Bronchopulmonary carcinoid tumours are now classified under the 7th edition TMN staging. Carcinoid tumours are potentially malignant neuroendocrine tumours. The spectrum of disease ranges from low-grade typical carcinoids, through atypical carcinoids to higher-grade large cell and small cell carcinomas. The distinction between these neuroendocrine tumours is based on pathological analysis. The field is also slightly complicated by the relatively small numbers available for analysis and the phenomenon of a preinvasive lesion of diffuse idiopathic pulmonary neuroendocrine-cell hyperplasia (DIPNECH), to be distinguished from genuine metastatic disease.
The presence of multiple small nodules of less than 5 mm in size in association with mosaic attenuation pattern within the lungs in the setting of a known carcinoid tumour should now raise the possibility of DIPNECH.
Bronchial carcinoids are uncommon, constituting less than 5% of pulmonary tumours. The peak age at diagnosis is in the fifth decade, but the age range is wide and includes children. Two forms of bronchial carcinoid are described: typical (85–90%) and atypical (10–15%). Typical carcinoids most commonly arise in central airways. Atypical carcinoids usually arise in the lung periphery. Bronchial carcinoids can invade locally and may metastasise to hilar and mediastinal lymph nodes as well as to the brain, liver and bone. The atypical carcinoids have histological and clinical features intermediate between typical bronchial carcinoid and small cell carcinoma of the lung and have a poorer prognosis.
Bronchial carcinoid may present with wheeze, pneumonia, or haemoptysis. Even when small, tumours may secrete adrenocorticotrophic hormone (ACTH) in sufficient quantities to cause Cushing's syndrome. Carcinoid syndrome is very rare if the tumour is still confined to the lung.
Radiographic appearances vary with location of the tumour. There is no lobar predilection and on rare occasions carcinoids may arise in the trachea. Bronchial carcinoids, particularly those located centrally, may calcify and occasionally ossify. Calcification is seen on CT in up to one-third of cases, but is only occasionally visible on chest radiography.66 Marked contrast enhancement may be seen on CT.
Carcinoids arising in central bronchi (80–90% of cases) often show a larger mass external to the bronchus than within the lumen ('iceberg' lesions), and the extrabronchial component may be visible as a hilar mass (Fig. 1). Central lesions usually produce partial or complete bronchial obstruction, resulting in atelectasis with or without pneumonia. Central bronchial obstruction may be complicated by development of distal bronchiectasis or lung abscess. Occasionally, a bronchial carcinoid in a segmental or subsegmental bronchus may obstruct bronchial secretions, thereby causing a mucocele.
Peripheral lesions (10–20% of carcinoids) present as solitary spherical or lobular nodules, 2–4 cm in diameter, with a well-defined smooth edge (Fig. 1). Noncalcified peripheral bronchial carcinoid tumours closely resemble bronchial carcinomas, both radiologically and cytologically, and are therefore frequently removed surgically in the belief that they are carcinomas.
FIGURE 1 ■ Carcinoid tumour. (A) A tumour is partially occluding the left main bronchus. (B) A well-defined perihilar carcinoid tumour (arrows) is demonstrated anterior to the artery to the right lower lobe. (C) On lung windows there is only a small band of atelectasis in the middle lobe. (D) A small peripheral carcinoid tumour indistinguishable from a number of other causes of a solitary pulmonary nodule.
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