Medial pectoral pedicle is a reliable landmark for axillary lymph node dissection

Summary

Background

The anatomical orientation of structures in the axilla has not been well studied, although it is essential for a neat and safe dissection. The objective of this study was to determine the relations between neurovascular structures in the axilla as they were encountered during axillary lymph node dissection (ALND) for breast cancer.

Methods

This was a prospective study of 29 consecutive ALNDs accompanying either mastectomy or wide local excision. The dissections were conducted in a stepwise manner and the orientation of the structures was determined as the dissections advanced from superficial to deeper planes.

Results

The medial pectoral pedicle was the most superficial neurovascular structure encountered during the dissections and was curled around the lateral border of the pectoralis minor muscle in most cases. The intercostobrachial nerve lay 1–2 cm behind and below, and the axillary vein was located 2–3 cm behind and above the pedicle. The long thoracic nerve was constantly found 2–3 cm behind the intercostobrachial nerve. The thoracodorsal nerve was always accompanied by a posterior tributary of the axillary vein.

Conclusion

Relations between neurovascular structures in the axilla are predictable. The medial pectoral pedicle, which is consistently found and superficially located, could be used as a landmark for ALND.

Keywords

axillary lymph node dissection;breast cancer;medial pectoral pedicle

1. Introduction

Axillary lymph node dissection (ALND) is important for prognostication and locoregional control of breast cancer. Recent years have seen it being replaced by a less invasive procedure, sentinel node biopsy, especially for node-negative and small tumors. This change in practice is, to a certain extent, driven by frequent morbidity attributed to ALND, namely lymphedema, chronic pain, altered sensorium, and restricted shoulder mobility. With the exception of lymphedema, the others are preventable by meticulous dissection and appreciation of axillary anatomy. Dissection in the axilla poses a unique challenge. The axilla is essentially a fat-filled space, with neurovascular structures blended within the fat tissue. Being loose and flimsy, fat tissue is difficult to hold or retract. This adverse feature of fat tissue restricts the ability to identify and preserve the structures that traverse within it. Therefore, it is important for surgeon to have a stepwise technique and foresee the location of the structures during dissection, to avoid injuries to these structures.

We conducted this study with the objectives of describing the relations among important neurovascular structures within the axilla as they were encountered during axillary dissection, and to identify a relatively superficial and constant structure that can be used as a surgical landmark for ALND.

2. Methods

This was a prospective study of patients who underwent ALND accompanying either mastectomy or wide local excision. None of the patients had previous surgery or radiotherapy to the axilla. Written informed consent was obtained from each patient. We described neurovascular structures in the axilla in sequential manner according to their emergence during dissection from superficial to deeper planes. The structures of concern were the medial pectoral pedicle, the axillary vein and its tributaries, the intercostobrachial nerve, the thoracodorsal nerve, and the long thoracic nerve. Distances between the structures were measured in the anteroposterior and craniocaudal planes using a sterile ruler.

2.1. Surgical technique

Patients were placed in the supine position with their arms abducted at 90 degrees and a sand bag placed under the shoulder. Access to the axilla was either through mastectomy wound or a separate incision along the lower axillary hairline for patients with wide local excision. Subcutaneous tissue was dissected until the pectoralis major muscle was identified. Incision of the axillary fascia was made along the pectoralis major muscle and the muscle was retracted medially to expose the underlying pectoralis minor muscle. The upwards extension of the axillary fascia (the suspensory ligament) was carefully incised along the lateral border of the pectoralis minor muscle. The medial pectoral pedicle was seen along the lateral border of the pectoralis minor muscle. Liberation of the pedicle was achieved via incision of the fascia lateral to it and ligating its branches that traversed the axilla. The pedicle was then retracted medially together with the pectoralis minor muscle. The axillary pad of fat was dissected away from the chest wall. Dissection in the deeper plane revealed the axillary vein and the intercostobrachial nerve; the former should lie above and the latter below the medial pectoral pedicle. Preservation of the intercostobrachial nerve was always attempted unless it was encased within matted metastatic lymph nodes. Dissection was further performed along the lower border of the axillary vein distally, and its tributaries were identified. The thoracodorsal nerve was located as it was accompanied by one of the tributaries of the axillary vein. The tributaries that traversed into the axillary fat were ligated. Further dissection of the axillary fat from the chest wall was carefully performed so as not to injure the long thoracic nerve that lay in a deeper plane. The axillary fat was then dissected completely in a downwards direction from the axillary vein and laterally from the chest wall.

