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Thoracic Imaging |
1 From the Departments of Radiology (T.S.K., K.S.L.) and Diagnostic Pathology (J.H.), Samsung Medical Center, College of Medicine, Sungkyunkwan University, 50, Ilwon-Dong, Kangnam-Ku, Seoul 135-710, Korea; the Department of Radiology, College of Medicine, Seoul National University, Korea (J.G.I., J.B.S.); the Department of Radiology, Sanggye Paik Hospital, Seoul, Korea (J.S.K.); the Department of Radiology, Asan Medical Center, College of Medicine, Ulsan University, Seoul, Korea (H.Y.K.); and the Department of Radiology, Kangdong Sungshim Hospital, Seoul, Korea (S.W.H.). Received August 5, 1998; revision requested September 25; final revision received December 17; accepted March 25, 1999. Address reprint requests to K.S.L. (e-mail: kslee@smc.samsung.co.kr).
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Abstract |
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MATERIALS AND METHODS: Chest radiographic and CT findings and clinical features of 12 histopathologically proved mucoepidermoid carcinomas in 12 consecutive patients (five male, seven female; age range, 9–72 years; mean age, 36 years) were reviewed retrospectively.
RESULTS: The tumors were located at the distal trachea (n = 1) or at a main (n = 2), lobar (n = 1), or segmental (n = 8) bronchus. On chest radiographs, the tumors appeared as central masses with postobstructive pneumonia or peripheral atelectasis in four patients and as solitary pulmonary or endotracheobronchial nodules in eight. At CT, the tumors were all smoothly oval (n = 6) or lobulated (n = 6) in shape (ranging 9–40 mm in diameter), adapting to the branching features of the airways. Punctate calcification within the tumor was seen in six patients. Neither metastasis nor recurrence was seen after the surgical resection (follow-up of 8–103 months; mean, 30 months).
CONCLUSION: Mucoepidermoid carcinoma of the tracheobronchial tree, usually located in a segmental bronchus, appears at CT as a smoothly oval or lobulated airway mass. It adapts to the branching features of the airways.
Index terms: Bronchi, CT, 671.12111, 671.12112 • Bronchi, neoplasms, 671.12111, 671.12112, 671.3113, 671.3115, 671.3116 • Trachea, CT, 671.3113 • Trachea, neoplasms, 671.12111, 671.12112, 671.3113
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Introduction |
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Reported radiographic findings of the bronchial mucoepidermoid carcinoma consist of a solitary nodule or a mass with or without findings of postobstructive pneumonia or atelectasis (6,7). Tracheal mucoepidermoid carcinoma may be seen as a localized endoluminal mass contrasting with the surrounding endoluminal air column.
Computed tomographic (CT) findings of the mucoepidermoid carcinoma of the tracheobronchial tree have been described in several case reports (8–10). Our study was aimed at determining the chest radiographic and CT findings and the clinical features of mucoepidermoid carcinoma in the tracheobronchial tree in 12 consecutive patients.
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MATERIALS AND METHODS |
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Both the initial chest radiographs and CT scans were available in all patients and were obtained within 5 days of each other (mean, 2.9 days). The chest radiographs were obtained by using a standard posteroanterior projection with a high-kilovoltage technique (125 kVp, 5 mAs, 10–12:1 grid ratio). The CT scans were obtained with a variety of machines, but mainly with a model 9800 or CT HiSpeed Advantage scanner (GE Medical Systems, Milwaukee, Wis) or Somatom Plus S scanner (Siemens Medical Systems, Erlangen, Germany). The helical technique (7–10-mm collimation, pitch of 1) was used and covered the area from the lung apices to the middle portion of both kidneys. Additional thin-section (1.0-mm collimation) scans were obtained when the lesion was a solitary nodule. Contrast medium–enhanced (iopamidol [Iopamiron 300, Bracco, Milan, Italy]; 30-g injection; n = 12) and nonenhanced (n = 6) CT scans were obtained. The chest radiographs and CT scans were analyzed simultaneously, retrospectively, and jointly by two chest radiologists (T.S.K., K.S.L.), and the decisions on the findings were reached by a consensus.
The analysis of the chest radiographs included the location of the main tumor and examination for the presence of post-obstructive pneumonia or atelectasis. When there was no evidence of associated postobstructive pneumonia or atelectasis, the lesion was regarded as a solitary nodule (less than 3 cm in diameter) or as a mass (3 cm or more in diameter).
The CT analysis included determination of the airway location, shape, and size and determination of the attenuation coefficient of the tumor. Tumors were subcategorized by location as tracheal or as main, lobar, segmental, or subsegmental bronchial. The tumors were also subcategorized according to shape as round, oval, or lobulated. Both the short and long diameters of the tumor were included in the measurement. When the tumors were located in a lobar or segmental bronchus and were oval or lobulated, the direction of the longest diameter of the tumor was compared with that of the branching airways (parallel or not).
