S2 Dissection

■ 5.2.1 Below the platysma, the region is invested with superficial cervical fascia, which divides into two at this level to envelop the gland. In the thickness of the fascia we can identify two of the inferior branches of the facial nerve, i.e., the marginal nerve and nerve serving the platysma muscle. The former runs 1 cm above the inferior margin of the corpus mandibulae; the latter, which is more difficult to find, runs through the posterosuperior angle of the region, descending to innervate the platysma (Fig. 5.2).

■ 5.2.2 After dissecting the superficial cervical fascia, the submandibular gland is exposed. On the surface of its posterior pole we look for the facial nerve, which in its downward course unites anteriorly with the submental vein and posteriorly with the retromandibular vein (or external carotid vein) to form the facial venous trunk. It should be borne in mind that venous circulation in this region is somewhat variable, and the situation described is the most frequent one. The interglandular

Thyrolinguofacial Trunk

Fig. 5.1 Ablation of the submandibular gland (I)

sm = submandibular gland p = parotid m = mandible i = hyoid bone

1 = posterior belly of digastric muscle

2 = stylohyoid muscle

3 = internal jugular vein

4 = external carotid artery

5 = internal carotid artery

6 = occipital artery

7 = posterior auricular artery

8 = hypoglossal nerve

9 = descending branch of hypoglossal nerve

10 = thyrolinguofacial venous trunk

11 = superior thyroid artery and vein

12 = superior laryngeal artery and vein

13 = lingual vein

14 = lingual artery

15 = facial vein

16 = facial artery

17 = retromandibular vein

18 = external jugular vein

19 = platysma branch (facial nerve)

20 = marginal branch (facial nerve)

21 = submental artery

22 = submental vein

23 = mylohyoid muscle

24 = anterior belly of digastric muscle

25 = thyrohyoid muscle

26 = omohyoid muscle

27 = sternohyoid muscle

Fig. 5.2 Fascial plane

m = mandible

1 = sternocleidomastoid muscle

2 = great auricular nerve

3 = external jugular vein

4 = angle of mandible

5 = masseter muscle

6 = marginal branch (facial nerve)

7 = facial pedicle

Thyrolinguofacial Trunk

sm = submandibular gland

1 = angle of mandible

2 = lymph node

3 = linguofacial venous trunk

4 = lingual vein

5 = retromandibular vein

6 = interglandular septum

7 = facial vein

8 = submental vein

9 = facial artery

10 = marginal branch (facial nerve)

11 = mandibular inferior margin

12 = mylohyoid muscle

13 = anterior belly of digastric muscle sm = submandibular gland

1 = angle of mandible

2 = lymph node

3 = linguofacial venous trunk

4 = lingual vein

5 = retromandibular vein

6 = interglandular septum

7 = facial vein

8 = submental vein

9 = facial artery

10 = marginal branch (facial nerve)

11 = mandibular inferior margin

12 = mylohyoid muscle

13 = anterior belly of digastric muscle septum can be viewed further behind, which is a thickening of the superficial cervical fascia separating the submandibular gland from the parotid (Fig. 5.3).

■ 5.2.3 Dissection then proceeds by elevating the superficial cervical fascia from the contents of the cavity, exposing at the top the distal part of the facial pedicle. At the bottom the two bellies are uncovered and the intermediate tendon of the digastric muscle that binds the submandibular cavity at the bottom (Fig. 5.4).

■ 5.2.4 The facial pedicle can be found straddling the inferior margin of the mandible, by the anterior border of the masseter muscle. The marginal branch of the facial nerve crosses the facial pedicle at the top and innervates the mimetic muscles of the lower lip. We ligate the distal facial pedicle 1 to 2 cm from the inferior margin of the mandible (Fig. 5.5).

Complications: Traumatization of the marginal nerve causes temporary paresis of the de pressor labii inferioris. It is therefore good practice to maintain a caudal position with respect to the cutaneous incision, to avoid exerting excessive traction on the flap in proximity to the mandibular margin and, where necessary, to dissect the facial pedicle as close as possible to the gland. In the latter case we are sure to preserve it by turning the sectioned pedicle upward. The nerve, which always passes over the pedicle, is thus stretched upward, away from the surgical field (Hayes Martin maneuver).

