【Imaging basis】Aortic interwall hematoma

Intramural hemorrhage and hematoma (IMH) refers to bleeding within the aortic wall or localized hematoma formation within the aortic wall
, which is a special type of aortic dissection.
In 1920 Krukenberg first described IMH as "an interlayer without an intimal fracture
".

1.
Epidemiology

The annual incidence of aortic dissection is about 5-30/1 million people, about 8~15% of acute aortic syndrome is aortic interwall hematoma, through various imaging examinations found that the proportion of intermural hemorrhage and hematoma in patients suspected of aortic dissection is about 10-30%,

10% of patients diagnosed with aortic dissection are intermural hematomas
.
The literature reports that this variant of acute dissection is more common in older people (mean age 70 years) with long-term hypertension and comorbidities of hypertension such as stroke and abdominal aortic aneurysm, while the typical dissection patient is younger (mean 56 years).

As with typical dissection, there are more males than females, but more
women have been reported in the literature for acute intermural hematomas.

2.
Etiology and pathogenesis

The most common cause is cystic necrosis of the middle layer of the aorta and rupture of trophoblastic vessels or "infarction of the aortic wall," with blood spilling into the outer layer of the middle membrane near the outer membrane, or plaque rupture
.
Stanson et al.
suggest that intermural hematomas can come from penetrating ulcers and plaque ruptures
.
Hypertension, blunt chest injury, and giant cell arteritis are also possible causes
.
Regardless of anatomical location, chronic hypertension (84%) and Marfan syndrome (12%) are the two main associated factors, and others such as diabetes, pregnancy, a history of heavy continuous smoking, or abdominal aortic disease are also common in IMH patients, so their causes are
multifactorial.

At present, there are two main views on the mechanism of aortic dissection: one is that aortic dissection originates from the rupture of the intima and then the tear and expansion
of the middle membrane.
The hydrodynamic force of the blood flow is generated by pulse wave conduction, and the production of blood pressure during each systolic phase acts kinetic energy on the aortic wall (the ascending aorta is maximum).

Part of the kinetic energy is stored in the vein wall as potential energy to maintain diastolic blood flow
.
The intensity of blood flow fluid dynamics is related
to mean BP and dP/dt.
The combination of these factors eventually leads to a tear of the aortic intima and the extension of the dissection to the middle layer of the aortic wall, especially in patients
with endometrial degeneration.
This is why intimal tears occur in the areas of maximum dP/dt and pressure pulsation of
the aorta.
Another view is that aortic dissection results from intermural hemorrhage and mid-membrane hematoma formation, followed by endometrial rupture and development into a classic dissection
.

The literature reports that the proportion of acute aortic dissection of intermural hematomas during follow-up is about 28-47% and is associated with
21-47% of aortic ruptures.
It has been argued that the aortic interwall hematoma should be considered a precursor to
classic aortic dissection.
Other authors have suggested that the clinical presentation of IMH is similar to classical aortic dissection, but the epidemiology and prognosis are different, and can be regarded as a different clinical event or a variant of aortic dissection, a view accepted
by the European Society of Cardiology in 2001.

The occurrence of intermural hematomas can be divided into primary and secondary
.
The former is caused by rupture of nourishing blood vessels, and various imaging examinations or surgery/autopsy have confirmed that there is no intimal tear or ulcer communicating with the aortic lumen
.
The latter is often secondary to a ruptured sclerosing plaque or aortic ulcer, but can also occur proximal to a typical or localized dissection, and may be formed by blood components forming through the ulcer orifice or dissection breakage through the ulcer orifice or dissection fracture under high pressure in the aortic lumen due to the loosening of the aortic wall due to mid-level lesions
.
An acute intermural hematoma of ascending aorta with detached ascending aorta reported by Nienaber et al.
is likely to fall into this category; Song JK et al.
have also reported a case
of proximal and ascending aortic interwall hematoma secondary to microfocal dissection.
Cases
of ulcers with intermural hematomas and microfocal dissection with intermural hematomas have also been seen in clinical practice.

3.
Clinical manifestations

As with typical dissection, almost all patients present with sudden, acute chest or back pain, some with abdominal pain, and some with asymptomatic
symptoms.
The pain can be sharp cut, tearing, or dull, and the patient's description of pain may vary from person to person, but pain in patients with aortic dissection is characterized by metastatic or extended chest pain
.
The initial pain may be followed by a painless phase that lasts for a few hours to a few days, and then some patients have pain again
.
Recurrent pain after this painless interval is a bad omen and usually signals impending rupture
.

