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Left main coronary artery (LMCA)

The left main coronary artery (LMCA), also called the left main stem, is the short but critically important proximal segment of the left coronary circulation. It arises from the left coronary sinus of the aortic root and courses between the pulmonary trunk and left atrial appendage before bifurcating into the left anterior descending artery (LAD) and the left circumflex artery (LCx). In some individuals, it trifurcates, giving rise to the ramus intermedius artery.

The LMCA is usually 10–15 mm in length, but its size and branching pattern vary. Because it supplies a vast myocardial territory through its branches, significant LMCA stenosis is associated with high mortality and often termed the “widow-maker” lesion when left untreated.

Synonyms

  • LMCA

  • Left main coronary artery stem

  • Left main trunk

Function

  • Provides the primary blood supply to the left heart via LAD and LCx

  • Indirectly supplies:

    • Anterior LV wall, septum, and apex (via LAD)

    • Lateral and posterior LV walls (via LCx)

  • Maintains cardiac contractility, conduction, and perfusion of the majority of the LV myocardium

  • Serves as a critical target for PCI, stenting, and CABG

Branches

  • Left anterior descending artery (LAD): anterior LV wall, septum, apex

  • Left circumflex artery (LCx): lateral and posterior LV wall

  • Ramus intermedius (when present): supplies intermediate territory between LAD and LCx

MRI Appearance

T1-weighted images:

  • Flowing blood appears as a signal void (black lumen)

  • LMCA seen as a tubular hypointense structure between pulmonary trunk and left atrial appendage

T2-weighted images:

  • Blood flow also appears as a signal void

  • Adjacent pathology (edema, mass, compression) shows hyperintensity

STIR (Short Tau Inversion Recovery):

  • Fat suppression improves visibility of vessel margins

  • Adjacent edema or inflammatory change appears bright hyperintense

T1 Post-Contrast (Gadolinium-enhanced):

  • Lumen enhances homogeneously and brightly

  • Useful for identifying stenosis, dissection, aneurysm, or anomalous origin

MRI Non-Contrast Cardiac-Gated 3D Coronary MRA:

  • ECG-gated, respiratory-navigated acquisition

  • LMCA visualized as a bright continuous lumen from aortic root to LAD/LCx bifurcation

  • Demonstrates origin, branching pattern, and anomalies

  • Valuable in patients unable to receive contrast or with congenital coronary anomalies

CT Appearance

Non-contrast CT (Calcium Scoring):

  • LMCA visualized for calcification assessment

  • Calcified plaques quantified by Agatston score for cardiovascular risk prediction

CT Coronary Angiography (CCTA):

  • Gold-standard non-invasive modality for LMCA imaging

  • Shows origin from left coronary sinus, course, bifurcation/trifurcation

  • Detects stenosis, occlusion, aneurysm, dissection, or anomalous course

  • Multiplanar and 3D reconstructions aid PCI and CABG planning

  • Essential in evaluating LMCA disease, plaque morphology, and stent patency

CT image

left main coronary artery (LMCA) mri axial image

CT image

left main coronary artery (LMCA) anantomy CT axial image -img-00000-00000