■ 5.2.5 Gland ablation begins from the posterior pole, demonstrating the course of the facial artery branch of the external carotid artery. It emerges behind the posterior belly of the digastric muscle, posteriorly skimming the submandibular gland; running backward and forward, and upward and downward, it surfaces to surround the inferior margin of the mandible, immediately anterior to the facial vein. We ligate the proximal facial pedicle where it appears behind the digastric muscle. In the benign pathology of the submandibular

Hayes Martin Maneuver
Fig. 5.4 Facial pedicle plane

sm = submandibular gland

1 = angle of mandible

2 = facial vein

3 = retromandibular vein

4 = submental vein

5 = facial artery

6 = submental artery

7 = mandibular inferior margin

8 = anterior belly of digastric muscle

9 = mylohyoid muscle

10 = intermediate tendon of digastric muscle

11 = posterior belly of digastric muscle

12 = stylohyoid muscle

1 = angle of mandible 4 = facial artery

2 = masseter muscle 5 = marginal branch (facial nerve)

3 = facial vein

sm = submandibular gland

1 = angle of mandible

2 = proximal portion of marginal branch (facial nerve)

3 = lymph node

4 = facial vein

5 = facial artery

6 = distal portion of marginal branch (facial nerve)

7 = stylohyoid muscle

8 = posterior belly of digastric muscle

9 = retromandibular vein

10 = facial venous trunk

11 = intermediate tendon of digastric muscle

12 = submental vein

13 = interglandular septum

14 = origin of submental artery

15 = mandibular inferior margin

16 = anterior belly of digastric muscle sm = submandibular gland

1 = angle of mandible

2 = proximal portion of marginal branch (facial nerve)

3 = lymph node

4 = facial vein

5 = facial artery

6 = distal portion of marginal branch (facial nerve)

7 = stylohyoid muscle

8 = posterior belly of digastric muscle

9 = retromandibular vein

10 = facial venous trunk

11 = intermediate tendon of digastric muscle

12 = submental vein

13 = interglandular septum

14 = origin of submental artery

15 = mandibular inferior margin

16 = anterior belly of digastric muscle gland, the facial artery is preserved as a rule (Fig. 5.6).

Its anterior branch, the submental artery, thrusts itself in an anteromedial direction, toward the submental region, and is the only important vessel above the mylohyoid muscle. Once we arrive at this plane, we reveal the posterior margin of the muscle (Fig. 5.7).

The gland is then raised from the deep muscle plane (hyoglossus muscle) and intermediate muscle plane (mylohyoid muscle) and everted. The submental artery is dissected together with the previously isolated venous collectors of the facial trunk (Fig. 5.8).

The exposure of the plane of the hyoglossus allows above all the identification of the hypoglossal nerve, which runs anteriorly beneath the mylohyoid muscle and above the intermediate tendon of the digastric muscle. Above the nerve we shall isolate Wharton's duct (Fig. 5.9).

A small Farabeuf is used to move the posterior margin of the mylohyoid muscle forward, revealing the hyoglossal plane. The following can be seen from the top downward:

1. The lingual nerve (a sensory nerve arising in the posterior trunk of the mandibular branch of the trigeminal nerve; it provides sensory and taste innervation of the mucosa in front of the lingual "V") connected to the submandibular ganglion (parasympathetic, with afferent impulses from the chorda tym-pani of the facial nerve, and efferent impulses to the lingual nerve with a submandibular and sublingual secretory function).

2. Wharton's duct, oriented anteriorly toward the sublingual gland.

3. The hypoglossal nerve (motor nerve of the tongue and—in concert with the descending branch of the cervical plexus—the subhyoid muscles, save the thyrohyoid muscle, which it innervates separately) (Fig. 5.10).

Complications: On reaching the hyoglos-sal muscle plane, it is essential when ligating Wharton's duct to avoid injuring the lingual nerve or, worse still, the hypoglossal nerve,

Thyrolinguofacial Trunk
Fig. 5.7 Ablation of the submandibular gland (II)

1 = posterior belly of digastric muscle

2 = stylohyoid muscle

3 = internal jugular vein

4 = external carotid artery

5 = internal carotid artery

6 = occipital artery

7 = posterior auricular artery

8 = hypoglossal nerve

9 = descending branch of hypoglossal nerve

10 = thyrolinguofacial venous trunk

11 = superior thyroid artery and vein

12 = superior laryngeal artery and vein

13 = lingual vein

14 = lingual artery

15 = facial vein

16 = facial artery

17 = retromandibular vein

18 = external jugular vein

19 = platysma branch (facial nerve)

20 = marginal branch (facial nerve)

21 = submental artery

22 = submental vein

23 = mylohyoid muscle

24 = anterior belly of digastric muscle

25 = thyrohyoid muscle

26 = omohyoid muscle

27 = sternohyoid muscle

28 = hyoglossus muscle

29 = anterior process of submandibular gland as by rash cautery. Lesion of the hypoglossal nerve causes dysphagia and the tongue, when protruded, deviates toward the paretic side.

