A Pictorial Review of CT Angiography Imaging Features of Aortic Dissection and Its Complications: Role of Emergency Teleradiology

Abstract

Aortic dissection is an acute emergency affecting the aorta with a mortality of 50% in the first 48 hours of onset. The clinical outcome is determined by the type and extent of dissection, and its associated complications. Thus, knowledge of computed tomography (CT) angiography imaging features of aortic dissection and its complications, coupled with a process for immediate interpretation such as teleradiology, is essential for early diagnosis and treatment. The purpose of this study is to assess the imaging findings of aortic dissection and its complications on CT angiography and present a pictorial review of its imaging manifestations. We retrospectively evaluated 441 CT angiography studies diagnosed to have aortic dissection based on keyword search from emergency teleradiology reports. Noncontrast CT examinations were excluded from the study. The results were analyzed and compiled in a pictorial review. Aortic dissections are classified according to the Stanford classification system. Early diagnosis of aortic dissection and its complications is important in planning prompt management and avoiding fatal outcomes. CT angiography is a highly accurate noninvasive imaging investigation in the detection of aortic dissection and its complications. When coupled with emergency teleradiology analysis, the clinical outcomes can be significantly improved.

Keywords

aortic dissection - Stanford classification - teleradiology

Introduction

Aortic dissection is an emergency condition of the aorta. It begins with a laceration of the intima and inner layer of the media, forming an entrance tear that allows the entering blood to split the media. This results in the formation of a double channel dividing the aortic lumen into true and false lumens.[1] It is an acute life-threatening condition often resulting in the death of the patient. Rupture of the aortic dissection is the most common cause of death in the majority of patients. Rupture of the aortic dissection into the pericardial sac results in cardiac tamponade. Rupture into the pleural cavity leads to hemothorax, while rupture into the mediastinum results in hemomediastinum. The overall outcome is determined by the type and extent of dissection and associated complications.[2] The most common presentation is tearing central chest pain radiating to the back. A few patients may present with syncope without a history of typical chest pain. Syncope is a result of hypotension due to cardiac tamponade or obstruction of the cerebral blood vessels. Patients present with symptoms of stroke if there is involvement of carotid vessels. It can cause severe aortic regurgitation resulting in heart failure. Involvement of the coronary arteries can lead to acute myocardial infarction. Limb ischemia may present as limb pain, pulse deficits, cold peripheries, discoloration, and gangrene. It is most commonly due to branch orifice occlusion involvement by the dissection flap or due to the narrowing of the true lumen by expanding the false lumen. Involvement of visceral branches leads to nausea, vomiting, abdominal pain, bloody diarrhea, and recurrent sepsis. Oliguria and anuria are indicators of renal artery involvement. Therefore, the evaluation of the entire aorta, branch vessels, and iliac and proximal femoral arteries is essential in treatment planning.[3]

Computed tomography (CT) is a widespread imaging modality with excellent spatial resolution, and the ability to completely evaluate the anatomy of the thoracoabdominal aorta and major branch vessels. CT angiography is a highly accurate noninvasive imaging investigation in the detection of aortic dissection and its complications in one rapid examination.[4] Early diagnosis and treatment are essential for optimal outcomes and is where emergency teleradiology plays a major role. Teleradiology provides round-the-clock services by transferring the images even during the night to the offsite expert radiologists to allow for timely reporting of emergency cases by helping the clinicians to initiate prompt and appropriate management. When CT angiography is coupled with emergency teleradiology analysis, the clinical outcomes can be significantly improved.

Aims and Objectives

The purpose of this study is to assess the imaging findings of aortic dissection and its complications on CT angiography and compile a pictorial review. This study further evaluates the role of teleradiology by assessing the turnaround time for reporting the aortic dissection cases.

Materials and Methods

This retrospective study involves the evaluation of 441 CT angiography studies acquired during an emergency teleradiology setting from various hospitals. The study was conducted by a teleradiology service provider. The DICOM images of the CT angiography scans were transmitted to the telereporting workflow platform “RADspa,” a cloud-based Radiology Information System (RIS)/Picture Archival and Communication System (PACS), over a high-speed internet connection. The scans were predominantly performed using imaging equipment from leading manufacturers, including GE Medical Systems, Philips, Siemens, and Toshiba. Board-certified radiologists empaneled with the teleradiology service provider interpreted the scans, and the finalized reports were transmitted back to the respective hospitals via the same workflow platform.

The study images were analyzed and imaging findings of aortic dissection with emphasis on complications were documented and compiled into a pictorial review.

