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Ulnar Neuropathy


KEY FACTS

Terminology

  • Synonyms: Ulnar nerve (UN) entrapment, cubital tunnel syndrome

  • Partial fixation, compression, or distortion of UN

Imaging

  • UN enlargement ± abnormal T2 hyperintensity, architectural distortion

  • Most commonly occurs within cubital tunnel (elbow); uncommon at Guyon tunnel (wrist) or brachial plexus

Top Differential Diagnoses

  • Acute direct nerve trauma

  • Idiopathic brachial plexitis (Parsonage-Turner syndrome)

  • Nerve sheath tumor

  • Enlarged perineural vein

  • Medial epicondylitis

Pathology

  • Edematous/indurated UN ± thickened retinaculum, fibrous infiltration, fascicular atrophy/loss

  • ± anconeus epitrochlearis, enlarged medial triceps head

Clinical Issues

  • Symptoms range from mild transient paresthesias of 4th and 5th digits → claw hand/digits, intrinsic muscle atrophy

  • ± severe elbow/wrist pain radiating proximally or distally

Diagnostic Checklist

  • Focal nerve enlargement, abnormal T2 hyperintensity distal to medial epicondyle

  • Search for anatomic abnormalities (enlarged triceps medial head or anconeus muscle, osteophyte, thickened retinaculum)

Coronal graphic of the right upper extremity demonstrates the normal course of the ulnar nerve
(yellow). Vulnerable locations to injury include the cubital tunnel
at the medial elbow and Guyon canal
at the medial wrist.

Axial T1WI MR of the right elbow demonstrates mild abnormal enlargement and rounded configuration of the right ulnar nerve
within the cubital tunnel.

Axial T2WI FS MR of the right elbow demonstrates mild enlargement and abnormal T2 hyperintensity of the right ulnar nerve
with complete loss of internal fascicular architecture, indicating an axonotmetic or neurotmetic injury rather than the less severe neuropraxic injury.

Axial T1WI C+ FS MR of the right elbow confirms diffuse abnormal enhancement of the mildly enlarged right ulnar nerve
. Note also mild edema and inflammation in the adjacent soft tissues
.

TERMINOLOGY

Synonyms

  • Ulnar nerve entrapment, cubital tunnel syndrome

Definitions

  • Partial fixation, compression, or distortion of ulnar nerve (UN)

    • Most commonly occurs within cubital tunnel at elbow; uncommon within Guyon tunnel at wrist, or 2° to brachial plexus inflammation

IMAGING

General Features

  • Best diagnostic clue

    • UN enlargement ± T2 hyperintensity at cubital or Guyon tunnel in symptomatic patient

  • Location

    • Most common at elbow near medial epicondyle (cubital tunnel); less common at ulnar wrist (Guyon tunnel)

  • Size

    • Usually enlarged 1.5-2x, with change from mildly flattened configuration → rounded

  • Morphology

    • Nerve swelling ± enlarged hyperintense fascicles (neuropraxic injury), axonal injury with loss of internal architecture (axonotmesis), or complete anatomic/functional transection (neurotmesis)

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