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(Radiographics. 2002;22:351-365.)
© RSNA, 2002

EDUCATION EXHIBIT

Bronchial Carcinoid Tumors of the Thorax: Spectrum of Radiologic Findings1

Mi-Young Jeung, MD, Bernard Gasser, MD, Afshin Gangi, MD, PhD, Dominique Charneau, MD, Xavier Ducroq, MD, Romain Kessler, MD, Elisabeth Quoix, MD and Catherine Roy, MD

1 From the Departments of Radiology B (M.Y.J., A.G., D.C., C.R.), Pathology (B.G.), Thoracic Surgery (X.D.), and Pulmonology (R.K., E.Q.), University Hospital of Strasbourg, 1 place de l’Hôpital, 67091 Strasbourg, France. Recipient of a Certificate of Merit award for an education exhibit at the 2000 RSNA scientific assembly. Received June 6, 2001; revision requested July 5 and received August 31; accepted August 31. Address correspondence to M.Y.J. (e-mail: mi-young.jeung@chru-strasbourg.fr).


   Abstract
Top
 Abstract
LEARNING OBJECTIVES
 Introduction
 Histologic Features
 Radiologic Features
 Conclusions
 References
 
Bronchial carcinoid tumors are neuroendocrine neoplasms that range from low-grade typical carcinoids to more aggressive atypical carcinoids and therefore demonstrate a wide spectrum of clinical behaviors and histologic features. Typical and atypical bronchial carcinoids have similar imaging features. Because most bronchial carcinoids are located in central airways, radiologic findings are usually related to bronchial obstruction. Central bronchial carcinoids manifest as an endobronchial nodule or hilar or perihilar mass with a close anatomic relationship to the bronchus. The mass is usually a well-defined, round or ovoid lesion and may be slightly lobulated at radiography and computed tomography (CT). Associated atelectasis, air trapping, obstructing pneumonitis, and mucoid impaction may also be seen. Peripheral bronchial carcinoids appear as solitary nodules. Calcification is common and is easily visualized at CT. Bronchial carcinoids demonstrate high signal intensity on T2-weighted and short-inversion-time inversion recovery magnetic resonance images. Prognosis of bronchial carcinoids is highly dependent on histologic findings: Atypical carcinoids have certain features that suggest a more aggressive nature. Typical bronchial carcinoids generally have an excellent prognosis, whereas atypical bronchial carcinoids have a worse prognosis. Therefore, understanding the histologic, clinical, and radiologic features of bronchial carcinoids facilitates accurate diagnosis and helps optimize surgical planning.

© RSNA, 2002

Index Terms: Bronchi, CT, 671.1211 • Bronchi, neoplasms, 671.3111 • Bronchi, stenosis or obstruction, 671.3111 • Bronchography, 671.122 • Carcinoid, 671.3111


   LEARNING OBJECTIVES
Top
 Abstract
 LEARNING OBJECTIVES
Introduction
 Histologic Features
 Radiologic Features
 Conclusions
 References
 
After reading this article and taking the test, the reader will be able to:


   Introduction
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
Histologic Features
 Radiologic Features
 Conclusions
 References
 
Bronchial carcinoid tumors are classified as neuroendocrine neoplasms of the lung. They arise in the bronchial and bronchiolar epithelium and may derive from existing Kulchitsky cells, neuroepithelial bodies, or pluripotential bronchial epithelial stem cells (1,2). Bronchial carcinoids are capable of synthesizing, storing, and secreting peptide hormones and neuroamines such as serotonin, adrenocorticotropic hormone (ACTH), somatostatin, and bradykinin (3–5).

Carcinoids occur most frequently in the gastrointestinal tract (90% of cases) (6). They can also occur in the lung, thymus, biliary tract, and ovary. Bronchial carcinoids are uncommon, comprising only 1%–2% of all lung tumors (1,2,7). All carcinoids are considered to be malignant with the potential for metastasis. In the past, the generic bronchial adenoma was used to refer to adenoid cystic and mucoepidermoid carcinoma as well as carcinoids. Today, the term adenoma is considered inaccurate because the tumors are neither uniformly glandular in origin nor consistently benign (2,8).

