Microsurgical Procedures: Vascularized Lymph Node Transfer from the Submental Region

Key Points

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The upper margin of the flap is designed at the lower border of the mandible to result in an inconspicuous scar.
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Preoperative Doppler ultrasound and magnetic resonance imaging are helpful for evaluating the number of sizable lymph nodes and the course of the facial artery.
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The indications for submental vascularized lymph node flap transfer include Cheng’s Lymphedema Grades 2–4, total obstruction of the lymphatic system in Taiwan Lymphoscintigraphy Staging (TLS) T4–T6, partial obstruction of TLS P1–P3, without patent lymphatic vessels, repeated episodes of cellulitis, and failure to complete decongestive physical therapy.
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The contraindications are local tumor recurrence and distant metastasis.
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One to three marginal mandibular nerves should be carefully preserved with a nerve stimulator under a microscope.
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Most submental lymph nodes around the submandibular gland and facial vessels should be delicately harvested.
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A width of 5 cm of the medial platysma muscle should be preserved in order to avoid marginal mandibular nerve pseudoparalysis.
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The submental artery should be retrogradely dissected from medial to lateral, and the capsule of the submandibular gland should be harvested with the flap.

Introduction

Increasing options for vascularized lymph node (VLN) donor sites have allowed surgeons to make individualized patient-specific decisions in every case. A variety of donor site options are paramount to decision-making because certain patients may or may not be candidates for flap harvest from specific donor sites. The groin donor site is a popular and common source for VLN transfer. In the setting of lower extremity lymphedema, this option may not always be indicated due to an increased risk of inducing morbidity in the unaffected extremity. The submental VLN flap represents a valuable option for a donor source of VLNs distant from the extremities.

A submental flap has been previously described in the setting of locoregional flap coverage of the head and neck region. This flap, based on the axis of the submental artery, was initially described in 1990 as a reliable cervical flap for a wide range of defects.

Since the initial description of a submental flap, further cadaveric and clinical studies have found this flap to be versatile in the free or pedicled variety. In addition, refined anatomic considerations have allowed versatility in the design of this flap. The recent cadaveric dissection for knowledge of the detailed anatomy of the facial artery and its perforators, as well as the number of sizable submental lymph nodes, has been quite useful in clinical practice. Although many of the advancements implemented for this flap have helped decrease donor site morbidity and improve flap design, special consideration must be given to the anatomic variation of the VLN flap. This chapter will highlight the specific anatomy and surgical technique related to the successful execution of this submental VLN flap.

Concepts

The submental VLN flap, based on the axis of the facial-submental artery, is not similar in design or elevation to the traditional submental flap, in which a skin paddle was designed in the midline below the chin and used for locoregional soft tissue coverage of the head and neck.

Instead, the submental VLN flap skin paddle was designed along the lower margin of the mandible. Initially, a width of 10×5 cm was used to include the anterior belly of the digastric muscle, and this approach has been altered to 6×2.5 cm (close to the mandibular angle) in order to include one to two skin perforators; additionally, a width of 5 cm of the medial part of platysma has been used to avoid the inability to lower the bottom lip, which is a symptom of marginal mandibular pseudoparalysis. Specific technical considerations must be given to the location, preservation, and perfusion of the lymph nodes in the region.

Regional Anatomy

Cheng et al. first described a mean of 3.3±1.5 sizable submental lymph nodes in a 10×5 cm skin paddle inferior to the mandibular line in 2012. Tzou et al. also reported a mean of 3±0.6 submental lymph nodes with a size of 4.5 ±1.8 mm×2.9±1.2 mm in the submental area. Most of these lymph nodes were found to be located 5–6.5 cm from the midline. There were a mean of four skin perforators between 4 and 6 cm from the midline. The vascular supply in the submental region is shown in Fig. 14.1 . In the subplatysmal space, key structures were found within the various layers of the cervical fascia. The main arterial sources of the neck structures included branches of the external carotid system. The arterial supply to the submental VLN flap was based on the submental artery, which is a consistent branch of the facial artery. The facial artery was found approximately 2–2.5 cm anterior to the mandibular angle at the level of the lower mandibular border. The submental artery with a mean diameter of 1.3±0.2 mm was found 6.4 cm from the midline, originating as an anterior branch of the facial artery (see Fig. 14.1 ). In an anatomic study, the facial artery was found to be superficial to the gland in 69% of the dissections, and in 31% of the cases, the facial artery was found to be penetrated between the gland, which required intraglandular dissection ( Fig. 14.2 ). Following the course of the submental artery past the submandibular gland, the artery traveled on the superficial surface of the mylohyoid muscle. During its arterial course, the submental artery supplies various skin perforators through the platysma muscle. The distal aspect of the submental artery can have a variable course in relation to the anterior belly of the digastric muscle. In approximately 70% of the patients, the distal submental artery traveled deep to the digastric muscle, while the remaining arteries traveled superficial to the muscle. The venous system paralleled the arterial system, with the submental vein draining into the anterior facial vein.

Special consideration is warranted for the location of the marginal mandibular branch of the facial nerve (MMN). The MMN, with a mean diameter of 1.0±0.1 mm, usually runs superficial to the facial vessels.