Attenuation of the tumor was compared with that of the chest wall muscle before and after the injection of contrast medium. Presence of postobstructive pneumonia, bronchial dilatation, mucoid impaction, or atelectasis was also described. The presence and type of intratumoral calcification were also recorded. By reviewing additional expiratory thin-section CT scans (1–2-mm collimation, 3–5-mm intervals, and reconstruction with a bone algorithm) obtained in four patients, the presence of air trapping was evaluated by identifying the localized area of low attenuation and the small vessels within this area.
In all patients, the tumors were resected surgically, and histopathologic specimens were available. An experienced lung pathologist (J.H.) reviewed the specimens. At histopathologic examination, the histologic grade (low or high) (1–3,6) of the tumor and the presence of the intratumoral calcification, tumor necrosis, and extraluminal parenchymal component of the tumor were evaluated.
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RESULTS |
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Radiographic Findings
The tumors were located in the distal part of the trachea (n = 1) (Fig 1) or in a main (n = 2), lobar (n = 1), or segmental (n = 8) bronchus (Table). On posteroanterior chest radiographs, the tumors were seen as an endotracheal or endobronchial nodule (n = 3), a solitary pulmonary nodule or mass (n = 5), a mass with postobstructive pneumonia or atelectasis (n = 3), or a mass with a distal cavitary lesion (n = 1).
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In one patient, the tumor showed mild, diffuse areas of high attenuation (mean, 80 HU) in addition to punctate calcifications at nonenhanced CT. The tumor turned out to have diffuse microcalcification at the histologic examination. Punctate calcification within the tumor was seen in six of 12 patients (including the patient just described) at nonenhanced CT.
The tumors in all patients were homogeneous and showed mild enhancement after the administration of the contrast medium; the attenuation was slightly less than (n = 1), the same as (n = 10), or slightly more than (n = 1) that of the chest wall muscle.
The measurement of Hounsfield unit data was possible in three patients. The attenuations of these lesions at nonenhanced CT were 20, 20, and 80 HU. The lesions were mildly enhanced to 30, 45, and 90 HU, respectively. (The actual increments were 10, 25, and 10 HU, respectively.)
Associated CT findings suggestive of airway disease were seen in 10 patients and included distal bronchial dilatation with mucoid impaction (n = 6), postobstructive pneumonia (n = 4), air trapping (n = 3), and subsegmental atelectasis (n = 2) (Figs 2, 3). A peripheral area of hypoattenuation or a crescent of air was also noted around the tumor, which was suggestive of a residual lumen of an ectatic bronchus occupied by the endobronchial tumor (n = 2) (Figs 2, 3). No mediastinal or hilar lymph node enlargement was observed.
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Intratumoral microscopic calcification was noted in seven patients. All six patients with punctate calcification on nonenhanced CT scans had histologic specimens that showed microscopic calcification. In the remaining patient with microcalcification, the nonenhanced CT scan did not reveal any gross calcification.
No tumor necrosis was observed. There was no metastatic regional lymphadenopathy. The detailed histopathologic record for sampled lymph nodes was available in four patients in whom eight to 30 regional lymph nodes all showed negative results when examined for malignancy.
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Histologically, mucoepidermoid carcinoma of the tracheobronchial tree consists of variable proportions of mucus-secreting cells, squamous cells, and so-called intermediate cells that show no particular differentiating characteristics (1). The tumor is histopathologically classified as a low- or high-grade malignancy. Mitoses, nuclear pleomorphism, and necrosis are usually absent or minimal (less than five mitoses per 50 high-power fields) in low-grade mucoepidermoid carcinomas (1,3). In high-grade tumors, mitoses are increased, averaging four per 10 high-power fields, and nuclear pleomorphism, hyperchromasia, and cellular necrosis are present (1,2,6,11). The tumor in the high-grade form invades the pulmonary parenchyma in nearly 46% (six of 13) of the cases (6). In our series, all low-grade mucoepidermoid carcinomas were well confined within the bronchial wall, and three of six (50%) high-grade tumors showed focal parenchymal involvement at pathologic examination.
It has been reported that patients with mucoepidermoid carcinoma range in age from 4 to 78 years, but nearly half are younger than 30 years (1,6,12). In our study, four of 12 patients were younger than 30 years (age range, 9–72 years; mean age, 36 years). Patients with mucoepidermoid carcinoma usually present with symptoms and signs of irritation in the large airways or obstruction (cough, hemoptysis, wheezing, and recurrent pneumonia), but 9%–28% are asymptomatic (1). In our study, three of 12 (25%) patients had no symptoms.
It is known that low-grade mucoepidermoid carcinomas grow slowly and are noninvasive and therefore rarely metastasize to regional lymph nodes or remote sites (1,2,6,13–15). In one study (6), only 2% (one of 45) of low-grade tumors and 15% (two of 13) of high-grade tumors metastasized to the regional lymph nodes. Completely resectable low-grade tumors generally have an excellent prognosis without recurrence or development of metastases (1,2,6).