Bronchial carcinoids range from low-grade typical carcinoids to intermediate-grade atypical carcinoids to high-grade small cell carcinomas and demonstrate a wide variety of clinical behaviors and histologic features (1,9). A recently described large cell neuroendocrine variant (intermediate cell neuroendocrine carcinoma) behaves in a manner somewhere between atypical carcinoid and small cell carcinoma (4,10,11). Bronchial carcinoids affect male and female patients equally over a wide age range, with a mean patient age of 45 years (7,12). In general, patients with bronchial carcinoids are younger than those with common primary pulmonary neoplasms such as bronchogenic carcinoma (7). On average, patients with atypical carcinoids are about 1 decade older than those with typical carcinoids (12,13). Bronchial carcinoids are the most frequent primary pulmonary neoplasm in childhood (14). There is no association with cigarette smoking or the inhalation of other carcinogens (7, 15,16).

Presenting symptoms include cough, fever, expectoration, wheezing, hemoptysis, and chest pain (17). Some patients present with symptoms that simulate asthma (18). Hemoptysis occurs in at least 50% of patients, reflecting the highly vascular nature of these neoplasms (8,19). About 25% of patients are asymptomatic, so that bronchial carcinoids are found incidentally (20). The majority of affected children present with symptoms of wheezing and atelectasis in addition to the characteristic adult triad of cough, hemoptysis, and pneumonitis (14). Rarely, patients may exhibit syndromes related to ectopic hormone production by the tumor, specifically, ACTH (21). Cushing syndrome is seen in only about 2% of bronchial carcinoids (18). Carcinoid syndrome is rare (2%–5% of cases) and is not produced by bronchial carcinoids unless liver metastases are present (3,6). Metastases occur in 15% of bronchial carcinoids and are typically located in the liver, bone, adrenal glands, and brain (19).

Bronchial carcinoids have a characteristic bronchoscopic appearance. Most bronchial carcinoids are in a central location within reach of a bronchoscope. They appear as smooth, cherry red, polypoid endobronchial nodules. The histologic diagnosis is made with bronchoscopic biopsy. Massive hemorrhage following endoscopic biopsy due to the highly vascular nature of carcinoids has been described (17). However, many bronchoscopic biopsies have been performed routinely without added morbidity (20,22). Histologic diagnosis of peripheral tumors can be made with computed tomography (CT)–guided transthoracic needle biopsy (16).

Prognosis is highly dependent on histologic features (23). Typical carcinoids have an excellent outcome, even with hilar or ipsilateral mediastinal lymph node metastasis (20,22). The overall survival rate at 5, 10, and 15 years is reported to be 92%, 88%, and 76%, respectively (20). Patients with atypical carcinoids have a worse prognosis, with 5- and 10-year survival rates of 69% and 24%–52%, respectively (22,24,25). In a study by Gould et al (23), tumor size, histologic subtype, and nodal involvement at initial diagnosis were the factors that most influenced recurrence and outcome. The only effective treatment for a bronchial carcinoid is complete surgical excision of the primary tumor (17,24). Surgical procedures range from radical resection (eg, pneumonectomy, bilobectomy, lobectomy) to conservative excision (eg, segmentectomy, wedge resection, sleeve lobectomy, sleeve bronchectomy) (20). Excellent results may be obtained even in patients with local nodal metastasis that does not preclude definitive surgical treatment (22).

In this article, we discuss, illustrate, and correlate the various histologic, radiologic, and gross pathologic features of bronchial carcinoids.


   Histologic Features
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Histologic Features
Radiologic Features
 Conclusions
 References
 
Typical carcinoids consist of uniform cells arranged in sheets, trabeculae, or small glandlike formations. A rich, fibrovascular stroma that is usually quite fine but may be thick and hyalinized separates the cellular sheets or trabeculae. The cells are polygonal with abundant eosinophilic granular cytoplasm and are arranged in nests or solid sheets (Fig 1). The nuclei are regular and rounded and contain a fine, stippled chromatin and small nucleoli. Typical carcinoids exhibit a wide variety of histologic patterns including spindle cell, trabecular, palisading, glandular, rosette-like, and sclerosing papillary patterns. Mitoses are less numerous or absent altogether (8,19). In addition, these tumors may exhibit dystrophic calcification, bone formation, or amyloid deposition (26).



