Preoperative imaging studies in candidate for minimally invasive, video-assisted parthyroidectomy. Early (a) and delayed (b) Tc-99m-sestamibi and SPECT-CT images (c) suggesting a parathyroid lesion posterior to the inferior pole of the right thyroid. These were concordant with transverse (d) and longitudinal (e) ultrasound images, which revealed a hypoechoic lesion posterior to the right lower thyroid
Since 80 % of patients presenting for parathyroid surgery having sporadic primary hyperparathyroidism due to a single adenoma , the majority of cases should be candidates for MIVAP. Most authors, however, report that fewer patients than expected are considered acceptable for MIVAP, with candidacy rates ranging from 37 to 78 % [7–10]. Patient eligibility for MIVAP depends not only on published selection criteria, but also on the prevalence of thyroid disease within a patient population, the reliability of preoperative imaging modalities in each specific institution, and the available of intraoperative parathyroid hormone (IOPTH) assays.
Eligibility will also depend on the surgeon’s experience and comfort with the procedure. Over time, some surgeons have selectively expanded the inclusion criteria to include patients with intrathymic adenomas, multigland disease requiring bilateral surgery, presence of nodular thyroid disease, or prior contralateral neck surgery [6, 7, 11–13]. When the inclusion criteria are also expanded to include patients who have nonlocalizing or discordant imaging, the candidacy rate has been reported as high as 81 % .
MIVAP can be performed with a limited number of instruments, many of which are already available in most operating rooms. A variety of general or customized retractors may be used to maintain the operative space, and an elongated, guarded electrocautery tip prevents inadvertent tissue injury in the narrow operative space. A blunt-tipped suction (Medtronic ENT, Jacksonville, FL) or 2 mm suction elevator facilitates dissection and prevents fogging of the endoscope. Small spatulas and atraumatic forceps are used to mobilize the adenoma, and cautery or vascular clips are used to ligate the vascular pedicle. The sine qua non of endoscopic parathyroid surgery, however, is a 30°, 5 mm, 29 cm long endoscope, which permits all members of the operating team to observe the operation on ergonomically placed monitors. With the exception of the vascular clips, all instruments required for MIVAP are reusable, which helps reduce the amortized costs of the procedure .
The ideal location for the incision is marked while the patient is sitting upright in the preoperative holding area. This ensures that the final scar will be concealed in the most favorable naturally occurring skin crease . The patient is then positioned supine on the operating table. The neck is gently extended, and no shoulder roll is used. The procedure may be performed under local or general anesthesia . General anesthesia permits the use of a laryngeal electromyographic (EMG) endotracheal tube if laryngeal nerve monitoring is desired. The operating table may be rotated 180° so the patient’s lower extremities are facing the anesthesia team. This facilitates access to the patient’s foot veins for peripheral blood acquisition in order to pursue IOPTH assessment and obviates the need for an arterial line. The surgeon repeats an ultrasound once the patient is in the final surgical position to help guide the subsequent dissection .
The primary surgeon generally stands at the patient’s right side. The camera operator is positioned on the patient’s left, and another assistant stands at the patient’s head and retracts to maintain the operative space. A monitor is placed at each side of the patient’s head to give all members of the surgical team an ergonomic view of the operative field .
The operation begins by creating a 1.5–2.0 cm incision in the center of the previously identified cervical crease [18, 19]. The midline location improves the cosmetic outcome, permits easy access to both sides of the neck, and can easily be extended if conversion to a conventional parathyroidectomy is required . Once the incision is complete any identifiable platysma fibers in the midline are divided transversely, preserving the anterior jugular veins, and the midline “linea alba” between the strap muscles is identified. No subplatysmal flaps are required. The strap muscles are separated with a combination of electrocautery and blunt dissection until the thyroid isthmus is identified. The muscles are then bluntly elevated off the thyroid gland on the side of the suspected adenoma, and dissection continues laterally and posteriorly until the posterior aspect of the thyroid gland and the carotid sheath are visualized.
Proper positioning of the retractors is imperative to ensure adequate visualization of the operative space (Fig. 18.2). The lateral retractor distracts the strap muscles and carotid sheath structures, while the medial retractor “hooks” the thyroid gland. Ventral and medial traction on the thyroid lobe retracts and elevates the lobe, further opening the operative pocket and facilitating dissection of the peri-thyroidal fibrofatty tissue.
Proper placement of the retractors to maintain the operative space during minimally invasive, video-assisted parathyroid surgery
Once the operative space has been exposed, the endoscopic portion of the procedure begins. While one assistant maintains the operative space with retractors, the camera operator introduces the endoscope through the incision. The endoscope is held with the 30o lens directed dorsally and inferiorly for most of the procedure. The tip of the scope can be rotated upward if dissection high in the neck is required. For mediastinal dissection, the camera operator moves to the head of the bed to angle the endoscope into the chest. Two hands are used to steady the endoscope and reduce image tremor .
Using primarily blunt dissection, the region of the suspected adenoma is gently explored. Any bleeding could stain the surrounding tissues or obscure the endoscopic view, so attention to absolute hemostasis is crucial. While not always necessary, identifying the recurrent laryngeal nerve (RLN) helps protect it from injury and serves as a landmark for the depth of dissection. Inferior parathyroid glands are always ventral to the coronal plane of the RLN and superior glands are dorsal to the nerve (Fig. 18.3) .
