arteries is indicated (see embolization bronchial arteries). With advanced disease, cor pulmonale may develop, resulting in increased heart size and hilar enlargement due to enlarging pulmonary arteries. MR imaging can differentiate between hilar enlargement due to large pulmonary arteries and enlargement due to large nodes due to chronic infection, a common sign in CF.
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