The high-grade form is known to have better prognosis than that of the common bronchogenic carcinomas (6,7). In a study of 13 patients with the high-grade form of mucoepidermoid carcinoma (6), only three patients died of the disease (including two patients with regional lymph node metastases). In our series, there was no metastasis in the regional lymph node, even in patients with high-grade forms. In one patient with the high-grade form, in whom CT scans prior to admission were available, it took 23 months for the tumor to double its size. This finding demonstrates the slow growth rate. Findings of the overall follow-up examinations confirmed the excellent prognosis of the tumors in our study (no evidence of tumor recurrence or metastasis during the mean follow-up of 30 months).
Radiographic manifestations of 58 cases of tracheobronchial mucoepidermoid carcinoma reviewed by Yousem and Hochholzer (6) consisted of a solitary nodule or mass in 41 cases (71%) and "pneumonic consolidation" in 16 cases (28%) (one case showed no abnormality on chest radiographs) (7). In our series, the prevalence (four of 12 patients [33%]) of postobstructive pneumonia or atelectasis on chest radiographs was similar to that in the study by Yousem and Hochholzer (6).
Mucoepidermoid carcinoma of the lung, an uncommon tracheobronchial tumor, manifests as a polypoid mass in the lumen of a main, lobar, or segmental bronchus. In our study, it was difficult to predict the exact endobronchial location of the tumors on chest radiographs, especially when they were present at the level of the segmental bronchus. When the tumor manifested as a solitary pulmonary nodule without any other associated findings, the radiographic finding was nonspecific and was not different from that of other benign and malignant nodules.
However, at CT, there were several clues that helped us to determine the endobronchial location of the tumors. With all tumors being nonspherical, the direction of the longest diameter of the tumor was parallel to the direction of the branching pattern in the corresponding airways containing the tumor. Associated findings of distal bronchial dilatation with mucoid impaction, postobstructive pneumonia, subsegmental atelectasis, or air trapping were suggestive of an endobronchial mass. Additional ancillary findings that indicated the endobronchial location of the tumors were areas of peripheral lucency or a crescent of air around the tumor. The findings were suggestive of a residual lumen of an ectatic bronchus that was occupied by the endobronchial tumor.
Foci of calcification or ossification have been reported to be present within the tumor (1). In our series, punctate calcification within the tumor was seen in six of 12 tumors (50%) on CT scans, whereas microscopic calcification was seen in seven of 12 tumors (58%) at histologic evaluation. The incidence of calcification in mucoepidermoid carcinoma of the lung was much higher than that of the more common forms of the pulmonary carcinomas (up to 14% [16]).
Mucoepidermoid carcinoma of the tracheobronchial tree shows CT findings similar to those of the bronchial carcinoid tumors. According to Zwiebel et al (17), bronchial carcinoid tumor also is associated with frequent postobstructive pneumonia or atelectasis, and the shape of the tumor is frequently nonspherical, with its long axis parallel to that of the nearest major bronchovascular bundle. The overall rate of intratumoral calcification of carcinoid tumor was 26% (eight of 31) (17). However, the tumor is known to be vascular, and marked enhancement of the tumor has been noted at CT (18,19), whereas mucoepidermoid carcinoma showed only mild enhancement in our series.
Adenoid cystic carcinoma, which is the second most common malignant tumor of the trachea and main bronchi (squamous cell carcinoma is the most common) and a kind of salivary gland–type airway tumor, can also be differentiated from mucoepidermoid carcinoma because of its frequent extraluminal extension. In a series of six cases of adenoid cystic carcinoma in the trachea (20), CT images demonstrated extratracheal extension in all cases. Moreover, adenoid cystic carcinomas usually arise in the lower trachea, main stem bronchi, or lobar bronchi. In our study, all mucoepidermoid carcinomas appeared as smoothly oval or lobulated intraluminal masses in the airways, and they were more likely to appear in the segmental bronchi.
In summary, mucoepidermoid carcinoma in the tracheobronchial tree is a rare airway tumor and is more common in the segmental bronchi than in the trachea or main bronchi. On chest radiographs, the tumor appears as a central mass with or without postobstructive pneumonia and/or peripheral atelectasis or as a solitary pulmonary nodule. Prediction of the endoluminal location of the tumor is plausible at CT, even when the tumor is located within a segmental bronchus. It appears as a sharply marginated oval or lobulated intraluminal mass adapting to the branching features of the airways. Postobstructive pneumonia or distal bronchial dilatation with mucoid impaction is frequently associated. Punctate calcification within the tumor is seen in about half of the patients. The tumor shows mild contrast medium enhancement. Metastasis to the regional lymph node is rare, and the prognosis is excellent.
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Footnotes |
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