Mucoepidermoid carcinoma of the lung: common findings and unusual appearances on CT
Article Outline
- Abstract
- 1. Introduction
- 2. Materials and methods
- 3. Results
- 4. Discussion
- Acknowledgments
- References
- Copyright
Abstract
Objectives
This study aimed to analyze the computed tomographic (CT) various findings of mucoepidermoid carcinoma of the lung and to improve the diagnostic efficacy for such tumor.
Materials and Methods
Sixteen consecutive patients with mucoepidermoid carcinoma of the lung confirmed by pathology were reviewed retrospectively. All the patients had undergone unenhanced and contrast-enhanced examinations; one of them also had undergone 18F-FDG PET/CT examinations.
Results
There were 6 males and 10 females with a mean age of 34.1 years.
On CT plain scan, 14 out of 16 cases showed a well-defined endobronchus mass (n=12) or single peripheral nodule (n=2) with obstructive pneumonia or atelectasis (n=4), one case appeared a cavity in the tumor mass, and one presented diffuse circumferential wall thickening. Punctate calcification was observed in four cases (25%). Tumors showed mild (n=4, 25 %), moderate (n=6, 37.5%), and marked (n=6, 37.5%) degrees of contrast enhancement. Two patients had mediastinal lymph node metastasis, and one of them also had bone metastasis.
Conclusions
Mucoepidermoid carcinoma of the lung likely affects young adults. The common findings included a well-defined ovoid or rounded intraluminal mass; and uncommon findings included cavitation, diffuse thickening, or spiculation. Although CT manifestations of it are variable and nonspecific, a well-defined ovoid or lobulated intraluminal or lung peripheral mass with moderate to marked heterogeneous contrast enhancement may suggest the diagnosis of mucoepidermoid carcinoma of the lung. It should be included in the differential diagnosis of regional tumors.
Keywords: Lung, Mucoepidermoid carcinoma, Computed tomography
1. Introduction
Mucoepidermoid carcinoma of the lung is a rare malignant neoplasm. According to a report by Colby et al., it represents about 0.1–0.2% of all pulmonary tumors and usually considered to derive from the minor salivary glands lining the tracheobronchial tree [1], [2], [3], [4]. Only a few radiological reports on mucoepidermoid carcinoma of the lung have been available in the literature [5], [6], [7], and the degree of contrast enhancement differs between reports [6], [7]. In two series on the radiological features of mucoepidermoid carcinoma of lung, Fisher et al. [6] reported mild enhancement in the majority of these tumors (12 cases). However, Ishizumi et al. [7] reported marked enhancement in four out of five cases. The cause of this difference is unknown due to few numbers in the two groups. Therefore, CT manifestations of mucoepidermoid carcinoma have not been well described up to now, and further analysis of the CT characteristics is needed in more cases. The purpose of our study was to discuss the variety of CT findings of mucoepidermoid carcinoma in 16 consecutive patients and the characteristics of enhancement.
2. Materials and methods
The findings of CT or 18F-FDG PET/CT in 16 patients with mucoepidermoid carcinoma of the lung that had been verified by pathology or bronchoscopy were evaluated retrospectively between March 2005 and June 2010. An institutional review board exemption and a waiver of the requirement for written informed consent were obtained to perform this retrospective study.
CT images were obtained with a 16-row multislice-spiral CT (Aquilion 16, Toshiba, Japan). The scan parameters were 23 cm field of view, 256×256 image matrix, 120 kV, 200 mAs; and slice thickness was 5-mm reconstructions. In 16 patients, the CT scan was performed both before and after the administration of the contrast agent. All patients were intravenously injected with 120 ml of a nonionic iodinated contrast agent (iopromide, Ultravist, Schering) at a rate of 2.0–3.0 ml/s. One case also underwent 18F-FDG PET/CT.
