Sternocleidomastoid Dissection

6.2.1 The neck is extended and rotated as far as possible in the opposite direction to the operator. If still present, the platysma is now completely resected, leaving the superficial cervical fascia in place. On the surface of the sternocleidomastoid muscle, under the superficial cervical fascia, three structures can clearly be seen which cross the muscle: (1) the

Fig. 6.2 Superficial cervical fascia plane

1 = great auricular nerve

2 = external jugular vein

3 = cutaneous cervical nerve

4 = superficial cervical fascia

5 = sternocleidomastoid muscle great auricular nerve, (2) the external jugular vein with its branches, and (3) the cutaneous cervical nerve; both nerves are cutaneous (sensory) branches of the cervical plexus (Fig. 6.2).

The superficial cervical fascia is dissected along the external surface of the sternocleido-mastoid muscle, in the center, following a cra-niocaudal direction, and so the abovemen-tioned structures are interrupted. The fascia is raised from the muscle fibers by holding the scalpel at a tangent to the muscle along its entire length (Fig. 6.3).

6.2.2 The dissection of level V begins with the identification and isolation of the spinal accessory nerve.

Sternocleidomastoid Dissection
Fig. 6.3 Sternocleidomastoid muscle

Fig. 6.4 Exercise 3: spinal accessory nerve scm = sternocleidomastoid muscle c = clavicle

1 = clavicular head of sternocleidomastoid muscle

2 = sternal head of sternocleidomastoid muscle

3 = intermediate omohyoid tendon

4 = superior belly of omohyoid muscle

5 = great auricular nerve (dissected)

6 = other branches of cervical plexus

7 = cutaneous cervical nerve (dissected)

8 = spinal accessory nerve (peripheral branch)

9 = sternohyoid muscle

The accessory nerve originates in the cranium from the union of the vagal accessory nerve (parasympathetic fibers/visceral effector) and spinal accessory nerve (somatic motor); it exits from the posterior foramen lacerum and divides once again - the vagal portion (internal or medial branch) joins the vagus nerve and participates in innervating the larynx. The spinal portion (external or lateral branch) passes anteriorly to the internal jugular vein, enters the sternocleidomastoid muscle (which it innervates), and exits in proximity to the posterior margin of the muscle. Running from top to bottom and from front to rear, the peripheral portion of the nerve then enters the trapezius, which it innervates.

■ 6.2.3 Exercise 3: Spinal Accessory Nerve (Fig. 6.4).

We shall look for the peripheral portion of the spinal accessory nerve in two points: 1. At the exit from the posterior margin of the sternocleidomastoid muscle, about 1 cm superiorly to Erb's point, i.e., where the great auricular nerve, which is part of the cervical plexus, surrounds the muscle and surfaces. 2. On entry to the trapezius, about 2 cm above the point where this muscle and the inferior belly of the omohyoid muscle cross.

The second approach is the more practical because neck dissection is normally performed from bottom upward and from back to front. First, we must identify the anterior margin of the trapezius just beneath the skin. The nerve, 6 which penetrates the muscle medially at its anterior margin, is thus more easily protected. Here we shall identify the cervical branch for the trapezius and, after that, the distal portion of the transverse pedicle of the neck.

Once identified, the spinal accessory nerve is isolated along its entire course from the trapezius to the sternocleidomastoid muscle (Fig. 6.5). During this procedure, some spinal chain lymph nodes may be found, which follow the course of the nerve.

Complications: The trapezius and the ster-nocleidomastoid muscle have a double innervation, one coming from the spinal accessory nerve and another pertaining to the roots C2 and C3 of the cervical plexus. The sectioning of both afferents leads to what is defined "shoulder syndrome", and consists of the lowering and anterolateral rotation of the shoulder and of pain associated with the movements of lifting the limb. In some cases, this may be followed by marked hypertrophy of the sternoclavicular articulation, due to microfractures or capsular distortions from lifting and anteriorization of the medial section of the clavicle. Clinically speaking, a clavicular "pseudotumor" is presented, which, at first sight, may lead to the suspicion of metastases at level IV or secondary bone localization.

■ 6.2.4 The medial surface of the trapezius is freed from the overlying loose connective tissue until, at the top and on a deeper plane, the levator scapulae muscle and the scalene muscles are revealed, covered by the deep cervical fascia (level VA). On the levator scapulae muscle the lesser occipital nerve can be identified, another cutaneous branch of the cervical plexus (Fig. 6.6).

Fig. 6.5 Spinal accessory nerve

scm = sternocleidomastoid muscle tr = trapezius muscle c = clavicle

1 = spinal accessory nerve

2 = superficial cervical fascia

3 = branches of cervical plexus

4 = levator scapulae muscle

5 = deep cervical fascia

6 = cervical nerve serving trapezius muscle

7 = transverse cervical artery

8 = inferior belly of omohyoid muscle

Dissection will encounter other posterior branches of the plexus, and will stop medially at the level where the anastomotic loops of the cervical plexus emerge, medially to which there are the Robbins levels II and III.