The MMN is one of the five major rami of the facial nerve. The clinically important location of the MMN is seen in the relationship of this nerve to the facial vessels, forming a junction with the facial vessels 7.2 cm from the midline. Although early cadaveric studies suggest that only a minority of patients have an MMN that is present below the lower border of the mandible, more recent anatomic studies suggest that this location is a more common clinical finding. Following the emergence of the MMN from the lower portion of the parotid gland, the nerve coursed deep to the mandibular angle, where variability in the branching pattern exists (see Fig. 14.1 ). In a cadaveric evaluation, Nelson and Gingrass found that the MMN had discrete, identifiable nerve branches to the depressor anguli oris (DAO), the depressor labii inferioris (DLI), and the mentalis. Branches to the mentalis and DLI were consistently located below the mandibular border. Anterior to the facial artery, the larger branch to the DAO was commonly located above the mandibular border and coursed deeply to innervate the muscle. Lower cervical branches were also identified at the lowest margins to innervate the platysma. The nerve branches were contained within a thin fascial layer superficial to the submandibular gland. In a clinical evaluation, Nason et al. found that the MMN traveled below the level of the mandibular border by approximately 0–1.5 cm but was more inferiorly displaced, as much as 3 cm, when the head was extended. Injury to the MMN manifests as weakness and/or an inability to move the ipsilateral lower lip downward and laterally. Injury is apparent by examining the angle and asymmetry of the mouth during smiling, and this injury can be avoided by dissecting the MMN under a microscope with a nerve stimulator.

The submental VLN flap mainly includes the level I nodes in the submental (IA) and submandibular (IB) regions. These lymph nodes are located in the subplatysmal plane atop the deep cervical musculature. The hyoid bone, the mandible, and the anterior belly of the digastric muscle designate the submental triangle. The anatomic landmarks of the submandibular group of lymph nodes are posterior to the submental region and continue from the digastric muscle posteriorly to the posterior aspect of the submandibular gland. Altogether, both groups comprise the level I lymph nodes and are in close proximity to the submental/facial artery system (see Fig. 14.1 ). Poccia et al. recently reported that platysma-sparing submental VLN flap harvest may decrease the complication of marginal mandibular nerve pseudoptosis with the preservation of the medial part of the platysma 5 cm from the midline. This modified technique might minimize the difficulty with depressive motion of the lower lip, which is controlled in part by the platysma.

Patient Selection: Adapted from Cheng’s Lymphedema Grading and Taiwan Lymphoscintigraphy Staging

Patient counseling prior to the VLN transfer procedures helps to meet patient expectations in the postsurgical period. The indications for submental VLN flap transfer include Cheng’s Lymphedema Grades 2–4, total obstruction of the lymphatic system in Taiwan Lymphoscintigraphy Staging (TLS) T4–T6, partial obstruction of TLS P1–P3, without patent lymphatic vessels, repeated episodes of cellulitis, and failure to complete decongestive physical therapy. The contraindications are local tumor recurrence and distant metastasis. In addition, previous surgery and radiation in the upper portion of the neck are the relative contraindications of flap harvest, as scarring occurs, and the reliability of lymph node inclusion is questionable. When evaluating a donor site for submental VLN flap harvest, scar or contour irregularities of the neck are the most likely concerns for patients. The resulting scar in the submental area is actually inconspicuous. In these cases, counseling on the possibility of contralateral neck procedures will help to balance the asymmetry in the lower face and neck. Iatrogenic injury to the marginal mandibular branch of the facial nerve is a potential serious complication following harvest of the submental VLN flap. A thorough understanding of the course and relationship of this nerve to the vascular pedicle will minimize the occurrence of nerve injury (discussed earlier). The most important approach for avoiding this complication is to dissect the MMN with a nerve stimulator under a microscope.

In the setting of lower extremity lymphedema, the submental flap represents a remote VLN source that eliminates the chance of inducing lymphedema in the contralateral, normal extremity. Harvest of level I lymph nodes in the neck has not been reported to cause iatrogenic lymphedema in the head and neck, and our clinical experience has also supported this finding.

Preoperative Considerations

A detailed patient history related to other medical conditions allows for appropriate perioperative risk stratification. Cardiopulmonary considerations are typically the main determinants of microsurgical candidacy. Optimizing these systems will help to minimize the risks associated with long operative interventions and anesthesia-related morbidity.

Lymphatic function testing in the preoperative setting is crucial to establish the diagnosis and to stratify patients for the most applicable procedure. Lymphoscintigraphy is the mainstay diagnostic test and is routinely used to assess lymphatic function. In regard to the submental donor site, preoperative lymphatic function testing in the donor site is not necessary because lymph node harvest from this region rarely results in head and neck lymphedema. Doppler ultrasound is useful for the assessment of recipient vessels and the possible comorbidity of proximal vascular diseases. Magnetic resonance imaging is indicated for the number of submental lymph nodes and the course of the facial artery related to the submandibular gland. In advanced-stage lymphedema patients, skin changes, cellulitis episodes, and the presence of open wounds may change the preferred recipient site to an alternate site unburdened by these infectious foci in order to eliminate the chance of complications related to infection. Compliance with compression therapy and possibly antibiotics are necessary to eliminate swelling and infectious burden.

Flap Design

Design of the submental VLN flap begins with palpation and identification of the facial artery, usually approximately 2–2.5 cm anterior to the mandibular angle at the level of the lower mandibular border ( Figs. 14.2 and 14.3 ). In most cases, a skin island of 6×2.5 cm is needed to include at least one of four skin perforators and to allow for recipient site closure without tension. A 5-cm width of the medial platysma is marked and preserved. The skin incision is deepened to the subplatysmal plane except the medial 5 cm. The facial vessels are dissected, usually at their more distal site. The MMN is delicately identified with a nerve stimulator under a microscope. The lower half of the ellipse skin incision is then made and is adjusted based on neck skin laxity and the possibility of donor site closure. The limits of the skin paddle can extend to the midline or may further depend on the needs of the recipient site. A modified skin paddle design measuring 6×2.5 cm is shown in Fig. 14.2 . Narrower skin islands may be designed that allow for decreased tension along the donor closure site and potentially result in a smaller scar along the lower border of the mandible.