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  		Figures 1.  Typical carcinoid. Photomicrograph (original magnification, x100; hematoxylin-eosin stain) shows uniform polygonal cells with stippled nuclear chromatin growing in an organoid nesting pattern.

 
Atypical carcinoids resemble typical carcinoids but also have certain histologic and cytologic features that suggest a more aggressive nature. Arrigoni et al (12) defined the following diagnostic criteria for these tumors: increased mitotic activity (ie, at least one mitotic figure in every one to two high-power fields), nuclear pleomorphism and hyperchromatism associated with prominent nucleoli, increased cellularity, disorganized architecture, and tumor necrosis (Fig 2) (1,12). Travis et al (27) modified these diagnostic criteria to include tumors of lower histologic grade. Atypical carcinoids have neuroendocrine morphologic characteristics (eg, two to 10 mitoses per 2 mm2 of viable tumor, areas of coagulative necrosis). They are relatively uncommon, accounting for 11%–24% of pulmonary carcinoids in most series (12,27,28).



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  		Figure 2.  Atypical carcinoid. Photomicrograph (original magnification, x100; hematoxylin-eosin stain) demonstrates nuclear pleomorphism and three mitoses (arrows).

 
Ultrastructural studies demonstrate neurosecretory granules, which are homogeneous in size and are more numerous and generally larger in typical carcinoids than in atypical carcinoids. The results of immunohistochemical staining for neuron-specific enolase and various hormones are usually positive (29).


   Radiologic Features
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Histologic Features
 Radiologic Features
Conclusions
 References
 
Typical and atypical bronchial carcinoids have the same radiologic features, which depend largely on tumor location. About 80% of bronchial carcinoids arise centrally in the main, lobar, or segmental bronchi and demonstrate no specific lobar distribution (30). Radiologic findings include hilar or perihilar masses, endobronchial nodules, findings related to bronchial obstruction, and peripheral nodules.

Hilar or Perihilar Masses
Central bronchial carcinoids most frequently manifest as a hilar or perihilar mass. The mass is usually a well-defined, round or ovoid lesion and may be slightly lobulated at radiography and CT (Fig 3). The tumors range from 2 to 5 cm in size (30–32). Masses with irregular or ill-defined margins are sometimes seen (Fig 4). Rarely, carcinoids will display a more aggressive nature, extending directly to the mediastinal structures. This mediastinal extension can be clearly seen at CT (Fig 4). Multifocal tumors are rarely observed (20,30).



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  		Figure 3.  Central bronchial carcinoid in a 26-year-old woman with hemoptysis. Posteroanterior chest radiograph demonstrates a round nodule located partially within the lateral aspect of the right main bronchus (arrow).

 


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  		Figure 4a.  Typical carcinoid in a 42-year-old man with cough. (a) Posteroanterior chest radiograph reveals a lobulated right hilar and paratracheal mass. (b) Contrast material-enhanced CT scan (mediastinal windowing) shows a precarinal mass with adjacent aortopulmonary nodes. (c) Contrast-enhanced CT scan obtained at a lower level shows an irregular hilar mass extending into the mediastinum.

 


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  		Figure 4b.  Typical carcinoid in a 42-year-old man with cough. (a) Posteroanterior chest radiograph reveals a lobulated right hilar and paratracheal mass. (b) Contrast material-enhanced CT scan (mediastinal windowing) shows a precarinal mass with adjacent aortopulmonary nodes. (c) Contrast-enhanced CT scan obtained at a lower level shows an irregular hilar mass extending into the mediastinum.

 


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  		Figure 4c.  Typical carcinoid in a 42-year-old man with cough. (a) Posteroanterior chest radiograph reveals a lobulated right hilar and paratracheal mass. (b) Contrast material-enhanced CT scan (mediastinal windowing) shows a precarinal mass with adjacent aortopulmonary nodes. (c) Contrast-enhanced CT scan obtained at a lower level shows an irregular hilar mass extending into the mediastinum.

