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KEY FACTS

Terminology
- Blood enters media of aortic wall through intimal defect and splits wall longitudinally
Imaging
- 2 distinct lumina (false and true) with interposed intimal flap - False lumen: Larger cross-sectional area, beak sign, cobweb sign, thrombosis, and delayed enhancement - True lumen: Continuity with undissected portion of aorta and smaller cross-sectional area
- Radiograph: Progressive aortic enlargement, widened mediastinum (> 8 cm), and abnormal (blunted) aortic knob
- CT: Highly accurate - Slightly less accurate for ascending aorta unless ECG-gated study
- MR: Well-suited for follow-up
- Transesophageal echocardiography: Operator dependent and with limited field of view
Top Differential Diagnoses
- Thrombosed aneurysm
- Aortic wall hematoma
- Syndromes associated with aortic dissection
Pathology
- Media degeneration associated with many diseases and syphilitic aortitis, crack cocaine use, and iatrogenic (catheter angiography, cardiac surgery, valve replacements)
- Tear in intimal layer leading to formation and propagation of subintimal hematoma
Clinical Issues
- Type A: Surgery due to involvement of aortic root
- Type B: Medical control of hypertension is standard
- Percutaneous therapy for complicated nonsurgical patients with type B dissections

TERMINOLOGY

Abbreviations
- Aortic dissection (AD)
Definitions
- Blood enters media of aortic wall through intimal defect and splits wall longitudinally

IMAGING

General Features

Best diagnostic clue

- 2 distinct lumina with interposed intimal flap: Double-barrel aorta
- Displacement of intimal calcification or compression/distortion of aortic lumen

Location

- Stanford classification
        - Type A (60%): Involves ascending aorta
                  - 90% within 10 cm of aortic valve
        - Type B (40%): Does not involve ascending aorta
- DeBakey classification
        - Type I: Originates in ascending aorta, involves at least aortic arch, and may involve descending aorta
        - Type II: Originates in and confined to ascending aorta
        - Type III: Originates in descending aorta; IIIa: Limited to descending aorta; IIIb: Extends below diaphragm

Additional imaging should evaluate involvement of great vessels and celiac, renal, superior mesenteric, and iliac arteries

Radiographic Findings

Radiography

- Often abnormal CXR but nonspecific
        - 25% are normal
- Widened mediastinum (> 8 cm)
- Abnormal (blunted) aortic knob in 66%
- Ring sign: > 5-mm displacement of aortic lumen past calcified aortic intima
        - Apparent displacement of intimal calcification may be projectional artifact
- Left apical cap, tracheal deviation, depression of left mainstem bronchus, esophageal deviation, loss of paratracheal stripe, pericardial effusion, and hemothorax
- Progressive aortic enlargement on serial images
        - Enlarged arch is not specific for diagnosis; usually results from hypertension or atherosclerosis

CT Findings

NECT

- Widening of aorta, irregularity of aortic wall, and intramural or periaortic acute thrombus
- Hyperattenuating mediastinal, pericardial, or pleural fluid (blood)
- Internally displaced intimal calcification

CECT

- ECG gating allows delineation of proximal extent of intimal flap in relation to aortic valve and coronary ostia
- Intimal flap separates true and false lumina
- True vs. false lumen
        - False lumen is larger than true lumen
        - False lumen wedges around true lumen, beak sign
        - Cobweb sign of false lumen due to collagenous media remnants
- False lumen contrast attenuation
        - Usually, slower flow with lower contrast attenuation on arterial phase
        - Thrombosis leads to nonenhancement
                  - Complete thrombosis/reduced flow in false lumen decreases risk of aortic dilatation
- Windsock appearance: Dissection of entire intima leads to circumferential intimal flap
        - Filiform-shaped, narrow true lumen
        - Leads to intimointimal intussusception
- Triple-channel dissection: Secondary dissection within 1 channel (Mercedes-Benz sign)
- Complications of AD
        - Rupture into pericardium, left pleural cavity, mediastinum, right ventricle, left atrium, vena cavae, pulmonary arteries
        - Pericardial tamponade
        - Acute aortic regurgitation
        - Major aortic branch obstruction
        - Visceral or extremity malperfusion
                  - Compression of true lumen by false lumen
                  - Intimal flap in renal, celiac, mesenteric, or extremity arteries
                  - Renal: Absence of nephrographic effect in late phase of CT
- Retrograde dissection into aortic arch
        - In 27% of type B dissections; higher mortality (43%)