Endoscopic view of the parathyroid adenoma (white arrow) corresponding to the lesion seen in Fig. 18.1. The location deep to the recurrent laryngeal nerve (black arrow) confirms it to be an overly descended superior adenoma. The retractors are distracting the carotid sheath structures (left) and thyroid gland (right) to maintain the operative space
Identification of the parathyroid gland(s) is enhanced by the magnified endoscopic visualization. If the adenoma is not encountered in the expected location, the medial retractor can be repositioned to ensure that the gland was not inadvertently captured under the retractor blade. Once the abnormal gland is identified it is bluntly freed from the surrounding tissue and the vascular pedicle is ligated with either clips or an energy device, taking care to avoid injuring the RLN or violating the capsule of the gland. IOPTH levels are assessed according to the surgeon’s preference. The surgeon may wish to halt the operation after removal of the abnormal gland or examine the other ipsilateral gland. If the IOPTH levels fail to decrease appropriately or if inspection of the second gland suggests multigland disease, a contralateral exploration for the remaining parathyroid glands can be performed through the same incision in the manner described above .
Once all abnormal parathyroid tissue is removed, hemostasis is obtained and half-sheet of Surgicel (Ethicon, Inc., Somerville, NJ) is placed into the wound bed. The strap muscles are either reapproximated in the midline with a single 3-0 Vicryl (Ethicon, Inc., Somerville, NJ) figure-of-eight suture or left open. Retraction on the small incision may traumatize the skin edges, which are therefore trimmed so that fresh tissue is available for wound closure . The subcutaneous tissue is closed with buried interrupted 4-0 Vicryl sutures and the skin edges are sealed with DermaFlex adhesive (Chemence Medical Products, Inc., Alpharetta, GA) and a single transverse Steri-Strip (3M Corporation, St. Paul, MN) (Fig. 18.4). No drains or external sutures are required [22–24]. Deep extubation is performed whenever possible to limit coughing or bucking that can occur on emergence from anesthesia with an endotracheal tube in place.
Successful MIVAP requires proper patient selection, surgeon skill and experience, and appropriate use and interpretation of perioperative adjuncts such as imaging techniques and the IOPTH assay. When these elements are combined, cure rates with MIVAP have been shown to equal or exceed the 95 % success rate with traditional bilateral neck exploration . In one of the few published comparisons of MIVAP versus traditional four-gland exploration, Del Rio et al found no differences in the recurrence rates between the two approaches (2.6 % vs. 3.7 %, respectively) . Other authors have consistently reported cure rates higher than 97 % when MIVAP is performed on patients with localizing imaging studies and with use of IOPTH assessment [6, 8, 14, 26, 27].
Routine use of IOPTH assessment significantly improves the cure rate and decreased the operative time in minimally invasive parathyroid surgery, including MIVAP, when compared to unilateral open surgery without IOPTH assessment . The sensitivity of IOPTH in MIVAP is 97 %, with a specificity of 88 %, a positive predictive value of 99.6 %, and an accuracy of 97 % . Barczyński et al found that using IOPTH directly improved cure rates in minimally invasive parathyroid surgery from 91 to 99 % , and is especially beneficial in patients with only one positive preoperative localization study [11, 28]. IOPTH assessment in MIVAP also decreases the inadvertent removal of physiologically normal parathyroid glands, and may contribute to the decreased incidence of hypocalcemia seen in MIVAP when compared to conventional bilateral neck exploration .
Cosmetic Outcome and Patient Satisfaction
The cosmetic benefit of MIVAP is one of its greatest advantages and one of the main reasons the procedure was developed. It is commonly performed through a 1.5 cm incision [8, 30], with minimal tissue disruption. In a retrospective series comparing MIVAP to open minimally invasive parathyroid surgery, Barczyński et al found that MIVAP was associated with a shorter scar and higher patient scar satisfaction , and in a randomized study comparing MIVAP and open surgery patients these differences persisted for at least 6 months after surgery . In Miccoli’s prospective randomized trial of MIVAP versus bilateral neck exploration, significantly improved cosmetic outcomes were observed in patients undergoing MIVAP . Casserly et al also reported smaller scars and improved scar ratings in their MIVAP group (mean 1.7 cm), compared with bilateral neck exploration (mean 4.3 cm) . These improved cosmetic outcomes were confirmed in a large systematic review of video-assisted minimally invasive parathyroid surgery by Lombardi et al . The small scar and minimal dissection in MIVAP also results in less pain and lower use of pain medication after surgery [7, 11, 26, 31].
Recurrent Laryngeal Nerve Injury
Recurrent laryngeal nerve injury in MIVAP is uncommon, with transient injury reported in up to 3 % of cases and permanent injury in 0.8 % of cases [6, 9, 27, 30, 31, 33]. These low rates compare favorably with conventional bilateral neck exploration, and are likely due to the magnified visualization of the RLN afforded by the endoscope as well as the limited extent of dissection around the nerve [11, 33].
Conventional bilateral parathyroid surgery results in transient postoperative hypocalcemia in approximately 12 % of patients; this rate increases to 25 % if biopsy of the glands is performed [26, 31]. Permanent hypocalcemia occurs in up to 2.3 % of patients after bilateral exploration . This risk of hypocalcemia is reduced in focused minimally invasive procedures such as MIVAP, when only one gland is exposed. Transient hypocalcemia after MIVAP is reported in 2.5–11 % of cases [6, 9, 14, 27, 30, 31], while permanent hypocalcemia occurs in no more than 0.4 % of patients . Unilateral parathyroid surgery is also associated with less severe hypocalcemia and a lower postoperative calcium requirement than conventional surgery .