 
Eccentric calcifications are common, especially in central carcinoids, with foci of calcification or even ossification seen at histologic analysis in up to 30% of cases (Fig 5). These calcifications are usually not identified at conventional radiography but are easily identified at CT (31,32). Carcinoids may calcify diffusely and thereby simulate broncholithiasis (33). In fact, it has been suggested that the diagnosis of bronchial carcinoid be made if there is a well-defined, centrally located tumor that narrows, deforms, or obstructs an adjacent airway and contains diffuse or punctuate calcification (31,34). Cavitations are rare (30,35).



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  		Figure 5a.  Central carcinoid in a 26-year-old woman with hemoptysis who had given birth 2 months earlier. (a) CT scan (mediastinal windowing) shows a nodule with eccentric calcifications (arrow) obstructing the posterior segmental bronchus of the right upper lobe. (b) Photograph of a cut section of the surgical specimen shows an endobronchial tumor with focal hemorrhage (arrow).

 


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  		Figure 5b.  Central carcinoid in a 26-year-old woman with hemoptysis who had given birth 2 months earlier. (a) CT scan (mediastinal windowing) shows a nodule with eccentric calcifications (arrow) obstructing the posterior segmental bronchus of the right upper lobe. (b) Photograph of a cut section of the surgical specimen shows an endobronchial tumor with focal hemorrhage (arrow).

 
Carcinoids are characteristically highly vascular. At CT, a carcinoid in a perihilar location with marked, homogeneous contrast enhancement may mimic a pulmonary varix or pulmonary artery aneurysm (Fig 6) (34,36). However, not all carcinoids enhance, and enhancement alone neither allows bronchial carcinoid to be differentiated from bronchogenic carcinoma nor excludes the diagnosis (36). Furthermore, atypical carcinoids may have irregular contours and less uniform contrast enhancement (Fig 7) (34). At ultrafast contrast-enhanced magnetic resonance (MR) imaging, a pronounced and rapid increase in signal intensity has been reported in bronchial carcinoids (37).



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  		Figure 6a.  Typical carcinoid in a 49-year-old woman with a 5-year history of recurrent pneumonia and asthma. (a) Chest radiograph demonstrates a small left perihilar nodule (arrow). (b) High-resolution CT scan (lung windowing) shows a well-defined, round, partially endobronchial nodule (arrow) in the lateral subsegmental branch of the anterior segmental bronchus of the left upper lobe. (c) On a contrast-enhanced CT scan (mediastinal windowing), the nodule (arrow) demonstrates marked contrast enhancement and mimics a vascular structure.

 


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  		Figure 6b.  Typical carcinoid in a 49-year-old woman with a 5-year history of recurrent pneumonia and asthma. (a) Chest radiograph demonstrates a small left perihilar nodule (arrow). (b) High-resolution CT scan (lung windowing) shows a well-defined, round, partially endobronchial nodule (arrow) in the lateral subsegmental branch of the anterior segmental bronchus of the left upper lobe. (c) On a contrast-enhanced CT scan (mediastinal windowing), the nodule (arrow) demonstrates marked contrast enhancement and mimics a vascular structure.

 


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  		Figure 6c.  Typical carcinoid in a 49-year-old woman with a 5-year history of recurrent pneumonia and asthma. (a) Chest radiograph demonstrates a small left perihilar nodule (arrow). (b) High-resolution CT scan (lung windowing) shows a well-defined, round, partially endobronchial nodule (arrow) in the lateral subsegmental branch of the anterior segmental bronchus of the left upper lobe. (c) On a contrast-enhanced CT scan (mediastinal windowing), the nodule (arrow) demonstrates marked contrast enhancement and mimics a vascular structure.

 


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  		Figure 7a.  Atypical carcinoid in a 67-year-old man with hemoptysis. (a) Contrast-enhanced CT scan (mediastinal windowing) demonstrates an irregular mass in the left lower lobe. (b) Photograph of a cut specimen taken from the resected left lower lobe shows an irregular, white peripheral tumor with a distal mucus plug (arrow).