MR Findings
- T1WI
```
- Site of intimal tear; type and extent of dissection
- Signal intensity within false lumen is variable
        - Depends on blood flow; thrombus: Presence, age, composition; and pulse sequence
        - Usually signal is seen due to slow flow
                  - Flow void in true lumen
- Useful in abdominal arterial involvement and monitoring of progression of dissection and aneurysm formation
- Aortoannular ectasia
```
- MRA
```
- Demonstrates flap, true and false lumen
- Extent of flap into branch vessels can be seen
- End-organ perfusion can be evaluated
```
- SSFP cine
```
- Intimal flap: Intermediate signal
- Reentry site: Low-signal turbulent flow between lumina
- False lumen with blood flow/thrombus: Medium to low signal
- Aortic insufficiency and pericardial rupture
```
- Phase-contrast imaging - Flow dynamics of lumina can be evaluated - 4D flow MR - Detailed evaluation of hemodynamics - Flow/thrombosis of false lumen evaluated more reliably than CT - Retrograde flow is less in true than false lumen - Helical flow in false lumen is sign of aortic expansion
- Progressive aortic enlargement evaluated by MR/cardiac CT - Features predictive of descending aortic enlargement - > 10-mm primary intimal tear in descending aorta - Descending aorta > 35 mm - False lumen > 22 mm in proximal descending aorta - False lumen > 2/3 of total descending aorta - Partially thrombosed distal false lumen - Distal suture line leak - Helical flow in false lumen
- Remodeling: 10% volumetric difference of aorta - Favorable remodeling: > 10% decrease in false lumen or > 10% increase in true lumen diameter - Unfavorable remodeling: Increased diameter of false and decreased diameter of true lumen - Due to persistent refilling of false lumen - After surgical repair of type A: Persistent arch intimal tear; leak of distal graft anastomosis; refilling from false lumen of dissected aortic arch vessel - After thoracic endovascular aortic repair (TEVAR): Incomplete seal of proximal landing zone due to aortic tortuosity; arch branch stump, supraarch chimney stent or TEVAR technique

Echocardiographic Findings

Echocardiogram

- Transesophageal echocardiography (TEE)
        - Undulating intimal flap within aortic lumen
        - May identify entry site, presence of false lumen thrombus, abnormal flow characteristics, involvement of coronary and arch vessels, pericardial effusion, and aortic valve regurgitation
        - False-positives: May occur if calcified aorta mimics intimal flap

Color Doppler

- Identifies flow in false lumen, site of intimal tear, and presence or absence of aortic insufficiency

Angiographic Findings
- Conventional - False lumen is visualized in 87%, intimal flap in 70%, and site of intimal tear in 56% - May show site of intimal tears, aortic valve regurgitation, coronary artery involvement, and filling of branch vessels - Indirect signs of AD: Compression of true lumen by false lumen and abnormal appearance of branch vessel origins - False-negative angiogram may occur due to thrombosis of false lumen
Imaging Recommendations
- CT: Highly accurate and rapid; imaging procedure of choice - ECG gating or high-pitch helical mode is necessary to avoid risk of false-positives in aortic root
- MR: Better suited in nonemergent setting: Anatomic information; flow dynamics of false and true lumen
- TEE: Possible in most patients, including unstable - Highly dependent on operator experience - Not used if esophageal varicosities or stenosis - Limited view of dissection

DIFFERENTIAL DIAGNOSIS

Thrombosed Aneurysm
- Large aorta and aortic lumen size
Intramural Hematoma
- Hemorrhage within wall with no identifiable intimal tear, flap, or false lumen
- Caused by bleeding from vasa vasorum into media
Penetrating Aortic Ulcer
- Perforation of aortic wall in region of ulcerated atherosclerotic plaque
- Most common in descending aorta
- May progress to dissection
Syndromes and Conditions Associated With Aortic Dissection
- Marfan syndrome, Ehlers-Danlos syndrome, bicuspid aortic valve

