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Clinical case: Pectoralis minor syndrome: want to learn more about it?

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Clinical case: Pectoralis minor syndrome

This clinical case is about a female which presents with recurrent swelling, pain, numbness, and tingling of the upper extremity due to an obstruction of the neurovascular bundle by the pectoralis minor muscle. Find out the route to diagnosis and all the anatomical considerations related to this case in this article.

Key facts
Venous drainage pattern of the upper limb Dorsal venous network of the hand -> Cephalic and basilic veins -> Median cubital vein at the elbow -> Brachial and axillary veins
Adson's test It hecks for compression of the subclavian artery by a cervical rib or spastic anterior and middle scalene muscle (thoracic outlet syndrome)
Functions of the pectoralis muscles

Pectoralis major: adduction and medial rotation of the arm, partial help with upper limb flexion

Pectoralis minor: stabilizes the scapula, elevation of upper ribs during respiratory distress

Intercostobrachial nerve Supplies cutaneous sensation to the upper arm (superior half of the medial and posterior parts). It is also important in the referred pain from a myocardial infarction.

After reviewing this case you should be able to describe the following:

  • The venous drainage pattern of the upper limb.
  • Adson’s test, how the test is done and the anatomical basis of this test.
  • The functional anatomy of the pectoral muscles.
  • Why did the surgeons wish to avoid injuring the intercostobrachial and pectoral nerves?

This article is based on a case report published in the Journal "Case Reports in Surgery" in 2015, by Caroline C. Jadlowiec, Beata E. Lobel, Namita Akolkar, Michael D. Bourque, Thomas J. Devers, and David W. McFadden.

Case description

History

A 29-year-old healthy female presented with complaints of recurrent swelling and pain of the right upper extremity. The patient’s condition started at age 21, with episodes occurring once every three to five months, but with increasing frequency over the previous three months. 

Figure 1. Dissection image of the axillary region highlighting the anatomical position of pectoralis minor and intercostobrachial nerve. 


Episodes were associated with numbness and tingling in the hand associated with a bluish discoloration of the fingers. Swelling of the extremity was observed at rest and increased upon exercise and/or elevation of the arm. The patient recalled a history of right upper extremity trauma at age 17. She had had multiple emergency department visits for her condition, during which she underwent a complex series of lab and imaging studies, including venous duplex ultrasound of the upper extremity, which failed to reveal evidence of either deep or superficial venous thrombosis.

Figure 2. Similar image to Figure 1 but with pectoralis minor reflected showing the underlying cords of the brachial plexus, and axillary artery and vein.

Chest and cervical spine radiographs failed to show any cervical pathology. Venography and MR venography initially found no evidence of thoracic outlet syndrome (TOS). EMG of the upper extremity showed normal nerve conduction velocities, with no electrophysiological evidence of cervical root disease, brachial plexus lesion, TOS, or focal nerve entrapment in the right upper extremity.

Physical exam

On physical exam, she had swelling in the right upper extremity; no point tenderness over supra- or infraclavicular regions; palpable brachial, radial, and ulnar pulses in resting position and in Adson’s maneuver. Lastly, elevated arm stress test was negative.

Imaging and diagnosis

Venography was repeated with a catheter inserted into the basilic vein; this result showed no significant abnormality in resting position or during Adson’s maneuver with arm elevation and 180-degree abduction. However, when the pectoralis minor muscle was stretched medially and the arm pulled inferiorly, an obstruction of the brachial/axillary veins was noticed (Figures 3+4).

Figure 3. Venographic image of patient’s arm being pulled inferiorly while pectoralis minor muscle stretched by fixing the breast medially. Note the narrowing of the lateral brachial and basilic veins near where they anastomose to form the axillary vein.The blue dashed circle represents location of venous obstruction. The medial brachial vein does not fill at all in this maneuver in this patient and thus does not appear in the radiograph, but is drawn in (dashed line) to show its path.

Management and evolution

The obstruction was relieved with relaxing the inferiorly pulled arm. Contralateral side venography with the same maneuver was normal, with no evidence of axillary vein obstruction or thrombosis. In order to alleviate the patient’s condition, general anesthesia was induced in the patient and a right pectoralis minor tenotomy (PMT) via transaxillary approach was performed.

Figure 4. Dynamic venographic image with the upper limb pulled inferiorly and then released: Occlusion of the axillary vein was completely resolved upon releasing the tension. The blue dashed circle represents the location of the venous obstruction.

A five (5) cm incision was made, beginning one (1) cm from the inferior aspect of the hairline. The pectoralis major muscle was separated from the pectoralis minor and retracted anteriorly. The minor muscle was found to be hypertrophied and it was transected distal to its insertion on the coracoid process while avoiding injury to the pectoral nerves. No additional pathology was found that could compress the axillary vein.

The patient was discharged the next day. At the six months follow-up exam, the patient was free of symptoms, leading to a normal daily life activity.

Surgical and anatomical considerations

The thoracic outlet syndrome (TOS) is characterized by compression of the upper extremity’s neurovascular bundle in the scalene triangle. This triangle is bordered by the clavicle, first rib, and the anterior and middle scalene muscles superior to the clavicle (Figure 5).

Figure 5. Dissection image showing the roots of the brachial plexus emerging between the anterior and middle scalene muscles (scalene triangle) in the posterior triangle of the neck.

Vascular and/or neurological signs and symptoms can characterize TOS. However, a similar infrequent vascular condition, pectoralis minor syndrome (PMS), is characterized by axillary vein obstruction by compression from the pectoralis minor muscle inferior to the clavicle (Figure 6).

Importantly, although PMS is distinct from TOS, it is often subsumed under the latter condition. In PMS the patient presents with pain, weakness, cyanosis, numbness, paresthesia, and swelling of the upper extremity. The causes of PMS may be associated with trauma, sports injuries, repetitive movements, weight lifting, or be idiopathic.

Figure 6. Drawing showing how the pectoralis minor could compress the axillary vein. Modified with permission from an original image by Dr. Phil Sizer.

Deep to the PM are the axillary artery and vein and the cords of the brachial plexus. EMG is usually normal in PMS and can be used to rule out neurological conditions. Although duplex ultrasonography is sensitive for detecting venous thrombosis, it may not identify a subtle degree of compression as in this case. Instead, dynamic venography is considered the most helpful diagnostic tool in PM. In this “radiographic” procedure, an x-ray is taken of the patient before and after the injection of iodinated contrast material (by catheter into the basilic vein in this case). A digital algorithm then subtracts the pre-injection image from a post-injection image. Pixels in the images that do not change between the two essentially disappear and what remains visible on the screen is the veins filled with contrast material. For the patient in this case, this procedure clearly showed the venous obstruction.

Treatment procedures for PMS range from PM stretching, to PM injection block. When such conservative measures fail, PMT becomes the treatment of choice. Rather than the axillary approach to the PM as done for this patient, the PM tendon could be transected via an infraclavicular approach. However, the latter technique risks injury to the intercostobrachial nerve. Recovery time form PMT is often just a few days, with a recommendation that the patient refrain from using the arm for activities above the level of the shoulder for 2-3 months to permit adherence of the resected PM muscle to the chest wall.

Figure 7. Cadaver photograph showing superficial veins of the upper limb, the cephalic vein on the left penetrates the deltopectoral groove to join the axillary artery; the basilic vein on the left pierces the deep fascia of arm to become brachial vein.

Clinical case: Pectoralis minor syndrome: want to learn more about it?

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