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1
Department of Radiology, Omura Municipal Hospital, Kogashima-chou 133-22,
Omura 856-0817, Japan.
2
Department of Radiology, Nagasaki University School of Medicine, 1-7-1
Sakamoto, Nagasaki 852-8501, Japan.
Received April 17, 2000;
accepted after revision May 31, 2000.
Address correspondence to E. Sueyoshi.
Abstract
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MATERIALS AND METHODS. We reviewed the files of 31 patients with Takayasu's arteritis between January 1990 and March 1999. All patients were followed up for more than 6 months with CT, and the mean follow-up period was 52.9 months (median, 36.0 months). In all patients, initial CT was performed within 6 months of diagnosis of Takayasu's arteritis. The study group comprised 24 female patients and seven male patients; their ages at the first CT examination ranged from 8 to 72 years (mean, 42.6 ± 16.5 years).
RESULTS. Seventeen aortic aneurysms were found in 14 (45.2%) of the 31 patients. Patients with severe calcification of the aorta showed significantly lower incidence of aneurysm formation than those without severe calcification of the aorta (p < 0.05). Of the 17 aneurysms, three were not present at the time of initial CT and appeared during the follow-up period. Nine of 17 aneurysms increased in size during the follow-up period. Three of the nine aneurysms rapidly increased in size and ruptured during the follow-up period. In all three of these aneurysms, aortic wall thickening was identified on CT. The remaining six aneurysms slowly increased in size but did not rupture.
CONCLUSION. Aortic aneurysm associated with Takayasu's arteritis is not rare. The aorta with little calcification has a greater possibility of aneurysm formation in patients with Takayasu's arteritis. Aortic aneurysms with wall thickening can have fatal consequences.
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The long-term prognosis for patients with Takayasu's arteritis is relatively good [6, 7]. However, an aneurysm that forms can progress to a fatal outcome such as heart failure due to aortic valve regurgitation and aneurysm rupture, which is the most frequent fatal course in Takayasu's arteritis [6, 7].
We reviewed cases of aortic aneurysm due to Takayasu's arteritis and evaluated the CT appearances of the aorta using follow-up results. The purpose of this study was to evaluate aortic aneurysm formation and the fate of aortic aneurysms in patients with Takayasu's arteritis.
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Imaging Methods
The initial and follow-up imaging studies were performed with unenhanced
and enhanced CT in all patients. For enhanced CT, a bolus of 100 mL of
non-ionic contrast material was injected. CT was performed on either a 9800
scanner (General Electric Medical Systems, Milwaukee, WI) or a Somatom Plus
32S (Siemens, Erlangen, Germany). Axial images were generated with 5-mm-thick
sections and 5-mm-thick intervals from the top of the aortic arch to the
abdominal aorta. CT follow-up was planned at 4-month intervals (20 patients)
or 6-month intervals (11 patients); CT scans were obtained sooner if warranted
by clinical symptoms. A total of 424 CT studies were performed (mean, 13.7
studies per patient).
Analysis of Images
CT images were evaluated by two experienced cardiovascular radiologists
according to the following features. The final decisions about the findings
were reached by consensus.
Aortic wall thickening.—Aortic wall thickening was defined as the wall being more than 1 mm thick with enhancement on a contrast-enhanced CT image when the previous study had revealed that the aortic wall was either less than 1 mm thick or imperceptible in healthy adults [3, 10].
Calcification of the aortic wall.—Calcification of the aortic wall was classified as none, moderate, and severe. Severe calcification referred to calcification that was completely circumferential and involved thickness of the aortic wall [10].
Diameter of the aorta.—CT measurements were obtained by measuring several diameters with a direct-reading caliper from hard copy images and correcting for appropriate scale [11]. The largest short-axial diameter of the outer contour of the affected aorta was measured. In saccular aneurysm, the diameter from the outer contour of the native aorta to the outer contour of the aneurysm was measured. In the aortic arch, the diameter perpendicular to the curvature was measured.
An aneurysm was defined as a local increase in the diameter of the aorta (increase in diameter of >50% compared with the normal adjacent segment) and was categorized as either fusiform or saccular on the final CT examination [12]. A fusiform aneurysm was defined as circumferential enlargement of the aorta, and a saccular aneurysm was defined as enlargement predominantly involving a portion of the aorta [12].
Growth rate of the aneurysm.—The mean difference in the aortic size between the initial and final examinations was measured at approximately the same aortic portion where the aneurysm had increased in size. The growth rate of the aneurysm was calculated in patients who were followed up for more than 6 months from the initial examination. The growth rate of the aneurysm was obtained by dividing the difference in the diameter between the initial (D1) and the final (D2) measurements by the time interval (T) between the two measurements [11]: growth rate = (D2-D1)/T.
