Median Neuropathy

Fascicles indistinct

• Perineural enhancement

• ± mass compressing nerve

• Denervation changes in muscles distal to entrapment

Top Differential Diagnoses

• Cervical radiculopathy

• Tenosynovitis

• Peripheral nerve sheath tumor

• Thoracic outlet syndrome

Pathology

• Overuse

• Arthritis

• Tumors

• Fractures

• Anatomic variants

Clinical Issues

• Tinel sign: Tingling along course of nerve when nerve tapped at point of entrapment

• Electrodiagnosis standard for diagnosis

Diagnostic Checklist

• Imaging diagnosis challenging

Nerve normally high signal intensity (in carpal tunnel) on FSE T2WI

Nerve normally flattened at level of hook of hamate

• Diagnosis usually made on EMG, not MR

(Left) Graphic of anterior elbow shows median nerve passing anterior to brachialis muscle. It extends between the heads of the pronator teres and beneath the biceps aponeurosis . Entrapment of the nerve in this region is rare compared to carpal tunnel syndrome. It usually presents with numbness with repeated pronation/supination of the forearm.

(Left) Graphic of anterior elbow shows median nerve passing anterior to brachialis muscle. It extends between the heads of the pronator teres and beneath the biceps aponeurosis . Entrapment of the nerve in this region is rare compared to carpal tunnel syndrome. It usually presents with numbness with repeated pronation/supination of the forearm.

(Right) Coronal graphic of the carpal tunnel shows the median nerve at the ventral margin of the carpal tunnel, superficial to the flexor tendons.

(Right) Coronal graphic of the carpal tunnel shows the median nerve at the ventral margin of the carpal tunnel, superficial to the flexor tendons.

(Left) Axial T2 FS MR performed at the wrist demonstrates a ganglion cyst in the carpal tunnel, exerting mass effect on the median nerve .

(Left) Axial T2 FS MR performed at the wrist demonstrates a ganglion cyst in the carpal tunnel, exerting mass effect on the median nerve .

(Right) Axial T1WI MR reveals a lipoma within the carpal tunnel. The flexor tendons are displaced ulnarly, and the median nerve is compressed.

(Right) Axial T1WI MR reveals a lipoma within the carpal tunnel. The flexor tendons are displaced ulnarly, and the median nerve is compressed.

TERMINOLOGY

Synonyms

• Pronator syndrome: Nerve entrapment at pronator teres

• Carpal tunnel syndrome: Nerve entrapment at carpal tunnel

Definitions

• Carpal tunnel: Fibroosseous tunnel at volar aspect of wrist

Contains median nerve and flexor tendons

IMAGING

General Features

• Best diagnostic clue

Increased intrinsic nerve signal on STIR MR

• Location

Elbow or wrist

MR Findings

• Nerve enlargement distal to region of entrapment

• Indistinct nerve fascicles on cross-sectional T2WI

Normal nerve is high signal intensity; no additional increase in signal intensity usually seen

• Perineural enhancement with gadolinium (Gd)

• Increased anterior bowing of flexor retinaculum

Distance from hook of triquetrum to hook of hamate (TH)

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Tags: Diagnostic Imaging Spine

Oct 5, 2016 | Posted by admin in NEUROLOGICAL IMAGING | Comments Off

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