What is a mural thrombus?

What is a Mural Thrombus

A mural thrombus is a blood clot that adheres to the wall of a blood vessel or cardiac chamber, protruding into the lumen but remaining attached to the vessel/chamber wall rather than completely occluding it.

Anatomic Definition and Characteristics

A mural thrombus represents organized clot material that forms along and attaches to the inner surface (intima) of a blood vessel or heart chamber 1. The key distinguishing feature is that it projects from the wall into the lumen while maintaining attachment to the underlying surface, creating an irregular luminal contour 1.

Imaging Appearance Across Modalities

On CT angiography, mural thrombus appears as a lower-attenuation filling defect along the vessel wall that does not enhance with contrast, distinguishing it from flowing blood 1:

• The thrombus causes irregular narrowing of the vessel lumen from the wall inward
• External aortic diameter may appear normal despite significant luminal narrowing from thrombus 1
• Pre-contrast images show the thrombus as intermediate density, while post-contrast images demonstrate it as relatively lower attenuation compared to the contrast-filled lumen 1

On echocardiography, mural thrombus appears as a mass attached to the luminal surface with distinct characteristics 1:

• May be visualized as stationary or, in some cases, moving in real-time imaging
• In cardiac chambers, appears as an echodense mass adherent to wall motion abnormalities (particularly in left ventricular thrombus)
• Intravascular optical coherence tomography can distinguish red (RBC-rich) thrombus, which is highly backscattering with high attenuation, from white (platelet-rich) thrombus, which shows homogeneous, less backscattering appearance with low attenuation 1

Critical Distinction from Other Pathologies

Mural thrombus must be differentiated from intramural hematoma (IMH), which represents hemorrhage within the aortic wall itself rather than luminal clot formation 1, 2:

• IMH shows crescentic wall thickening with a smooth inner luminal surface
• Mural thrombus protrudes into the lumen, creating irregular luminal contours
• Atherosclerotic plaque also protrudes into the lumen but has calcification and different density characteristics 1

Pathophysiology and Formation

Mural thrombus formation involves the concerted action of platelet aggregation and fibrin deposition at sites of endothelial injury or flow disturbance 1, 3:

• Platelet adhesion and aggregation initiate the process, forming an early platelet-rich thrombus 1
• Fibrin stabilizes the fragile platelet thrombus, creating a more organized structure 1
• Under high shear conditions, intra-thrombus fibrin development determines the final size and shape of the mural thrombus 3

Location-Specific Considerations

In the aorta, mural thrombus most commonly occurs in the descending thoracic aorta, though it can develop in the arch, ascending aorta, or abdominal aorta 4, 5:

• In aneurysmal aortas, mural thrombus is common and expected
• In normal or minimally atherosclerotic aortas, mural thrombus is rare but highly significant due to embolic risk 4, 5
• Thrombus location in the ascending aorta or arch carries higher recurrence risk (OR 12.7-18.3) 5

In cardiac chambers, left ventricular mural thrombus typically forms in areas of wall motion abnormality 6:

• Most commonly associated with apical akinesis or dyskinesis following myocardial infarction
• Persistent wall motion abnormalities maintain risk even after initial thrombus resolution 6

Clinical Significance and Embolic Risk

The primary clinical danger of mural thrombus is systemic embolization, causing stroke, limb ischemia, or visceral infarction 7, 4, 5:

• Aortic mural thrombus accounts for approximately 5% of peripheral arterial emboli 8
• Mobile or poorly adherent thrombus carries substantially higher embolic risk than firmly adherent thrombus 7, 2
• Without treatment, embolic recurrence rates reach 25-50% with anticoagulation alone 4
• Mortality from complications including stroke and limb loss ranges from 5-6% even with treatment 5

High-Risk Features Requiring Urgent Intervention

Specific thrombus characteristics mandate aggressive management 7, 2:

• Mobile thrombus with poor wall adherence
• Location in high-flow areas (ascending aorta, arch)
• Thrombus causing hemodynamic obstruction or valve dysfunction
• Presentation with embolic stroke or acute limb ischemia

Common Pitfalls in Recognition

Mural thrombus can be confused with other imaging findings, leading to diagnostic errors 1:

• Atherosclerotic plaque: Distinguished by calcification and different enhancement pattern
• Intramural hematoma: Shows smooth inner lumen rather than irregular protrusion
• Imaging artifacts: Venous streaks on CT vary slice-to-slice and extend beyond aortic wall 1
• Aortic motion artifacts: Reduced with ECG-gating and modern reconstruction algorithms 1

In brain capillaries, the term "mural" refers to pericytes and smooth muscle cells surrounding vessels, which is completely unrelated to mural thrombus 1. This represents a different use of the anatomic term "mural" (meaning "of the wall") and should not be confused with intravascular thrombus.