 


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  		Figure 7b.  Atypical carcinoid in a 67-year-old man with hemoptysis. (a) Contrast-enhanced CT scan (mediastinal windowing) demonstrates an irregular mass in the left lower lobe. (b) Photograph of a cut specimen taken from the resected left lower lobe shows an irregular, white peripheral tumor with a distal mucus plug (arrow).

 
Both typical and atypical carcinoids may be associated with hilar or mediastinal lymphadenopathy due to hyperplasia from recurrent pneumonia or metastasis (Fig 4). These lymphadenopathies are well visualized at CT (38). Lymph node metastases occur more frequently with atypical carcinoids (23).

Endobronchial Nodules
Central carcinoids often demonstrate radiologic evidence of an endobronchial component. Although most carcinoids are primarily endobronchial lesions, they may extend into the adjacent parenchyma. Such tumors may display a dominant extraluminal component with a very small endoluminal portion ("iceberg" lesion) (39). CT provides anatomic localization of both intra- and extraluminal components (Figs 6, 8) (34).



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  		Figure 8a.  Typical carcinoid in a 16-year-old boy with chest pain. (a) Posteroanterior chest radiograph shows atelectasis in the left upper lobe. (b) Contrast-enhanced CT scan (mediastinal windowing) helps confirm the complete collapse of the left upper lobe. (c) Contrast-enhanced CT scan obtained at a lower level shows a highly enhanced endoluminal nodule with a small extraluminal component at the origin of the left upper lobe (arrow).

 


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  		Figure 8b.  Typical carcinoid in a 16-year-old boy with chest pain. (a) Posteroanterior chest radiograph shows atelectasis in the left upper lobe. (b) Contrast-enhanced CT scan (mediastinal windowing) helps confirm the complete collapse of the left upper lobe. (c) Contrast-enhanced CT scan obtained at a lower level shows a highly enhanced endoluminal nodule with a small extraluminal component at the origin of the left upper lobe (arrow).

 


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  		Figure 8c.  Typical carcinoid in a 16-year-old boy with chest pain. (a) Posteroanterior chest radiograph shows atelectasis in the left upper lobe. (b) Contrast-enhanced CT scan (mediastinal windowing) helps confirm the complete collapse of the left upper lobe. (c) Contrast-enhanced CT scan obtained at a lower level shows a highly enhanced endoluminal nodule with a small extraluminal component at the origin of the left upper lobe (arrow).

 
Some small carcinoids are located entirely within the bronchial lumen (Fig 9). CT can demonstrate that these lesions are entirely intraluminal without extraluminal components.



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  		Figure 9a.  Typical carcinoid in a 46-year-old man with a 1-year history of wheezing. (a) Posteroanterior chest radiograph demonstrates an endobronchial nodule within the left main bronchus (arrow). (b) CT scan (lung windowing) shows a well-circumscribed, ovoid, completely endoluminal nodule (arrow). (c) Photograph of the hilar side of the resected left lung shows a fleshy tumor within the left main bronchus (arrow).

 


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  		Figure 9b.  Typical carcinoid in a 46-year-old man with a 1-year history of wheezing. (a) Posteroanterior chest radiograph demonstrates an endobronchial nodule within the left main bronchus (arrow). (b) CT scan (lung windowing) shows a well-circumscribed, ovoid, completely endoluminal nodule (arrow). (c) Photograph of the hilar side of the resected left lung shows a fleshy tumor within the left main bronchus (arrow).

 


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  		Figure 9c.  Typical carcinoid in a 46-year-old man with a 1-year history of wheezing. (a) Posteroanterior chest radiograph demonstrates an endobronchial nodule within the left main bronchus (arrow). (b) CT scan (lung windowing) shows a well-circumscribed, ovoid, completely endoluminal nodule (arrow). (c) Photograph of the hilar side of the resected left lung shows a fleshy tumor within the left main bronchus (arrow).

