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Original Research |
1 Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine, 388-1, Pungnap-2dong, Songpa-gu, Seoul 138-736, South Korea.
Received September 25, 2004;
accepted after revision November 15, 2004.
Address correspondence to J. B. Seo
(seojb{at}amc.seoul.kr).
Abstract
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MATERIALS AND METHODS. We retrospectively reviewed 401 contrast-enhanced chest CT scans of 147 consecutive patients (male-female ratio, 123:24; mean age, 60 years) who underwent pneumonectomy (right, 60; left, 87) from 1996 to 2002 in our institution. CT findings were analyzed for the presence or absence of a filling defect in the vascular stump and its size, shape, and interval change on follow-up CT. CT findings were also evaluated for the length of the vascular stump and the presence of embolism in the contralateral pulmonary arteries, pneumonia, bronchopleural fistula, and bronchiolitis obliterans with organizing pneumonia. Intrathoracic or stump recurrence was also assessed in patients with lung cancer. The medical records of lung cancer patients were reviewed for the cause of pneumonectomy and stage and cell type of cancer at surgery. Statistical tests were performed to determine the relationship between the filling defect and other radiologic and clinical findings.
RESULTS. A filling defect in the vascular stump was seen on CT scans of 18 patients after pneumonectomy (12%), and all had undergone the surgery for lung cancer. It was more frequently found in the right-sided stump (23.3%) than in the left-sided stump (4.6%) (p = 0.001). The vascular stump was longer in patients with a filling defect (37.2 ± 6.8 [1 SD] mm) than those without this finding (25.0 ± 12.5 mm) (p < 0.001). Other radiologic and clinical findings were not significantly related to the presence of the filling defect in the vascular stump.
CONCLUSION. A filling defect in the pulmonary arterial stump seen on CT after pneumonectomy is thought to be an in situ thrombus caused by stasis of blood flow and is not related to pulmonary embolism, tumor recurrence, or other complications after pneumonectomy.
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The study population consisted of 123 men and 24 women, with a mean age of 60 years (range, 28-81 years). Sixty patients underwent right pneumonectomy and 87 patients, left pneumonectomy. The causes of pneumonectomy included lung cancer (n = 136), pulmonary tuberculosis (n =4), mesothelioma (n = 2), sarcoidosis (n = 1), bronchiectasis (n = 1), pleural synovial sarcoma (n = 1), malignant fibrous histiocytoma (n = 1), and metastasis from rectal cancer (n = 1). We reviewed 401 contrast-enhanced chest CT scans of 147 patients for the presence of a filling defect in the pulmonary arterial stump (mean, 2.7 CT scans per patient). The mean time interval between surgery and CT ranged from 0.1 to 64.4 months (mean, 13.6 months). CT scans were obtained using various helical CT scanners with a pitch of 1.5 or 2 and a section thickness of 5-10 mm. The scanning parameters varied depending on the indications. All scans were obtained 35 sec after administration of 100 mL of a 300 mg I/mL IV contrast medium (Omnipaque [iohexol], Amersham Health) at a rate of 2.5 mL/sec.
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Data were presented as a range and mean or as a percentage of patients in a group. The patients were divided into two groups according to the presence or absence of a filling defect in the pulmonary arterial stump. The relationships between the presence or absence of a filling defect in the stump and the other radiologic and clinical findings were assessed using Pearson's chi-square test, Fisher's exact test, Student's t test, and multiple logistic regression tests. All statistical analyses were performed using standard statistical software (SPSS [version 10.0], Statistical Package for the Social Sciences) for Windows (Microsoft).
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Follow-up CT scans were available in 13 of the 18 patients with a filling defect on the initial CT scans (mean follow-up period, 26 months; range, 2-34 months; 7.5 CT scans per patient). On follow-up CT scans, the size of the filling defect had decreased (Figs. 2A, 2B and 2C) or showed no change in eight patients (62%) and had increased in five patients (38%). Reviews of the clinical data failed to yield laboratory results or symptoms suggesting an increase in the size of the filling defect.
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Since Chuang et al. [1] reported two cases of filling defect in pulmonary arterial stump with lethal embolization to the contralateral lung in patients after right pneumonectomy in 1966, this finding was once thought to be a part of a thromboembolic event [1, 2]. However, other investigators assumed this finding might represent postsurgical in situ thrombosis rather than thromboembolic disease or intrathoracic recurrence [3, 5]. Most recently, it was reported that a filling defect in the vascular stump after combined right middle and lower lobectomy had not changed during the 6-month follow-up [4].
In most instances, there is no clear method even at autopsy to separate old organized pulmonary emboli from thrombi formed in situ [6]. Also, in our study, no pathologic confirmation was obtained. However, we presume that a filling defect most likely represents in situ thrombus rather than pulmonary embolism for the following reason: Of 18 patients with filling defects in the vascular stump, there was only one pulmonary thrombus found in areas remote from the stump site, even though CT scans in our study were obtained with relatively thick sections. It has been reported that approximately 75% of the emboli were multifocal in the study involving incidental pulmonary emboli detected on CT scans [7].
In our experience, a filling defect in the arterial stump was not related to the intrathoracic recurrence of lung cancer. Recurrence in the bronchial stump was detected in one patient with and in another without a filling defect in the vascular stump, and although recurrence in other sites was seen in three patients with this finding, it was seen in 19 patients without this finding. Also, in 13 of 18 patients with a filling defect on the initial CT scans, more than half were stable for up to 34 months of follow-up. Differentiation of in situ thrombosis from vascular stump recurrence was not possible in our study because no case of vascular stump recurrence was detected in our series. However, a well-defined soft-tissue lesion located at the end of a vascular stump without evidence of extravascular extension and its stability on follow-up CT scans may suggest that this finding most likely represents in situ thrombosis rather than vascular stump recurrence.
Other radiologic and clinical findings such as pneumonia, bronchopleural fistula, the BOOP reaction, and cancer stage and cell type at surgery in cancer patients were not related to the presence of the filling defect.
The three primary factors (Virchow's triad) in the pathogenesis of thrombosis are stasis of blood flow in the vessels, damage to the intimal surface, and hypercoagulability, and all of these factors can be applied to the patients who underwent pneumonectomy [4]. In our results, on multiple logistic regressions, the only factor associated with arterial stump clot was the length of the stump. Therefore, we presume that blood flow stasis in the stump may be a major contributing factor to the formation of a thrombus in the vascular stump. Surgical material in the arterial stump might be associated with local trauma or inflammation of the vessels. The hypercoagulable state of blood in patients with malignant disease or those who have undergone surgery has been shown in many studies [8, 9].
There are several limitations in our study. First, no pathologic confirmation was obtained. However, it is not possible to obtain pathologic results for those lesions in a clinical situation. Second, the incidence of local recurrence and pulmonary thromboembolism in our study group was low, which weakens the value of our statistical results.
In conclusion, development of a clot in the arterial stump after pneumonectomy is not rare. This phenomenon is probably in situ thrombus, which is not related to pulmonary embolism, tumor recurrence, or other complications after pneumonectomy.
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  C. Kotoulas and S. Lachanis Embolism of the pulmonary artery stump after right pneumonectomy Interactive CardioVascular and Thoracic Surgery, May 1, 2009; 8(5): 563 - 564. [Abstract] [Full Text] [PDF]
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