3. Results

A total of 29 patients (all female, age: 26–60 years, mean age: 46.9 years) were recruited into the study from October 2008 until September 2009. Clinical characteristics of the patients are shown in Table 1. The medial pectoral pedicle was encountered in 27 (93.1%) patients. Of these, the pedicle wound around the lateral border of the pectoralis minor muscle in 24 (88.9%) and pierced the posterior surface of the muscle in three patients. The pedicle was not seen in two patients. Both of these patients had no previous operation or radiotherapy to the axilla, no adhesion, and no enlarged axillary nodes. There was no other structural abnormality found in them.

Table 1. Patient characteristics.

Characteristics	n
Mean age (y) (range)	46.9 (26–60)
T stage, n (%)
T0	3 (10.3)
T1	3 (10.3)
T2	11 (37.9)
T3	8 (27.6)
T4	8 (27.6)
N stage, n (%)
N0	21 (72.4)
N1	5 (17.2)
N2	3 (10.3)
Access to axilla, n (%)
Through mastectomy wound	17 (58.6)
Separate incision in axilla	12 (41.4)

One patient had dense desmoplastic changes in the axilla from metastatic lymph nodes and previous chemotherapy for contralateral breast cancer. In this patient, the medial pectoral pedicle was seen at the lateral border of the pectoralis minor muscle, but the intercostobrachial nerve, the thoracodorsal nerve, and the long thoracic nerve could not be identified.

The intercostobrachial nerve was located 1–2 cm behind and below the medial pectoral pedicle in 21 (80.8%) patients, and 1–2 cm directly behind the pedicle in five (19.2%) patients (Fig. 1). The nerves were sacrificed in 13 patients because they were encased within matted metastatic nodes. There was no unintentional injury to the nerve. Seventeen patients (62.9%) had the axillary vein approximately 2–3 cm above and behind the medial pectoral pedicle. In one patient the vein lay close at 0.5 cm above the pedicle. The thoracodorsal nerves were accompanied by the posterior tributary of the axillary vein in 24 (85.7%) patients. In 26 (96.3%) patients the long thoracic nerves were identified 2–3 cm behind the intercostobrachial nerve, and in one patient the nerve lay 1 cm behind the intercostobrachial nerve. Fig. 2 represents the most commonly observed orientation of the neurovascular structures in the axilla. Details on the relations between the structures are shown in Table 2.

Figure 1. Photograph of right axillary lymph node dissection performed through a lower axillary incision showed a rare occasion on which the intercostobrachial nerve lay directly under the medial pectoral pedicle. AV = axillary vein; ICBN = intercostobrachial nerve; LTN = long thoracic nerve; MPP = medial pectoral pedicle; TDN = thoracodorsal nerve.

Figure 2. Photograph of right axillary lymph node dissection performed through mastectomy wound represents the most commonly observed orientation of neurovascular structures in the axilla. Also shown is the lateral cutaneous branch of the third intercostal nerve. AV = axillary vein; ICN = intercostal nerve; ICBN = intercostobrachial nerve; LTN = long thoracic nerve; MPP = medial pectoral pedicle; Pm = pectoralis minor muscle; PM = pectoralis major muscle; TDN = thoracodorsal nerve.

Table 2. Relations between structures in the axilla.

Relations between structures in the axilla	n (%)
MPP occurrence
Curled around lateral border of Pm	24 (82.8)
Pierced posterior surface of Pm	3 (10.3)
Not seen	2 (6.9)
Distance of ICBN from MPPa
AP plane
1.0 cm	12 (46.1)
1.5 cm	5 (19.2)
2.0 cm	9 (34.6)
CC plane
0 cm	5 (19.2)
1.0 cm	9 (34.6)
1.5 cm	5 (19.2)
2.0 cm	6 (23.1)
3.0 cm	1 (3.8)
Distance of AV from MPPa
AP plane
0.5 cm	3 (11.1)
1.0 cm	7 (25.9)
1.5 cm	2 (7.4)
2.0 cm	14 (51.9)
3.0 cm	1 (3.7)
CC plane
0.5 cm	1 (3.7)
1.0 cm	6 (22.2)
1.5 cm	3 (11.1)
2.0 cm	15 (55.6)
3.0 cm	2 (7.4)
Distance of LTN from ICBN
AP plane
1.0 cm	1 (3.7)
2.0 cm	11 (40.7)
3.0 cm	14 (51.9)

AP = anteroposterior; AV = axillary vein; CC = craniocaudal; ICBN = intercostobrachial nerve; LTN = long thoracic nerve; MPP = medial pectoral pedicle; Pm = pectoralis minor muscle.

a. Distance from the point the medial pectoral pedicle winds around the lateral border of the pectoralis minor muscle or pierces the posterior surface of the muscle.

