The accessory coracobrachialis muscle: ultrasound and MR features.
OBJECTIVE
To present the prevalence, clinical relevance, and ultrasound (US) and magnetic resonance imaging (MRI) appearances of the accessory coracobrachialis (ACB) muscle.


METHODS
We present an US prospective study of the ACB muscle over a 2-year period. Five of the eight patients with suspected ACB on US were subsequently examined by MRI.


RESULTS
An ACB muscle was demonstrated by US in eight patients (eight shoulders), including seven females, one male, with mean age 39 years, over 770 (664 patients) consecutive shoulder US examinations referred to our institution yielding a prevalence of 1.04%. In dynamic US assessment, one case of subcoracoid impingement secondary to a bulky ACB was diagnosed. No thoracic outlet syndrome was encountered in the remaining cases. MRI confirmed the presence of the accessory muscle in five cases.


CONCLUSIONS
ACB muscle is a rarely reported yet not uncommon anatomic variation of the shoulder musculature encountered only in eight of 664 patients referred for shoulder US study. Its US and MRI appearance is described. One of our patients presented with subcoracoid impingement related to the presence of an ACB.
Department of Radiology, Hôpital Saint-Luc, Centre hospitalier de l'Université de Montréal (CHUM), 1058 rue Saint-Denis, Montreal, Québec, H2X 3 J4, Canada, salem.bauones@umontreal.ca.
Salem
S
Bauones
Antoine
A
Moraux
D000328:Adult; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000473:pathology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012785:Shoulder Joint / Q000002:abnormalities* / Q000000981:diagnostic imaging / Q000473:pathology*; D014463:Ultrasonography / Q000379:methods*