PATHOLOGY

General Features

Etiology

- Medial degeneration is associated with many diseases that predispose to dissection
        - Hypertension (70%), atherosclerosis
        - Structural collagen disorder (Marfan or Ehlers-Danlos syndrome)
        - Congenital disease (aortic coarctation; bicuspid or unicuspid valve); pregnancy
- Syphilitic aortitis, crack cocaine use, and iatrogenic (catheter angiography, cardiac surgery, valve replacements)

Dissections almost exclusively originate in thoracic aorta and secondarily involve abdominal aorta
SMMHC marker is helpful in diagnosis

Gross Pathologic & Surgical Features
- Intimal tear: Formation/propagation of subintimal hematoma - 5-10% are without intimal tear; dissection is attributed to rupture of aortic vasa vasorum
- Diseases that weaken aortic wall predispose to AD

CLINICAL ISSUES

Presentation

Most common signs/symptoms

- Sudden onset of ripping or tearing chest pain
- Anterior chest pain: Ascending AD
- Neck or jaw pain: Aortic arch dissection
- Back tearing or ripping pain: Descending AD
- Myocardial infarction
- 50% of AD: Women < 40 years, related to pregnancy

Sudden onset of aortic insufficiency, neurologic deficits in 20% of cases, and ischemic extremity

Demographics

Age

- 75% in 40-70 years; peak at 50-65 years

Sex
```
- M:F = 3:1
```
Ethnicity
```
- Black > White > Asian patients
```

Natural History & Prognosis
- Acute AD: < 2 weeks from initial onset of symptoms; subacute: 2 weeks to 3 months; chronic: > 3 months
- Complications: Rupture, cardiac tamponade, aortic insufficiency with acute heart failure, occlusion of coronary or supraaortic vessels
- 21% of patients die before hospital admission
- If untreated, 33% die within 24 hours; 50% within 48 hours
- < 10% of untreated patients with type A live 1 year
Treatment
- Type A: Surgery due to involvement of aortic root - Ascending aorta only: Supracoronary ascending aorta replacement, intimal resection, aortic valve repair/replacement - Arch/hemiarch: Antegrade thoracic endovascular aortic repair (TEVAR), elephant trunk, frozen elephant trunk, or multibranched arch graft - Bentall procedure: If valve cusps are dissected or with Marfan syndrome with preexisting root aneurysm
- Type B: Conservative treatment is standard (Rx of hypertension) - Surgery in complicated cases - Mesenteric, renal, extremity ischemia - Rupture, aneurysmal enlargement of false lumen; descending aorta > 6 cm - Hemodynamic instability, pseudocoarctation syndrome, distal embolization - Percutaneous therapy (aortic stent graft or fenestration of flap) for complicated nonsurgical patients with type B dissections - Visceral malperfusion, dilated aortic arch or proximal descending aorta (≥ 4.5 cm), impending rupture
- Type A mortality: 60% of medically treated; 30% of surgically treated
- Type B mortality: 10% of medically treated; 30% of surgically treated
- DISSECT classification system for endovascular decision making - Based on 6 features: Duration, intimal tear, size of dissected aorta, segmental extent of involvement, clinical complications, thrombosis of false lumen
- TEVAR in subacute/chronic setting - Descending aorta > 5.5 cm, > 5-mm growth/6 months, refractory pain, impending aortic rupture

DIAGNOSTIC CHECKLIST

Consider
- AD in patient with acute chest pain
- ECG-gated CTA in acute AD; MRA for follow-up
Image Interpretation Pearls
- Identify origin of intimal flap, extent of dissection, and origin of aortic branches from true or false lumen

