British Journal of Radiology 74 (2001),959-961 © 2001 The British Institute of Radiology
Anterior mediastinal bronchogenic cyst: demonstration of complicating malignancy by CT and MRI
K Ashizawa, MD1,
T Okimoto, MD1,
T Shirafuji, MD2,
H Kusano, MD3,
H Ayabe, MD2 and
K Hayashi, MD1
1Department of Radiology and 2First Department of Surgery, Nagasaki University School of Medicine, 1-7-1 Sakamoto, Nagasaki 852-8501 and 3Department of Surgery, Ekisaikai Nagasaki Hospital, Nagasaki, Japan
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Abstract
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A case is presented of anterior mediastinal bronchogenic cyst associated with adenocarcinoma arising from the cyst wall. The presence of a solid component in the lower portion of the mass was suspected from CT and confirmed by MRI.
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Introduction
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Bronchogenic cysts are congenital lesions resulting from the embryological development of the tracheobronchial tree and are commonly located in the mediastinum or lung [1]. Malignant transformation is very rare and, to our knowledge, only four cases of mediastinal bronchogenic cysts associated with malignancy have been reported in the English literature [2–5]. We report a rare case of mediastinal bronchogenic cyst associated with adenocarcinoma arising from the cyst wall.
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Case report
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A 42-year-old asymptomatic man was admitted to hospital for further examination of an abnormal opacity on a chest radiograph obtained during a medical check-up. There were no abnormal findings in laboratory tests that included tumour markers. A chest radiograph showed a mass lesion superimposed on the aortic arch (Figure 1
). Unenhanced CT showed an anterior mediastinal mass that was encapsulated and contained multiple punctate calcified foci (Figure 2). The CT number of the mass was 40 Hounsfield units (HU). The mass, except for the capsule, did not show contrast enhancement on CT, consistent with a cystic nature. Although the presence of a solid component was suspected in the lower portion of the mass on CT, this was not a definite finding because of a partial volume effect due to 10 mm slice thickness (Figure 3). On MRI, the mass was hyperintense to muscle, and septal structures were evident on T1 weighted images. On T1 weighted sagittal images, a small hypointense area suggesting a solid component was seen in the lower portion of the mass (Figure 4). This mass was hyperintense on T2 weighted images. Unfortunately, a contrast enhanced study was not performed.
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Figure 2. Unenhanced CT showing an anterior mediastinal mass with a capsule and multiple calcific deposits.
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Figure 3. The presence of a solid component is suspected in the lower portion of the mass on contrast enhanced CT 3 cm caudal to Figure 2 .
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Figure 4. T1 weighted sagittal MRI showing a small hypointense area (arrow), suggesting a solid component in the lower portion of the mass.
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Tumour resection was performed. The resected mass was multiseptal and cystic, and contained a small solid component. On histopathological examination, the cyst wall consisted of bronchus-like tissue including ciliated epithelium, hyaline cartilage and mucoserous glands (Figure 5). Foci of adenocarcinoma were found in the thickened cyst wall, corresponding to the hypointense area on T1 weighted images (Figure 6). The tumour was diagnosed on these pathological appearances as a bronchogenic cyst with foci of adenocarcinoma.
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Figure 5. Histopathological appearance of the cyst wall shows bronchus-like tissue including ciliated epithelium, hyaline cartilage and mucoserous glands (hematoxylin and eosin stain, x 10).
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Figure 6. Foci of adenocarcinoma are seen in the thickened cyst wall (hematoxylin and eosin stain, x 50).
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Discussion
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Bronchogenic cysts are congenital lesions thought to originate from the primitive ventral foregut [1]. They account for 40–50% of all congenital mediastinal cysts and there is a slight male predominance. These tumours are commonly asymptomatic in adults and are discovered incidentally on chest radiographs. In contrast, cough, dyspnoea, stridor and cyanosis often occur in infants.
Bronchogenic cysts are usually found within the lung or the middle or posterior mediastinum [1]. When cysts are located in the anterior mediastinum, as in the present case, it may be necessary to differentiate them from other cystic lesions such as cystic teratoma, thymic cysts or cysts derived from ectopic thyroid glands, which occur in the anterior mediastinum more frequently than bronchogenic cysts. Bronchogenic cysts may have a higher CT number than water because of an increased calcium content of the cyst fluid [6]. In this case the tumour showed a CT number of about 40 HU. This characteristic feature, which may sometimes lead to misdiagnosis as a solid tumour, is an important clue in differentiating bronchogenic cysts from other cystic lesions [6].
Squamous metaplasia is often present in bronchogenic cysts, but malignant transformation is very rare. To the best of our knowledge only four cases of mediastinal bronchogenic cysts associated with malignant transformation have been described in the English literature [2–5]. The histological types of reported malignancy include adenocarcinoma, anaplastic carcinoma and leiomyosarcoma. In the present case, foci of adenocarcinoma were found in the thickened wall of the bronchogenic cyst. Although this small solid component was indeterminate on CT, it would have been appreciated if CT examination with thin slice thickness had been performed. The solid nodule could be recognized as a hypointense area on T1 weighted MRI images. The finding on MRI of a mediastinal bronchogenic cyst associated with malignancy has not been reported. Although malignant tumours harboured in bronchogenic cysts are usually found incidentally after surgery, the possibility of malignancy should be considered when a solid component is seen in a cyst wall on CT or MRI.
The majority of adult patients with bronchogenic cysts are asymptomatic and have a favourable clinical course [7, 8]. However, some cysts may cause symptoms because of infection or compression of surrounding organs such as the oesophagus, bronchi and heart. Complete surgical removal is performed in such cases. Treatment of patients with uncomplicated bronchogenic cysts is controversial. Some authors recommend conservative treatment for asymptomatic cysts in adults [8]. However, an aggressive surgical approach may be acceptable owing to the risk of malignant transformation [7]. Surgical treatment should be chosen in cases where the possibility of malignancy is suspected from imaging findings, as in the present case.
Received for publication February 7, 2001.
Revision received May 9, 2001.
Accepted for publication May 14, 2001.
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References
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Abstract
Introduction
