Minimally Invasive Approach to the Thyroid and Parathyroid Glands
In 1996, Gagner1 described endoscopic subtotal parathyroidectomy for secondary hyperparathyroidism, which represented the first application of a minimally invasive technique to the field of endocrine neck surgery. Since then, several minimally invasive approaches to the thyroid gland2–7 have been described, all aiming to improve cosmetic outcome, reduce postoperative pain and improve postoperative recovery, either by performing the incision in an area that is not visible such as the axilla or around the nipple, or by minimizing hyperextension of the neck to reduce the length of the scar in the neck. Table 23.1 summarizes the different mini-invasive approaches.
The development of these new techniques also added new types of complications to those already typical of traditional thyroid and parathyroid surgery. Subcutaneous emphysema was described first by Gottlieb et al8 after endoscopic parathyroidectomy,1 although this complication, also associated with hypercarbia and tachycardia, is possible during any endoscopic neck procedure in which the operative space is maintained by gas insufflation. In fact, the neck cannot be considered a predetermined cavity because it is not circumscribed by a continuous serosal layer such as the pleura or the peritoneum, which avoids massive passage of carbon dioxide from the cavity to the bloodstream. Some authors with extensive experience with the procedure suggest that lowering the carbon dioxide pressure to 4 mmHg can help to avoid subcutaneous emphysema.9,10
The gasless anterior neck skin-lifting method described by Shimizu and Tanaka11 and based on the Nagai method for the abdomen,12 in which the edges of the chest wall wound and the lateral neck wound are pulled by sutured threads to create the working space, can potentially create a new complication, namely the rupture of the skin through excessive traction.
In this chapter, we will discuss complications following a minimally invasive approach to the neck, both for thyroid and parathyroid glands, with particular focus on minimally invasive video-assisted thyroidectomy (MIVAT) and parathyroidectomy (MIVAP).
Video-assisted Thyroidectomy and Parathyroidectomy
These two techniques were first described in 1997 in Pisa, and, after more than 10 years, have gained acceptance worldwide as the preferred mini-invasive techniques for the surgical treatment of thyroid and parathyroid diseases, not only because they have similar results to traditional techniques concerning safety and curative results, but also because of improvements in postoperative course and cosmetic outcome.
Briefly, both techniques are characterized by a single central cervical incision, 1.5 cm in length, at the same level as Kocher′s incision. Operative space is maintained by small retractors without gas insufflation. The operation is performed mostly endoscopically under magnified vision with a 30° 5-mm endoscope ( Fig. 23.1 ). The dissection of the thyrotracheal groove is completed by using small (2 mm in diameter) instruments: atraumatic spatulas in different shapes, spatula-shaped sucker, ear-nose-throat forceps and scissors ( Fig. 23.2 ). Coagulation and sectioning of principal vessels can be performed with any energy device (ultrasonic, high frequency, etc.) or by vascular clips and cauterization.
Up to 15% of thyroid diseases with surgical indications can be treated by MIVAT, and ~ 80% of patients affected by primary hyperparathyroidism can be treated by MIVAP.
Exclusion criteria for these two techniques are: active thyroiditis, parathyroid adenomas > 4 cm, parathyroid carcinoma, goiter > 25 mL in total thyroid volume, thyroid carcinomas > 2 cm or synchronous metastases at the central or lateral compartments. Therefore, careful selection of patients is the only guarantee of a low incidence of complications and good outcome. An important limit is, at present, the volume of both the nodule and the gland. The parathyroid adenoma, as well as the thyroid nodule, has to be removed without disrupting their capsule because of the necessity for accurate histologic evaluation and to avoid cellular spread. Other limits of these techniques are the presence of adhesions that can make dissection difficult: this can happen in revision surgery, and also in thyroiditis unveiled both by increased thyroid antibodies and ultrasound aspects.
Injuries to the Inferior Laryngeal Nerve and External Branch of the Superior Laryngeal Nerve
During thyroidectomy and parathyroidectomy both the inferior laryngeal nerve (ILN) and the external branch of the superior laryngeal nerve (EBSLN) can be transiently or definitively injured. Nerve injury can be temporary (resolution within 6 months to 1 year) or definitive, monolateral or bilateral. The causes most frequently responsible for nerve damage are accidental sectioning of the nerve, perineural edema consequent to manipulation, stretching, and heating.