 
Findings Related to Bronchial Obstruction
Because of the central location of carcinoids, initial radiographs usually demonstrate findings related to bronchial obstruction. When a lesion is large enough to partly occlude a bronchus, expiratory air trapping or overinflation can be produced by a ball-valve obstruction (Fig 10) (34). In most cases, obstruction is complete, resulting in peripheral atelectasis and postobstructive pneumonia (30). Radiographs demonstrate the characteristic homogeneous increase in opacity confined to a lobe or to one or more segments, usually with considerable loss of volume (Fig 8). Contrast-enhanced CT allows differentiation of a centrally enhancing carcinoid from adjacent atelectasis or consolidation (36). Recurrent infection distal to the tumor can result in bronchiectasis (Fig 11) or lung abscess.



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  		Figure 10a.  Atypical carcinoid in a 43-year-old man with a 6-month history of wheezing. (a) Expiratory posteroanterior chest radiograph demonstrates air trapping in the left lower lobe. (b) CT scan (lung windowing) shows overinflation and a small area of parenchymal consolidation around the superior segmental bronchus secondary to a nodule (arrow) obstructing the lower lobe bronchus.

 


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  		Figure 10b.  Atypical carcinoid in a 43-year-old man with a 6-month history of wheezing. (a) Expiratory posteroanterior chest radiograph demonstrates air trapping in the left lower lobe. (b) CT scan (lung windowing) shows overinflation and a small area of parenchymal consolidation around the superior segmental bronchus secondary to a nodule (arrow) obstructing the lower lobe bronchus.

 


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  		Figure 11a.  Typical carcinoid in a 17-year-old girl with a 3-year history of cough and recurrent pneumonia. (a) Posteroanterior chest radiograph shows atelectasis in the middle lobe. (b) CT scan (lung windowing) demonstrates bronchiectasis within the completely collapsed middle lobe (arrow).

 


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  		Figure 11b.  Typical carcinoid in a 17-year-old girl with a 3-year history of cough and recurrent pneumonia. (a) Posteroanterior chest radiograph shows atelectasis in the middle lobe. (b) CT scan (lung windowing) demonstrates bronchiectasis within the completely collapsed middle lobe (arrow).

 
Occasionally, retention of mucus distal to the tumor results in mucoid impaction (bronchocele, mucocele) without atelectasis. At chest radiography, mucoid impaction is seen as a round or elliptic area of increased opacity pointing toward the hilum (Fig 12). The lesion is sharply marginated, with branches that look like fingers ("gloved finger shadow"). Conventional radiographs obtained with the x-ray beam perpendicular to the impacted bronchi demonstrate a V- or Y-shaped shadow that radiates from the hilum (Fig 13). However, the lesion is difficult to appreciate on both posteroanterior and lateral chest radiographs because of the varying orientation of the linear branching bronchi (40,41). CT is valuable for revealing mucoid impaction. Mucoid impaction of the airways is easily identifiable by the presence of characteristic focal fluid-filled, nonenhancing, and branching structures, frequently associated with peripheral areas of emphysema. Bronchi distended with mucus appear as a V- or Y-shaped area of increased opacity when oriented transversely (Fig 13) and as a round area of increased opacity when oriented craniocaudally. Intravenous bolus administration of contrast material may help in differentiating the centrally enhancing carcinoid from the peripheral fluid-filled airway (42). Alternatively, these mucus-filled bronchi may demonstrate homogeneous high signal intensity on T2-weighted MR images, which may allow differentiation from tumors (Fig 12) (43).



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  		Figure 12a.  Typical carcinoid in a 32-year-old woman with a 2-year history of recurrent pneumonia. (a) Posteroanterior chest radiograph demonstrates consolidation in the middle lobe. (b) Follow-up posteroanterior chest radiograph obtained 1 month later shows an ovoid area of increased opacity at the previous site of pneumonia (arrow). (c) Contrast-enhanced CT scan (mediastinal windowing) shows a low-attenuation mass in the middle lobe (arrow). (d) T2-weighted MR image demonstrates a bronchocele with homogeneous high signal intensity. The central tumor (arrow) can be distinguished from the distal high-signal-intensity bronchocele. (e) Photograph of a cut specimen of the resected middle lobe (axial section) shows the endobronchial tumor (short arrow) with distal mucoid impaction (long arrow).

