Middle Collateral Artery: Anatomy, Course, Function, Imaging

Topic

Middle collateral artery

The middle collateral artery (MCA) is one of the terminal branches of the profunda brachii artery (deep brachial artery). It plays an important role in the posterior collateral circulation of the elbow joint. The artery descends along the posterior aspect of the humerus, traveling with the nerve to the triceps and contributes to the periarticular arterial anastomosis around the elbow, particularly on the posterior and lateral aspects.

It forms a key anastomosis with the interosseous recurrent artery, helping maintain distal limb perfusion during elbow flexion or when the brachial artery is compressed.

Synonyms

Posterior descending branch of profunda brachii artery
Posterior collateral branch of deep brachial artery

Origin, Course, and Termination

Origin: Arises from the profunda brachii artery, usually near its bifurcation in the posterior compartment of the arm.
Course:
- Descends posteriorly along the medial head of the triceps brachii.
- Follows the course of the radial nerve within the radial groove on the posterior humerus.
- Continues distally along the posterior aspect of the humerus toward the olecranon fossa.
Termination:
- Ends by anastomosing with the interosseous recurrent artery (branch of the posterior interosseous artery) posterior to the elbow joint, forming part of the posterior anastomotic network.

Relations

Anteriorly: Posterior surface of the humerus (radial groove).
Posteriorly: Medial and lateral heads of the triceps brachii.
Laterally: Radial nerve (travels with the artery in the groove).
Inferiorly: Posterior elbow capsule and olecranon fossa.
Superiorly: Profunda brachii artery at origin.

Branches

Muscular branches: To triceps brachii, anconeus, and surrounding fascia.
Articular branches: Supply posterior and lateral parts of the elbow joint.
Anastomotic branches: Communicate with the interosseous recurrent artery and posterior ulnar recurrent artery, completing the posterior collateral network.

Function

Posterior elbow supply: Provides blood to triceps and posterior elbow capsule.
Collateral pathway: Ensures blood flow to the forearm during elbow flexion or brachial artery obstruction.
Anastomotic role: Links upper arm profunda brachii circulation to the interosseous arterial system of the forearm.

Clinical Significance

Collateral circulation: Integral in maintaining distal forearm perfusion when brachial or profunda brachii flow is compromised.
Vascular injury: Can be involved in humeral shaft fractures or iatrogenic injury during posterior arm surgery.
Surgical relevance: Important during posterior approaches to the humerus and triceps repair.
Aneurysm/pseudoaneurysm: Rare but possible following penetrating trauma or fracture.
Embolism or thrombosis: May cause ischemic compromise if collateral network is insufficient.

MRI Appearance

T1-weighted images:
- Normal artery: flow void (dark linear structure).
- Adjacent fat planes: bright, enhancing vessel outline.
- Thrombosed segments: intermediate to bright intraluminal signal.
T2-weighted images:
- Flowing blood: low signal (flow void).
- Vessel wall thickening or hematoma: intermediate to bright signal intensity.
- Posterior arm muscles (triceps) provide contrasting intermediate background signal.
STIR:
- Normal: artery appears dark flow void.
- Pathology: perivascular edema or inflammation appears bright hyperintense.
- Helpful for detecting hematoma or vascular injury in trauma.
Proton Density Fat-Saturated (PD FS):
- Artery: dark flow void with surrounding fat suppression.
- Vasculitis or thrombus: bright signal changes along vessel course.
- Defines perivascular soft-tissue edema clearly.
T1 Fat-Sat Post-Contrast:
- Normal artery: brisk uniform enhancement of lumen.
- Aneurysm: focal rounded enhancement.
- Occlusion or stenosis: absent enhancement in affected segment with collateral vessel visualization.

MRA (Magnetic Resonance Angiography) Appearance

Normal:
- The middle collateral artery appears as a small enhancing vessel branching from the profunda brachii artery, coursing posteriorly in the arm toward the olecranon region.
- Best seen on contrast-enhanced MRA or 3D TOF sequences.
Pathology:
- Occlusion: segmental loss of signal with distal reconstitution via collaterals.
- Aneurysm: focal dilation with homogeneous enhancement.
- Vasculitis: irregular vessel contour and concentric wall enhancement.
- Trauma: perivascular signal abnormality and flow disruption.

CT Appearance

Non-Contrast CT:

Artery itself not visible without contrast.
Calcified segments (rare) appear as thin, high-density curvilinear foci.
Provides bone and soft-tissue landmarks for arterial course assessment in trauma.

Post-Contrast CT (standard):

Enhancing tubular structure running posteriorly along humerus, lateral to triceps.
Distinguishable from veins by enhancement timing and smaller caliber.
Useful in detecting hematoma, pseudoaneurysm, or post-traumatic changes.

CTA (CT Angiography) Appearance

Normal:
- Appears as a contrast-filled vessel arising from the profunda brachii artery, descending posterior to humerus and joining interosseous recurrent artery near the olecranon.
- Visible on arterial-phase CTA with thin (0.5–1 mm) slice reconstructions.
Pathology:
- Occlusion or thrombosis: abrupt cutoff or non-opacified segment.
- Aneurysm: well-defined focal bulge with contrast filling.
- Dissection: thin intraluminal flap or double lumen.
- Collateral formation: small serpiginous channels reconstituting distal flow.