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Medial segmental artery of right lung

The medial segmental artery (A5) is one of the segmental branches of the right pulmonary artery, specifically supplying the medial segment (S5) of the right middle lobe. It originates from the middle lobar artery, which itself arises from the interlobar portion of the right pulmonary artery.

The medial segmental artery runs anteromedially toward the right middle lobe bronchus, closely accompanying the medial segmental bronchus (B5). It distributes oxygen-poor blood to the capillary network of S5, where gas exchange occurs. Anatomically, it runs in parallel with the medial segmental vein (V5), which drains oxygenated blood back into the right superior pulmonary vein.

This artery is clinically significant in pulmonary embolism, lung resections, and segmentectomies, where precise knowledge of segmental arterial anatomy is crucial to preserve lung function while removing diseased tissue. Variations in its origin and branching pattern are not uncommon and must be recognized during surgical or interventional procedures.

Synonyms

  • A5 (right lung)

  • Right middle lobe medial segmental artery

  • Medial branch of middle lobar artery

Function

  • Supplies deoxygenated blood to the medial segment (S5) of the right middle lobe

  • Ensures perfusion for gas exchange in the segment

  • Provides segmental arterial contribution that parallels the bronchopulmonary anatomy

  • Serves as a surgical and imaging landmark in segmentectomy and pulmonary interventions

Branches

  • Small intrasegmental arterial branches supplying the subsegments of S5

  • Anastomotic connections with adjacent segmental arteries of the lateral segment (A4) and inferior lobe

MRI Appearance

T1-weighted images:

  • Lumen appears as a signal void (black) due to arterial flow

  • Surrounded by hypointense vessel wall and mediastinal fat

T2-weighted images:

  • Appears as a dark tubular structure due to flow void

  • Intraluminal thrombus, if present, may appear hyperintense

T2 TRUFISP (cardiac/respiratory-gated):

  • Depicts A5 as a bright, continuous arterial lumen with excellent contrast against surrounding lung parenchyma

  • Provides cine-like evaluation of branching and flow dynamics

STIR (Short Tau Inversion Recovery):

  • Suppresses fat, enhancing conspicuity of A5 in the hilum and middle lobe

  • Useful for identifying perivascular edema or infiltration

T1 Post-Contrast (Gadolinium-enhanced MRI):

  • A5 enhances brightly and homogeneously with contrast

  • Filling defects indicate embolus, stenosis, or tumor invasion

MRI Non-Contrast Cardiac-Gated 3D Imaging:

  • Provides detailed 3D mapping of the middle lobar artery and A5 without contrast

  • Useful for pre-surgical planning, congenital anomaly evaluation, or in patients with contrast contraindications

MRA (Magnetic Resonance Angiography):

  • Contrast-enhanced MRA visualizes the origin, course, and subsegmental branches of A5

  • Helpful in identifying vascular variations, stenosis, or collateral supply

CT Appearance

CT Pulmonary Angiography (CTPA):

  • Gold-standard for evaluating A5

  • Contrast opacifies the middle lobar artery and its medial segmental branch

  • Multiplanar and 3D reconstructions demonstrate course with bronchus B5 and vein V5

  • Detects pulmonary embolism, vascular anomalies, or extrinsic compression

  • Essential in planning lobectomy or middle lobe segmentectomy

CT image

Medial segmental artery of right lung anatomy CT axial image -img-00000-00000

MRI image

Medial segmental artery of right lung MRI IMAGE