 


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  		Figure 12b.  Typical carcinoid in a 32-year-old woman with a 2-year history of recurrent pneumonia. (a) Posteroanterior chest radiograph demonstrates consolidation in the middle lobe. (b) Follow-up posteroanterior chest radiograph obtained 1 month later shows an ovoid area of increased opacity at the previous site of pneumonia (arrow). (c) Contrast-enhanced CT scan (mediastinal windowing) shows a low-attenuation mass in the middle lobe (arrow). (d) T2-weighted MR image demonstrates a bronchocele with homogeneous high signal intensity. The central tumor (arrow) can be distinguished from the distal high-signal-intensity bronchocele. (e) Photograph of a cut specimen of the resected middle lobe (axial section) shows the endobronchial tumor (short arrow) with distal mucoid impaction (long arrow).

 


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  		Figure 12c.  Typical carcinoid in a 32-year-old woman with a 2-year history of recurrent pneumonia. (a) Posteroanterior chest radiograph demonstrates consolidation in the middle lobe. (b) Follow-up posteroanterior chest radiograph obtained 1 month later shows an ovoid area of increased opacity at the previous site of pneumonia (arrow). (c) Contrast-enhanced CT scan (mediastinal windowing) shows a low-attenuation mass in the middle lobe (arrow). (d) T2-weighted MR image demonstrates a bronchocele with homogeneous high signal intensity. The central tumor (arrow) can be distinguished from the distal high-signal-intensity bronchocele. (e) Photograph of a cut specimen of the resected middle lobe (axial section) shows the endobronchial tumor (short arrow) with distal mucoid impaction (long arrow).

 


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  		Figure 12d.  Typical carcinoid in a 32-year-old woman with a 2-year history of recurrent pneumonia. (a) Posteroanterior chest radiograph demonstrates consolidation in the middle lobe. (b) Follow-up posteroanterior chest radiograph obtained 1 month later shows an ovoid area of increased opacity at the previous site of pneumonia (arrow). (c) Contrast-enhanced CT scan (mediastinal windowing) shows a low-attenuation mass in the middle lobe (arrow). (d) T2-weighted MR image demonstrates a bronchocele with homogeneous high signal intensity. The central tumor (arrow) can be distinguished from the distal high-signal-intensity bronchocele. (e) Photograph of a cut specimen of the resected middle lobe (axial section) shows the endobronchial tumor (short arrow) with distal mucoid impaction (long arrow).

 


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  		Figure 12e.  Typical carcinoid in a 32-year-old woman with a 2-year history of recurrent pneumonia. (a) Posteroanterior chest radiograph demonstrates consolidation in the middle lobe. (b) Follow-up posteroanterior chest radiograph obtained 1 month later shows an ovoid area of increased opacity at the previous site of pneumonia (arrow). (c) Contrast-enhanced CT scan (mediastinal windowing) shows a low-attenuation mass in the middle lobe (arrow). (d) T2-weighted MR image demonstrates a bronchocele with homogeneous high signal intensity. The central tumor (arrow) can be distinguished from the distal high-signal-intensity bronchocele. (e) Photograph of a cut specimen of the resected middle lobe (axial section) shows the endobronchial tumor (short arrow) with distal mucoid impaction (long arrow).

 


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  		Figure 13a.  Typical carcinoid in a 19-year-old woman with recurrent pneumonia. (a) Chest radiograph shows a Y-shaped area of increased opacity in the left lower lobe (arrow). (b) CT scan (lung windowing) shows a V-shaped mucoid impaction (arrow). (c) Bronchoscopic image shows a polypoid red nodule that obstructs the entrance to the lower lobe bronchus.

 


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  		Figure 13b.  Typical carcinoid in a 19-year-old woman with recurrent pneumonia. (a) Chest radiograph shows a Y-shaped area of increased opacity in the left lower lobe (arrow). (b) CT scan (lung windowing) shows a V-shaped mucoid impaction (arrow). (c) Bronchoscopic image shows a polypoid red nodule that obstructs the entrance to the lower lobe bronchus.

 


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  		Figure 13c.  Typical carcinoid in a 19-year-old woman with recurrent pneumonia. (a) Chest radiograph shows a Y-shaped area of increased opacity in the left lower lobe (arrow). (b) CT scan (lung windowing) shows a V-shaped mucoid impaction (arrow). (c) Bronchoscopic image shows a polypoid red nodule that obstructs the entrance to the lower lobe bronchus.

