^1,2,3Associate Professor, Department of Radiology, Government Medical College, Vishnupuri, Nanded, Maharashtra, INDIA.

Email: aniltap@yahoo.co.in , ashok.kadam@gmail.com

Figure 1: FLOWCHART SHOWING THE STUDY DESIGN

Inclusion criteria: Patients of any age group, gender with clinically suspected cases of aortic dissection with suboptimal Trans-thoracic echocardiography, underwent surgical or endovascular stent graft repair.

Exclusion criteria: Other causes of acute aortic syndrome (aortic intramural hematoma, penetrating atherosclerotic ulcer, aortic aneurysmal rupture, traumatic aortic transection) and acute coronary syndrome/acute myocardial infarction. Patients with known contrast allergy. Patients with Chronic Kidney Disease.

All CT images are interpreted by research person, by guide and by senior consultant radiologist, specialist in cardiovascular imaging. Initially Plain CT Study was done and findings noted. Non-contrast CT scan images were analysed to see internal displacement of intimal calcifications and hyper-attenuation of false lumen. For imaging sections were taken from the root of neck to the level of femoral arteries, with specifications as series – plain, Arterial and Venous Phases, kVp – 120 and mAs – 300(varies), collimation – 64 x 0.6mm, slice thickness – 5mm with increment – 0.6mm. Contrast used was nonionic contrast media (OMNIPAQUE 350), by bolus tracking method, intravenous with flow rate – 4 ml/sec by an injection pump and about 1.5 ml /kg. The examination initiated 5 sec after attenuation of the region of interest. For three dimensional images, the volumetric CT data sets were processed on a separate workstation with multi-planar reformatting, maximum intensity projection and volume rendering. Axial source images, the two- and three-dimensional data sets were evaluated for each subject. ECG gating was used because it allows delineation of the aortic root and of coronary artery involvement. It also allows clear differentiation of motion artefact in the ascending aorta from true aortic dissection. CT images were reconstructed into Axial, Coronal and Sagittal Planes. Reconstruction images obtained using multi-planar reformations, volume rendering and maximum intensity projection techniques. Contrast-enhanced CT scan images were analysed to see intimal flap that separates the true lumen from false lumen. False lumen was identified by features like large cross-sectional area, attenuation values, cob-web sign and beak sign. True lumen was identified by features like small cross-sectional area, attenuation values and its continuity with un-dissected portion of aorta. Imaging features are divided into Stanford type-A aortic dissection and Stanford type-B aortic dissection. A CT scan was read as positive for Stanford type-A aortic dissection when dissection is involving ascending thoracic aorta with or without involvement of arch of aorta, descending thoracic aorta or abdominal aorta. A CT scan was read as positive for Stanford type-B aortic dissection when dissection was involving descending thoracic aorta distal to left subclavian artery with or without involvement of abdominal aorta. The collected data were entered and analyzed using Microsoft office window excel 2007 and SPSS version 16 (SPSS 16.0 for Windows, release 16.0.0. Chicago: SPSS Inc). To assess the diagnostic ability of a test, we calculated sensitivity and accuracy. Chi-square test was used and considered to be significant when the p-value was less than0.05.

RESULTS

In present study, 25 out of 40 cases with suspicion of aortic dissection who met our study criteria were evaluated.

Patients ranging from 21-70 years underwent MDCTA, however, majority of patients belonged to age group of 51 to 60 years (52%), 31-40 years (24%) ,41- 50 years (16%), 21-30 years (4%) and 61-70 years(4%). Gender distribution in our study was 15 males (60%) and 10 female patients (40%) (Ratio 1.5:1).

Table 1: Age and gender distribution

In our study, intimal flap was identified easily and readily and thus true lumen was differentiated from false lumen in all 25 subjects. True lumen was identified with features of its continuity with un-dissected portion of aorta and smaller than false lumen in all subjects. False lumen was identified with features of large cross-sectional area, Beak sign and Cobweb sign and False lumen was thrombosed in 5 subjects. On MDCTA, 10 subjects showed left renal artery arising from false lumen, 5 subjects showed celiac axis arising from false lumen, and 3 subjects showed superior mesenteric artery arising from false lumen. 20 cases (80%) were STANFORD-A and 5 (20%) were STANFORD-B types of aortic dissection.

Table 2: MDCT angiography findings and Stanford classification

20 subjects underwent MDCT angiography who were diagnosed as Stanford-A aortic dissection are confirmed with surgical findings. Remaining 5 subjects underwent MDCT angiography who were diagnosed as Stanford-B aortic dissection are confirmed with endovascular stent graft repair findings. Out of 25 operated/endovascular repair cases of aortic dissection, 25 were detected on MDCTA (100% Sensitivity and 100% Accuracy). MDCT Angiography diagnosis was highly significantly (p < 0.001) correlated with Surgical /endovascular repair findings.

