Ulnar Artery: Anatomy, Course, Branches, Function & Imaging

Topic

Ulnar artery

The ulnar artery is one of the two terminal branches of the brachial artery, arising in the cubital fossa at the level of the neck of the radius. It supplies the medial aspect of the forearm, wrist, and hand, forming the superficial palmar arch—the principal arterial network of the palm.

It courses along the medial side of the forearm, accompanied by the ulnar vein and ulnar nerve (though these are excluded here), deep to the flexor carpi ulnaris. It gives off several muscular and recurrent branches and continues into the hand through Guyon’s canal. The ulnar artery is clinically important for hand perfusion assessment, Allen’s test, and catheterization procedures.

Synonyms

Medial terminal branch of the brachial artery
Arteria ulnaris

Origin, Course, and Termination

Origin: From the brachial artery in the cubital fossa, opposite the neck of the radius.
Course:
- Initially deep to the pronator teres, then passes between the flexor digitorum superficialis and profundus muscles.
- In the distal two-thirds of the forearm, it runs along the medial side, covered by the flexor carpi ulnaris.
- Enters the palm superficial to the flexor retinaculum through Guyon’s canal (ulnar tunnel).
Termination: Divides into the superficial and deep branches forming the superficial and deep palmar arches.

Branches

In the forearm:
- Anterior ulnar recurrent artery
- Posterior ulnar recurrent artery
- Common interosseous artery (divides into anterior and posterior interosseous arteries)
- Muscular branches to flexor muscles of the forearm
At the wrist and hand:
- Palmar carpal branch
- Dorsal carpal branch
- Deep palmar branch (joins radial artery to form deep palmar arch)
- Superficial palmar branch (forms superficial palmar arch with radial contribution)

Relations

Proximally: Deep to pronator teres and flexor digitorum superficialis
Distally: Covered by flexor carpi ulnaris, then lies lateral to the pisiform bone in Guyon’s canal
Medially: Flexor carpi ulnaris muscle
Laterally: Flexor digitorum profundus and superficialis
Anteriorly: Skin, fascia, and flexor retinaculum at wrist
Posteriorly: Flexor digitorum profundus muscle

Function

Main arterial supply to the medial forearm and hand
Forms superficial palmar arch, supplying the majority of the palmar digits
Contributes to deep palmar arch and palmar carpal network
Important in thermoregulation and collateral circulation of the upper limb

Clinical Significance

Arterial variations: High origin or accessory ulnar artery in ~10% of cases
Allen’s test: Used to assess patency of ulnar and radial arteries before cannulation
Thrombosis or occlusion: Can cause hand ischemia, particularly with radial dominance
Aneurysm or pseudoaneurysm: May occur at wrist due to trauma or repetitive pressure (e.g., hypothenar hammer syndrome)
Catheterization: Common site for transulnar arterial access in angiography or intervention
Imaging importance: MRI, MRA, and CTA essential in evaluating occlusive, traumatic, and vascular anomaly cases

MRI Appearance

T1-weighted images:
- Arterial lumen: Low signal (dark) due to flowing blood
- Arterial wall: Thin low-to-intermediate signal ring
- Surrounding fat: Bright signal delineating artery margins
- Thrombosed segments: Intermediate to high signal (depending on clot age)
T2-weighted images:
- Patent artery: Flow void (dark lumen)
- Wall: Thin low-signal rim
- Thrombosis or occlusion: Bright or intermediate signal filling the lumen
- Adjacent edema or inflammation: Hyperintense signal in perivascular tissues
STIR:
- Normal artery: Dark flow void
- Pathology: Bright perivascular signal in vasculitis, inflammation, or trauma
- Useful for identifying soft-tissue edema or hematoma around the vessel
Proton Density Fat-Saturated (PD FS):
- Normal artery: Dark flow void with smooth contour
- Pathologic: High signal intensity in thrombus, dissection, or periarterial edema
T1 Fat-Sat Post-Contrast:
- Normal artery: Enhancing lumen; thin, smooth arterial wall
- Inflammatory or aneurysmal wall: Focal or diffuse enhancement
- Thrombosed segment: Non-enhancing intraluminal signal with peripheral rim enhancement

MRA (Magnetic Resonance Angiography) Appearance

Normal MRA:
- Ulnar artery appears as a continuous bright tubular structure extending from brachial bifurcation to superficial palmar arch.
- Uniform enhancement with sharp margins and clear branching pattern.
Abnormal MRA findings:
- Occlusion: Segmental loss of signal or abrupt cutoff
- Stenosis: Focal luminal narrowing with signal drop-off
- Aneurysm: Focal dilatation with increased diameter and peripheral enhancement
- Arteriovenous malformation: Irregular flow-related hyperintensity
- Time-of-flight (TOF) and contrast-enhanced MRA best for flow visualization and collateral mapping

CT Appearance

Non-Contrast CT:

Ulnar artery visible as soft-tissue tubular structure; lumen density similar to surrounding muscle
Calcified plaques: Appear as high-density foci along arterial wall
Limited in differentiating lumen from soft-tissue unless calcified or enlarged

Post-Contrast CT (standard):

Arterial lumen shows high-attenuation enhancement
Wall thickening or mural thrombus visible as low-density crescent
Useful in detecting trauma, aneurysm, or occlusive lesions

CTA (CT Angiography) Appearance

Normal CTA:
- Ulnar artery shows bright homogeneous contrast opacification from origin to hand
- Smooth, uniform caliber and branching to superficial and deep palmar arches
Pathologic CTA findings:
- Occlusion: Abrupt contrast cutoff with distal non-opacification
- Stenosis: Focal narrowing or irregular luminal contour
- Aneurysm: Focal saccular or fusiform dilation with wall enhancement
- Thrombosis: Central low-attenuation filling defect within opacified lumen
- Collateral flow: Visualized via interosseous or radial anastomoses
CTA is excellent for three-dimensional vessel mapping and preoperative vascular assessment