Classification of Aortic Dissection

The Stanford classification divides the aortic dissection into two types: Stanford type A and Stanford type B. These categories distinguish between dissections affecting different segments of the aorta. Stanford type A dissection involves the ascending thoracic aorta, where the dissection flap may or may not extend into the descending aorta. On the other hand, a Stanford type B dissection specifically involves the descending thoracic aorta beyond the left subclavian artery. These classifications delineate the anatomical regions affected by aortic dissections, with type A primarily involving the ascending portion and potentially extending further, while type B confines the dissection to the descending segment beyond a defined landmark[1] ([Fig. 1]).

Fig. 1 Classification of aortic dissection. The graph illustrates that out of 441 patients, 141 are categorized as Stanford type A, while 300 are classified as Stanford type B.

Differences between True and False Lumen

True and false lumens within aortic dissections exhibit notable distinctions. Typically, the true lumen serves as the origin site for major arteries such as the celiac trunk, superior mesenteric artery, and right renal artery. It tends to be smaller in size, showing higher contrast density, and remains contiguous with the aortic root. Conversely, the false lumen commonly accommodates the left renal artery, presenting as larger in size with lower contrast density. Moreover, it often demonstrates thrombosis and is associated with radiographic signs like the beak sign or cobweb sign. These characteristics underscore the contrasting features between the true and false lumens in aortic dissections.[5]

CT Imaging Features of Aortic Dissection

The aortic intimal flap is the key imaging finding in aortic dissection and divides the aortic lumen into a true and a false lumen, which is seen in almost all cases. The aortic dissection demonstrates several distinct signs in CT angiography. The “beak sign” of the false lumen is characterized by an acute angle formed at the edge of the false lumen in axial sections, delineated by the borders of the outer aortic wall and the intimal flap. This sign serves as a reliable indicator for distinguishing the false lumen from the true lumen. Another specific feature, the “cobweb sign” of the false lumen, presents as thin filiform defects representing strands or ribbons of media crossing the false lumen in CT imaging. While less commonly observed, it remains a distinct sign for identifying the false lumen. The “windsock sign” indicates a circumferential dissection of the aortic lumen with intimo-intimal intussusception. It often results in obstruction of the origin of supra-aortic vessels or occlusion of the aortic lumen. In chronic dissections, notable CT imaging features include a straight, thicker, and less mobile appearance of the dissection flap, often accompanied by thrombosis and outer wall calcification of the false lumen. These characteristics provide valuable insights into the chronicity and nature of the aortic dissection.[6]

Complications of Aortic Dissection

The complications of aortic dissection are depicted in [Fig. 2].

Fig. 2 Complications of aortic dissection. The graph depicts complications arising from aortic dissection, which encompass a range of serious outcomes. These include rupture, hemopericardium, hemothorax, renal infarction or ischemia, occlusion of major arteries including the superior mesenteric artery (SMA), inferior mesenteric artery (IMA), and celiac artery, as well as the extension of dissection into branches of the ascending aorta. These complications highlight the diverse and potentially life-threatening consequences associated with aortic dissection.

Case Examples

The case examples are presented in detail in [Figs. 3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14].

Fig. 3 (A, B) Axial and sagittal computed tomography (CT) angiography images of a 60-year-old male patient presents with type A dissection originating from the aortic root extending to the abdominal aorta. (C, D) Axial and sagittal CT angiography maximum intensity projection images of a 49-year-old male patient presents with type B dissection distal to the origin of the left subclavian artery.

Fig. 4 (A, B) Axial computed tomography (CT) images of a 60-year-old male patient. The venous images demonstrate intimal flap dividing the aortic lumen into true and false lumen. The left renal artery is originating from the false lumen which is undergoing thrombosis with resultant left renal ischemia.

Fig. 5 (A) Windsock sign. (B) Beak sign. (C) Cobweb sign. (D) Straight and thick flap with outer wall calcification in chronic dissection.

Fig. 6 (A–K) Sagittal and axial computed tomography (CT) angiography images of a 70-year-old male patient with chest pain radiating down through the left hip demonstrate type A aortic dissection with moderate hemopericardium. The dissection flap extends into the celiac artery causing occlusion of hepatic arteries and the left gastric artery resulting in necrosis of the gallbladder and thickening of the pylorus indicating ischemia. There is an extension of the dissection into the superior mesenteric artery causing thickening of the jejunal loops, indicating bowel ischemia. There is a further extension of dissection into the left common iliac, external iliac arteries, and left common femoral artery indicating limb ischemia.