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References

Selected References

Cases

{'cases': [{'authors': [{'key': '3d1e4c57-c1cf-4c89-b0f0-5d82b29a31e1', 'value': 'Suhny Abbara, MD, FACR, MSCCT, FNASCI'}], 'caseVersionId': '9f6396b1-70ae-4cf3-9985-f5018fc0256a', 'description': 'A type A dissection flap within the ascending aorta (arrow, #1) and high density hemopericardium (open arrows, #1) are evident (#1). Note the dense contrast in the azygos system. There is dissection in the abdominal aorta and superior mesenteric artery (#2). Note that there is dense contrast refluxed and layering in the SVC, due to pericardial tamponade. There is a patent right common iliac artery, and contrast is void in the left common iliac artery (curved arrows, #3), which is occluded by the dissection flap (#3).', 'history': 'Acute onset of tearing pain between scapulas.', 'imagePoolId': 'b20e0be4-906f-477d-9e41-4fd4d7a78023', 'name': 'Type A dissection hemopericardium/tamponade', 'teachingPoint': None, 'demographics': '52 Years old male'}, {'authors': [{'key': '612e745f-e298-40da-8326-de2c383c4fc1', 'value': 'Jud W. Gurney, MD, FACR'}], 'caseVersionId': 'c4211efd-db8c-425c-ab52-babc85237512', 'description': 'Typical radiographic and CT features of ascending aortic dissection in Marfan syndrome.\n\nPortable radiograph (#1) shows prominent ascending aorta (arrow). CECT (#2) shows dilatation of ascending aorta (arrows) and intimal flap (open arrow). Coronal reconstruction (#3) shows intimal flap (open arrow) in ascending aortic dissection.', 'history': 'Chest pain.', 'imagePoolId': '94201114-7b96-4ad9-a6e1-9707e4e48bb7', 'name': 'Ascending aortic dissection', 'teachingPoint': None, 'demographics': '34 Years old male'}, {'authors': [{'key': 'd69a0534-8989-4b83-b19d-c3b640f22e53', 'value': 'Megan R. Saettele, MD'}, {'key': '90e33361-cf04-431b-a6fb-4a18e6aa42a1', 'value': 'Joseph P. Koury, MD'}, {'key': '2e78a4ff-418e-46f9-93e4-c6d95d960e35', 'value': 'Brandt C. Wible, MD'}], 'caseVersionId': 'd806de07-6560-4a7e-99ea-6e0c12d137aa', 'description': 'Axial computed tomography images (#1-7) show acute aortic dissection with the intimal flap (arrows) that extends from the aortic root, into the celiac axis (#4) and superior mesenteric artery (#5), and down through the common iliac arteries (#7). This a Stanford type A, DeBakey type I aortic dissection. Sagittal (#8) and coronal (#9) reconstructions again identify the aortic dissection (arrows) extending throughout the length of the aorta and into the common iliac arteries.\n\nComment: Aortic dissections are described according to the Stanford or DeBakey classification systems. Stanford classification divides aortic dissections into either Type A or Type B, with Type A dissections involving the ascending aorta. Type A dissections are more common (60-70%) than Type B dissections, often requiring surgical treatment, and may or may not involve the descending aorta. Type B dissections involve only the descending aorta distal to the origin of the left subclavian artery. Type B dissections can often be managed with medical therapy. The DeBakey classification system divides aortic dissection into type I (involves the ascending and descending aorta), type II (confined to the ascending aorta), and type III (confined to the descending aorta). A key finding on contrast-enhanced CT images, such as was seen in this patient, is an intimal flap between the true and false lumens. It is important to identify the extent of the dissection as well because they can extend cranially to involve the carotid or vertebral vessels or caudally to involve the celiac, SMA, IMA, renal, or iliac vessels.', 'history': 'Patient presented to the emergency room complaining of tearing chest and back pain.', 'imagePoolId': 'e36adebd-8d00-4674-9e0a-f0e1102822b7', 'name': 'Acute aortic dissection type A and B', 'teachingPoint': None, 'demographics': '59 Years old male'}, {'authors': [{'key': '612e745f-e298-40da-8326-de2c383c4fc1', 'value': 'Jud W. Gurney, MD, FACR'}, {'key': '509cdc73-5701-4807-90e5-cf244eb473c8', 'value': 'Tan-Lucien H. Mohammed, MD, FCCP'}], 'caseVersionId': '857e6cd9-44b3-4f9f-8d73-dcc0d6001d8a', 'description': 'Typical CT features of chronic consolidation from lipoid pneumonia.\n\nCECT (#1,2) shows multifocal consolidation particularly in the right middle lobe (arrows). CECT (#3-9) shows descending aortic aneurysm (arrows). Consolidated lung is of fat density (open arrows, #5-8). Mineral oil aspiration.', 'history': 'Cough.', 'imagePoolId': 'c37cbfc6-9157-46d1-bd7f-9c4920969fb8', 'name': 'Chronic consolidation', 'teachingPoint': None, 'demographics': '65 Years old male'}, {'authors': [{'key': 'd06dfcc4-4b3a-4c2a-b6ae-6ac081d23b98', 'value': 'Jonathan Hero Chung, MD'}, {'key': '3d1e4c57-c1cf-4c89-b0f0-5d82b29a31e1', 'value': 'Suhny Abbara, MD, FACR, MSCCT, FNASCI'}], 'caseVersionId': '229680f9-ecb1-4f64-a6ba-0f0715b5b91f', 'description': 'Axial (#1) and coronal (#2) images from a contrast-enhanced CTA show a dissection flap (arrows) in the ascending aorta, consistent with a type A aortic dissection. Axial VR image (#3) shows that the dissection flap (arrow) does not extend to the distal aspect of the aortic arch. \n\nComment: Typically, type A aortic dissections are treated surgically given their mortal complications, such as cardiac ischemia (from extension into coronary arteries), pericardial tamponade (from rupture into pericardium), and acute heart failure (from involvement of the aortic valve leading to uncompensated aortic insufficiency).', 'history': 'Patient with history of intermittent chest pain.', 'imagePoolId': 'f4acd209-2f91-458a-910c-a4617997c7bf', 'name': 'Type A aortic dissection', 'teachingPoint': None, 'demographics': '66 Years old male'}], 'caseType': 'typical', 'name': 'TYPICAL'}

