Periscalene soft tissue: the new imaging hallmark in Erb palsy.

BACKGROUND AND PURPOSE Pseudomeningocele is a well-known MR imaging finding in Erb palsy. Our aim was to evaluate the prevalence and imaging features of PST, a lesser known but, in our experience, more common finding in Erb palsy. MATERIALS AND METHODS This retrospective study consisted of 37 subjects with Erb palsy from birth trauma. MR imaging examinations of the brachial plexus were evaluated independently by 2 neuroradiologists for the presence and signal-intensity characteristics/configuration of PST. Other findings included pseudomeningocele and posterior humeral head subluxation. The Blyth-Still-Casella procedure was used to construct an exact 95% CI for the percentage of patients seen to be positive for a specific imaging or anatomic feature by at least 1 observer and for the percentage positive according to both readers. RESULTS The percentage of subjects found to have PST by both readers was 95% (35/37) (95% CI, 86.2%-99.9%). The PST was typically isointense to muscle on T1- and hyperintense on T2-weighted images. The most common morphology of the PST was a round or oval mass, though other morphologies were observed. Pseudomeningocele and posterior humeral head subluxation were reported in 40% (15/37) and 81% (30/37) of subjects, respectively. CONCLUSIONS PST was the most common MR imaging finding in our series of subjects with Erb palsy and was observed more frequently than currently used imaging features. Although the morphology of PST is somewhat variable, several distinct patterns were observed, possibly reflecting different histologic compositions.