1. Classification of acute aortic syndromes

Acute aortic syndromes (AOS) are emergency conditions involving the aorta that share similar characteristics. They occur when blood pervades the aortic wall, either due to disruption of the intima/media layers or to rupture of the vasa vasorum. The local inflammatory response to blood may provoke aortic dilation and rupture.

Apart from the DeBakey and Stanford classification systems, Svensson et al. established a classification differentiating five types of AOS, which was later adopted by the European Society of Cardiology and the American Heart Association guidelines (Fig. 1). Whilst AOS classes 1, 2, 4 and 5 are widely recognized amongst radiologists, AD3 has been reported to be less acknowledged, and only a few cases have been published in the literature.

2. Aortic dissection class 3: a brief overview

Over the years, AD3 has received different nomenclatures, including “limited intimal tear”, “incomplete”, “subtle” or “discrete” dissection. AD3 is uncommon (≈5% of AOS), slightly predominates in males, and preferentially affects the ascending aorta. A number of heart conditions have been associated with AD3, including hypertension, angina pectoris, syncope, aortic aneurysm, abnormal aortic valve, and pericardial effusions. Recently, two case series of AD3 have been published, enabling a better understanding of this entity (Table 1). Nevertheless, AD3 remains difficult to detect on imaging.

Anatomically, AD3 consists of a linear or stellate tear of the aortic outline with retracted edges that may be undermined to a variable degree and an outward bulge of the outer aortic contour (Fig. 2). Historically, these lesions have been referred to as “mushroom cap lesions” or “stretch marks" based on their angiographic appearance.

The typical CT appearance of AD3 consists of an oval or band-like luminal contour defect, with subtle step-offs representing the retracted edges. When undermined, the edges are easier to identify as linear filling defects (“focal flaps”) with or without associated subtle wall hematoma. The base of the defect typically bulges outward. Other CT findings that can be associated with AD3 include infiltration of the mediastinal fat by fluid or blood, pericardial effusion, and other AOS -particularly CAD and IH-.

In the next sections, the CT imaging findings of AD3 and common associated features will be illustrated apropos of 5 cases diagnosed in our hospital.

3. Case 1. Non-treated AD3 that evolved to CAD

A 52-year-old male patient, with a history of obesity, heavy-smoking, and hypertension presented to the emergency department (ED) with a chief complaint of oppressive chest pain. His systolic BP was over 200 mmHg, but no other abnormalities were detected. On suspicion of AOS, a CT angiography of the aorta (CTA) was ordered, showing irregularity of the aortic contour that was initially interpreted as an artifact. The patient was admitted to the cardiology department and a CT scan with cardiac gating was performed 24 hours later (Fig. 3A-B), revealing the same findings, which were then interpreted as a “small fissure”.

The patient’s condition improved with conservative treatment, thus he was discharged. A control CT scan performed one month later revealed a Stanford A CAD (Fig. 3C-D), and the patient underwent immediate aortic valve replacement. Retrospectively, we came to the conclusion that this case was initially an AD3.

4. Case 2. AD3 with secondary saccular dilation

A 63-year-old male with several cardiovascular risk factors was referred to the cardiology department due to a history of weight loss and syncopes for 3 months. An echocardiogram showed an enlarged ascending aorta and a possible IH, with no evidence of AD. A CTA was ordered to rule out AD, revealing a large-size saccular aneurysm emerging from the left anterolateral wall of the aortic arch, with a “mushroom cap” appearance (Fig. 4). The patient was diagnosed with a Stanford A AD 3 with secondary saccular dilation. Aortic surgery was performed, with resection of the defect and aortic replacement. Surgery was uneventful, although the patient developed embolic bowel ischemia during the post-operative period. After bowel resection, he evolved favorably and remains asymptomatic to date.

5. Case 3. AD3 in an aortic aneurysm with associated mediastinal hematoma

A 71-year-old female patient was referred to our department to confirm an aneurysm of the ascending aorta incidentally detected in the cardiology department. CTA confirmed a large aneurysm, with a diameter of approximately 7 cm (Fig. 5A). Because the patient was not symptomatic, she was scheduled for surgery in the upcoming months. However, one month after the CTA, she presented to the ED with oppressive central chest pain and systolic pressure over 200 mmHg. A CTA was ordered on suspicion of aortic complication. The CT revealed a limited aortic dissection in the left anterolateral wall of the ascending aorta that was not previously present associated with a mediastinal hematoma (Fig. 5B).

The patient underwent emergent surgery, consisting of replacement of the ascending aorta using a supracoronary tube graft. Surgery and postoperative were uneventful and the patient was discharged a few days later, remaining asymptomatic and with normal control exams to the present date.

6. Case 4. AD3 managed conservatively

An 81-year-old male patient presented to the ED with a chief complaint of central chest pain and dyspnea for 2 days. His history revealed a myocardial revascularization surgery one month earlier due to severe coronary disease. On suspicion of post-surgical complications, he was admitted to the cardiac surgery department for a complete work-up. An echocardiogram, showing an image suggestive of atherosclerotic ulcer. The patient was referred to our tertiary hospital, and a CTA was performed, revealing a Stanford A AD3 in the left anterolateral wall of the aorta (Fig. 6).

Given the high surgical risk of the patient, he was managed conservatively and was discharged a few days later. In the follow-up (12 months), the patient was admitted to the hospital on several occasions due to episodes of chest pain, but he responded well to medical treatment.

7. Case 5. AD3 after implantation of an aortic valve

A 70-year-old female patient with a history of severe aortic valve stenosis was admitted to the cardiac surgery department for scheduled implantation of a sutureless biological aortic valve. Surgery was uneventful, but on the 3^rd day after surgery, the patient developed an acute episode of dizziness and syncope. On medical treatment, her condition improved but two days later she abruptly complained of intense chest pain and her general status quickly worsened. She was admitted to the ICU and, on suspicion of postoperative complications, a CTA was ordered.

The CTA showed a Stanford A AD3 on the lateral wall of the ascending aorta (Fig. 7). The patient was admitted to the operating room, where the dissection was confirmed, and a supracoronary tube was implanted. The patient evolved favorably and was discharged one week later. She remains asymptomatic to the present date.