Topics

Topic

design image
Left auricle

The left auricle (also called the left atrial appendage, LAA) is a finger-like muscular pouch projecting from the superior and left aspect of the left atrium. It has a narrow tubular junction with the atrium and irregular internal ridges formed by pectinate muscles. Its shape varies (cactus, chicken wing, windsock, cauliflower), and it serves as an important anatomical and clinical landmark, particularly as the most common site for thrombus formation in atrial fibrillation. The left auricle plays a role in modulating atrial compliance and may contribute to atrial endocrine function by secreting atrial natriuretic peptide (ANP).

Synonyms

  • Left atrial appendage (LAA)

  • Auricula atrii sinistri

  • Left atrial auricle

Function

  • Acts as a reservoir to accommodate changes in left atrial volume and pressure

  • Contributes to atrial contractility through pectinate muscle contraction

  • Plays a role in atrial natriuretic peptide secretion, regulating fluid and blood pressure

  • Clinically important as a site of thrombus formation in atrial fibrillation

MRI Appearance

T1-weighted images:

  • Left auricle lumen appears as signal void if blood flow is normal

  • Thrombus appears as low signal intensity filling defect, not enhancing with contrast

  • Surrounding myocardium appears intermediate signal

T2-weighted images:

  • Flowing blood appears signal void, while slow or stagnant blood may appear variable hyperintense

  • Thrombus appears as a well-defined hypointense mass within the lumen

  • Useful for identifying stasis or thrombus formation

STIR (Short Tau Inversion Recovery):

  • Fat suppression improves visualization of pericardial fat around the auricle

  • Helps distinguish between pericardial pathology vs. intrinsic auricular pathology

T1 Post-Contrast (Gadolinium-enhanced):

  • Thrombus remains as a non-enhancing filling defect

  • LAA function and flow dynamics can be studied with contrast-enhanced cardiac MRI

CT Appearance

Non-contrast CT:

  • Left auricle is seen as a finger-like projection from the left atrium with soft tissue density walls

  • Lumen may contain hypodense thrombus, seen as a filling defect against atrial tissue

Contrast-enhanced CT (Cardiac CTA):

  • Clearly demonstrates the shape, size, and orientation of the left auricle

  • Thrombus appears as a non-enhancing filling defect against contrast-opacified atrium

  • CTA is the gold standard for pre-procedural mapping (e.g., LAA closure devices) and thrombus detection

CT Image

Left auricle anatomy CT axial image -img-00000-00000