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ECR 2018 / C-1522
Computed Tomography Angiography in Aortic Disease: what the surgeon needs to know.
Congress: ECR 2018
Poster No.: C-1522
Type: Educational Exhibit
Keywords: Cardiovascular system, Arteries / Aorta, Emergency, CT-Angiography, CT, Image manipulation / Reconstruction, Contrast agent-intravenous, Technical aspects, Computer Applications-Detection, diagnosis, Aneurysms, Dissection, Dilatation
Authors: G. Gentile1, V. Carollo2, G. Mamone3, G. Marrone1, G. Raffa1, S. Caruso4, M. Milazzo3, F. Crinò2, R. Miraglia5; 1Palermo/IT, 2Palermo (PA)/IT, 3Palermo, It/IT, 4Palermo (PA), italy/IT, 5Palermo /IT
DOI:10.1594/ecr2018/C-1522

Findings and procedure details

TABLE OF CONTENTS

 

Overview

 

- Technical issue: scan protocol, contrast media administration, post-processing

 

-  CT radiological findings in acute aortic syndrome, structured reporting and checklist of important findings to be mentioned

 

-  Brief outline of management options


 

-  Possible post-operative complications and their radiological appearance

 

Technical Issue

 

Computed tomography plays a central role in the diagnosis, risk stratification, and management of aortic diseases. Its advantages over other imaging modalities include the short time required for image acquisition and processing, the ability to obtain a complete 3D dataset of the entire aorta, and its widespread availability. Electrocardiogram (ECG)-gated acquisition protocols are crucial 
in reducing motion artefacts of the aortic root and thoracic aorta (Fig. 4).
 High-end MSCT scanners (16 detectors or higher) are preferred for their higher spatial and temporal resolution compared with lower-end devices. In suitable candidates scanned on 64-detector systems
 or higher-end devices, simultaneous CT coronary angiography may 
allow confirmation or exclusion of the presence of significant coronary artery disease before transcatheter or surgical repair. 

 

Fig. 4: Standard Thoraco-Abdominal CT Angiography Scan Protocol. Non-enhanced CT, followed by CT
contrast-enhanced angiography, is the recommended protocol, particularly when intramural hematoma or aortic dissection are suspected. Venous Phase is recommended after stent-graft repair of aortic aneurysms, to detect
endoleaks. The average effective radiation dose during aortic computed tomography angiography is estimated to be within the 10–15 mSv range.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

In our Unit it is used a non-ionic, monomeric, extracellular contrast agent with an iodine concentration of 370 mg/mL, prepared at 37°C, and injected into an antecubital vein through a 20- or 18-gauge catheter using a dual-shot injector. All enhanced CT acquisitions were performed using a dedicated multiphasic injection protocol. The total amount of CM was tailored to the patient’s BMI and was administered with five boluses at different flow rates (Fig. 5). 

 

Fig. 5: Contrast Media injection protocol.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

The 3D reconstruction techniques are an important tool for the diagnosis of Acute Aortic Syndromes, particularly in patients undergoing endovascular procedures (Fig. 6 - Fig. 7 - Fig. 8).

 

Fig. 6: Multiplanar Reconstruction (MPR) (left lateral image) allows images to be created from the original axial plane in either the coronal, sagittal, or oblique plane; Curved-MPR straights the vessel along the centerline; Maximum Intensity Projection consists of projecting the voxel with the highest attenuation value on every view throughout the volume onto a 2D image; Volume Rendering Volume not only allows display of the vascular anatomy but also provides definition of soft tissue, muscle, and bone.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

Fig. 7: Cine Loop Reconstructions are obtained from row data, reconstructing all phases from 0 to 90% of RR interval (increment 10%). (Video 1 - Video 2)
References: Radiology, UPMC Italy, ISMETT - Palermo/IT
Table 1: Video 1 - CineLoop Reconstruction: Calcified Bicuspid Aortic Valve.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT
Table 2: Video 2 CineLoop Reconstruction: Mitral Valve Prolapse.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

Fig. 8: Vantages and Disadvantages of post-processing techniques.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

CT Findings

 

Although echocardiography remains the principal imaging technique for assessment of the Cardiac Valves, ECG-gated CT angiography is proving to be an increasingly valuable complementary modality in this setting. CT angiography allows excellent visualization of the morphologic features and function of the normal valves, as well as of a wide range of valve diseases, including congenital and acquired diseases, infectious endocarditis, and complications of valve replacement. CT angiography also permits simultaneous assessment of the valves and coronary arteries, which may prove valuable in presurgical planning. Bicuspid Aortic Valve (BAV) is the most common congenital cardiac anomaly, with an estimated incidence of 0.9% to 2% in the general population. The “purely” BAV is composed of two cusps, morphologically and functionally (Fig. 9). Associated with a certain proportion of BAVs is a dilatation of the ascending aorta, especially in young patients, exposing these patients to an increased risk of comorbidity owing to aneurysm formation and dissection. 