The following structures are sought and isolated below the spinal accessory nerve (level VB):

1. The distal portion of the transverse cervical artery.

Fig. 6.6 Robbins level V

1 = levator scapulae muscle

2 = scalene muscles

3 = trapezius muscle

4 = lesser occipital nerve

5 = spinal accessory nerve

6 = sternocleidomastoid muscle

2. The cervical plexus branch serving the trapezius.

These structures are exposed by medially lifting the loose connective tissue from the supraclavicular fossa with the scissors (Fig. 6.7).

6.2.5 The omohyoid muscle is identified in the superficial portion of the supraclavicular triangle. The external jugular vein is evident in the immediate subfascial plane, thus above the plane of the omohyoid muscle. It arises from the external surface of the sternocleido-mastoid muscle, lateralizes and descends toward the clavicle, and then meets the subclavian vein. It is served laterally by a single significant venous branch, i.e., the transverse cervical vein. These vessels are isolated and dissected at their ends (Fig. 6.8).

■ 6.2.6 The next step is to isolate the inferior belly of the omohyoid muscle, which is invested in the more lateral portion of the mid-cervical fascia divided into two (Fig. 6.9).

■ 6.2.7 We section the omohyoid muscle distally and evert it. Any hypertrophic lymph nodes of the supraclavicular chain lying on the posterosuperior margin of the clavicle are identified. With the aid of dry gauze, the adipose tissue is lifted medially, thus revealing the deep plane where we identify the plane of the scalene muscles, the brachial plexus and the overlying transverse cervical artery.

■ 6.2.8 There are three scalene muscles: the anterior, medial, and posterior. They descend from the cervical column, diverging laterally, and inserting in the first and second ribs. They are invested by the deep cervical fascia, which continues medially on the prevertebral muscles (Fig. 6.10).

■ 6.2.9 The brachial plexus is formed by the anterior branches of the fifth through eighth cervical nerves and of the first thoracic nerve. Three primary nerve trunks exit between the anterior scalene muscle and the median scalene muscle. One branch of the brachial plexus, the dorsal scapular nerve, exits between the median scalene and the posterior scalene muscles. The brachial plexus innervates the upper limb.

Remarks: Pancoast syndrome is the painful symptom complex propagated to the arm due to compression of the brachial plexus by laterocervical metastasis or a primary tumor of the apex of the lung.

Complications: In neck surgery, particularly neck dissection, lesions of the brachial plexus are very rare. The plexus is readily identifiable as a white, fibrous, triangular-shaped cord with an inferior base, forming the space between the scalene muscles. The plexus

Fig. 6.7 Inferior subfascial plane

scm = sternocleidomastoid muscle tr = trapezius muscle c = clavicle

1 = spinal accessory nerve (peripheral branch)

2 = cervical plexus nerve

3 = intermediate omohyoid tendon

4 = external jugular vein

5 = cervical nerve serving trapezius muscle

6 = transverse cervical artery

Fig. 6.8 Omohyoid muscle plane

scm = sternocleidomastoid muscle tr = trapezius muscle c = clavicle

1 = spinal accessory nerve (peripheral branches)

2 = inferior belly of omohyoid muscle

3 = intermediate omohyoid tendon

4 = external jugular vein

5 = transverse cervical vein

6 = transverse scapular artery

scm = sternocleidomastoid muscle c = clavicle

1 = intermediate omohyoid tendon

2 = superior belly of omohyoid muscle

3 = middle cervical fascia

4 = sternothyroid muscle

5 = sternohyoid muscle

6 = transverse scapular artery and vein

7 = clavicular insertion or sternocleidomastoid muscle

Fig. 6.10 Deep cervical muscles a = transverse process of atlas c = clavicle Ic = first rib s = scapula

1 = anterior scalene muscle

2 = medial scalene muscle

3 = posterior scalene muscle

4 = levator scapulae muscle

5 = splenius capitis muscle

Fig. 6.10 Deep cervical muscles a = transverse process of atlas c = clavicle Ic = first rib s = scapula

1 = anterior scalene muscle

2 = medial scalene muscle

3 = posterior scalene muscle

4 = levator scapulae muscle

5 = splenius capitis muscle

Fig. 6.11 Brachial plexus c = clavicle

1 = posterior scalene muscle

2 = medial scalene muscle

3 = anterior scalene muscle

4 = phrenic nerve

5 = internal jugular vein

6 = anthracotic lymph node

7 = transverse cervical artery and vein

8 = deep cervical fascia

9 = dorsal scapular nerve

10 = brachial plexus

11 = transverse artery of the scapula

Fig. 6.11 Brachial plexus c = clavicle

1 = posterior scalene muscle

2 = medial scalene muscle

3 = anterior scalene muscle

4 = phrenic nerve

5 = internal jugular vein

6 = anthracotic lymph node

7 = transverse cervical artery and vein

8 = deep cervical fascia

9 = dorsal scapular nerve

10 = brachial plexus

11 = transverse artery of the scapula and muscles are invested by the deep cervical fascia (Fig. 6.11).

