Parathyroid Minimally Invasive Surgery

Anatomy and Physiology

The inferior and superior parathyroid glands originate from the third and fourth branchial or pharyngeal pouches, respectively. The 4 glands, weighing approximately 20 to 40 g each, are located posterior to the thyroid. The superior glands are typically found mid-thyroid and approximately 1 cm above the intersection of the inferior thyroid artery and recurrent laryngeal nerve. The inferior glands can be more variable in location, as they develop with the thymus and can be found at any point along the path of its descent. However, they are most commonly found in the inferior third of the thyroid. Both the superior and inferior glands are supplied by the inferior thyroid artery, which originates laterally from the thyrocervical trunk. In 20 to 45% of cases, the superior glands may also receive blood supply from the superior thyroid artery directly or through an anastomotic connection to the inferior thyroid artery.

Indications

Surgical intervention is indicated in any patient with symptomatic hyperparathyroidisms, for example, patients with renal, gastrointestinal, or neuromuscular dysfunction. In patients with asymptomatic hyperparathyroidism, the National Institute of Health (NIH) has set the following parameters as indications for parathyroidectomy:

• Serum calcium 1.0 mg/dL above the upper limit of normal
• 24-hour urinary calcium greater than 400 mg
• Creatinine clearance reduced by 30%
• Bone mineral density T score less than -2.5 SD at any site
• Age younger than 50 years

Contraindications

Localization studies are critical to the performance of a minimally invasive parathyroidectomy (MIP). If these studies have not been completed or are equivocal or discordant, a MIP should not be attempted. Traditional, bilateral exploration rather than minimally invasive thyroidectomy is recommended in cases of familial hyperparathyroidism (such as the MEN syndromes) as these tend to be caused by 4-gland hyperplasia rather than a single adenoma. Suspected or known cases of parathyroid carcinoma or concomitant thyroid disease are also contraindications for a MIP, and these patients should undergo radical resection instead. Finally, a history of previous neck irradiation is an absolute contraindication for MIP. It should be noted that previous neck surgery does not exclude a MIP, as it is a relative contraindication rather than absolute.

Equipment

Several intra-operative adjuncts may be utilized. High-definition ultrasound may be used to correlate with preoperative localization studies just prior to surgery. Along with FNA, ultrasound can be used to investigate hypoechoic structures seen intraoperatively.

Frozen section analysis is commonly used to confirm that the specimen removed is, in fact, parathyroid tissue. While a frozen section of a single gland cannot delineate an adenoma from multi-gland hyperplasia, the sensitivity of distinguishing parathyroid from the non-parathyroid tissue is greater than 99%.

A rapid PTH assay is utilized intraoperatively to confirm the removal of the hyperfunctioning tissue. As the half-life of PTH is 2 to 4 minutes, the commonly used Miami criterion states that the level of PTH should fall by 50% 10 minutes after gland removal. PTH is drawn preoperatively, immediately after gland resection (to capture a possible “spike” from manipulation of parathyroid tissue), and then at 5 and 10 minutes post-resection.

Preparation

Prior to MIP, a localization study is critical to guide operative planning. The gold standard of parathyroid localization is single-radioisotope scintigraphy with technetium-99m (99mTc). In this study, the radioisotope is administered, and either planar or single-photon emission computed tomography (SPECT) imaging follows. An alternative is dual-radioisotope imaging, in which both 99mTc pertechnetate and thallium-201 (201Tl) are given. Thallium is taken up by both the thyroid and parathyroid, while pertechnetate only has avidity for the thyroid. Subtraction imaging is then used to visualize the glands. Drawbacks to this method include the necessity of a subtraction program, long imaging times, and limited views. Other methods of localization such as CT, MRI, and ultrasound are available but are less sensitive.

Technique or Treatment

A MIP may be performed under general anesthesia or with a superficial cervical block and sedation. Proper positioning of the patient involves their neck in an extended, “semi-Fowlers” position. This may be achieved by placing a roll beneath the shoulders. Neck hyperextension should be avoided.

There are several forms of minimally invasive therapy, including open approaches (open minimally invasive parathyroidectomy [OMIP]), minimally invasive radio-guided parathyroidectomy (MI-RP), video-assisted parathyroidectomy (VAP), and purely endoscopic parathyroidectomy (EP).

