Aortic intramural hematoma (IMH) is a hematoma within the media layer of the aortic wall caused by spontaneous rupture of the vasa vasorum without an intimal tear. It falls within the acute aortic syndrome spectrum and accounts for 5-20% of cases. Unlike classic dissection, there is NO intimal flap or false lumen flow. Crescent-shaped hyperdense wall thickening on non-contrast CT is pathognomonic. 10-30% of cases may progress to classic dissection.
Age Range
50-85
Peak Age
65
Gender
Male predominant
Prevalence
Uncommon
In IMH, the vasa vasorum (small vessels supplying the vessel wall) within the aortic wall spontaneously rupture, causing hemorrhage within the media layer. This hemorrhage pushes the intima toward the lumen, causing wall thickening but does not create an intimal tear. On non-contrast CT, fresh blood appears hyperdense (60-70 HU) due to the high protein content of hemoglobin, forming crescent-shaped wall thickening. On contrast-enhanced CT, the hematoma does not enhance because there is no communication with the lumen — this feature is the critical distinguishing finding from false lumen enhancement in dissection. On MRI, T1 hyperintense signal in the subacute period due to methemoglobin formation is pathognomonic.
Crescent-shaped hyperdense (60-70 HU) wall thickening without intimal flap on non-contrast CT — pathognomonic finding of IMH.
Crescent-shaped hyperdense thickening in the aortic wall on non-contrast CT. Acute hematoma density is 60-70 HU, denser than surrounding soft tissue and intraluminal blood. Wall thickness typically ranges from 5-15mm.
Report Sentence
Crescent-shaped hyperdense wall thickening is identified in the aortic wall on non-contrast CT, consistent with acute intramural hematoma.
No intimal flap is seen on contrast-enhanced CT and the wall thickening does not enhance. There is no communication between the lumen and hematoma. This is the fundamental distinguishing finding from false lumen enhancement in dissection.
Report Sentence
No intimal flap or enhancement of the wall thickening is identified on contrast-enhanced CT, supporting the diagnosis of intramural hematoma.
Hyperintense crescent-shaped thickening in the aortic wall on MRI T1-weighted sequences. T1 hyperintensity becomes prominent in the subacute period (3-14 days) due to methemoglobin formation. Black-blood sequences best demonstrate the wall hematoma.
Report Sentence
Hyperintense crescent-shaped thickening in the aortic wall is identified on MRI T1-weighted sequences, consistent with subacute intramural hematoma.
Variable signal on MRI T2-weighted sequences depending on hematoma stage: low signal in acute phase (deoxyhemoglobin), high signal in subacute phase (extracellular methemoglobin), low signal in chronic phase (hemosiderin).
Report Sentence
Variable signal characteristics corresponding to hematoma stage are identified in the aortic wall on MRI T2-weighted sequences.
Smooth inner surface of the aortic lumen on non-contrast CT — absence of intimal flap or irregularity. The hematoma remains confined within the wall and the luminal surface is undisturbed.
Report Sentence
The inner surface of the aortic lumen is smooth without intimal flap, supporting the diagnosis of intramural hematoma.
Crescent-shaped echogenic thickening in the aortic wall on transesophageal echocardiography (TEE). No intimal flap or intraluminal flow duplication is observed. TEE has high sensitivity for ascending aorta IMH.
Report Sentence
Crescent-shaped echogenic thickening in the aortic wall without intimal flap is identified on TEE, consistent with intramural hematoma.
In some IMH cases, a small focal contrast outpouching within the hematoma (ulcer-like projection — ULP) may be seen on CT angiography. This finding represents a localized intimal defect within the hematoma and carries progression risk.
Report Sentence
An ulcer-like projection (ULP) is identified within the intramural hematoma area; close follow-up is recommended due to progression risk.
Criteria
Intramural hematoma involving the ascending aorta. Considered Stanford Type A dissection equivalent.
Distinct Features
May require surgical intervention (especially in Asian populations). Risk of tamponade and aortic regurgitation. Progression rate higher than Type B.
Criteria
Intramural hematoma involving only the descending aorta.
Distinct Features
Generally medical management. 60-80% of cases show spontaneous regression. ULP or size increase is considered complicated.
Criteria
Focal intimal defect and contrast leakage into hematoma in the setting of IMH. ULP size typically 3-10mm.
Distinct Features
Increased risk of progression to classic dissection. More aggressive treatment (TEVAR) should be considered. Strict imaging follow-up required.
Distinguishing Feature
Dissection HAS intimal flap and false lumen enhancement. IMH has NO intimal flap and wall thickening does not enhance.
Distinguishing Feature
PAU shows a prominent focal contrast outpouching (ulcer crater). Isolated IMH has no focal outpouching (except ULP).
Distinguishing Feature
Aortic rupture has active contrast extravasation and periaortic/retroperitoneal hematoma. In IMH, bleeding is confined within the aortic wall.
Distinguishing Feature
Takayasu arteritis has long-segment concentric wall thickening that enhances. IMH wall thickening does not enhance and appears hyperdense on non-contrast CT.
Urgency
emergencyManagement
medical/surgical depending on typeBiopsy
Not NeededFollow-up
serial CTA at 48h, 1 week, 1, 3, 6, 12 monthsType A IMH is managed surgically like Type A dissection (ascending aorta replacement). Type B IMH is generally managed with medical therapy (antihypertensives, pain control). TEVAR is considered for ULP, size increase, or worsening symptoms. Strict imaging follow-up is mandatory because 10-30% of cases progress to classic dissection.
IMH is part of acute aortic syndromes with 16-47% risk of progression to dissection. Surgery should be considered for Stanford A IMH (debated), while medical therapy is preferred for Stanford B. Serial CT/MR follow-up (1, 3, 6 months) assesses regression, stabilization, or progression.