Pronator teres syndrome
Pain and hypesthesia of the volar forearm and radial three digits. No relevant history, especially of trauma.
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Fig. 1: Pronator teres syndrome: Transverse T2w image at the level of the right radial head showing impingement of the median nerve (red arrow) under the lacertus fibrosus / biceps aponeurosis (white arrow).
Fig. 2: Pronator teres syndrome: PD transverse image of the proximal lower right arm showing hyperintense signal secondary to denervation edema of the flexor carpi radialis (FCR), palmaris longus (PL) and flexor digitorum superficialis (FDS) muscles.
Fig. 3: Pronator teres syndrome: PD transverse image of the proximal lower right arm showing hyperintense signal secondary to denervation edema of the flexor digitorum profundus (FDP) and flexor digitorum superficialis (FDS) muscles.
Fig. 4: Pronator teres syndrome: PD transverse image of the proximal lower right arm showing hyperintense signal secondary to denervation edema of the pronator quadratus (PQ) muscle.
Pronator teres syndrome (PTS) can present with volar pain of the lower arm, paresthesia of the volar forearm and the radial three digits and radial aspect of the fourth digit; weakness, on the other hand, is variable, often with unspecified grip clumsiness.
Apart from compromise by primary nerve sheath tumors, ganglion cysts, osseous spurs, anatomical variants (e.g. Gantzer muscle), PTS can have 4 distinct specific anatomical causes: entrapment between the humeral and ulnar heads of the pronator teres muscle (the most common cause), under the proximal edge of the FDS (flexor digitorum superficialis muscle) arch, under a thickened bicipital aponeurosis (or lacertus fibrosus), or a ligament of Struthers, originating from a supracondylar process.
In complete PTS, affected muscles are the pronator teres (PT), flexor carpi radialis (FCR), palmaris longus (PL), flexor digitorum superficialis (FDS), along with muscles innervated by the anterior interosseous nerve. The pattern of signal changes can readily be detected on fluid-sensitive (STIR, PD or T2w fat sat) sequences, which will show hyperintense muscle signal secondary to denervation and thus point to the affected nerve (section).
PTS can be treated conservatively in 50–70% of cases with extremity rest and NSAR; corticosteroids have been used, as well. Surgical decompression is indicated in space-occupying lesions and failure of conservative treatment over 12 weeks, with success rates of up to 90%.
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