Age / Sex : 35 / M

Chief complaint : right hand weakness after carrying a heavy object two months ago

What is your diagnosis?

Two weeks later, you can see the final diagonosis with a brief discussion of this case (Please submit only one answer).


Courtesy : 홍지현, Ji Hyun Hong, 강동성심병원, Kangdong Seong-Sim Hospital

Anterior interosseous nerve syndrome

Discussion

Findings:

T2W increased signal intensity with enhancement in the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus muscles

No evidence of abnormality along the median and anterior interosseous nerve

Discussion:

Anterior interosseous nerve syndrome

1) Definition

Caused by entrapment or compression of the anterior interosseous nerve in the proximal part of the forearm

2) Causes

- direct traumatic damage: result of surgery, venous puncture, injection or cast pressure

- external compression: bulky tendinous origin of the ulnar head of the pronator teres muscle, soft tissue mass, accessory muscle or fibrous band

3) Clinical findings

-  dull pain in the volar aspect of the forearm, combined with an acute onset of muscle weakness

- circle sign: not able to form an “O” with the thumb and index finger

• MRI features

- acute or subacute onset: increased signal intensity in the flexor digitorum profundus, flexor pollicis longus, and pronator quadratus muscles on axial T2-weighted fat-suppressed or STIR images

- Edema in the pronator quadrates muscle – the most reliable sign

- Normalization of T2-weighted muscle signal intensity or of abnormalities on

STIR images --> the recovery of nerve function

- additional development of T1-weighted MR signal intensity abnormalities -->  worsening and chronicity

References:

Andreisek G, Crook DW, Burg D, Marincek B, Weishaupt D. Peripheral neuropathies of the median, radial, and ulnar nerves: MR imaging features. Radiographics 2006;26:1267-87