The follow-up comparison of 37 cases of type B IMH and 69 cases of typical type B dissection by Sueyoshi et al.
showed that there was no difference
in age, sex, and concomitant diseases.
A comparison of 51 cases of IMH and 45 cases of typical dissection by Shimizu et al.
showed that the distal side of IMH was more common, while the proximal end of typical dissection (type A) was more, and the systolic blood pressure of IMH patients was higher
on admission.
Most patients with aortic dissection have hypertension, but 25% have systolic blood pressure < 100 mmHg, and hypotension and shock are caused by
acute severe aortic regurgitation or dissection rupture, cardiac tamponade, or left ventricular insufficiency.
About 42% of patients with IMH have aortic reflux, and a diastolic murmur may be detected on examination, pericardial effusion occurs in 60% to 100% of patients with ascending aortic involvement, pleural effusion occurs in 47% to 50% of patients, and there can also be peri-aortic or mediastinal effusion
.

4.
Diagnosis

The diagnosis of IMH is established primarily by imaging studies
.

CT inferior intermural hematoma is defined as crescent-shaped or circumferential aortic wall thickening > 0.
7 cm, which may be accompanied by intimal calcified plaque inversion
.
The appearance of the stratification extends longitudinally for 1~20cm, without inner diaphragm or inner membrane tear.

The density of fresh intermural hematoma is stronger than that of the adjacent aortic wall, and the CT value is usually 60~70HU; When partial or complete thrombosis manifests as multi-layered manifestations
of increased density.
CT with contrast may clearly show crescent-shaped or circumferential thickened aortic walls
.
CT sensitivity 83~94%, specificity 87~100%.

IMH appears on MRI as a crescent-shaped or high-density area
of circumferential travel along the aortic wall.
T1 image is indistinguishable, while T2 is like fresh blood high signal, while 1~5 days IMH shows low signal intensity
.
Subacute IMH exhibits strong T1T2 signaling
due to methemoglobin formation.
MRI sensitivity and specificity are 95~100%.

Yamada et al.
noted that due to the slow blood flow at the edge of the blood vessel, the thickness of the hematoma shown by MRI may be greater than it really is
.

TTE diagnostic sensitivity 35~80%, specificity 39~96%.

The presence or absence of aortic regurgitation
can be known at the same time.
Ultrasound Doppler can distinguish anterior, backward, or delayed blood flow
in the pseudoluminus.

The main points of TEE diagnosis of IMH include: 1.
thickening of the local aortic wall; 2.
no echoic cavity between the walls; 3.
no dissection membrane, traffic blood flow or Doppler blood flow signal; 4.
Intrinsic calcification
of the inner membrane.
The sensitivity of TEE diagnosis is 98%, and the specificity is 63~96%.

The main limitation of TEE is the examiner's experience, which is limited to the thoracic aorta and proximal abdominal aorta, and is difficult to see
below the abdominal trunk.
Esophageal varices cannot be done
.

Endovascular ultrasound: IMH shows thickening of the aortic wall, including aechoic zones (images that cause stratification of the aortic wall) or structures
with uneven echo within the aortic wall.

Aortogram: because there is no intimal rupture, aortogram is of little diagnostic significance for IMH, but careful and thorough examination can help rule out aortic ulcers or intermural hematomas
secondary to minor partial dissection.

The diagnosis of aortic interwall hematoma is mainly based on radiographic data, and the aortic wall shows separated multi-layer manifestations or > aortic wall thickening of 0.
5 cm
due to bleeding.
On the tomogram, the aortic wall changes in crescent-shaped or annular thickening
.

5.
Classification

In 2001, the European Society of Cardiology confirmed the classification method of aortic dissection proposed by Svensson et al.
, which divided dissection into 5 categories, including:

Class I is typical AD, that is, the avulsed inner diaphragm divides the aorta into true and false two lumen;

Class II aortic middle degeneration, subintimal hemorrhage and secondary hematoma;

Thrombosis secondary to class III microdissection;

Class IV aortic plaque ulcer formed by rupture of aortic plaque;

Class V iatrogenic or traumatic AD
.

Intermural hematomas, as a special type of dissection, can be divided into two subcategories:

Subclass A shows that the inner wall of the aorta is smooth, the diameter of the aorta does not exceed 3.
5 cm, and the thickness of the aortic wall does not exceed 0.
5 cm
.
About one-third of these patients on ultrasonography can find a hypoechoic area in the aortic wall, no blood flow signal in the hypoechoic area, and the average length of the hematoma is about 11 cm, which is common in the ascending aorta
.

Subclass B mostly occurs in patients with aortic atherosclerosis, there are rough atherosclerotic plaques and calcified areas on the inner wall of the aorta, the diameter of the aorta is more than 3.
5cm, the average thickness of the aortic wall is about 1.
3cm, and about 70% of such patients can find hypoechoic areas
on ultrasound.
These lesions are more likely to occur in the descending aorta than in the ascending aorta
.

