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Case Report |
1 Department of Radiology, Taichung Veterans General Hospital, No. 160, Sec. 3,
Taichung Harbor Rd., Taichung 407, Taiwan, R.O.C.
2 Faculty of Medicine, Medical College of Chung Shang Medical University,
Taiwan, R.O.C.
3 Department of Pathology, Taichung Veterans General Hospital, Taichung, Taiwan,
R.O.C.
Received April 30, 2004;
accepted after revision September 14, 2004.
Address correspondence to I.-C. Tsai
(sillyduck{at}vghtc.gov.tw).
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Intracardiac bronchogenic cysts are exceedingly rare with only three cases reported in the literature. Furthermore, no bronchogenic cyst inside the left atrium has been documented. Combined persistent left SVC with intracardiac bronchogenic cyst also is unique. We report such a case based on CT and MRI. Animation of the cardiac cycle from an MRI cardiac functional study and the hemodynamic change associated with the lesion are presented. The possible embryologic explanation also is discussed.
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The chest radiograph was within normal limits. Contrast-enhanced chest helical CT showed a mass lesion approximately 3.5 cm in size in the left atrium (LA). Cylindric bronchiectasis was noted predominantly in the right middle and both lower lobes. Some patches of air-space consolidation also were noted around the bronchiectasis. Superimposed pneumonia was considered. The detailed condition about the intracardiac mass could not be evaluated clearly because of severe volume averaging and motion artifacts. The average attenuation value inside the left atrial tumor was approximately 12 H. Persistent left SVC and absence of the normal right-side SVC also were noted. The patient decided against open-heart surgery because she considered herself too old for major surgery. Therefore, no further management for the incidental mass lesion in the left atrium was performed.
Two years later, follow-up chest CT and cardiac MRI were performed. The patient did not complain about any specific symptoms at this time. The chest CT showed no obvious change in the mass lesion in the LA. The cardiac MRI revealed a 3.5 x 3.2 x 3.0 cm left atrial tumor in cine MRI with true fast imaging with steady-state free precession (true FISP) sequence (Figs. 1A, 1B, 1C, 1D, 1E, 1F, 1G, and 1H), slightly high signal intensity in the T1-weighted image (T1WI), and no significant enhancement in the gadolinium-enhanced T1WI. The left atrium was slightly enlarged. The normal function and movement of the mitral valve were preserved except for minimal mitral regurgitation. Due to a poor signal-to-noise ratio, a traditional T2-weighted image was not acquired. MRI of the heart also showed persistent left SVC draining in to the right atrium via the dilated coronary sinus behind the LA. Minimal bilateral pleural effusion also was noted.
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Midline partial sternotomy with cardiopulmonary bypass was performed. Persistent left SVC was identified and handled with care. While opening the left atrial chamber, a unilocular brown soft cyst was noted and then removed. The location and the relation between the lesion and left atrium were just as predicted by preoperative imaging studies. After incising the capsule, some tan jellylike seromucinous content was found. Under microscopy, the cyst, which was composed of smooth muscle wall, was found to be lined by ciliated pseudostratified or so-called respiratory epithelium. Bronchogenic cyst in the left atrium was diagnosed. The postoperative period was uneventful and the patient was discharged 7 days later. At the time of this writing, the patient's condition is good and she has been receiving regular outpatient follow-up for 8 months.
Just after the operation, the ECG monitor showed paroxysmal atrial fibrillation. Pro-pafenone was given orally, and the paroxysmal atrial fibrillation gradually changed into first-degree atrioventricular block within weeks. The follow-up transthoracic echocardiogram showed a dilated coronary sinus, mild tricuspid regurgitation, and a 20-mm Hg peak systolic pressure gradient. The gradient was decreased after which no more pulmonary regurgitation could be identified. Thus, the pulmonary hypertension and bilateral pleural effusion were considered to be caused by the lesion.
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The location of the bronchogenic cyst can be explained by embryogenesis. Bronchogenic cysts are believed to represent a localized portion of the tracheobronchial tree that becomes separated from normal airways during the branching process and does not undergo further development. Most probably develop between the 26th and the 40th day of intrauterine life, during the most active period of airway development. As in bronchopulmonary sequestration, the timing of the abnormal budding may determine the eventual location of the cyst: earlier, in the mediastinum; later, within lung tissue [1].
