Ulnar Veins: Anatomy, Course, Function, MRV & CTV Imaging

Topic

Ulnar veins

The ulnar veins are paired deep veins that accompany the ulnar artery along the medial aspect of the forearm. They play a vital role in the venous drainage of the hand and forearm, collecting blood from the superficial and deep palmar venous arches, and conveying it proximally toward the brachial veins.

Each ulnar vein lies on either side of the ulnar artery, connected by frequent venous cross-communicators (venae comitantes). They form part of the deep venous system of the upper limb and communicate extensively with the radial veins through the deep venous arches.

The ulnar veins serve as important collateral channels and are clinically significant in deep vein thrombosis (DVT) of the upper limb, post-catheterization complications, and venous mapping for surgical procedures.

Synonyms

Venae comitantes of the ulnar artery
Deep ulnar veins

Origin, Course, and Termination

Origin: Begin in the deep palmar venous arch and from the venous plexuses of the hand.
Course:
- Ascend along the medial side of the forearm, one vein on each side of the ulnar artery.
- Connected by small transverse veins forming a network.
- Accompany the ulnar artery deep to the flexor carpi ulnaris and between the superficial and deep flexor muscle groups.
Termination:
- Unite with the radial veins near the cubital fossa to form the brachial veins, which continue as the axillary vein.

Relations

Anteriorly: Flexor digitorum superficialis and skin of the medial forearm
Posteriorly: Flexor digitorum profundus
Medially: Ulnar nerve (in the distal forearm)
Laterally: Ulnar artery
Proximally: Brachial veins and deep venous arch
Distally: Palmar venous arches and digital veins

Tributaries

Venae comitantes of the common interosseous artery
Deep venous branches from flexor muscles of the forearm
Communicating branches connecting with superficial veins (basilic and median antebrachial veins)

Function

Venous return: Drains deoxygenated blood from the deep structures of the forearm and hand.
Pressure regulation: Aids in thermoregulation and venous capacitance of the limb.
Collateral pathway: Contributes to venous return when superficial or proximal veins are obstructed.
Clinical relevance: Important in diagnosing deep venous thrombosis and post-catheterization thrombophlebitis.

Clinical Significance

Deep vein thrombosis (DVT): May occur secondary to trauma, infection, or prolonged immobilization.
Catheter-related thrombosis: Can follow central line insertion or venous cannulation.
Venous insufficiency: Chronic obstruction may lead to venous congestion in distal forearm.
Surgical relevance: Assessed in vascular graft planning and venous mapping for forearm flaps.
Imaging importance: MRI, MRV, and CTV help evaluate venous patency, thrombosis, and collateral formation.

MRI Appearance

T1-weighted images:
- Normal flowing blood: signal void (dark) due to rapid movement.
- Slow-flowing blood: may appear intermediate-to-bright, simulating thrombus.
- Thrombus (subacute): bright from methemoglobin; chronic thrombus: intermediate or low signal.
- Vessel wall: thin, low signal; surrounding fat: bright, enhancing vessel contrast.
T2-weighted images:
- Flowing blood: dark signal (flow void).
- Slow flow: intermediate-to-bright signal due to incomplete dephasing.
- Acute thrombus: bright, subacute: variable, chronic: dark fibrotic signal.
- Vessel wall thickening or edema: hyperintense surrounding rim.
STIR:
- Normal veins: dark or intermediate depending on flow.
- Slow flow or thrombosis: bright hyperintense signal filling the lumen.
- Perivenous edema or inflammation: bright hyperintense halo.
Proton Density Fat-Saturated (PD FS):
- Normal vein: dark to intermediate, flow-related void.
- Slow-flowing blood: intermediate or faintly bright intraluminal signal.
- Acute DVT: bright intraluminal signal with loss of compressibility and wall definition.
- Chronic thrombus: dark with narrowed lumen and fibrotic wall thickening.
T1 Fat-Sat Post-Contrast:
- Patent vein: brisk homogeneous enhancement of lumen.
- Acute thrombus: non-enhancing intraluminal filling defect.
- Chronic recanalization: linear or serpiginous enhancement within organized thrombus.
- Perivenous enhancement indicates inflammation or thrombophlebitis.

MRV (Magnetic Resonance Venography) Appearance

Normal:
- Ulnar veins visualized as paired enhancing channels flanking the ulnar artery.
- Best seen in contrast-enhanced MRV or phase-contrast MRV sequences.
Slow flow: may cause reduced signal intensity or non-visualization in TOF MRV.
Thrombosis: appears as filling defect or absence of enhancement within expected venous course.
Collateral formation: seen as multiple serpiginous enhancing channels around the thrombosed segment.
Advantages: Excellent for detecting non-occlusive thrombi and perivenous inflammation without ionizing radiation.

CT Appearance

Non-Contrast CT:

Veins appear as soft-tissue density channels adjacent to the ulnar artery.
Difficult to differentiate from surrounding tissue without contrast.
Chronic thrombus may appear as hyperdense lumen or calcified linear density.

Post-Contrast CT (standard):

Veins enhance during the venous phase; appear as paired contrast-filled channels.
Thrombosis: filling defect or non-opacified lumen with surrounding perivenous enhancement.
Useful for detecting perivascular inflammation, abscess, or postsurgical change.

CTV (CT Venography) Appearance

Normal:
- Paired ulnar veins are clearly seen flanking the ulnar artery, filling symmetrically with contrast.
- Best visualized during the delayed venous phase.
Thrombosis:
- Non-enhancing intraluminal filling defect.
- Acute: smooth central defect; chronic: irregular or narrowed lumen with collateral veins.
Slow flow: causes heterogeneous or delayed contrast filling.
Collateral pathways: seen as serpiginous enhancing veins along the medial forearm in chronic DVT.
Advantages: Rapid evaluation of venous anatomy, occlusion, and collateralization with high spatial resolution.