In class III and class IV dissections can also be accompanied by aortic interwall hematomas, so a total aorta or contrasted CT
is required.
Nevertheless, diagnosis based on a variety of clinical examinations may overestimate the proportion of aortic interwall hematomas, as endometrial tears are often found during surgery or autopsy
.

6.
Treatment

Except for those with low blood pressure, all patients should start intravenous antihypertensive drugs
as soon as they are considered for diagnosis of acute aortic dissection.
The goal of drug treatment is to reduce left ventricular contractility, thereby reducing the dP/dt of the aortic pulse wave, and the lower the blood pressure without affecting the perfusion of vital organs, the better
.
The current standard medical treatment for aortic dissection is a combination of β blockers and vasodilators (e.
g.
, nitroprusside).

β blockers should be started before nitroprusside, otherwise vasodilation causes increased reflex catecholamine release, leading to increased left ventricular contractility and increased aortic dP/dt, which will accelerate the development of
dissection.
Labetalol is a α-receptor and β-antagonist that can be used as an alternative to β combination of receptor blockers and nitroprusside
.

Once a diagnosis of aortic dissection is considered, the patient should be referred to a medical center
with interventional or surgical support.
Active surgical intervention should be performed if:

1.
Pain does not decrease or pain recurs under aggressive medical treatment;

2.
Rapid local expansion of the aorta;

3.
There is leakage or the risk of rupture, especially on the basis of the original aortic aneurysm;

4.
Compression of large branch blood vessels;

5.
The original connective tissue is abnormal.

Ascending aorta involvement is generally considered an indication
for surgery due to its intrinsic rupture, cardiac tamponade, and risk of coronary sinus compression.
Data from Asia suggest that conservative treatment of proximal IMH is more
effective.
Distal IMH recommends close observation, elective or emergency stent prosthetic vascular implantation
.

Mohr-Kahaly S, et al.
report that TEE can see contradictory movements
between the parietal layers of intermural hematomas with the cardiac cycle.
This contradictory movement is not conducive to the hemostasis of the nourishing blood vessels ruptured between the walls, and this fluctuation is not conducive to the stimulation of the aortic epimembrane is not conducive to pain relief and thus affects the control of blood pressure, there was a case of conservative treatment of distal intermural hematoma patients, using a variety of intravenous antihypertensive drugs, blood pressure gradually stabilized
after 3 weeks.
The covered stent can effectively inhibit this contradictory movement of the intima, reduce the direct impact of blood flow on the tube wall, and form a certain compression on the intermural hematoma, so that the intermural hematoma stops developing and gradually absorbs
.
There were no perioperative deaths of distal intermural hematomas treated with stents, and intermural hematomas were rapidly absorbed
.
Aggressive endoluminal stent therapy
is indicated for type B aortic interwall hematomas with pain, difficulty controlling blood pressure, some compression of the false lumen on the true cavity, or various signs of rupture.

7.
Prognosis

The natural history of aortic interwall hematomas is similar to typical dissection, and morbidity and mortality are related to
the site of involvement.
In addition to intimal rupture to typical dissection, deep perforation of the aortic wall can lead to rupture or pseudoaneurysm formation
.
Among the 25 patients with aortic interwall hematoma reported by Nienaber et al.
, 8 patients progressed to typical dissection rupture and/or acute cardiac tamponade within 24~72 hours (32%)
.

Pericardium, thoracic, or mediastinal effusion is important and indicates impending rupture and should be actively intervened
.
The proportion of spontaneous remission is about 6% in the ascending aorta and about 45%
in the descending aorta.
The European guidelines for aortic dissection point out that follow-up data confirm that 28%~47% of patients with bleeding and hematoma formation in the aortic wall will develop class I AD, and 10% of patients can heal
on their own.
The mortality rate of ascending aortic interwall hematoma reached 80% after 30 days of conservative treatment, and no death within 30 days after surgical replacement of artificial blood vessels; At 1 year of follow-up, the survival rate was 71.
4% in the surgical group compared with 20%
in the medical treatment group.
Early mortality of arch intermural hematoma is 50%
with conservative treatment.
One person died in the descending aortic interwall hematoma group and no deaths in the surgical treatment group, but there was no statistical difference, and there was no difference
in the 1-year survival rate between surgery and medical treatment.
Shimizu et al.
reported that aortic intermural hematomas are not uncommon in acute aortic dissection (53%), with mortality of 13% in the surgical group compared to 42% for typical dissection, and 9% for in-hospital hematomas and 39%
for dissection in the conservative group.
Mortality from open heart surgery or conservative management was higher than that from endoluminal therapy
.
Endoluminal aortic stent therapy is an important method
for the treatment of aortic dissection, especially type B dissection, which has been widely used in recent years.

Intermural hematomas of type B aortic that are potentially at risk of rupture should be aggressively implanted with endoluminal stents
.