Two experienced radiologists who were unaware of the histopathological diagnoses analyzed the CT image characteristics of each lesion including location, shape, size, number, edge, and attenuation of the unenhanced and contrast-enhanced lesions and compared the results with the pathology. In the unenhanced CT images, attenuation or intensity was classified as hypo-, iso-, or hyperintense with respect to the adjacent muscle. The CT attenuation coefficient (Hounsfield unit, or Hu) at mediastinal window was measured on the workstation using the region-of-interest (ROI) technique in CT images by the same operator before and after administration of the contrast agent at the same slice. Regions of necrosis and calcifications were excluded carefully from the ROI; the oval ROI was about 100 mm2 for measurement of CT attenuation coefficient. Measurement of every patient was repeated three times, and the mean CT attenuation coefficient was calculated. In the contrast-enhanced CT images, the degree of enhancement was classified as mild, moderate, or marked enhancement. The difference between pre- and postcontrast Hus was calculated. When the difference between pre- and postcontrast Hus was between 20 and 40 Hus, it was considered as the mild contrast enhancement, between 40 and 60 Hus was considered as moderate contrast enhancement, and over 60 Hus was considered as marked contrast enhancement. Similarly, the difference between pre- and postcontrast Hus of chest muscle in 16 patients was also assessed. After that, the difference between pre- and postcontrast Hus of the tumors was compared with that of the chest muscle.
An expert pathologist, focusing on the histological grade of the tumor, necrosis, and calcifications, reviewed the histopathological findings from all the tumors. The tumors were classified into low and high histological grades according to mitotic activity, cellular necrosis, and nuclear pleomorphism according to the literature [1]. Hematoxylin and eosin were used in all patients; periodic acid–Schiff and Alcian blue stains were used in 11 patients. Diagnosis was confirmed histologically and imununohistochemically.
3. Results
3.1. Clinic data
There were 16 patients (6 men, 37.5%; 10 women, 62.5%) with an age range of 14–62 years (mean 34.1 years). None of the patients were smokers, and no patient had any family history of mucoepidermoid carcinoma. Levels of carcinoembryonic antigen and carbohydrate antigen 125 were high in three patients. Ten patients complained of a cough, five suffered from hemoptysis, four had wheezing, three had fever, and one had chest pain. Two cases were asymptomatic.
3.2. CT manifestations
In the 15 patients in the study, the tumor diameter ranged from 8 to 62 mm. One tumor appeared as a diffuse wall thickening along the trachea and left main bronchus, and measurement of tumor size is difficult. The tumors were located in the trachea (n=2), main bronchus (n=2), lobular bronchus (n=4), segmental bronchus (n=5), trachea and main bronchus (n=1), or the peripheral lung tissue itself (n=2). On unenhanced CT, 12 tumors appeared as single mass with well-defined margins within the endobronchial area (Fig. 1); multiplanar reconstruction showed that the longest diameter of the tumors was parallel to the bronchi and resulted in narrowing of the tracheobronchial tree. In two patients, the scan showed a well-defined peripheral nodule; one of them showed spiculation pleural indentation sign (Fig. 2). In one case, there was a thick-walled cavity within the tumor mass (Fig. 3). One tumor showed a diffuse thickening of the airway wall and invaded the entire thickness of the trachea and the left main bronchial wall with diffuse calcification (Fig. 4). The contour of the tumors was oval (n=6), round (n=4) or lobulated (n=5), or diffuse thickening of the airway wall (n=1). Four of the 16 cases may have led to the obstructive pneumonia or atelectasis that was observed (Fig. 5). Punctate calcifications (Fig. 6) were found in four out of 16 lesions including the patient showing a diffuse thickening of the airway wall described above. Ectatic bronchi arounding mass was found in 2 patients. On enhanced CT, six (37.5%) cases exhibited a marked homogeneous or heterogeneous contrast enhancement (the difference between pre- and postcontrast Hus was 60 Hus, Fig. 6). Six cases (37.5%) showed moderate contrast enhancement (the difference between pre- and postcontrast Hus was 40–60 Hus), and four cases showed mild contrast enhancement (the difference between pre- and postcontrast Hus was 20∼40 Hus) (Fig. 7). The chest wall muscle revealed mild contrast enhancement (the difference between pre- and postcontrast Hus was 15–30 Hus). The degree enhancement of the 12 tumors (75%) was much higher than that of chest wall muscle. Two cases showed metastasis to hilar and mediastinal lymph nodes; one of them also showed pleural metastases (Fig. 7). One scan was also performed using a whole-body 18F-FDG PET/CT study and showed obvious increased 18F-FDG uptakes within the tumor; the standardized uptake value (SUV) was 4 and multiple bone metastases were also found (Fig. 8).
