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Left internal thoracic veins

The left internal thoracic veins (also called the internal mammary veins) are paired venous channels that accompany the left internal thoracic artery along the posterior surface of the anterior thoracic wall. They begin as venae comitantes of the internal thoracic artery, arising from the superior epigastric and musculophrenic veins, and ascend vertically on either side of the sternum.

The two veins usually form a venous plexus that converges superiorly into a single trunk, which drains into the left brachiocephalic vein. They receive tributaries from the anterior intercostal veins, pericardiophrenic vein, superior epigastric vein, and musculophrenic vein.

These veins are clinically important because of their role as collateral pathways in superior vena cava (SVC) obstruction, providing alternative drainage via the epigastric and intercostal systems. They are also relevant in cardiothoracic surgery (e.g., internal thoracic artery harvesting for CABG), where venous variations may affect operative planning.

Synonyms

  • Left internal mammary veins

  • Venae thoracicae internae sinistrae

Function

  • Drain the anterior thoracic wall and breasts

  • Receive tributaries from anterior intercostal, pericardiophrenic, superior epigastric, and musculophrenic veins

  • Provide important collateral circulation in SVC obstruction

  • Serve as surgical landmarks in cardiothoracic and breast surgery

MRI Appearance

T1-weighted images:

  • Appear as low-signal tubular structures (flow voids) accompanying the internal thoracic artery

  • Surrounded by intermediate signal mediastinal fat

T2-weighted images:

  • Lumen appears as signal void

  • Perivascular edema or collateral dilation may appear hyperintense

STIR:

  • Suppresses fat, improving delineation of veins against the thoracic wall

  • Highlights venous congestion or perivascular inflammatory changes

T1 Fat-Saturated (Pre-contrast):

  • Veins may show intermediate signal lumens, standing out against suppressed fat planes

T1 Fat-Saturated Post-Contrast (Gadolinium):

  • Enhance brightly in venous phase

  • Demonstrates venous tributaries, confluence into the left brachiocephalic vein, and collateral pathways

MRV (Magnetic Resonance Venography):

  • Provides clear mapping of the left internal thoracic venous system

  • Identifies variations, collateral formation in SVC obstruction, and communication with epigastric veins

  • Important for preoperative planning in CABG and oncology cases

CT Appearance

CT Pre-Contrast:

  • Veins appear as small tubular soft-tissue densities alongside the artery

  • Often difficult to distinguish from surrounding mediastinal fat without contrast

CT Post-Contrast:

  • Enhance strongly during venous phase

  • Show clear drainage into the left brachiocephalic vein

  • Dilatation is readily visible in cases of venous hypertension or SVC obstruction

CTV (CT Venography):

  • Provides high-resolution 3D visualization of the entire venous pathway

  • Identifies tributaries, confluence, and collateral venous networks

  • Essential in evaluating SVC obstruction, venous anomalies, or surgical planning

MRI image

Left internal thoracic veins MRI coronal anatomy image -img-00000-00000

CT image

Left Internal Thoracic Veins Anatomy ct axial