 

Fig. 9: Upper right: Schematic presentation of the developmental phenotypes of the aortic valve and typical characteristics; Prominent line in schematic drawings represents a raphe, which is the nonseparated or conjoint segment of two underdeveloped cusps extending into the commissural area. Upper left: Multiplanar Reconstruction planes orientation for valvular anatomy assessment . Bottom left: axial view of aortic valve and diameters (average of three measurements). Bottom middle and right: examples of Bicuspid Aortic Valve with and without raphe.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

The main principle of surgery for Ascending Aortic Aneurysms is that of
preventing the risk of dissection or rupture by restoring the normal
 dimension of the ascending aorta (Fig. 10). 


 

Fig. 10: Left side: Multiplanar Reconstruction planes orientation for ascending aorta assessment. Right side: guidelines for surgery and risk classification based on diameter of ascending aorta and body surface area.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

Presence of Penetrating Aortic Ulcer (PAU) represents another high risk aortic condition. Such lesions represent 2–7% of all Acute Aortic Syndrome. Propagation of the ulcerative process may either lead to Intramural Hematoma, Pseudoaneurysm, or even Aortic Rupture, or an acute Aortic Dissection (Fig. 11). PAU is often encountered in the setting of extensive atherosclerosis of the thoracic aorta, may be multiple, and may vary greatly in size and depth within the vessel wall. The most common location of PAU is the middle and lower descending thoracic aorta (Type B PAU). Less frequently, PAUs are located in the aortic arch or abdominal aorta, while involvement of the ascending aorta is rare. 

 

Fig. 11: Curved Multiplanar Reconstruction shows Penetrating Aortic Ulcer of the aortic arch.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

Intramural Hematoma (IMH) (Fig. 12) is hemorrhage localized to the aortic media in the absence of a visible intimal tear. IMH is considered equivalent to aortic dissection regarding prognostic and therapeutic implications because an IMH may progress to aortic dissection and rupture. IMH may develop secondary to spontaneous rupture of vasa vasorum of the medial aortic layer, penetrating aortic ulceration, or blunt trauma. Hypertension is the most common predisposing risk factor. 

 

Fig. 12: Unenhanced CT is extremely valuable in identifying Intramural Hematomas (Upper Left). Several findings help differentiate IMH from a thrombosed false lumen of an aortic dissection: IMHs do not enhance; no intimal tear is seen; IMHs maintain a constant circumferential relationship with the aortic wall; the false lumen of a dissection has a longitudinal spiral geometry.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

Aortic Dissection results from an intimal tear extending into the inner layer of the aortic media; an intimal flap separates the false and true lumens. The blood within the false lumen may be free flowing or thrombosed. Risk factors for aortic dissection include preexisting thoracic aortic aneurysm, chronic hypertension, Marfan syndrome, bicuspid aortic valve, infection, and prior cardiovascular surgery. The dissected aorta can be dilated or normal in caliber. Dissections involving the ascending aorta (Stan- ford A; DeBakey I and II) are surgical emergencies because dissections in this area are prone to rupture or other critical complications, including development of hemopericardium, pericardial tamponade, and death. Other potential complications of ascending aortic dissections include aortic valve rupture, aortic insufficiency, coronary artery dissection, stroke, and myocardial infarction. The course of Type B dissection is often uncomplicated so, in the absence of malperfusion or signs of (early) disease progression, the patient can be safely stabilized under medical therapy alone, to control pain and blood pressure. MDCT is the most common modality to detect aortic dissections. Its high sensitivity for detecting dissection, wide availability, and ability to identify alternative diagnoses for chest pain makes MDCT an excellent first choice in evaluating suspected dissection (Fig. 13 - Fig. 14).

 

Fig. 13: Multiplanar Reconstruction planes show the right position to obtain axial view of dissected aorta, true and false lumen diameters. Differentiation of the false and true lumen is imperative in surgical repair and percutaneous treatment with endografts. Customarily, the most reliable way to identify the true lumen is by determining continuity with the undissected portion of the aorta. The cross-sectional area of the false lumen is also often larger than that of the true lumen. The beak sign is another helpful diagnostic sign: focal low-density thrombus is present in the beaked margin of the false lumen, which helps delineate the false from the true lumen.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT
Fig. 14: Main MDCT findings in aortic dissection to search and report. Recommendations for treatment.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

Traumatic Aortic Injury (Fig. 15) is a tear involving all layers of the aortic wall, usually caused by rapid deceleration (high-speed motor vehicle accident or fall from significant height). The mortality rate is high, with most patients dying in the field. Survival is highest for tears at the aortic isthmus. Proposed mechanisms for aortic injury include shearing and hydrostatic forces secondary to rapid deceleration and osseous pinching. 

