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Idiopathic Brachial Plexus Neuritis


KEY FACTS

Terminology

  • Parsonage-Turner syndrome

Imaging

  • Can affect any muscle innervated by brachial plexus

    • Most common: Rotator cuff, deltoid, biceps, triceps

  • Denervation edema is earliest finding

    • Diffuse, homogeneous high signal on T2WI, STIR throughout affected muscle

      • –

        Often, muscles innervated by 2 or more different peripheral nerves are affected

    • ± T2/STIR hyperintensity of plexus

  • Fatty atrophy occurs in chronic denervation (uncommon)

Top Differential Diagnoses

  • Cervical radiculopathy

  • Suprascapular nerve entrapment

  • Brachial plexus neoplasm

  • Brachial plexus or cervical nerve root avulsion

  • Radiation neuritis/myositis

  • Quadrilateral space syndrome

  • Pancoast tumor

  • Muscle injury

Pathology

  • Often idiopathic; can be associated with viral or bacterial infection

  • Can also be posttraumatic or postsurgery condition

Clinical Issues

  • Sudden onset of pain, followed by weakness, paresthesias

  • M > F

  • Most cases resolve in 3 months to 2 years

  • Physical therapy to preserve range of motion

Diagnostic Checklist

  • Often an unexpected finding on shoulder MR performed to evaluate weakness, pain

  • Abnormal muscle signal often involves >1 peripheral nerve distribution

Coronal STIR MR shows diffusely increased signal intensity in brachial plexus
due to idiopathic brachial neuritis.

Coronal oblique T2WI MR shows denervation edema of the teres minor
due to brachial neuritis. Edema is homogeneous and uniform, and there is no disruption of muscle fibers. Quadrilateral space
shows no evidence of mass involving axillary nerve. Whenever denervation edema is seen, a search should be made for nerve mass or extrinsic compression.

Coronal oblique T2WI MR shows diffuse increase in signal intensity throughout superior fibers of infraspinatus muscle
. Interestingly, the inferior portion of the muscle
is spared. Unusual distributions of denervation edema are common in brachial neuritis.

Sagittal T2WI MR shows diffusely abnormal signal intensity in the infraspinatus
and supraspinatus muscles
. Differential diagnosis, in this case, includes suprascapular nerve entrapment.

TERMINOLOGY

Synonyms

  • Parsonage-Turner syndrome

  • Acute brachial neuritis

  • Neuralgic amyotrophy

Definitions

  • Immune-mediated neuropathy of brachial plexus

IMAGING

General Features

  • Best diagnostic clue

    • Homogeneously increased signal on T2WI in 1 or more muscles of shoulder

  • Location

    • Any muscle innervated by brachial plexus

      • –

        Most common: Rotator cuff, deltoid, biceps, triceps

      • –

        Uncommon: Brachialis, forearm muscles, diaphragm, serratus anterior (long thoracic nerve)

    • Sometimes bilateral

    • May cause pure sensory nerve deficit

  • Size

    • Mild, uniform enlargement of affected muscles

    • Muscle atrophy seen in chronic cases

  • Morphology

    • Diffuse involvement of muscle without focal mass

CT Findings

  • Used to exclude mass involving brachial plexus or peripheral nerves

  • Muscle atrophy, fatty infiltration evident in chronic cases

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