Fig. 7 (A–D) Axial computed tomography (CT) angiography images of a 67-year-old female patient with chest pain demonstrate Stanford type B aortic dissection. The left renal artery is arising from a false lumen resulting in occlusion leading to left renal ischemia. There is thrombosis of the false lumen distally with aneurysmal dilatation of the proximal aorta.

Fig. 8 (A–C) Axial and coronal computed tomography (CT) angiography images of a 77-year-old male patient with type B aortic dissection demonstrate an inferior mesenteric artery originating from the false lumen with occlusion of distal branches leading to ischemia of the descending colon.

Fig. 9 (A–D) Axial and sagittal computed tomography (CT) angiography images of a 78-year-old male patient with chest pain radiating to the left arm demonstrate type A aortic dissection involving the ascending aorta with rupture/leak causing mediastinal hemorrhage and hemothorax.

Fig. 10 (A–D) Axial computed tomography (CT) angiography images of an 80-year-old male patient with a three-channel chronic aortic dissection demonstrate aneurysmal dilatation of the aorta with thrombosis of the false lumen. There is hemothorax indicating rupture. The left renal artery originating from the false lumen underwent occlusion leading to left renal ischemia.

Fig. 11 (A–F) Axial computed tomography (CT) angiography images of a 77-year-old male patient with left leg numbness and left groin pain demonstrates type B aortic dissection with a dissection flap extending into the right common iliac artery. There is an occlusion of the left common iliac and partial occlusion of the left femoral artery. There is periaortic stranding and thickening around the left femoral artery indicating periaortic hematoma, leading to limb ischemia.

Fig. 12 (A, B) Axial and coronal computed tomography (CT) angiography images of an 88-year-old female patient with chest pain demonstrate dilated and ectatic thoracic aorta with Stanford type A dissection. There is an extension of dissection to the brachiocephalic artery. The left common carotid artery is arising from the false lumen.

Fig. 13 (A–D) Axial and sagittal CT angiography images of a 67-year-old male patient with chest pain and palpitations demonstrate Stanford type A dissection. There is an extension of dissection to the brachiocephalic and left common carotid arteries.

Fig. 14 (A–L) Axial and coronal images of a 64-year-old male patient presenting with chest pain and left lower leg pain with tingling demonstrate type A aortic dissection extending into the left common carotid artery, left subclavian artery, abdominal aorta, and right common iliac and external iliac arteries. There is complete obliteration of the true lumen by increased pressures within the false lumen causing narrowing of the ostium of the left common iliac artery with less contrast opacification of the left common iliac artery, external iliac artery, and internal iliac artery. The patient underwent vascular surgery consultation and was treated by placing a bilateral femoral artery bypass graft. The pressure within the false lumen was reduced. There was expansion of the true lumen, and flow in the left common iliac, external iliac, internal iliac, and femoral arteries was restored.

Teleradiology Reporting Turnaround Time Analysis

Analysis of the turnaround time for generating reports showed that 65% were produced within 1 hour, with 88% completed within 90 minutes ([Fig. 15]). Teleradiology facilitates the transfer of radiological images to off-site experts, enabling swift review and interpretation. This approach expedites diagnosis and hastens the commencement of suitable treatment protocols.

Fig. 15 Turnaround time for reporting cases.

Discussion

Hemopericardium indicating rupture of aortic dissection is the most common imaging complication seen in our study, indicating the fatality and acuteness of aortic dissection. It is due to rupture of the thoracic aortic dissection into the pericardium. We also found rupture of thoracic aortic dissection into the pleural cavity and mediastinum, which led to hemothorax and mediastinal hematoma. In our study, we found an extension of dissection into the branches of the ascending aorta, especially the brachiocephalic trunk and carotid arteries, which may lead to the complication of cerebral ischemia/infarction. These patients with involvement of the ascending aorta categorized as Stanford type A aortic dissection should undergo immediate surgical intervention.

