Langer’s axillary arch or axillopectoral muscle is a supernumerary muscle and is the most common and the best-known anatomical variant of the axilla, with clinical and surgical implications. The axillary arch is ordinarily classified as a vestigial muscle of the panniculus carnosus (a layer of striated muscle deep to the panniculus adiposus) and is considered to have no functional significance.
Langer's axillary arch is also known as:
- axillary arch
- axillopectoral muscle
- muscular axillary arch
- muscle of Langer
- pectorodorsalis muscle
- “arcus axillaris” (Latin)
Substantial variation in the reported incidence in cadaveric studies is published, from 1.7% (Turkish population) to 43.8% (Chinese population). The incidence is significantly less in surgical series at 0.25%.
Langer's axillary arch seems to be more frequent in females than in males. Probably, this is to be ascribed to the bias of surgical observations made mainly on female patients.
Langer's axillary arch is usually asymptomatic and accidentally found during axillary surgery giving its difficult preoperative detection. Nonetheless, it can be suspected during a routine clinical examination for the loss of the normal axillary concavity and for the presence of an axillary palpable mass, usually confused with an enlarged lymph node.
Langer's axillary arch is usually unilateral, without a side preference, and is rarely bilateral. This anomaly is a muscular slip extending from the anterior border of the latissimus dorsi muscle, both from the muscle and the tendon, crossing over the axillary neurovascular bundle and inserting deep to the tendons, muscles or fasciae around the superior part of the humerus, generally to the pectoralis major or onto the coracoid process. Other insertions are to the coracobrachialis or to the short head of the biceps brachii.
The origin of the Langer's axillary arch from the latissimus dorsi is constant, while there is wide variation in the shape, size, insertion as well as its blood and nerve supply. Its size may vary from 7-10 cm in length and 0.5–1.5 cm in width.
Langer's axillary arch can be divided into two groups, namely muscular form (type I) and fibrous form (type II).
Langer's has been described in association with other anomalies:
- chondroepitrochlear muscle or the fourth pectoral muscle
- two axillary veins
- variants of the brachial plexus
- absence of the intercostobrachial nerve
Sometimes Langer's axillary arch may be symptomatic; the patient complains of circulatory deficiency, chronic pain, and paresthesia, swollen arm. The sign and symptoms are caused by the compression of adjacent neurovascular and lymphatic structures, especially when the arm is abducted (hyperabduction syndrome).
Langer's axillary arch can be seen in the axillary region by ultrasound, mammography, and CT; MRI is helpful for a conclusive evaluation of its anatomic relations and is indicated when symptoms of neurovascular entrapment are present.
Occasionally, a mediolateral oblique mammogram might show an ovoid density that could be confused as a mass in the axilla or a smoothly wavy, band-like structure overlapped with pectoralis muscle.
- isoechoic muscular structure, extending from the lateral edge of the latissimus dorsi to the tendon of insertion of the pectoralis major
- axillary lymphadenopathy
- soft tissue tumor
Treatment and prognosis
If the Langer's axillary arch is symptomatic, its excision should be curative. The knowledge of this anomaly is crucial for surgeons performing safe axillary surgery.
The LAA should be identified and divided during sentinel node biopsy, axillary dissection, vascular bypass operations, and when using latissimus dorsi myocutaneous flap during breast reconstruction for a clear identification of the anatomic landmarks of the axilla, thus preventing axillary vein compression developing into a lymphedema of the arm.
During sentinel node biopsy, Langer's axillary arch can obscure and shift the sentinel lymph node(s) higher and can obscure lateral axillary nodes increasing the risk of recurrence.
History and etymology
After having been observed firstly by Ramsay in 1795, the muscle has been named after the 1846 more accurate description of Karl Langer, who named it “Achselbogen” (axillary arch).
- Langer's axillary arch is the common muscular anatomic variation in the axilla
- the surgeon must be aware of this anomaly
- usually asymptomatic
- should always be divided when identified in the surgical field: during sentinel node biopsy, axillary dissection and also if latissimus dorsi myocutaneous flap is used for breast reconstruction
- may cause neurovascular compression syndromes, including thoracic outlet syndrome, hyperabduction syndrome, and brachial plexus impingement
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