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Right middle lobe vein

The right middle lobe vein (RMLV) is one of the pulmonary venous tributaries responsible for draining oxygenated blood from the right middle lobe of the lung into the left atrium. It is typically formed by the confluence of medial and lateral segmental veins of the middle lobe (segments 4 and 5 in the Boyden classification).

Most commonly, the RMLV joins the right superior pulmonary vein (RSPV) before entering the left atrium, though variations exist where it may drain independently into the atrium or join with the right inferior pulmonary vein (RIPV). Knowledge of these anatomical variations is crucial for pulmonary vein isolation (PVI) in atrial fibrillation ablation, lung resections, and thoracic surgical planning.

Synonyms

  • Middle lobe pulmonary vein

  • Vein of right middle lobe

  • Segmental pulmonary venous tributary (S4, S5)

Function

  • Returns oxygenated blood from the right middle lobe of the lung to the left atrium

  • Contributes to pulmonary venous return via the right superior pulmonary vein

  • Provides key anatomical landmarking for thoracic surgery and electrophysiology

Tributaries

  • Medial segmental vein (V4)

  • Lateral segmental vein (V5)

MRI Appearance

T1-weighted images:

  • RMLV appears as a flow void (black lumen) adjacent to the right middle lobe bronchus and pulmonary artery branches

T2-weighted images:

  • Venous lumen shows signal void; surrounding pulmonary parenchyma provides contrast

  • Thrombus or flow obstruction may appear as intermediate to high signal within the lumen

T2 TRUFISP (cardiac/respiratory-gated):

  • Vein visualized as a bright, continuous vascular channel draining toward the left atrium

  • Provides cine-like evaluation of venous flow and relationships with adjacent bronchi and arteries

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, improving visualization of vein against mediastinal fat planes

  • Highlights perivascular edema or pathology if present

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • RMLV enhances brightly and homogeneously

  • Useful for mapping pulmonary venous drainage patterns and identifying variants

MRI Non-Contrast 3D Cardiac-Gated Imaging (Whole-heart):

  • Provides high-resolution visualization of pulmonary veins without contrast

  • RMLV depicted as a small venous channel joining the RSPV or independently draining into the atrium

  • Valuable for pre-ablation mapping in atrial fibrillation or when contrast is contraindicated

MRA (Magnetic Resonance Angiography):

  • Contrast-enhanced MRA depicts venous anatomy clearly, showing RMLV confluence with RSPV and any variations

  • Important in pulmonary venous isolation planning and thoracic surgery

CT Appearance

CT Coronary Angiography (CCTA):

  • Gold standard for non-invasive visualization of pulmonary venous anatomy

  • RMLV typically seen draining into the RSPV, with tributaries from S4 and S5

  • Variations (independent drainage into LA, connection with RIPV) are easily identified

  • Essential in atrial fibrillation ablation planning, lobectomy, and thoracic oncology

  • 3D reconstructions allow detailed pre-surgical mapping

CT image

Right middle lobe vein anatomy CT axial image -img-00000-00000

MRI image

Right middle lobe vein mri axial image