Fig. 1.
Mucoepidermoid carcinoma in a 21-year-old girl. Contrast-enhanced CT reveals a well-defined mass in the trachea, which shows marked heterogeneous enhancement.
Fig. 2.
Mucoepidermoid carcinoma in a 33-year-old woman. CT lung window shows a peripheral node with pleural indentation sign and long speculation at anterior medial basal segment of the left inferior lung.
Fig. 3.
Mucoepidermoid carcinoma in a 62-year-old woman. CT lung window shows a well-defined thick-walled cavity with lobulation at left upper lung.
Fig. 4.
Mucoepidermoid carcinoma in a 56-year-old man. (A) Coronal reformation image shows diffuse circumferential wall thickening along the trachea and left main bronchus with calcification. (B) Hematoxylin and eosin staining (200×) shows the tumor's mucin-secreting cells as well as squamoid cells.
Fig. 5.
Mucoepidermoid carcinoma in a 34-year-old woman. Enhanced CT shows single mass with obstructive atelectasis and consolidation at the anterior segmental bronchus of left upper lobar bronchus with marked enhancement.
Fig. 6.
Mucoepidermoid carcinoma in a 19-year-old girl. Non-contrast-enhanced CT shows a well-defined mass at left inferior lung hilum; punctate calcification is revealed in the tumor.
Fig. 7.
Mucoepidermoid carcinoma in a 53-year-old man. Enhanced CT shows metastases to the pleura of a mucoepidermoid carcinoma in the right middle segmental bronchus.
Fig. 8.
PET/CT images show a multiple focus of abnormal F-18FDG uptake in metastases of multiple vertebral body.
3.3. Pathological manifestations
On gross examination, these tumors were gray-white in color. Fourteen cases showed a well-circumscribed mass. The tumors were oval, round, or lobulated. A thick-walled cavity in the tumor mass was visible in one case. Another case showed a diffuse thickening of the airway wall and invaded the entire breadth of the trachea and left main bronchial wall. Patchy cystic areas were observed in four cases. These findings were consistent with their CT manifestations.
On microscopy, the tumor cells were seen to include epithelioid and intermediate as well as mucus-producing cells arranged in gland-like structures including high histological grade (n=3) and low grade (n=13; Fig. 4B). Periodic acid–Schiff and Alcian blue stains were positive in all 11 patients who had undergone periodic acid–Schiff and Alcian blue stains.
4. Discussion
Rare low-grade malignant tumors of the lung primarily include mucoepidermoid, carcinoid, and adenoid cystic carcinomas. Of these, mucoepidermoid carcinoma has the highest grade of malignancy, as was first reported by Smetana et al. (1952). Yousem and Hochholzer [8] have studied the greatest number of mucoepidermoid carcinomas of the lung (n=56). They found mucoepidermoid carcinoma can affect any age group, but nearly 50% occur in individuals under 30 years of age without gender predominance [8], [9]. In our series, the ages of patients ranged from 14 to 62 years (mean 34.1 years). Four patients were younger than 20 years of age, and only two tumors occurred in an individual older than 60 years at the time of diagnosis. These findings were consistent with the published literature [8], [9]. There were 6 male and 10 female patients in our series. This predominance of females may be due to the low patient numbers in this study. The common symptoms mainly result from bronchial obstruction and include wheezing, dyspnea, hemoptysis, and recurrent pneumonia. A small number of tumors have been discovered incidentally without symptoms; in a study by Fisher et al. [6], about 25% of patients presented without symptoms. In the current study, two (12.5%) patients showed no symptoms [10].
Histologically, mucoepidermoid carcinomas are considered to derive from the serous gland and mucus gland of the trachea and bronchi and are similar to those that arise in salivary gland tissue. Their etiology is still unknown. They can be divided into low-grade and high-grade mucoepidermoid carcinomas on the basis of cellular differentiation and mitotic activity [11]. The tumors are composed of squamous epidermoid, intermediate, and mucous cells. In a study by Yousem et al., 45 of 58 (77.6%) patients had low-grade mucoepidermoid carcinoma. In our study, low-grade mucoepidermoid carcinoma was found in 13 (81.3%) cases, while high-grade mucoepidermoid carcinoma was found in three cases.
