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Median Neuropathy
KEY FACTS
Terminology
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Pronator syndrome: Nerve entrapment at pronator teres
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Carpal tunnel syndrome: Nerve entrapment at carpal tunnel
Imaging
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Nerve enlargement distal to region of entrapment
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Fascicles indistinct
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Perineural enhancement
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± mass compressing nerve
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Denervation changes in muscles distal to entrapment
Top Differential Diagnoses
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Cervical radiculopathy
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Tenosynovitis
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Peripheral nerve sheath tumor
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Thoracic outlet syndrome
Pathology
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Common etiologies
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Overuse, arthritis, anatomic variants
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Fractures
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Less common = neoplasm
Clinical Issues
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Tinel sign: Tingling along course of nerve when nerve tapped at point of entrapment
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IF bilateral look for diabetes, hypothyroid, rheumatoid arthritis
Diagnostic Checklist
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Diagnosis usually made on EMG, not MR
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Ultrasound is option
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Imaging diagnosis challenging
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Nerve normally high signal intensity (in carpal tunnel) on FSE T2WI
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Nerve normally flattened at level of hook of hamate
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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 with carpal tunnel syndrome. It usually presents with numbness with repeated pronation/supination of the forearm.
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 with carpal tunnel syndrome. It usually presents with numbness with repeated pronation/supination of the forearm.
Coronal graphic of the carpal tunnel shows the median nerve
at the ventral margin of the carpal tunnel, superficial to the flexor tendons.
at the ventral margin of the carpal tunnel, superficial to the flexor tendons.
Axial T2 FS MR performed at the wrist demonstrates a ganglion cyst
in the carpal tunnel, exerting mass effect on the median nerve
.
in the carpal tunnel, exerting mass effect on the median nerve .
Axial T1WI MR reveals a lipoma
within the carpal tunnel. The flexor tendons
are displaced ulnarly, and the median nerve
is compressed.
within the carpal tunnel. The flexor tendons are displaced ulnarly, and the median nerve is compressed.
TERMINOLOGY
Synonyms
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Pronator syndrome: Nerve entrapment at pronator teres
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Carpal tunnel syndrome: Nerve entrapment at carpal tunnel
Definitions
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Carpal tunnel: Fibroosseous tunnel at volar aspect of wrist
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Contains median nerve and flexor tendons
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IMAGING
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