Cystic fibrosis


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Cystic fibrosis,
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(also called mucoviscoidosis), hereditary systemic disease, affecting exocrine glands, primarily in the respiratory and the gastrointestinal systems. While the presentation may be due to gastrointestinal manifestations or failure to thrive, the commonest presentation is with recurrent chest infection. Almost all patients with cystic fibrosis will develop pulmonary disease. Sinus disease is almost universal, with opaque sinuses on radiography, and the development of nasal polyps.

Thickened mucus plugs the small airways, with resulting obstruction. Infection supervenes, initially usually due to Staphylococcus aureus, followed by Haemophilus influenzae. Subsequent colonisation is by Pseudomonas aeruginosa, with Cepacia Burkholderia seen later. Localized infection damages the mucosa and ciliary function. It also causes bronchial wall damage and bronchiectasis. There is a predisposition for the upper lobes.

This condition, seen mainly in the white population, is inherited as an autosomal recessive disease. The responsible gene is found on the long arm of chromosome 7. There are multiple mutations. If carriers are identified during prenatal screening, the fetus can be tested for common mutations antenatally.

Radiography of the chest shows findings varying from near normality to bronchial wall thickening (Fig.1) and mucous plugging, bronchiectasis (Fig.2) (Fig.3) and bulla formation. Patchy areas of atelectasis may be seen, particularly in younger patients. The cavities of bronchiectasis may be air-filled, or, in infective episodes, fluid filled. Occasionally airfluid levels may be seen. Tension pneumothorax is a life-threatening complication. Pulmonary hypertension may also be seen late in cystic fibrosis. The heart normally looks quite small in chest radiographs of patients with cystic fibrosis, due to hyperinflation, so enlargement raises the possibility of cor pulmonale. Most hilar prominence is due to lymphadenopathy.

Imaging

Radiographic assessment of severity is by standardized scoring. There are several scoring systems in use, most based on hyperinflation, linear and round markings, nodularity and large opacities.

CT scanning is very sensitive for the detection of early changes of bronchiectasis but is not performed routinely. It is used to show the appearance of the remainder of the lung if a lobectomy is considered for apparently localized disease or if there is disproportionate symptomatology relative to the appearances on a chest radiograph. The aim of CT is to look for air trapping. Expiratory sequences are required. In long-standing cystic fibrosis, the bronchial arteries enlarge, with an increase in the bronchial circulation, due to chronic and acute inflammation. Focal infection may erode vessels causing fistula formation between the bronchial and the pulmonary circulation, with thin, fragile walls. These abnormal vascular structures are very susceptible to rupture, with resultant haemoptysis. Bronchial arteriography is usually required to identify the source of haemorrhage, and transcatheter embolization may be useful in treatment.

Treatment of respiratory manifestations of cystic fibrosis include early diagnosis and treatment of infection with antibiotics by aerosol, orally, or often using a long-term central venous line. Mucolytics, particularly Dnase, may be used to improve clearing of secretions. Vigorous chest physiotherapy is important in treatment.


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The Encyclopaedia of Medical Imaging Volume VII
Cystic fibrosis, Fig. 1
10-year-old girl with cystic fibrosis. There is bronchial wall thickening, ring shadows and some nodular opacities.
Cystic fibrosis, Fig. 2
10-year-old boy with cystic fibrosis. There is mild, widespread bronchial wall thickening. In the left lower lobe there is volume loss, with thickening and irregularity of the bronchial walls, typical of bronchiectasis.
Cystic fibrosis, Fig. 3
(a) Chest radiograph and (b) CT scan of a teenager with severe cystic fibrosis. Note the gross bronchiectatic changes in both mid and lower zones, with an apparently small heart due to hyperinflation of the lungs. The CT scan confirms the bronchiectasis and shows in addition areas of air trapping in the lung.