Images

Selected Images

Frontal chest radiograph shows subtle abnormal contour of the ascending aorta, suggestive of ascending aortic aneurysm , but this finding is nonspecific. The descending aorta is tortuous, which can be seen in systemic hypertension.

Frontal radiograph in the same patient presenting a few months later with acute chest pain shows increased abnormal contour and abnormal widening of the mediastinum , suggestive of aortic dissection.

Axial CTA through the thorax in a patient with Stanford type A dissection shows a nearly circumferential dissection flap involving the ascending and descending aortas. Note the small true lumen in the ascending aorta . The intimal flap can be quite mobile on gated cine imaging.

Axial CTA at the level of arch in the same patient shows extension of the dissection flap into the right brachiocephalic artery . Note the displaced intimal calcification in the descending aorta .

DeBakey type I and Stanford class A include dissections that involve the ascending aorta. DeBakey type II is confined to the ascending aorta, and type I extends beyond. DeBakey type III dissections are confined to the descending aorta. Stanford class B includes all dissections not involving the ascending aorta (involving arch &/or descending aorta).

"Candy cane" sagittal oblique (left) and axial (right) CTA views show Stanford type A aortic dissection with partially thrombosed false lumen .

Axial and VR CTA show Stanford type B aortic dissection involving descending thoracic and abdominal aorta. The true lumen is smaller and located laterally. Note the infrarenal abdominal aortic aneurysm .

Transthoracic echocardiogram shows ascending aortic dissection with dissection flap (white interface ) separating true and false lumina. Most of the false lumen is hyperechoic, suggesting thrombosis . The small, anechoic portion corresponds to a patent false lumen .

Axial CECT shows acute type A aortic dissection with flap that is convex toward false lumen . Note that a beak sign is present in the false lumen. The appearance of a beak sign is attributed to the higher systolic pressure in the true lumen.

Axial MRA shows chronic type B aortic dissection with partial thrombosis of the false lumen (hypointense area) . Compared with the false lumen, the true lumen is relatively small . Note the perfused portion of the false lumen .

Axial NECT, CTA, and MR in a patient with type B aortic dissection are shown. The aortic dissection is not seen on NECT. Axial unenhanced MR shows aortic dissection on HASTE (dark blood) and SSFP (bright blood) , an advantage over NECT.

