MRI of the axillary arch muscle: prevalence, anatomic relations, and potential consequences

The purpose of this study was to use MRI of the shoulder to analyze the axillary arch muscle and its anatomic relations to lymph nodes and the brachial plexus. In this retrospective study at a single clinic, five observers blinded to the patient's condition assessed images from 1,109 consecutiv...

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Bibliographic Details
Published in:	American journal of roentgenology (1976) Vol. 196; no. 1; pp. W52 - W57
Main Authors:	Guy, Matthew S, Sandhu, Sandra K, Gowdy, John M, Cartier, Cameron C, Adams, James H
Format:	Journal Article
Language:	English
Published:	United States 01-01-2011
Subjects:	Adolescent Adult Axilla - anatomy & histology Chi-Square Distribution Female Humans Joint Diseases - diagnosis Lymph Nodes - anatomy & histology Magnetic Resonance Imaging - methods Male Middle Aged Muscle, Skeletal - anatomy & histology Retrospective Studies Shoulder Joint - anatomy & histology
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Summary:	The purpose of this study was to use MRI of the shoulder to analyze the axillary arch muscle and its anatomic relations to lymph nodes and the brachial plexus. In this retrospective study at a single clinic, five observers blinded to the patient's condition assessed images from 1,109 consecutive initial shoulder MRI examinations for the presence and anatomic relations of the axillary arch. MRI interpretation reports were reviewed for documentation of previous injuries and upper extremity radicular pain or numbness for possible correlations between presence of the arch and symptoms of nerve entrapment. Results were reported as prevalence percentage or mean ± SD with 95% CI. Groups were compared by use of Student's t test or chi-square test as indicated (p < 0.05). An arch muscle was found in 71 of 1,109 (6%) examinations, and variability was found in arch insertion and visualization. A statistically significant 65 of 71 (92%) arches had a course superficial to the lymph nodes. The insertion of 50 of 71 (70%) arches was within 5 mm of the brachial neurovascular bundle. Excluding documented injuries, significantly more patients with an arch had upper extremity neurologic abnormalities than did patients without an arch (p = 0.02). The axillary arch muscle is situated in such a way that it can conceal lymph nodes and impinge on the brachial plexus, causing symptoms of upper extremity nerve entrapment. Radiologists' familiarity with the arch can improve their recognition of this muscular variant so that they can communicate appropriate clinical correlations to referring physicians.
Bibliography:	ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23
ISSN:	0361-803X 1546-3141
DOI:	10.2214/AJR.10.4380