It is generally easy to elevate the supraclavicular cellulo-adipose tissue from the scalene plane with gauze since the surface of the deep cervical fascia is an excellent cleavage plane. Since the superior primary nerve trunk (C5-C6) is in a more superficial position than are the medial and inferior trunks, it is more exposed to trauma or lesions. Anatomic variants are also possible: In the loose supracla-vicular cellular tissue, I personally witnessed the C5-C6 trunk running superficially and consequently, accidentally sectioned. This iatrogenic lesion induces motor impairment in the shoulder, which becomes lowered, with frequent dislocation of the head of the humerus; the arm droops on the trunk, exhibiting internal rotation and pronation. There is abduction paralysis of the arm and flexion paralysis of the forearm; 2 to 3 weeks later, atrophy appears in the muscles concerned.

■ 6.2.10 The transverse cervical artery (and vein) (or superficial cervical artery) and transverse scapular artery (and vein) (or su-

prascapular artery) originate from the thyrocervical trunk. They enter the region medially and diverge laterally, crossing at two different levels of the brachial plexus. They must be isolated and their course followed to the region boundaries.

■ 6.2.11 The phrenic nerve is a ramus muscu-laris of the four of the cervical plexus. It induces movement of the diaphragm, and contains sensory fibers for the pulmonary pleura and pericardium. It rests on the surface of the anterior scalene muscle, taking a slightly diverging lateromedial course with respect to the brachial plexus (as a memory aid, the phrenic nerve can be thought of as the thumb of a hand, while the other four fingers represent the branches of the brachial plexus).

The phrenic nerve can be easily identified by continuing digital elevation medially along the cleavage plane formed by the deep cervical prescalene fascia. It appears medially to the brachial plexus, invested by fascia on the external surface of the anterior scalene muscle. Dissection of the cutaneous branches of the cervical plexus, with the scissor point craniad, must be performed on a more super ficial plane to the course of the phrenic nerve, which must always be identified beforehand.

Complications: Injury to or dissection of a phrenic nerve presents as paralysis of a hemidiaphragm and its elevation. Patients with monolateral phrenoplegia are generally asymptomatic; however, they may complain of dyspnea when lying down, since the contents of the abdomen tend to raise the flaccid hemidiaphragm. The resulting compensatory expansion of the rib cage forces the intercostal and accessory muscles to work hard to produce an effective inspiratory volume. Spirometry in patients with monolateral phrenoplegia exhibits a 25% decrease in total lung capacity (TLC), vital capacity (VC), inspiratory capacity and maximum inspiratory pressure (MIP), while the reduction in forced expiratory volume at the first second (FEVI) may be as high as 40%. These values are not normally associated with important clinical consequences, except in the presence of previous pulmonary pathologies with reduced respiratory functioning.

Bilateral phrenoplegia, which is very rare in cervical surgery, is more commonly related to central or systemic neurological pathologies. Transitory bilateral paralysis may in some cases result from heart surgery-related hypothermia. Assisted ventilation is required in such cases. Reparatory operations, requiring optimum physical performance, may also be conducted in patients with monolateral phrenoplegia, and consist of "folding" the flaccid hemidiaphragm to reduce compliance.

■ 6.2.12 To conclude dissection of this region, it may be worth seeking and isolating the sub-clavian artery. It lies immediately inferomedi-ally to the brachial plexus in the tract where the artery, straddling the first rib beneath the scalene muscles and, passing below the clavicle, becomes the axillary artery. Its passage on the first rib occurs immediately laterally to Lisfranc's tubercle, which is a bony prominence where the anterior scalene muscle is attached. This is an excellent landmark for ligat-ing the interscalene portion of the subclavian artery. To reveal it, it is advisable to dissect the lateral portion of the anterior scalene muscle, of course after having identified and preserved the phrenic nerve.

Fig. 6.12 Exercise 4: subclavian artery

■ 6.2.13 Exercise 4: Subclavian Artery (Fig. 6.12). We identify the attachment of the anterior scalene muscle on the first rib and seek Lisfranc's tubercle by palpation. We look for the artery at the superior margin of the first rib, under the emergence of the brachial plexus. We can reveal it better by dissecting the lateral portion of the anterior scalene muscle, always after having revealed and preserved the phrenic nerve.

Remarks: At this point we recall the rare anterior scalene muscle syndrome, which consists of ischemic disturbances of the upper limb and of the hand and of ulnar neuralgia; these disturbances are accentuated with the limb hanging down and are alleviated when it is raised; they are due to compression of the subclavian artery and of the brachial plexus in the fissure between the median and anterior scalene muscles. The disturbances are cured by sectioning the anterior scalene muscle.

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