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Original Report |
1 Department of Radiology, Samsung Medical Center, Sungkyunkwan University
School of Medicine, 50, Ilwon-Dong, Kangnam-Ku, Seoul 135-710, Korea.
2 Department of Thoracic Surgery, Samsung Medical Center, Sungkyunkwan
University School of Medicine, Seoul 135-710, Korea.
3 Department of Diagnostic Pathology, Samsung Medical Center, Sungkyunkwan
University School of Medicine, Seoul 135-710, Korea.
Received December 11, 2001;
accepted after revision January 14, 2002.
Address correspondence to K. S. Lee.
Abstract
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CONCLUSION. Intrapulmonary bronchogenic cysts in adults appear on CT as well-defined ovoid lesions with the attenuation of soft tissue or water, similar to their mediastinal counterparts. Associated with these cysts are areas of mosaic low attenuation and bandlike linear attenuation representing histopathologically confirmed emphysema and bronchiolization or fibrotic change or both in the surrounding lung.
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Radiologic findings of mediastinal bronchogenic cysts are well known [1]. The CT findings show the cyst as a well-defined spherical mass—either with or without mass effect—with the attenuation of water or soft tissue. Clinical and surgical findings of pulmonary bronchogenic cysts have been reported [3, 4]. However, little has been reported on the imaging findings of intrapulmonary bronchogenic cysts in adults [1]. The purpose of our study was to describe the CT and pathologic findings of intrapulmonary bronchogenic cysts in adults.
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CT scans were available for all patients. The scans were obtained with a HiSpeed Advantage scanner (General Electric Medical Systems, Milwaukee, WI). Helical CT scans were obtained from the lung apices to the midportion of both kidneys with 7-mm collimation and a pitch of 1. The scans were obtained after IV injection of contrast medium (100 mL of iopamidol [Iopamiron 300; Bracco, Milan, Italy]) at a rate of 2 mL/sec using a power injection (MCT Plus; Medrad, Pittsburgh, PA). The scanning parameters were 120 kVp, 250 mA, and scanning time, 1 sec. High-resolution CT scans were also obtained through the lesion with 1-mm collimation at 5- to 10-mm intervals. The image data were reconstructed with 7-mm collimation and a bone algorithm. Images with both lung window settings (width, 1500 H; level, -700 H) and mediastinal window settings (width, 400 H; level, 20 H) were printed. MR images were available for only one patient, in whom CT scans showed a soft-tissue-attenuation lesion. Both T1-weighted and fast spin-echo T2-weighted images were obtained.
CT and MR images were assessed retrospectively by two chest radiologists. Decisions concerning the findings were reached by a consensus. The CT analysis included the location, size, shape, and marginal and internal characteristics (initial attenuation value, degree of enhancement, and homogeneity) of lesions. The presence or absence of a visible cystic wall and mass effect on the surrounding organs were also evaluated. The longest diameter of the tumor was measured at the level at which the tumor appeared to be the largest on axial images. Characteristics of the margin of the tumor were subdivided into smooth, lobulated, and irregular. The attenuation value of cysts was classified as low (lower than muscle), intermediate (similar to muscle), and high (higher than muscle). The degree of enhancement was expressed with changes in attenuation (H values) on both unenhanced (high-resolution CT) and enhanced (helical CT) scans. Other associated findings, if any, were also described.
Pathologic specimens of the cysts were available in all patients and were reviewed by an experienced lung pathologist. The cystic contents as well as the gross and microscopic findings in the cystic wall were recorded. Pathologic findings in the surrounding lung were also recorded.
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Areas of mosaic low attenuation in the surrounding lung parenchyma of the cystic lesions were seen on high-resolution CT scans in all patients (Figs. 1A,1B,1C,1D,1E and 2A,2B). In four patients, the areas were so extensive that the entire pericystic lung was involved. In the patient with the cyst showing an air—fluid level, the area of mosaic low attenuation was relatively localized and was seen mainly in the inferior portion of the lesion. Associated bandlike linear opacities also were seen in the surrounding lung in four patients. In three patients, high-resolution CT showed the cysts to be associated with an incomplete major fissure.
MR images in the one patient who underwent MR imaging showed a homogenous high-signal intensity without internal septation on both T1-weighted and T2-weighted images (Fig. 1A,1B,1C,1D,1E).
In all patients, the gross pathologic specimen showed a unilocular cyst. None of the patients had cysts that communicated with the bronchial tree. In the patient in whom an air—fluid level was seen on CT, a communication was found between the cyst and the adjacent lung parenchyma. In this particular patient, the surrounding lung showed suppurative inflammation, suggesting a previous infection, and cystic walls were less than 3 mm in thickness. The inner surface was smooth in three patients and trabeculated in the other two. The areas of mosaic low attenuation in the surrounding lung parenchyma on CT corresponded histopathologically to areas of emphysema (Fig. 1A,1B,1C,1D,1E). The bandlike linear opacities in the surrounding lung corresponded to areas of bronchial epithelial metaplasia (bronchiolozation) and fibrosis in the surrounding lung parenchyma (Fig. 1A,1B,1C,1D,1E).
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Nuchtern and Harberg [2] described the typical intrapulmonary bronchogenic cyst as an isolated abnormality not associated with any other anomaly and as usually located in the lower lobes. In our study, we also found that intrapulmonary bronchogenic cysts showed a predilection for forming in the lower lobes (4/5 patients).
We found three cysts that were associated with an incomplete major fissure both on high-resolution CT and at surgery. The relationship between the presence of cysts and an incomplete fissure, however, remains to be clarified.
In our study, CT showed mosaic low-attenuation areas in the lung surrounding the cyst in all patients. The areas were found to correspond to the areas of emphysema at histopathologic examination. The areas of bandlike linear attenuation on high-resolution CT corresponded to the areas of fibrosis with an inner portion of bronchiolization of alveoli. Bronchiolization of alveoli is a histologically distinct lesion that occurs in a variety of abnormal conditions, including inflammation, chemical irritation, and exposure to carcinogens [11]. We think that longstanding multiple episodes of subclinical inflammation may have led to bronchiolization and fibrotic change in the surrounding alveoli in our patients.
It may be difficult to differentiate a bronchogenic cyst from acquired cystic lesions, such as an abscess and infected bulla, especially when the lesions manifested are air-filled or have an air—fluid level. Because there are no specific CT or MR imaging findings that allow easy differentiation, reviewing the patient's clinical history and previous radiologic studies may be helpful [12].
The reported complications of bronchogenic cysts include infection; compressive symptoms, such as dysphagia or arrhythmia; malignant transformation; and the rare but fatal air embolism [4, 13]. Therefore, the appropriate treatment of a bronchogenic cyst may be surgery, especially in patients with a history of repeated infections [2].
The limitations of our retrospective study include a small study population completely composed of patients who had the intrapulmonary bronchogenic cyst surgically removed. Therefore, our results may not represent the generalized CT findings of intrapulmonary bronchogenic cysts.
In summary, an intrapulmonary bronchogenic cyst appears on CT as a well-defined, homogeneous, ovoid lesion with variable attenuation and a smooth or lobulated margin. Infection may lead to an air—fluid level in the cystic lesion. Areas of mosaic low attenuation and bandlike linear attenuation, representing histopathologically confirmed emphysema and bronchiolization or fibrotic change or both in the surrounding lung, are frequently associated with intrapulmonary bronchogenic cysts.
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