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Guyon’s canal

Guyon’s canal is a short, oblique passage approximately 4 cm long, extending from the proximal wrist crease to the level of the pisiform. It transmits the ulnar nerve and artery into the palm and provides protection as they traverse the transition between forearm and hand.

  • Length: ~4 cm

  • Orientation: Oblique, distally and laterally directed

  • Type: Fibro-osseous tunnel formed by bones, ligaments, and soft tissue fascia

Boundaries

  • Roof (superficial boundary): Palmar carpal ligament and palmaris brevis muscle

  • Floor (deep boundary): Transverse carpal ligament (flexor retinaculum) and hypothenar muscles (mainly flexor digiti minimi brevis and opponens digiti minimi)

  • Medial wall: Pisiform bone and pisohamate ligament

  • Lateral wall: Hook of hamate and palmaris brevis fascia

  • Proximal opening: Just distal to the pisiform bone (entry of ulnar nerve and artery)

  • Distal opening: At the level of the hook of hamate (where the nerve divides into its superficial and deep branches)

Contents

  • Ulnar nerve (divides within the canal into superficial sensory and deep motor branches)

  • Ulnar artery and accompanying venae comitantes

  • Connective tissue and fat providing cushioning around neurovascular structures

Relations

  • Anteriorly: Palmar fascia and palmaris brevis muscle

  • Posteriorly: Flexor retinaculum and hypothenar muscles

  • Medially: Pisiform and pisohamate ligament

  • Laterally: Hook of hamate and deep palmar arch (distally)

  • Superiorly: Continuity with ulnar neurovascular structures in the distal forearm

  • Inferiorly: Continuation into the palm beneath hypothenar muscles

Function

  • Protection: Shields the ulnar nerve and artery as they pass into the hand

  • Passageway: Provides an organized route for ulnar neurovascular structures from wrist to palm

  • Mechanical stability: Maintains positional relationship between the ulnar nerve and surrounding tissues during wrist motion

  • Vascular support: Allows branching of the ulnar artery into superficial and deep palmar branches

Clinical Significance

  • Ulnar Tunnel Syndrome (Guyon’s Canal Syndrome): Compression of the ulnar nerve within the canal causing sensory loss over the ulnar side of the hand and motor weakness in hypothenar and interosseous muscles

  • Causes: Ganglion cysts, lipomas, anomalous muscles, ulnar artery thrombosis, or repetitive trauma (e.g., cyclists’ handlebar palsy)

  • Symptoms:

    • Numbness or tingling in the ring and little fingers

    • Weakness in finger abduction/adduction

    • Clawing of the 4th and 5th digits (advanced cases)

  • Zones of compression:

    • Zone 1: Proximal canal – both motor and sensory branches affected

    • Zone 2: Deep motor branch – motor weakness only

    • Zone 3: Superficial branch – sensory loss only

  • Imaging relevance: MRI and CT can identify compressive lesions, structural variations, and inflammatory or traumatic causes

MRI Appearance

  • T1-weighted images:

    • Ulnar nerve: low-to-intermediate signal, continuous cord-like structure

    • Ulnar artery: flow void (dark) due to flowing blood

    • Surrounding fat: bright signal, delineating canal borders

    • Mass lesions (e.g., ganglion, lipoma): intermediate-to-bright signal depending on composition

    • In entrapment: Nerve may appear thickened or flattened with loss of normal fascicular pattern

  • T2-weighted images:

    • Nerve: intermediate-to-bright signal in edema or neuritis

    • Normal nerve remains relatively low-to-intermediate signal

    • Ganglion cysts or inflammatory lesions: bright hyperintense signal

    • Edema or tenosynovitis in adjacent tissues: hyperintense regions outlining canal

  • STIR:

    • Normal structures: intermediate-to-dark signal

    • Pathology: bright hyperintense signal in nerve or surrounding soft tissue (nerve edema, inflammatory changes, cystic lesions)

  • Proton Density Fat-Saturated (PD FS):

    • Normal nerve: intermediate-to-dark signal

    • Nerve entrapment: focal bright hyperintensity with possible proximal nerve swelling

    • Differentiates cystic from solid compressive lesions and assesses perineural edema

  • T1 Fat-Sat Post-Contrast:

    • Normal canal: minimal enhancement

    • Pathologic enhancement: seen in synovitis, vascular malformations, neuritis, or scar tissue

    • Ganglion cysts: typically non-enhancing with thin peripheral rim enhancement

    • Tumors (schwannoma, hemangioma): show variable enhancement pattern

CT Appearance

Non-Contrast CT:

  • Canal boundaries: defined by pisiform medially and hook of hamate laterally

  • Bony walls: clearly visualized; important for detecting fractures or exostoses causing compression

  • Nerve and soft tissue: isodense, usually indistinct without contrast

  • Pathology: ganglion cysts appear as low-density lesions; calcifications or ossified masses may compress canal contents

Post-Contrast CT (standard):

  • Enhancing soft tissues or mass lesions may be visualized

  • Ulnar artery enhances vividly within the canal

  • Detects vascular anomalies, soft-tissue thickening, and perineural inflammatory changes

  • Valuable for evaluating post-traumatic or post-surgical canal narrowing

MRI images

Guyon’s canal axial cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000

MRI images

Guyon’s canal coronal cross sectional anatomy 3T MRI AI enhanced radiology image-img-00000-00000