CT examinations play an important role in the diagnosis of mucoepidermoid carcinoma [12]. The CT appearance has been reported to be a well-defined oval or lobulated mass with smooth margins arising within the bronchus. In our study, three kinds of CT findings were observed. Firstly, in 14 patients, there was a well-circumscribed mass within the bronchus or peripheral pulmonary nodule. Four cases showed consolidation and atelectasis (25%). Secondly, in one patient, the tumor appeared as a thick-walled cavity. Finally, in another patient, the tumor appeared as a diffuse mass along the trachea and main bronchial wall. Cavitation and diffuse thickening of the trachea wall are extremely rare findings of mucoepidermoid carcinoma of the lung and, to the best of our knowledge, this is the first described manifestation in the literature. Diffuse thickening of the bronchial wall and calcifications were difficult to differentiate from myeloid degeneration. Unlike previous studies [5], [6], [7], in which mucoepidermoid carcinoma appeared to have smooth margins, spiculations and the pleural indentation sign were found in one patient. Mucoepidermoid carcinoma with spiculation and the pleural indentation sign has also been reported for the first time in our study. These characteristics make differentiation of mucoepidermoid carcinoma from bronchiogenic carcinoma difficult, and further observation is needed.
The incidence of calcification in mucoepidermoid carcinoma is much higher than in bronchiogenic carcinoma. Calcification indicates tumor necrosis. Radiological and CT findings of 12 patients reviewed by Fisher et al. [6] showed punctate calcification in six cases (50%) and obstructive consolidation or atelectasis in six patients (50%). In our study, the presence of calcification (n=4, 25%) and consolidation or atelectasis (n=4, 25%) was found, which was lower than that in the study by Fisher et al. [6].
Mucoepidermoid carcinoma of lung demonstrated a different degree of heterogeneous enhancement reported in the literature. In the research performed by Kim et al., all 12 tumors showed mild enhancement; and the authors considered that the enhanced degree of the tumor was similar to chest-wall muscle. However, Ishizumi et al. [7] reported five cases in their group, of whom four showed marked enhancement (attenuation coefficient range 95–139 HU); and they considered that degree of enhancement of the tumor was 2.0 times higher than chest-wall muscle except in only one case with mild enhancement. In our 16 cases, 6 of 16 tumors presented marked enhancement, six showed moderate enhancements, and four cases showed mild enhancement. The degree enhancement of the 12 tumors (75%) was much higher than that of chest wall muscle. This suggests that the majority of these tumors show moderate to marked enhancement and a minority show mild enhancement. Our results support the findings of Ishizumi et al. FDG-PET/CT of mucoepidermoid carcinoma in the lung has been reported in several cases up to now [13], [14], [15]. In the report by Lee et al., the SUV was 6.2 [15]. SUV in our one case was 4.0 due to small numbers in the literature; the PET/CT features of mucoepidermoid carcinoma should be further investigated.
It has been reported that mucoepidermoid tumors grow slowly and have minimal metastatic potential; hilar or mediastinal lymph node and distant metastases are uncommon [8], and so the prognosis is usually excellent. In a study of 12 patients including those with low-grade mucoepidermoid carcinoma (n=6) and high-grade mucoepidermoid carcinoma (n=6), there were no lymph node or distant metastases [6]. In our study, 13 cases (81.3%) were diagnosed as low-grade mucoepidermoid carcinoma without regional lymph node or remote metastases. Three cases were high-grade mucoepidermoid carcinoma; among these, one patient was found to have mediastinal lymph node and pleural metastases and one patient had mediastinal lymph node and bone metastases.
In conclusion, mucoepidermoid carcinoma of lung displays variable radiographic findings including an oval or lobulated intraluminal mass with smooth margins or single peripheral node with moderate to marked enhancement, occasionally appearing as cavity lesion, diffuse thickening of the tracheobronchial tree, or spiculation. Although imaging features are nonspecific, recognition of these imaging features may be helpful in suggesting the possibility of lung mucoepidermoid carcinoma.
Acknowledgments
We thank Mr. Yuxin Wu for the pathological diagnosis in this article.
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PII: S0899-7071(11)00049-0
doi:10.1016/j.clinimag.2011.03.003
© 2012 Elsevier Inc. All rights reserved.