■ 5.2.6 The lingual artery, which is the second branch of the external carotid artery, is sought and bound. Almost immediately after its origin, accompanying the middle constrictor of the pharynx, it meets the posterior margin of the hyoglossal muscle, which takes a horizontal, parallel route to the greater cornu of the hyoid bone, approximately half a centimeter above it (Fig. 5.11).

In clinical practice, the seeking and binding of the lingual artery are indicated at the preliminary stage of surgery of the oropharynx and of the oral cavity, and are carried out at the point of origin. In dissection classes, it is nonetheless interesting to isolate it behind and in front of the posterior belly of the digastric muscle, where anatomists locate Beclard's triangle and Pirogoff's triangle, respectively. The former is bounded by the posterior belly of the digastric muscle, the greater cornu of the hyoid bone, and the posterior margin of the hyoglossal muscle. Dissection in this space involves the hyoglossal fibers, just below the hypoglossal nerve and the lingual vein. The latter triangle is formed by the intermediate tendon of the digastric muscle, the hypoglossal nerve, and the posterior margin of the mylohyoid muscle. In this case too, the lingual artery is isolated by dissecting the hyoglossal muscle fibers. Such well-defined anatomic details enable the lingual artery to be identified and ligated with extreme precision.

■ 5.2.8 To conclude the exercise, dissection is extended anteriorly to the submental region, which lies between the two anterior bellies of the digastric muscles. We shall remove the adipose tissue that fills this space until we expose the plane of the mylohyoid muscles, which, uniting on the median line, form a fibrous raphe extending from the hyoid bone to the mental protuberance, known as the suprahy-oid linea alba (Fig. 5.13).

Rotting Skin
Fig. 5.8 Mylohyoid muscle plane (I)

sm = submandibular gland

1 = masseter muscle

2 = facial vein

3 = hyoglossus muscle

4 = retromandibular vein

5 = stylohyoid muscle

6 = posterior belly of digastric muscle

7 = intermediate tendon of digastric muscle

8 = hypoglossal nerve

9 = mylohyoid muscle

10 = anterior belly of digastric muscle

11 = submental artery

12 = mandibular inferior margin

13 = apex of great cornu of hyoid bone

Fig. 5.9 Mylohyoid muscle plane (II)

sm = submandibular gland

1 = angle of mandible

2 = interglandular septum

3 = facial artery

4 = lingual nerve

5 = Wharton's duct

6 = hypoglossal nerve

7 = intermediate tendon of digastric muscle

8 = mylohyoid muscle

9 = anterior belly of digastric muscle s

Fig. 5.10 Hyoglossal muscle plane

sm = submandibular gland

1 = angle of mandible

2 = interglandular septum

3 = parotid region

4 = stylohyoid muscle and posterior belly of digas tric muscle

5 = facial artery

6 = origin of submental artery

7 = lingual nerve

8 = submandibular ganglion

9 = Wharton's duct

10 = hypoglossal nerve

11 = intermediate tendon of digastric muscle

12 = anterior belly of digastric muscle

13 = mylohyoid muscle

Fig. 5.11 Ablation of the submandibular gland (III)

1 = posterior belly of digastric muscle

2 = stylohyoid muscle

3 = internal jugular vein

4 = external carotid artery

5 = internal carotid artery

6 = occipital artery

7 = posterior auricular artery

8 = hypoglossal nerve

9 = descending branch of hypoglossal nerve

10 = thyrolinguofacial venous trunk

11 = superior thyroid artery and vein

12 = superior laryngeal artery and vein

13 = lingual vein

14 = lingual artery

15 = facial vein

16 = facial artery

17 = retromandibular vein

18 = external jugular vein

19 = platysma branch (facial nerve)

20 = marginal branch (facial nerve)

21 = submental artery

22 = submental vein

23 = mylohyoid muscle

24 = anterior belly of digastric muscle

25 = thyrohyoid muscle

26 = omohyoid muscle

27 = sternohyoid muscle

28 = hyoglossus muscle

29 = anterior process of submandibular gland

30 = Wharton's duct

31 = submandibular ganglion

32 = lingual nerve

Facial Artery
Fig. 5.12 Exercise 2: lingual artery
Rotting Skin

Fig. 5.13 Submental region sm = submandibular gland

1 = mylohyoid muscle

2 = anterior belly of digastric muscle

3 = suprahyoid white line

Fig. 5.13 Submental region

4 = mandibular inferior margin

5 = intermediate tendon of digastric muscle

6 = hyoid bone

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