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

image Nerve normally flattened at level of hook of hamate

• Diagnosis usually made on EMG, not MR

image
(Left) Graphic of anterior elbow shows median nerve image passing anterior to brachialis muscle. It extends between the heads of the pronator teres and beneath the biceps aponeurosis image. 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.


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

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


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


IMAGING


General Features




• Best diagnostic clue
image Increased intrinsic nerve signal on STIR MR

• Location
image Elbow or wrist


MR Findings




• Nerve enlargement distal to region of entrapment

• Indistinct nerve fascicles on cross-sectional T2WI
image Normal nerve is high signal intensity; no additional increase in signal intensity usually seen

• Perineural enhancement with gadolinium (Gd)

Oct 5, 2016 | Posted by in NEUROLOGICAL IMAGING | Comments Off on Median Neuropathy

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