Statistical Analysis
The data are expressed as means plus or minus the standard deviation.
Comparison of the means between the groups was performed with the Mann-Whitney
U test. Statistical comparisons of characteristics were made with
Fisher's exact test because the expected number of cells was less than five.
Analysis was performed with STAT-VIEW software for Macintosh (Abacus Concepts,
Berkeley, CA). A p value of less than 0.05 was considered
significant.
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Aortic aneurysms were present in 14 (45.2% [17 lesions]) of 31 patients with Takayasu's arteritis. Of the 17 aneurysms identified on CT, two were located in the ascending aorta, three in the aortic arch, one in the descending aorta, eight in the abdominal aorta, one from the ascending to the descending aorta, and two from the aortic arch to the descending aorta. The mean diameter of the aneurysms was 4.69 ± 0.79 cm at initial CT examination and 5.90 ± 1.17 cm at final CT examination. None of the patients in this study had both wall thickening and severe calcification.
Of the 14 patients with aortic aneurysms (mean age, 42.1 ± 16.3 years), two were male and 12 were female. Five of these 14 patients had hypertension. During the follow-up period aortic wall thickening was identified in six of the 14 patients, and severe calcification of the aortic wall was seen in two.
Of the 17 patients without aortic aneurysms (mean age, 46.7 ± 16.8 years), five were male and 12 were female; seven had hypertension. During the follow-up period aortic wall thickening was identified in three of the 17 patients, and severe calcification of the aortic wall was detected in nine.
There was a significant difference in the presence of severe calcification of the aortic wall between patients with and those without aortic aneurysms (p < 0.05). However, no significant difference (p > 0.05) in terms of hypertension, aortic wall thickening, sex, or age was detected between the two groups.
Outcome of Aneurysms in Patients with Takayasu's Arteritis
Seventeen aortic aneurysms in 14 patients included one saccular aneurysm
and 16 fusiform aneurysms. Of the 17 aneurysms, three were not present at the
time of the initial CT study and appeared during the follow-up period. During
the follow-up period nine of the 17 aneurysms increased in size and the
remaining eight aneurysms did not increase in size. Of the nine aneurysms that
increased in size during the follow-up period, five were located in the
thoracic aorta and four in the abdominal aorta (mean increase in aortic
diameter, 2.33 ± 1.94 cm). The mean growth rate of aneurysms was 0.04
cm/year.
Three aneurysms rapidly increased in size and ruptured (mean increase in aortic diameter, 4.67 ± 1.53 cm). Of these three aneurysms, two were located in the thoracic aorta and one in the abdominal aorta. The mean growth rate of these three aneurysms was 1.16 cm/year. In all three aneurysms, aortic wall thickening was identified on CT (Figs. 2A,2B,2C and 3A,3B,3C,3D), and neither severe calcification nor hypertension was detected. Steroid therapy was not effective in these patients.
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Six of nine aneurysms slowly increased in size but did not rupture (mean increase in aortic diameter, 1.67 ± 0.41 cm) (Fig. 4A,4B,4C). Three were located in the thoracic aorta and three, in the abdominal aorta. The mean growth rate was 0.03 cm/year. No severe calcification of the aortic wall was identified in any of the six aneurysms. In four of the six aneurysms, aortic wall thickening was identified during the follow-up period. Of the six patients (mean age, 47.5 ± 18.1 years) with these six aortic aneurysms, one was male and five were female; all had hypertension.
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Eight of the 17 aneurysms did not increase in size (Fig. 5A,5B). Four were located in the thoracic aorta and four, in the abdominal aorta. During the follow-up period severe calcification of the aortic wall was identified in two of these eight aneurysms, and aortic wall thickening was identified in three. In the eight patients with these eight aortic aneurysms (mean age, 41.9 ± 11.8 years), one was male, seven were female, and two had hypertension. Comparing the six aneurysms that increased slowly in size with the eight aneurysms that did not increase in size, there was a significant difference in the presence of hypertension (p < 0.01). However, no significant difference was detected between the two groups in terms of severe calcification of the aortic wall, location (thoracic aortic aneurysm versus abdominal aortic aneurysm), aortic wall thickening, age, and initial diameter of the aorta (p > 0.05).
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For the diagnosis of Takayasu's arteritis, conventional angiography has been regarded as necessary. However, a recent report has shown that CT can clearly delineate aortic mural changes that are difficult to detect on conventional angiography including wall thickening, calcification, and mural thrombus [3].
Several reports have described aneurysm formation as being rarely associated with Takayasu's arteritis. The incidence of aneurysm formation in previous reports about patients with Takayasu's arteritis varies from 0% to 87.5% [13, 14]. In the present study, aortic aneurysms were identified in 45.2% of the patients. This result suggests that aneurysm formation is not rare in patients with this disease. However, this finding may have some bias because patients were not selected randomly and because the definition of aneurysm varies. More studies are needed to clarify this issue.
