Focal brachial enhancement deficit: a normal anatomic variant?

To identify the incidence of brachialis enhancement deficits (BEDs) on contrast-enhanced elbow MRIs and determine if there is an association between the presence of BEDs and presenting symptoms, other imaging findings, or patient positioning. Elbow MRIs from 138 patients (64 males, mean age 45.3 years) were reviewed. The presence, size, and degree of enhancement of BEDs as well as degree of elbow flexion, relative degree of forearm rotation, and additional finding of pathology on the MRI were recorded. BEDs were found in 54 % (75/138) of contrast-enhanced elbow MRIs. No statistically significant difference was seen between age, gender, presenting symptoms and the presence of BEDs. The BEDs varied considerably in size and degree of diminished enhancement compared to adjacent muscle. There was a very significant correlation between degree of elbow flexion and presence of BEDs (p < 0.0001) and a significant inverse correlation between cross-sectional size of BEDs and degree of flexion (p < 0.01). There was no significant correlation between BED enhancement difference and degree of flexion and no significant correlation between degree of forearm rotation and cross-sectional area or enhancement difference of the BEDs. No correlation was found between the presence of BEDs and other pathology present on the MRI. BEDs are a common, likely asymptomatic phenomenon seen on post contrast elbow MRIs. The etiology of BEDs is uncertain, but they may represent a vascular phenomenon related to elbow flexion causing diminished enhancement related to brachialis compression. (orig.)