Table 3: Correlation of MDCT angiography diagnosis and surgical treatment/endovascular repair

DISCUSSION

Aortic dissection is an acute aortic disorder, with an incidence up to 0.2– 0.8%, and also carries the highest mortality rate.¹ The overall outcome is determined by the type and extent of dissection and the presence of associated complications; therefore, evaluation of the entire aorta, branch vessels, and iliac and proximal femoral arteries is recommended to aid in treatment planning.² CT with contrast injection is indicated in the diagnosis of Aortic dissection.¹⁰ CT was the most common initial diagnostic test performed in patients enrolled in the International Registry of Acute Aortic Dissection.¹⁰ More recent MDCT studies enrolling up to 57 patients have reported sensitivities and specificities of 100%.¹¹ Patients with Stanford type A dissection traditionally undergo surgical replacement of the ascending aorta while patients with Stanford type B dissection are increasingly undergoing endovascular stent-graft treatment. Of the 30 subjects who were diagnosed as Stanford-A aortic dissection non MDCT angiography, 20 subjects underwent surgery and were confirmed as Stanford type-A aortic dissection. Remaining 10 subjects were died even before surgery as Stanford type-A aortic dissection causes high mortality. Of the 10 subjects who were diagnosed as Stanford-B aortic dissection non MDCT angiography, 5 subjects underwent endovascular stent graft repair under fluoroscopy guidance and were confirmed as Stanford type-B aortic dissection. Remaining 5 subjects were conservatively managed and advised follow-up (FLOWCHART). The above findings confirmed that MDCT angiography is 100 % sensitive and 100% accurate in diagnosing aortic dissection, type of aortic dissection and decides the treatment for which the patient should undergo. These results are in close agreement with Yoshida S et al.¹² studied 57 patients with acute chest pain underwent emergency helical CT and subsequent surgery for type A Aortic Dissection .Sensitivity, specificity, and accuracy of helical CT, along with 95% CIs, were calculated by using surgical confirmation as the reference standard and concluded that helical CT was 100% sensitive,100% specific and 100% accuracy in diagnosing aortic dissection arising from ascending aorta, aortic arch and descending aorta. Our results are also in close agreement with Zeman RK et al.¹³ studied 23 patients with suspected Aortic Dissection and performed helical CT in those patients and found that axial sections resulted in 15 true-negative, 7 true- positive, and 1 false-positive interpretation. In three of seven patients with dissection, they found difficult to determine the extent of the intimal flap on axial sections; multi-planar reformation or 3D views clarified the relevant anatomy in all these 3 cases and concluded that multi-planar reformation and 3D rendering of helical CT scans would be a valuable addition to axial display of CT studies used to detect Aortic Dissection and to determine the extent of the intimal flap and concluded that CT findings agreed with angiographic and surgical findings in all patients with type- A and type-B dissection. Our results are also in close agreement with Adachi H et al.¹⁴ studied 68 patients with 3D-CTA, 35 patients were diagnosed as aortic dissection. Surgical intervention was used in most of the patients and concluded that preoperative 3D-CTA findings were quite similar to intraoperative findings, and were useful in determining operative procedures. Rapid and accurate assessment of aortic disease was achieved by 3D-CTA. 3D-CTA can play an important role in the preoperative assessment of Aortic Dissections leading to successful surgical treatment. Our results are also in close agreement with Small JH et al.¹⁵ evaluated in 81 patients with suspected acute aortic dissection who were examined on a fast CT system capable of a 1s data acquisition time. 17 patients had Type A and nine had Type B dissections. When 78 confident reports alone were considered, both sensitivity and specificity reached 100% and concluded that CT can often be used as the single investigation prior to surgery for acute Type A dissections. Our results are also in close agreement with Sommer T et al.¹⁶ in their study in 1996, studied on forty-nine symptomatic patients with clinically suspected Aortic Dissection Aortic Dissection were examined with contrast material- enhanced spiral CT and concluded that sensitivity and specificity of contrast material- enhanced spiral CT was 100% in detection of thoracic aortic dissection. Sakamoto et al.¹⁷ studied 107 patients with clinical suspicion of Acute Aortic Dissection who underwent non-enhanced MDCT had a sensitivity of only 87% which is less than our sensitivity which is100%. In present study, we used the parameters of 120 kVp and 231 mAs (varied automatically according to body size) to provide optimal quality images without any significant loss of diagnostic data. Because of the radiation burden and invasiveness, we were not able to compare this technique with conventional angiography. Our study has few limitations. such as small sample size, lack of conventional angiography and MRA to assess the accuracy of the MDCT data. Sample size (n=25) was less because study was done for a limited period (two years). Aortic dissection is a rare disease and is frequently lethal and can easily be mistaken for less serious pathology. Some of the aortic dissections are missed at presentation and first diagnosed at autopsy. This study may have substantial impact on economic costs, patient experience, radiation that we cannot comment upon.

CONCLUSION

MDCT has the advantages of shorter acquisition time, wide availability, and high diagnostic accuracy and has, therefore, classically been the modality of choice for the evaluation of aortic dissection. Modern MDCT allows rapid image acquisition and data reconstruction and aids in treatment planning. Multimodality approach of using MDCT angiography, MRA and TEE also can be practiced if the patients are stable.

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