Pathologic studies of Takayasu's arteritis have revealed marked thinning of the media, marked disruption of the elastic fibers, pronounced fibrotic thickening of the adventitia, and intimal thickening, all of which are causes of stenotic lesions [1, 16]. Previous studies described aneurysm formation as possibly caused by the degeneration and weakening of the media [1, 15]. In the present study, there was a significant difference between patients with and those without aortic aneurysms in the presence of severe calcification of the aortic wall. This finding suggests that aneurysm formation can occur in patients without severely scarred changes in the aortic wall because dystrophic calcification represents deposition of calcium in the scarred media and intima [1, 17]. Therefore, the aorta with no or little calcification has a greater possibility of aneurysm formation in patients with Takayasu's arteritis. Kumar et al. [14] reported that the aneurysmal form of Takayasu's arteritis was associated with a higher incidence of aortic valve regurgitation, which may result from enlargement of the ascending aorta and an elevated erythrocyte sedimentation rate. In the acute (early) phase of Takayasu's arteritis, abnormal laboratory findings are often identified, such as persistent elevation of erythrocyte sedimentation rate and a positive C-reactive protein test [1, 18]. Although laboratory findings were not evaluated in detail because our study was based on CT findings, aortic wall thickening is often characteristic on CT during the acute phase of Takayasu's arteritis [1,2,3]. In the present study, there was no significant difference between patients with and those without aortic aneurysms in the presence of aortic wall thickening. One possible reason for this finding could be that steroid therapy was promptly initiated during the acute phase.
In the present study, three of 17 aneurysms rapidly increased in size and ruptured. In all these aneurysms, aortic wall thickening was identified. By showing arterial wall changes, cross-sectional imaging techniques such as CT play an important role in the early diagnosis of Takayasu's arteritis [1,2,3]. Although the clinical and radiologic features of the acute (early) phase of Takayasu's arteritis differ from those of the late (occlusive or pulseless) phase, the two phases of the disease are not clearly different because of the insidious onset of the disease and the relapse of active arteritis in some patients. In some patients with acute phase Takayasu's arteritis, the significant feature is aortic wall thickening. Histologic examination of aortic wall thickening yields findings of florid inflammation in the media and adventitia [1, 10, 19]. According to our results, aortic wall thickening is not necessarily a trigger of aneurysm formation if proper steroid therapy is administered. However, close follow-up examination is needed in aneurysms with aortic wall thickening because this type of aneurysm can be fatal.
In the present study, six of 17 aneurysms slowly increased in size but did not rupture. All six aneurysms were fusiform and similar in appearance to atherosclerotic aneurysms. Comparing the six aneurysms that slowly increased in size with the eight aneurysms that did not increase, we did not find a significant difference in the presence of hypertension (p < 0.01). A previous report described the growth of atherosclerotic aortic aneurysms as being related to the location in the aorta, the initial diameter of the aneurysm, and the patient's age and blood pressure [11]. The growth of atherosclerotic aortic aneurysms is more closely related to the location, and, in addition, thoracic aortic aneurysms are more easily dilated than abdominal aortic aneurysms [11]. In the present study, no significant difference in terms of location was detected. Our results suggest the growth of aortic aneurysms in Takayasu's arteritis is more closely related to blood pressure than to location. Histologic differences between the thoracic and abdominal aortas have been reported [11, 20]. The thoracic aortic media contains vasa vasorum thicker than that in the abdominal portion and contains more lamellar units. This finding suggests that aortic wall scars are more severe in the thoracic aorta than in the abdominal aorta. Scars can limit further enlargement of thoracic aortic aneurysms in Takayasu's arteritis. Hirose et al. [11] reported that the growth rate of atherosclerotic aortic aneurysms was 0.34 cm/year, whereas the present study showed the growth rate of six aneurysms in patients with Takayasu's arteritis was 0.03 cm/year, which is slower than that of the previous study. This result suggests that aortic wall scars are more severe in patients with Takayasu's arteritis than in those with atherosclerosis. Therefore, aneurysms associated with Takayasu's arteritis increase in size more slowly than atherosclerotic aortic aneurysms.
In conclusion, aortic aneurysms associated with Takayasu's arteritis are not rare. The aorta with little calcification has greater possibility of aneurysm formation in Takayasu's arteritis.
Some aortic aneurysms can rapidly increase in size and rupture. In particular, aortic aneurysms with aortic wall thickening should be closely followed up. In patients with aortic aneurysm without aortic wall thickening, long-term follow-up examination is also needed because the aneurysms may increase in size as a late complication.
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