The EBSLN innervates the cricothyroid muscle, which is responsible for vocal fold tension and pitch modulation. The nerve is jeopardized during sectioning of the upper pedicle because of the variability of its course. The incidence of this complication is underestimated because symptoms are moderate and objective demonstration of damage is difficult. During MIVAT, endoscope magnification provides an optimal view of the EBSLN, which is far better than in an open field ( Fig. 23.3 ).
The rate of injury to the ILN is highly variable depending on the characteristics of disease, type of procedure, and surgeon′s experience. The rate of definitive palsy is around 1%, but ranges from 0.5 to 14% in the literature.13–18 In our MIVAT series, the rate of injury to the ILN (both temporary and definitive) did not differ from literature reports. Complications included transient monolateral ILN palsy in 2.4% of cases, definitive monolateral palsy in 1.1%, and bilateral transient palsy in 0.3% of cases ( Table 23.2 ). In addition, the ILN can be easily identified during MIVAT thanks to the magnification provided by the endoscope.
An excellent anatomical landmark when searching for the ILN is the posterior lobe of the thyroid because it generally lies over the nerve. In conventional surgery, the ILN is generally prepared where it emerges from the thoracic outlet, but this area can be difficult to visualize with the endoscope; the middle part of the thyroid gland is clearly visible and optimal nerve dissection can be performed.
Some concerns should be expressed about stretching the parenchyma and the ILN during the extraction phase. At the beginning of our experience, we recorded some transient nerve palsies that were probably a result of this maneuver. Since then, complete dissection of the nerve during the endoscopic phase and placing lower traction on the lobe during extraction have avoided this type of complication.
In addition, the incorrect use of the new harmonic scalpel can jeopardize the nerve. The surgeon should always remember to keep the inactive blade of the instrument oriented during artery sectioning to avoid jeopardizing the nerve, which always lies posterior to it and is very sensitive to heat transmission ( Fig. 23.3 ). Safety of the harmonic scalpel, with low thermal injury or energy diffusion, has been demonstrated by other authors.19–24 However, we think that a minimal distance should be maintained between the inactive blade and the nerve, and small clips should be used when dealing with small vessels crossing the nerve near its entrance into the larynx.
During MIVAT and MIVAP, intraoperative nerve monitoring can also be used. In fact, nerve and laryngeal palpation or the use of magnifying glasses during MIVAT and MIVAP are not feasible given the small cervical incision. Some authors demonstrated that intraoperative nerve monitoring is feasible, easy, safe, and effective during MIVAT.25–28 Terris et al25 demonstrated that intraoperative nerve monitoring serves as an adjunct to visual identification of nerves in different minimal access thyroid procedures performed through incisions < 6 cm in length, both endoscopic, nonendoscopic, and reoperative cases. Dionigi et al26 proposed a standardized intraoperative nerve monitoring technique with vagal stimulation during MIVAT. Regarding voice and swallowing changes in the absence of laryngeal nerve injury, MIVAT seems to have significant advantages compared with conventional thyroidectomy. Lombardi et al,29 in a recently published study, found that even if voice and swallowing changes were reported in both groups of patients (MIVAT and conventional thyroidectomy), their comparison demonstrated that MIVAT had significant advantages. Indeed, patients in the MIVAT group had significantly lower postoperative scores at each time-point and showed a trend toward more rapid return to the preoperative condition. A similar trend was also observed for swallowing impairment. Patients who underwent MIVAT reported significantly lower scores at 1 week and 1 month after surgery. In conclusion, the study found that voice and swallowing changes are significantly less important and show a tendency to recover more rapidly in patients who undergo MIVAT.
This important finding likely has multiple causes. First, the reduction in surgical trauma of thyroidectomy seems to determine a better outcome. Nonetheless, the less extensive and finer dissection of the thyroid bed, which characterizes MIVAT, could be responsible for a reduced risk of lesion to the perivisceral neural plexus, formed by small branches connecting the recurrent laryngeal nerve, EBSLN and the sympathetic chain, which is considered to be involved in the pathogenesis of postthyroidectomy aerodigestive symptoms by some authors.30,31 Finally, a functional component related to the reduced local neck pain, and consequently reduced psychologic reaction to postoperative stress, should be taken into account.32