Axial NECT and CTA show chronic descending thoracic aortic dissection with a flat dissection flap. Outer wall calcification and thrombus are present in the false lumen .

Axial CECT shows a high-attenuation pericardial effusion , consistent with a hemopericardium, as well as bilateral trace pleural effusions . The dissection flap is clearly visible in the descending thoracic aorta .

Axial CTA shows abdominal aortic dissection with Mercedes-Benz sign relating to a triple-channel dissection resulting in 2 false lumina . One of the 2 intimal flaps extends to the origin of the right renal artery .

Axial (left) and oblique (right) CTA demonstrate a type A aortic dissection involving the right coronary artery ostium in a patient status post percutaneous aortic valve implantation/replacement (TAVI/R).

Axial CTA shows an abdominal aortic dissection . Note that the dissection flap does extend into the superior mesenteric artery , which remains well perfused.

Axial CTA shows partial eccentric thrombosis of the false lumen in a chronic aortic dissection. The celiac artery arises from the false lumen and is thrombosed.

Oblique MIP CTA shows dissection of the descending thoracic and abdominal aorta. Note main and accessory renal arteries arising from the partially thrombosed false lumen and a subtotal infarct of the left kidney . Main and accessory renal arteries demonstrate partial flow.

Axial CTA shows a dissection flap extending into the left common carotid artery . The true lumen is smaller and enhances more than the false lumen .

Axial (left) and coronal (right) CTA show atypical appearance of an aortic dissection involving the entire intima of the thoracic aorta circumferentially. This phenomenon may subsequently lead to intimointimal intussusception.

Sagittal MRA shows an aortic dissection, which is seen starting from the arch distal to the origin of the left subclavian artery , and extends into the abdominal aorta, extending into the iliac arteries. The true lumen enhances more than the false lumen .

Coronal MR cine shows the false lumen supplying the left renal artery. The small, compressed true lumen supplies the right renal artery. The false lumen is thrombosed in the infrarenal area.

Additional Images

Coronal CTA shows marked compression of the true lumen by the false lumen . There is partial thrombosis of the false lumen, although still with some enhancement.

Coronal CECT shows a dissection flap extending from the aortic arch into the descending aorta. The flap is spiraling down the aorta with involvement of the aortic branches.

Coronal CTA shows compression of the true lumen in the abdominal aorta . Right renal artery is supplied by the true lumen . Left renal artery originates from the false lumen.

Oblique catheter angiography shows both the true lumen and the false lumen . There is a flap in the innominate artery and decreased flow in other great vessels .

Axial CECT shows a chronic dissection of the abdominal aorta. There are 2 regions of perfusion , and the rest of the aorta is thrombosed .

DSA shows a bizarre appearance of the abdominal aorta. Note marked smooth narrowing of the infrarenal aorta with change in caliber and contrast enhancement. Also note narrowing of the left renal artery , which may be related to involvement by dissection.

Sagittal CTA shows a dissection. The false lumen compresses the true lumen . The true lumen supplies the celiac axis and superior mesenteric artery .

45 KiB Raw Permalink Blame History

KEY FACTS

Terminology

Imaging

Top Differential Diagnoses

Pathology

Clinical Issues

TERMINOLOGY

Abbreviations

Definitions

IMAGING

General Features

Best diagnostic clue

Location

Radiographic Findings

Radiography

CT Findings

NECT

CECT

MR Findings

T1WI

MRA

SSFP cine

Echocardiographic Findings

Echocardiogram

Color Doppler

Angiographic Findings

Imaging Recommendations

DIFFERENTIAL DIAGNOSIS

Thrombosed Aneurysm

Syndromes and Conditions Associated With Aortic Dissection

PATHOLOGY

General Features

Etiology

Gross Pathologic & Surgical Features

CLINICAL ISSUES

Presentation

Most common signs/symptoms

Demographics

Age

Sex

Ethnicity

Natural History & Prognosis

Treatment

DIAGNOSTIC CHECKLIST

Consider

Image Interpretation Pearls

References

Selected References

Cases

Images

Selected Images

Additional Images

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