D

figure 4-57 Adenoid cystic carcinoma of the larynx and trachea. Anteroposterior (A) and lateral (B) tomograms of the larynx and proximal trachea and computed tomography scans at the level of the hyoid bone (C) and proximal trachea (D) reveal a smooth nodular tumor with endophytic growth.

figure 4-58 Adenoid cystic carcinoma of the distal trachea and proximal left main bronchus. A, Anteroposterior tomogram of the trachea and carina reveals a smooth, well-defined mass arising from the left lateral wall of the trachea extending into the proximal left main bronchus. Computed tomography scans of the distal trachea (B, C) and proximal left main bronchi (D, E) demonstrate nodular thickening of the tracheal and left main bronchial walls. F, A postoperative anteroposterior tomogram of the trachea demonstrates a patent anastomosis following a carinal reconstruction.

figure 4-59 Mucoepidermoid carcinoma. Anteroposterior tomogram of the trachea (A) and computed tomography scan of the distal trachea (B) reveal a well-defined rounded mass in the distal trachea. A virtual bronchoscopic image (C) and the gross pathologic specimen (D) reveal an obstructing soft tissue mass in the distal trachea.

figure 4-59 Mucoepidermoid carcinoma. Anteroposterior tomogram of the trachea (A) and computed tomography scan of the distal trachea (B) reveal a well-defined rounded mass in the distal trachea. A virtual bronchoscopic image (C) and the gross pathologic specimen (D) reveal an obstructing soft tissue mass in the distal trachea.

Carcinoid Tumors. Carcinoid tumors are neuroendocrine tumors derived from Kulchitsky's cells.88 The typical carcinoid tumor represents the lowest grade subtype of a spectrum of tumors that includes the more aggressive atypical carcinoid tumor and the highly malignant small cell carcinoma. Typical carcinoids present in the fifth and sixth decades and tend to arise in the central bronchi, peripheral lung (10%), and rarely in the trachea. They tend to be smooth, well-defined, round masses that present as a nodular-filling defect, and may be associated with atelectasis, distal pneumonia, and/or bronchiectasis if they cause bronchial obstruction (Figure 4-60). Atypical carcinoid tumors tend to present in the sixth and seventh decades of life, may be either central or peripheral in the lung, and have a tendency to metastasize to regional hilar and mediastinal lymph nodes (Figure 4-61). Small cell carcinomas are extremely malignant tumors that present in the seventh and eighth decades. They are usually associated with large, bulky central hilar and mediastinal lymphadenopathy and distant metastases at the time of diagnosis. CT scans often reveal a small peripheral primary tumor within the lung, generally not visible on routine chest radiographs.

Carcinoid tumors have several distinguishing features on imaging studies. Typical carcinoid tumors generally exhibit slow growth and may contain calcifications. Carcinoid tumors are highly vascular and will demonstrate a high degree of contrast enhancement with iodinated contrast on CT scans (Figure 4-62).

figure 4-60 Typical carcinoid tumor. Posteroanterior chest radiograph (A) and anteroposterior tomogram (B) reveal an obstructing mass in the left main bronchus with partial volume loss in the left lung. C, A contrast enhanced computed tomography scan demonstrates a focal mass within the left main bronchus (arrow). D, An octreotide scan of the chest demonstrates a focal area of intense uptake in the left hilum (arrow).

figure 4-60 Typical carcinoid tumor. Posteroanterior chest radiograph (A) and anteroposterior tomogram (B) reveal an obstructing mass in the left main bronchus with partial volume loss in the left lung. C, A contrast enhanced computed tomography scan demonstrates a focal mass within the left main bronchus (arrow). D, An octreotide scan of the chest demonstrates a focal area of intense uptake in the left hilum (arrow).

figure 4-61 Atypical carcinoid tumor. Postero-anterior chest radiograph demonstrates a peripheral mass in the right upper lobe, associated with right hilar adenopathy.

figure 4-61 Atypical carcinoid tumor. Postero-anterior chest radiograph demonstrates a peripheral mass in the right upper lobe, associated with right hilar adenopathy.

figure 4-62 Typical carcinoid tumor. A, Posteroanterior chest radiograph demonstrates a left hilar mass. B, Computed tomography scan with contrast enhancement reveals intense enhancement of the carcinoid tumor in the left lower lobe bronchus.

Because somatostatin receptors are found in carcinoid tumors, radionuclide-coupled somatostatin analogues such as 123I-Tyr3-octreotide and mIn-octreotide can be used to identify carcinoid tumors. This diagnostic approach is helpful in identifying occult carcinoid tumors in those patients who present with clinical symptoms referable to serotonin, adrenocorticotropic hormone, or bradykinin production.

Mesenchymal Tumors

Mesenchymal tumors are rarely reported to occur in the trachea, and tend to occur in young adults. Fibrosarcoma, leiomyosarcoma, chondrosarcoma, hemangioendotheliosarcoma, and lymphomas have been reported (Figure 4-63).89 Except for calcifications in chondrosarcomas, there are no specific characteristics with which to differentiate mesenchymal tumors from other malignancies (Figure 4-64).

Secondary Malignant Tumors

Carcinomas, especially papillary and follicular types arising from the thyroid gland, may invade the larynx and cervical trachea in up to 5% of cases. The trachea may also be invaded by tumors of the esophagus and lung. The delineation of the extent of these tumors is best accomplished with CT and MRI (Figure 4-65).79,80

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