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.
"The axillary arch is usually asymptomatic, and it importantly causes confusion during routine axillary surgery ; in such cases, the surgeon must assume its possible presence and exercise caution during dissection. Guy et al.  found that 92% of arches had medial lymph nodes that may have been important to determine prior to sentinel node biopsy. The axillary arch is also associated with various surgical and medical problems because it is likely to present as an axillary mass, which can be confused with axillary lymph nodes. "
[Show abstract][Hide abstract] ABSTRACT: Anatomical variations of the nerves, muscles, and vessels in the upper limb have been described in many anatomical studies; however, the occurrence of 6 variations in an ipsilateral limb is very rare. These variations occur in the following structures: the pectoralis minimus muscle, the communication between the external jugular vein and cephalic vein, axillary arch, the Struthers ligament, the medial, lateral, and posterior cords of the brachial plexus, and the common arterial trunk from the third part of the axillary artery. The relationship of these variations to each other and their probable clinical presentation is discussed.
"Muscular variations in the axillary region may be involved in thoracic outlet syndrome, shoulder instability, development of lymph edema of the upper limb, and surgical interventions such as breast surgery [1-3]. By shoulder magnetic resonance imaging examination, Guy et al.  suggested that the axillary arch can cause lymph node concealment and brachial plexus impingement. "
[Show abstract][Hide abstract] ABSTRACT: Many origins and insertions of an axillary muscular slip (also known as Langer's or axillary arch muscles) have been documented previously. In this report, we found duplicated axillary arch muscles (two variant muscular slips) originating from the inferolateral border of the right side latissimus dorsi muscle. Obviously, these axillary arch muscles can be distinguished as short and long muscular strips. While the origin was the same, the short muscular slip inserts into the fascia covering on the pectoralis minor, whereas the longer one inserts on/into the aponeurosis of pectoralis major. For the surgery in the axillary region, this rare variation should be considered a cause of surgical interventions.
[Show abstract][Hide abstract] ABSTRACT: The axillary arch (AA) has been thoroughly studied and described as a supernumerary muscle, present unilaterally or bilaterally. This study aims to provide an in vivo demonstration of the influence of an AA on vascular, biometrical, and hemodynamic parameters. Two-hundred thirty-nine subjects with a mean age of 21.3 ± 2.7 years participated in this study. After visual screening by two independent experts, 20 subjects (8.4%) presented with an AA unilaterally (n = 12) or bilaterally (n = 8). An echo-Doppler examination of the vena and arteria axillaris was performed to measure blood flow, velocity of circulating elements, and blood vessel diameter in different positions of the arm (abduction: 45°, 90°, 90° combined with exorotation 'ER', 120°). The arteria axillaris parameters, measured in the test (n = 9; six women, three men) and control group (n = 11; six women, five men), were equivalent for all tested positions. The axillary vein parameters, compared to variations within the groups, revealed no significant differences. However, when comparing variation between groups, significant differences were found for (i) diameter in 90° abduction + ER and 120° abduction; (ii) velocity in 90° and 120° abduction. Blood flow demonstrated no significant difference between groups in any of the positions. The results of this study indicate that there is no functional vascular implication of the AA in the test samples. This study also questions the interpretation of some hypotheses regarding the AA and entrapment syndromes.
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