Open MIP is the most common of the minimally invasive techniques. It is performed through a 2.5 to 3 cm central incision. Alternatively, a lateral incision may be used that is made over the anterior border of the sternocleidomastoid muscle on the side of the affected gland. As with a conventional parathyroidectomy, the platysma is divided, and strap muscles are separated to reveal the thyroid. The gland is then gently medially rotated to visualize the adenoma. The blood supply is carefully ligated, and the adenoma is separated from surrounding tissue and removed.

With minimally invasive radio-guided parathyroidectomy, a gamma probe is utilized to permit intraoperative localization of the diseased gland. The patient is injected with technetium-99m sestamibi 2 to 4 hours prior to surgery, and the site with the highest counts are explored. After removal of the adenoma, the neck is again scanned. No more than 20% radioactivity of the adenoma should remain in the neck.

In video-assisted MIP, a small (1.5 to 2 cm) transverse incision is made 2 cm above the sternal notch. Once dissection has allowed one to rotate the thyroid medially and strap muscles laterally, a 30-degree, 5-mm endoscope along with dissection instruments are inserted through the single incision. No trocars are used. Advantages of this technique include a small incision and central access that permits further parathyroid or thyroid resection if necessary. Limitations include the need for 2 assistants and an adenoma size less than 3 cm.

Endoscopic MIP can be carried out through an anterior or lateral approach. In the anterior approach, a trocar is used to pass a 5-mm endoscope through a small central incision, with CO2 insufflation utilized. Two or 3 additional trocars are placed for instrumentation. Dissection is carried out beneath the platysma to develop an operative plane, and the strap muscles are then retracted to visualize the thyroid. In the lateral approach, a 12 mm incision is made along the anterior sternocleidomastoid, 4 cm above the sternal notch. Once a dissection plane has been developed above the prevertebral fascia, two 2.5-mm trocars are placed 4 cm above and below the initial incision to aid in further dissection. The skill required and the long learning curve for each of these approaches are limitations to this procedure.

Complications

Though traditional parathyroid surgery has an already low complication rate, a minimally invasive approach further decreases the risk of complications. Compared to conventional open exploration, it has a lower complication rate (1.2 vs. 3.1%), enhanced cure rates (99.4 versus. 97.1%), an approximate 50% reduction in operating time (1.3 versus 2.4 hours), a sevenfold reduction in length of hospital stay (0.24 versus 1.64 days), and a mean savings of $2700 per procedure.

However, complications are still present. Injury to the recurrent laryngeal nerve is a serious complication of endocrine surgery and has consequences of hoarseness (unilateral damage) or airway occlusion (bilateral damage). Damage can occur as a result of direct trauma to the nerve, such as clipping, grasping, stretching. Indirect deleterious effects on the nerve include skeletonization, thermal injury, or compression. The damage may be transient in cases of compression or stretching and may resolve in 4 to 6 weeks. However, if improvement in function is not seen after 6 to 12 months, the damage should be presumed to be permanent. If the damage is recognized intra-operatively, immediate primary repair or grafting should be performed.

Another serious is permanent hypoparathyroidism. While transient hypocalcemia may result in up to 50% of patients undergoing parathyroidectomy, permanent hypoparathyroidism is quite rare and is found in less than 1% of cases. Additionally, this is more commonly seen in cases of hyperplasia where all four parathyroid glands are removed. As MIP techniques are generally utilized in cases of single adenoma removal, this complication is much less of a concern.[6][7][8][9][10][11]

Clinical Significance

Technological advances have allowed a movement toward increasingly minimally invasive intervention in many specialties and pathologies. In the case of MIP, the benefits of decreased complication risk, enhanced cure rates, and better cosmetic outcomes will likely continue to move surgeons into advancing their practice and skill set in this area.

Enhancing Healthcare Team Outcomes

Today, resection of a parathyroid adenoma can be done with minimally invasive surgery. The procedure may be done by a general or otolaryngologic surgeon. The monitoring of these patients is usually done by the nurses. While rare, the two major complications after surgery include hypocalcemia injury to the recurrent laryngeal nerve. In most cases, the patients present with voice change or signs of hypocalcemia within 12 to 24 hours after surgery.