Our study demonstrated some cases of superior mesenteric artery, inferior mesenteric artery, and celiac artery occlusion; however, there was no demonstrable bowel ischemia in isolated cases of occlusion of these arteries because of collateral circulation between the branches of these vessels. Small bowel ischemia is seen in the form of thickening of the pylorus and jejunal loops in one case, where there is occlusion of both the celiac and superior mesenteric arteries. We also encountered necrosis of the gallbladder in the same patient, which is a rare complication. It was due to the extension of the dissection into the hepatic artery followed by its occlusion with a corresponding lack of collateral circulation from the superior mesenteric artery branches. In our study, 1.1% of cases presented with occlusion of the inferior mesenteric artery and its branches. However, there was no acute ischemia because of collateral circulation. In one of the patients, there were changes of chronic ischemia in the descending colon in the form of submucosal fat infiltration. This could be owing to the inferior mesenteric artery originating from the false lumen with its branches undergoing occlusion.[7] Renal ischemia was seen in 3.4% patients in our study, which was a result of extension of dissection into the renal artery followed by thrombosis and also due to the origin of the renal artery from the false lumen leading to thrombosis of the renal artery. Limb ischemia in our study is due to the extension of the dissection flap into the femoral artery followed by occlusion. There was also leak/rupture of the femoral artery with para-aortic hematoma formation.

Initial management of patients with aortic dissection include prompt admission to the intensive care unit and effective control of blood pressure and heart rate, which ultimately reduce aortic wall sheer stress by regulating the patient's cardiac output and prevent further progression of dissection. Beta-blockers are the principal medications utilized in initial medical management. The target is to achieve a systolic blood pressure of 100 to 120 mm Hg and a heart rate of 60 to 80 beats per minute. However, the target blood pressure can vary if static or dynamic obstruction is present. Further management is dependent on the type of aortic dissection. Standard treatment for patients with type A aortic dissection includes surgery via sternotomy and aortic reconstruction with a prosthetic graft. Patients with uncomplicated type B aortic dissections can be managed with medical therapy alone. For patients with complicated type B aortic dissections, endovascular repair has become the principal modality of treatment. It includes placement of a stent graft to cover the primary tear, which maintains patency of the true lumen and causes decompression and subsequent thrombosis of the false lumen.[8]

Turnaround time is the time from when a study is complete and available for interpretation by a radiologist until final signature. In our study, the majority of the reports were generated within a 60-minute time period, signifying the importance of teleradiology in emergency situations. Ensuring the early diagnosis of aortic dissection and detection of its complications helps in evaluating treatment options and guiding treatment decisions from the perspective of determining whether medical management or endovascular therapy is likely to result in optimal patient outcome.

Conclusion

Aortic dissection stands as the most prevalent acute emergency condition of the aorta, often resulting in fatal outcomes. Early diagnosis and treatment planning are pivotal in enhancing patient outcomes. CT angiography emerges as a valuable tool, allowing rapid and comprehensive imaging of the entire aorta and its branches in a single examination. This facilitates timely and accurate diagnosis of the type and extent of aortic dissection and associated complications, influencing early surgical planning or management decisions. Emergency teleradiology assumes a crucial role in the evaluation of aortic dissection, simplifying the process of early diagnosis and intervention.

Conflict of Interest

None.

• References

• 1 Kruse MJ, Fishman EK, Zimmerman SL. Characterization of aortic dissection: what the radiologist needs to know. Curr Cardiovasc Imaging Rep 2014; 7: 9273
• 2 Baliga RR, Nienaber CA, Bossone E. et al. The role of imaging in aortic dissection and related syndromes. JACC Cardiovasc Imaging 2014; 7 (04) 406-424
• 3 McMahon MA, Squirrell CA. Multidetector CT of aortic dissection: a pictorial review. Radiographics 2010; 30 (02) 445-460
• 4 Murillo H, Molvin L, Chin AS, Fleischmann D. Aortic dissection and other acute aortic syndromes: diagnostic imaging findings from acute to chronic longitudinal progression. Radiographics 2021; 41 (02) 425-446
• 5 Orabi NA, Quint LE, Watcharotone K, Nan B, Williams DM, Kim KM. Distinguishing acute from chronic aortic dissections using CT imaging features. Int J Cardiovasc Imaging 2018; 34 (11) 1831-1840
• 6 Macura KJ, Corl FM, Fishman EK, Bluemke DA. Pathogenesis in acute aortic syndromes: aortic dissection, intramural hematoma, and penetrating atherosclerotic aortic ulcer. AJR Am J Roentgenol 2003; 181 (02) 309-316
• 7 Ito T, Yasuda N, Kuroda Y, Sugawara M, Koyanagi T, Higami T. Acute gallbladder necrosis in a patient with acute type B aortic dissection. Ann Vasc Dis 2013; 6 (04) 748-750
• 8 Khayat M, Cooper KJ, Khaja MS, Gandhi R, Bryce YC, Williams DM. Endovascular management of acute aortic dissection. Cardiovasc Diagn Ther 2018; 8 (1, Suppl 1): S97-S107

Publication History

Article published online:
24 March 2025