More than 100 case reports about atypical locations of bronchogenic cysts are available in the English-language literature (Medline search, 1966-2004). The frequencies of atypical locations in descending order are: cutaneous (more than 60 cases), retroperitoneal (28 cases), cervical (approximately 18 cases), intra-diaphragmatic (six cases), intrapericardial (six cases), intraspinal (four cases), intracardiac (three cases), and intrapleural cavity (one case).
Only six intrapericardial bronchogenic cysts have been reported. Five of these six cases were symptomatic and hemodynamically altered.
There have been only three intracardiac cases reported in the literature [2-4], which includes one written in Japanese [2]. Therefore, ours is the third case of intracardiac bronchogenic cyst in the English-language literature. Furthermore, ours is the first case of intracardiac bronchogenic cyst to be found in the left atrium (see Table 1). Interestingly, these patients do not have severe symptoms compared with the intrapericardial group. This finding is considered to be related to the great compliance of the heart chambers. Good adaptation occurs while the lesion and the chambers grow together in childhood.
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Notably, the atrial fibrillation in the 68-year-old patient disappeared after the resection of the tumor. It already is known that atrial fibrillation can be caused by atrial enlargement or increased atrial pressure. Therefore, it is possible that the electrophysiology of the atrium was changed by the tumor in this patient. After resection, paroxysmal atrial fibrillation and then first-degree atrioventricular block developed. This probably was related to the inevitable injury while resecting the tumor.
Retrospectively, it is a pity that we did not measure the pre- and postoperative four chamber pressures. Because of this, the origin of the minimal bilateral pleural effusion cannot be definitely confirmed.
While considering a tumor in the cardiac chambers, myxoma, papillary fibroelastoma, rhabdomyoma, fibroma, hemangioma, lipoma, paraganglioma, sarcoma, and lymphoma usually are considered [5]. None of these show no enhancement after gadolinium injection. Their cystic nature contributes to this feature. Therefore, for a nonenhancing cystic tumor in the cardiac chamber, bronchogenic cyst should be in the differential diagnosis list. Other possibilities include cystic change of the above tumors; congenital cystic tumor of the atrioventricular node [6]; and, less likely, cavernous lymphangioendothelioma [7].
Regarding radiologic examinations for bronchogenic cyst patients, MRI and transthoracic and transesophageal echocardiography are the methods of choice. MRI is good for tissue characteristics and 3D anatomic delineation. Echocardiography is good for spatial resolution and hemodynamics. While performing MRI, HASTE, true FISP, and T1-weighted pre- and postgadolinium images are included in our protocol for study of morphologic, functional, and tissue characteristics. In our department, due to poor signal-to-noise ratio, T2-weighted images are not routinely acquired. Otherwise, the cystic content should be shown with homogeneously high signal intensity within the tumor.
In our case, the patient was found to have combined persistent left SVC, bronchiectasis, and left atrial bronchogenic cyst. Persistent left SVC is rare with a prevalence rate of only 0.3% in normal adults and 0.45% in patients with congenital heart disease [8]. Only 15% of persistent left SVC patients show no normal right SVC [9]. The anomaly is believed to be related to the development of the cardiovascular system. When the heart chamber formation in the 24th to 35th day of uterine life is impaired, the left anterior cardinal vein, which normally should regress, persists, while the right SVC, which is composed partly of the right anterior cardinal vein, disappears. During the period of active heart chamber formation, it overlaps with airway development (the 26th to 40th day). We postulate that there might be a minor insult at this critical point and that the abnormal tracheobronchial budding becomes embedded in the forming heart chambers. The regression of the cardinal vein also is impaired.
The association between bronchiectasis and bronchogenic cyst reported in the literature mostly involves congenital cystic types and early disease onset. In our case, the patient sought medical help at the age of 68, which was late in her life. The radiologic findings also suggested an acquired type, which usually is predominant in the middle to lower lobes. Therefore, the condition in our patient may just be coincidental.
Regarding clinical significance, persistent left SVC itself does not produce any physiologic disturbance. However, because these patients tend to have a higher rate of other congenital heart diseases, such as atrial septal defect, special surgical attention is required while doing open-heart surgery. In our case, after the persistent left SVC was identified, the cardiovascular surgeon was especially careful during the surgery to avoid injuring the persistent left SVC and the dilated coronary sinus. No complications have thus far been observed.
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