 

Fig. 15: Traumatic aortic pseudoaneurysm on contrast-enhanced CT. Upper left: MPR and VR images show irregular focal outpouching of the isthmic aorta, consistent with partial aortic transection and pseudoaneurysm formation in this patient who has a history of a high-speed motor vehicle collision. Bottom left and right side: control post-endovascular repair.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

Reporting CT Angiography

How to translate the evidences that we have seen in a structured report?

 

· Describe your findings using five “W” rules (Fig. 16

· Made a structured template report for CT Angiography (Fig. 17)

· Write your impressions

 

Fig. 16: Tips for describe your findings in emergency conditions.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT
Fig. 17: CT Angiography structured report template.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

Treatments Options

 

· Ascending Aortic Aneurysm: if the aneurysm is proximally
limited to the sinotubular junction and distally to the aortic arch, resection of the aneurysm and supra-commissural implantation of a
tubular graft is performed under a short period of aortic clamping,
with the distal anastomosis just below the aortic arch. If the aneurysm extends proximally below the sinotubular junction
and one or more aortic sinuses are dilated, the surgical repair is
guided by the extent of involvement of the aortic annulus and the
aortic valve (Fig. 18 A).

· Type A aortic dissection: surgery is the treatment of choice. Acute Type A aortic dissection has a mortality
of 50% within the first 48 hours if not operated. It is preferable to replace the aortic root if the dissection involves at least one sinus of Valsalva, rather than perform a supracoronary ascending aorta replacement only (Fig. 18 B).

· Type B aortic dissection: patients with uncomplicated Type B dissection receive medical therapy to control pain, heart rate, and blood pressure, with close surveillance to identify signs of disease progression and/or malperfusion. Thoracic Endovascular Aortic Repair (TEVAR) aims at stabilization of the dissected aorta, to prevent late complications by inducing aortic remodelling processes (Fig. 18 C). Obliterating the proximal intimal tear by implantation of a membrane-covered stent-graft redirects blood flow to the true lumen, thus improving distal perfusion. Thrombosis of the false lumen results in shrinkage and conceptually prevents aneurysmal degeneration and, ultimately, its rupture. over time. 

 

Fig. 18: Treatment Options.
References: Braunwald’s Heart Disease VII Edition – 2007 Elsevier Masson srl.

 

Postoperative Complications

 

After surgical repair, patients require regular screening to exclude signs of impending aortic rupture or other complications, including endoleak, prosthetic graft degeneration, infection, malfunction of aortic valve prosthesis, and aneurysm formation in other portions of the aorta (Fig. 19Fig. 20 - Fig. 21 - Fig. 22 - Fig. 23). Follow-up after thoracic endovascular repair is recommended at discharge, at 1, 3, and 6 months, and then yearly. Follow-up after surgical repair is recommended at discharge and then yearly but can be extended to 2 to 3 years if there is stability for the first year.

 

Fig. 19: Anastomotic Pseudoaneurysm is a form of false aneurysm, whose wall does not consist of all normal layers of arterial wall. Mechanisms implicated include infection, poor anastomotic technique, and intrinsic aortic wall disease. Surgical options vary according to pathologic features of the pseudoaneurysm, and operations can be challenging, especially in the presence of infection, previous cardiac surgery, or aortic valve regurgitation.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT
Fig. 20: Aortic Annular Abscess can occur as a complication of aortic valve endocarditis and is more common on a prosthetic aortic valve. Prosthetic valve dehiscence may occur. Early and extensive surgical reconstruction of major aortic annular abscess can be essential, because antibiosis alone is usually inadequate to arrest the destructive effect of the abscess.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT
Fig. 21: Aortic Root Redissection can occur in conservative approach of ascending aortic dissection. Multiple root repair techniques using prosthetic and biologic materials. The two most commonly described methods involve fortification of the aortic wall using Teflon felt and/or biologic glue. The results of using biologic glue as a stand-alone technique demonstrate acceptable operative results, but less durable long-term outcomes.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT
Fig. 22: Endoleak describes perfusion of the excluded aortic pathology and occurs both in thoracic and abdominal (T)EVAR. Different types of endoleaks are illustrated in Fig. 23.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT
Fig. 23: Different types of endoleaks.
References: Radiology, UPMC Italy, ISMETT - Palermo/IT

 

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