Ultrasonographic findings of posterior interosseous nerve syndrome

Abstract

Purpose: The purpose of this study was to evaluate the ultrasonographic findings associated with posterior interosseous nerve (PIN) syndrome.

Methods: Approval from the Institutional Review Board was obtained. A retrospective review of 908 patients' sonographic images of the upper extremity from January 2001 to October 2010 revealed 10 patients suspicious for a PIN abnormality (7 male and 3 female patients; mean age of 51.8±13.1 years; age range, 32 to 79 years). The ultrasonographic findings of PIN syndrome, including changes in the PIN and adjacent secondary changes, were evaluated. The anteroposterior diameter of the pathologic PIN was measured in eight patients and the anteroposterior diameter of the contralateral asymptomatic PIN was measured in six patients, all at the level immediately proximal to the proximal supinator border. The size of the pathologic nerves and contralateral asymptomatic nerves was compared using the Mann-Whitney U test.

Results: Swelling of the PIN proximal to the supinator canal by compression at the arcade of Fröhse was observed in four cases. Swelling of the PIN distal to the supinator canal was observed in one case. Loss of the perineural fat plane in the supinator canal was observed in one case. Four soft tissue masses were noted. Secondary denervation atrophy of the supinator and extensor muscles was observed in two cases. The mean anteroposterior diameter of the pathologic nerves (n=8, 1.79±0.43 mm) was significantly larger than that of the contralateral asymptomatic nerves (n=6, 1.02±0.22 mm) (P=0.003).

Conclusion: Ultrasonography provides high-resolution images of the PIN and helps to diagnose PIN syndrome through visualization of its various causes and adjacent secondary changes.

Keywords: Nerve compression syndromes; Posterior interosseous nerve; Radial nerve; Ultrasonography.

Fig. 1.. A 42-year-old man with swelling of the posterior interosseous nerve (PIN) proximal to the supinator muscle.

A. Longitudinal ultrasonogrphy demonstrates hypoechoic swelling of the left PIN (arrows) proximal to the supinator muscle. Compression by the hyperechoic thickened arcade of Fröhse (dashed arrow) is noted. B. Axial ultrasonography shows swelling of the left PIN (arrow) at a level just proximal to the arcade of Fröhse. The thickness of the swollen PIN was measured as 2.4 mm in anteroposterior diameter. C, D. Ultrasonography of the contralateral asymptomatic right forearm shows a gradual tapering appearance of the PIN (arrows) in the longitudinal scan (C) with a normal thickness (1.0 mm in anteroposterior diameter) of the PIN (arrow) in an axial scan (D).

Fig. 2.. A 51-year-old man with swelling of the posterior interosseous nerve (PIN) proximal to the supinator muscle.

Longitudinal (A) and axial (B) ultrasonography demonstrates hypoechoic swelling of the PIN (arrows) just proximal to the entrance site into the supinator canal, and diffuse hyperechoic change of the supinator (S) and mixed hyperechoic and hypoechoic changes of the extensor (E) muscles, which represent denervation atrophy.

Fig. 3.. A 49-year-old woman with swelling of the posterior interosseous nerve (PIN) distal to the supinator muscle.

A. Gray-scale ultrasonography shows hypoechoic swelling of the PIN (arrows) as it exits from the supinator canal (S). B. Color Doppler image demonstrates increased perineural vascularity at the site of hypoechoic swelling of the PIN.

Fig. 4.. A 54-year-old man with a ganglion cyst in the supinator canal.

A. A tubular, lobulated, anechoic ganglion cyst (arrows) is demonstrated from the site just proximal to the supinator muscle to the proximal supinator canal in a longitudinal ultrasonography. B. The posterior interosseous nerve (PIN) (dashed arrow) is displaced and followed due to an anechoic ganglion cyst (arrow) in the entrance site to the supinator canal in an axial ultrasonography. C. Surgical photograph demonstrates a ganglion cyst (arrows) and displaced PIN (arrowheads).