4. Discussion

The ALND remains important in breast cancer management despite the emergence of a less invasive procedure, sentinel lymph node biopsy, especially in node-positive and large breast cancer. In this current era of breast cancer therapy, the main concern in surgery is not merely achieving complete tumor removal, but as survival rate has dramatically improved, postoperative morbidity and patients' quality of life have become major considerations.

It is therefore important for surgeons to have a stepwise technique and foresee the location of the structures during dissection. Knowledge of the orientation of structures guides surgeons as deeper planes are entered and is imperative to avoid inadvertent injuries to these structures. This is particularly true when sharp dissection using scissors or ultrasonic dissection using harmonic scalpel is adopted where visibility of structures is paramount before the dissection can advance further. It is safer to use blunt dissection if the orientation of structures is not known but a longer operating time is expected. Some surgeons prefer to use electrocautery because it stimulates jerky movements when the dissection approaches the motor nerves. However, the integrity of the nerves could be jeopardized by the electrical stimulation. Furthermore, the same jerky response cannot be elicited from sensory nerves like the intercostobrachial nerve and blood vessels.

In the current study, we found that the medial pectoral nerve was the first neurovascular structure encountered during axillary dissection and present in 93% of the cases. Most pedicles curled around the lateral border of the pectoralis minor muscle rather than passed through the posterior surface of the muscle. This finding is contradictory to previously published descriptions^{1; 2 ;  3} on the course of the medial pectoral nerve, in which only a quarter to one third of the nerve wound around the lateral border of the pectoralis minor muscle. Therefore, we believe that most of the medial pectoral pedicles encountered during our dissections were devoid of their nerve component. The medial pectoral nerve rather traversed on its own and pierced the undersurface of the pectoralis minor muscle to innervate the more superficial pectoralis major muscle.

The point in the lateral border of the pectoralis minor muscle that is crossed by the medial pectoral pedicle provides an important landmark to the locations of the intercostobrachial nerve and the axillary vein. In this context, we agree with Nadkarni et al⁴ on the importance of the medial pectoral pedicle in axillary dissection. In most of our cases, the intercostobrachial nerve emerged from the chest wall approximately 1–2 cm behind and below this point. Previous studies have shown variations in the course and branching pattern of the nerve in the axilla.^{5; 6 ;  7} Therefore, we believe that the safest way to preserve the intercostobrachial nerve is by performing dissection commencing from its origin in the chest wall and carefully following the nerve laterally as it traverses towards the arm. The nerve should be preserved as long as it is not incorporated within a metastatic lymphatic mass. The same crossing point between the medial pectoral pedicle and the pectoralis minor muscle dictates the position of the axillary vein, where the vein lies 2–3 cm behind and above this point.

Once the two structures have been identified, the axillary content can be dissected away from the chest wall. As the dissection goes deeper and before reaching the posterior boundary of the dissection, namely the subscapularis muscle, the long thoracic nerve can be found as it traverses the side of the chest wall. We observed that the location of the nerve could be predicted by the intercostobrachial nerve, where the long thoracic nerve always lies 2–3 cm behind the intercostobrachial nerve. Standard anatomy texts describe the long thoracic nerve to run on the surface of the chest wall.¹ However, during the dissection, as the axillary fat is being pulled laterally, the nerve is expected to lie at some distance away from the chest wall.

Dissection along the axillary vein reveals its tributaries, which are frequently two or three in number. The posterior tributaries are those that run downwards and backwards, and one of them always accompanies the thoracodorsal nerve. Due to this close relation between the nerve and the tributary of the axillary vein, it is an important precautionary measure that no tributary of the axillary vein should be ligated before the thoracodorsal nerve is identified.

We conclude that the relations between the neurovascular structures in the axilla are predictable. The medial pectoral pedicle which is consistently present and relatively superficial in location could be used as a landmark for the ALND.

References

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