 
Peripheral Nodules
In about 20% of cases, a bronchial carcinoid manifests as a solitary pulmonary nodule in the lung periphery distal to the segmental bronchi. These lesions are usually round or ovoid with smooth or lobulated borders (Fig 14). Typical carcinoids in the periphery are slow growing and should be considered in the differential diagnosis of slow-growing solitary pulmonary nodules (30,31). Atypical carcinoids are more likely to occur in the lung periphery and are usually large (Fig 15) (31,35). CT can depict small peripheral tumors 5 mm or less in diameter; such tumors are rarely detected at conventional radiography (Fig 16). Thin-section CT may show the relationship between peripheral carcinoids and the recognizable small airways (Fig 17) (34,44). Bronchial carcinoids have high signal intensity on T2-weighted and short-inversion-time inversion recovery MR images (Fig 18) (37); thus, MR imaging may be helpful in distinguishing small carcinoids from the adjacent normal vascular structures (45). Use of this imaging modality should also be considered when an ACTH-producing carcinoid is suspected but is not found at CT.



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  		Figure 14.  Typical carcinoid in an asymptomatic woman who had undergone colon cancer resection 3 years earlier. Chest radiograph shows a well-defined, peripheral solitary nodule in the lingular segment.

 


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  		Figure 15.  Atypical carcinoid in an asymptomatic 49-year-old man. Contrast-enhanced CT scan shows a well-circumscribed lobular mass with slight enhancement in the lung periphery.

 


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  		Figure 16.  Typical carcinoid in a 67-year-old woman with hemoptysis. CT scan (lung windowing) reveals a small (5-mm-diameter), well-defined peripheral nodule in the middle lobe (arrow).

 


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  		Figure 17.  Typical carcinoid in an asymptomatic 44-year-old man. CT scan (lung windowing) shows a well-defined nodule (arrow) that abuts an adjacent small bronchus.

 


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  		Figure 18a.  Typical carcinoid in an asymptomatic 51-year-old woman. (a) T1-weighted MR image shows a well-circumscribed, round, slightly hyperintense nodule in the middle lobe. (b) On a short-inversion-time inversion recovery MR image, the nodule demonstrates high signal intensity.

 


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  		Figure 18b.  Typical carcinoid in an asymptomatic 51-year-old woman. (a) T1-weighted MR image shows a well-circumscribed, round, slightly hyperintense nodule in the middle lobe. (b) On a short-inversion-time inversion recovery MR image, the nodule demonstrates high signal intensity.

 
Carcinoids have somatostatin receptors and can be imaged with radionuclide-coupled octreotide, a somatostatin analog (46). Known tumor sites have been depicted with this imaging technique in 86% of patients with histologically proved carcinoids (47).

Positron emission tomography is a noninvasive imaging modality with which to obtain physiologic information that can help distinguish benign from malignant lesions. However, in one small series, positron emission tomography did not demonstrate sufficient uptake of 2-[fluorine-18] fluoro-2-deoxy-D-glucose to allow such differentiation, reflecting the low metabolism of bronchial carcinoids (48).


   Conclusions
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Histologic Features
 Radiologic Features
 Conclusions
References
 
Bronchial carcinoids are neuroendocrine tumors that range from low-grade typical carcinoids to more aggressive atypical carcinoids. Typical and atypical bronchial carcinoids have similar gross pathologic and radiologic features. The most common clinical symptoms and radiologic findings in bronchial carcinoids are related to bronchial obstruction. The characteristic imaging features of these lesions are centrally located tumors with well-defined borders and a clearly defined relationship with bronchi. Understanding these features facilitates accurate diagnosis and helps optimize surgical planning.


   Acknowledgments
 
The authors thank Gerard Vetter for his assistance with the preparation of the illustrations.


   Footnotes
 
Abbreviation: ACTH = adrenocorticotropic hormone


   References
Top
 Abstract
 LEARNING OBJECTIVES
 Introduction
 Histologic Features
 Radiologic Features
 Conclusions
 References
 

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