DOI:10.2214/AJR.04.1515
AJR 2005; 185:985-988
© American Roentgen Ray Society
Filling Defect in a Pulmonary Arterial Stump on CT After Pneumonectomy: Radiologic and Clinical Significance
So Yeon Kim1,
Joon Beom Seo1,
Eun Jin Chae1,
Kyung-Hyun Do1,
Jin Seong Lee1,
Jae-Woo Song1,
Koun-Sik Song1 and
Tae-Hwan Lim1
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
OBJECTIVE. The objectives of our study were to determine the
incidence of filling defects in pulmonary arterial stumps on CT after
pneumonectomy and to evaluate their radiologic and clinical significance.
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.
Introduction
A filling defect in a pulmonary arterial stump may occasionally be seen on
CT after pneumonectomy. It is important to know the radiologic and clinical
significance of this lesion because it may represent an in situ thrombus, an
embolus from deep vein thrombosis, or vascular stump recurrence in cancer
patients. Although a few case reports regarding this phenomenon have been
published
[1-4],
the incidence and clinical significance of this lesion have not been clearly
determined. Recently, to gain a radiologic perspective on this condition, we
retrospectively reviewed 401 contrast-enhanced chest CT scans of 147 patients
who underwent pneumonectomy in our institution. The purposes of this study
were to determine the incidence of a filling defect in an arterial stump seen
on CT after pneumonectomy and to evaluate its radiologic and clinical
significance.
Materials and Methods
Reviewing the medical database, we found 273 consecutive patients who had
undergone pneumonectomy from 1996 to 2002 in our institution. Of these
patients, 147 had one or more CT scans obtained during the postoperative
follow-up period and were entered in our study.
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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Fig. 1 —59-year-old man after right pneumonectomy for squamous cell
carcinoma of lung. Method to measure length of pulmonary arterial stump is
shown. Distance between origin of right or left pulmonary artery and end of
stump (biheaded arrow) is defined as length of pulmonary arterial
stump after pneumonectomy. CT scan obtained 16 months after pneumonectomy
shows flat filling defect at end of pulmonary arterial stump, presumed to be
in situ thrombus.
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The sole criterion for the filling defect was direct visualization of a
soft-tissue-density lesion confined within the pulmonary arterial stump. CT
scans were analyzed for the presence of the filling defect in the pulmonary
arterial stump and its size, shape, and interval change on follow-up CT
studies. The length of the vascular stump
(Fig. 1) and the presence or
absence of embolism in contralateral pulmonary arteries and of other
associated findings such as pneumonia, bronchopleural fistula, or
bronchiolitis obliterans with organizing pneumonia (BOOP) were also evaluated.
In 136 patients who underwent pneumonectomy for lung cancer, intrathoracic or
stump recurrence was also assessed. Medical records were reviewed for the
cause of pneumonectomy and also for the stage of the cancer and the cell type
at surgery in lung cancer patients.
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).
Results
In our experience, a filling defect in the stump was seen on CT scans in 18
(12%) of 147 patients after pneumonectomy. In all 18 patients with a filling
defect, the cause of pneumonectomy was lung cancer. The mean time interval
between surgery and the CT scan showing the filling defect was 14.8 months
(range, 4.4-61.2 months; median, 16.5 months). The shape of the lesion was
variable, from polypoid to flat, and the mean diameter was 18.7 mm (range,
11-26 mm). All of the filling defects were located at the end of the stump,
were confined within the lumen, and had a sharp margin.
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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Fig. 2A —68-year-old man with right pneumonectomy for squamous cell
carcinoma. CT scan obtained 18 months after pneumonectomy shows polypoid
filling defect (arrowheads) in pulmonary arterial stump.
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Fig. 2B —68-year-old man with right pneumonectomy for squamous cell
carcinoma. CT scan obtained 23 months after pneumonectomy shows lesion
(arrowheads) has decreased in size and become flat; these findings
suggest partial resolution of in situ thrombus.
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The relationships between the presence or absence of a filling defect in
the stump and the other radiologic and clinical findings are summarized in
Table 1. A filling defect in
the pulmonary arterial stump was seen in 14 (23.3%) of 60 patients after right
pneumonectomy and in four (4.6%) of 87 patients after left pneumonectomy.
Filling defects were more frequently found in the right-sided stump than in
the left-sided stump (p = 0.001). The mean length of the vascular
stump was 37.2 ± 6.8 (1 SD) mm in patients with a filling defect and
was 25.0 ± 2.5 mm in patients without a filling defect. It was
significantly longer in patients with a filling defect than in those without
this finding (p < 0.001, Student's t test). Other
radiologic findings such as emboli within the contralateral pulmonary
arteries, pneumonia, bronchopleural fistula, and the BOOP reaction were not
significantly related to the presence of a filling defect on CT. In the 136
patients who underwent pneumonectomy because of lung cancer, the stage and
cell type of the cancer at surgery and evidence of intrathoracic recurrence
were not significantly related to the presence of a filling defect. On the
multiple logistic regression test with stepwise selection, only the length of
the stump was a statistically significant factor related to the filling defect
in the stump (odds ratio, 1.077; p = 0.044).
Discussion
In our study, the incidence of a filling defect in the arterial stump after
pneumonectomy was 12%, which indicates that it is not a rare phenomenon.
Invariably this finding was seen in patients who underwent the surgery for
lung cancer and, among radiologic and clinical findings, only the length of
the stump was a statistically significant factor related to this finding.
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.
References
- Chuang TH, Dooling JA, Connolly JM, Shefts LM. Pulmonary
embolization from vascular stump thrombosis following pneumonectomy.
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- Schiller VL, Gray RK. Causes of clot in the pulmonary artery after
pneumonectomy. AJR 1994;163
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CT of in situ vascular stump thrombosis after pulmonary resection for cancer.
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pulmonary emboli detected at helical CT: effect on patient care.
Radiology 1996;201
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Abstract
Introduction
