Chapter 60 Minimally Invasive Single Gland Parathyroid Exploration
Since the early 2000s, scan-directed minimally invasive parathyroidectomy (MIP) has become the operation of choice for patients with primary hyperparathyroidism (Primary HPT) resulting from a solitary parathyroid adenoma. MIP uses preoperative 99mTc-sestamibi or ultrasound scans to precisely localize the hyperfunctioning parathyroid, thus enabling a less invasive procedure by removing only the affected gland. Parathyroid hormone (PTH) levels may be measured intraoperatively to ascertain that the correct gland has been excised and that no other hyperfunctional tissue is present. MIP can be simply defined as any surgical approach that preoperatively aims to identify and remove a single enlarged gland (i.e., focused parathyroid exploration) and may in certain circumstances allow examination of the ipsilateral gland as well (i.e., unilateral exploration). MIP can be done either through standard operative incisions, a smaller midline incision, an ectopically placed incision, or with video assistance (see Chapters 58, Principles in Surgical Management of Primary Hyperparathyroidism, 59, Standard Bilateral Parathyroid Exploration, 61, Minimally Invasive Video-Assisted Parathyroidectomy, 62, Local Anesthesia for Thyroid and Parathyroid Surgery, 63, Intraoperative PTH Monitoring during Parathyroid Surgery, and 64, Radio-Guided Parathyroid Exploration).
MIP has many advantages over the traditional four-gland exploration: MIP can be performed using local anesthesia, requires less operative time, results in decreased postoperative pain, and offers an improved cosmetic result.1,2 Additional advantages of MIP are earlier hospital discharge of patients and decreased overall associated costs.1
The diagnosis of Primary HPT is based on biochemical parameters that largely involve an inappropriate elevation in parathyroid hormone (PTH) (see Chapter 58, Principles in Surgical Management of Primary Hyperparathyroidism). Once Primary HPT is diagnosed, a preoperative evaluation using high-quality imaging studies to localize the tumor is essential if MIP is to be considered. The imaging results suggest to the surgeon where to begin the focused operation and serve as a road map to allow tailoring of an efficient, scan-directed dissection. It is the precise information from the imaging studies that enables the use of a minimally invasive technique that eliminates the unnecessary dissection of multiple glands or a bilateral exploration.3–6
This chapter addresses considerations for performing MIP, including anatomic considerations, the importance of a parathyroid localization nomenclature system, the role of preoperative imaging studies, and operative preparation and techniques.
Many patients with Primary HPT are candidates for an MIP. Several key elements help identify the most promising candidates, which essentially are those who are most likely to have a single parathyroid adenoma. The patient first must have biochemically proved Primary HPT, preoperative imaging results that are highly suggestive of parathyroid adenoma location, and access to an experienced parathyroid surgeon. MIP is not suited to multigland disease (such as that seen with multiple endocrine neoplasia type 1 [MEN 1], other familial syndromes, lithium use, or chronic renal failure) or if a diagnosis of parathyroid cancer is suspected (see Chapters 65, Surgical Management of Multiglandular Parathyroid Disease, 66, Surgical Management of Secondary and Tertiary Hyperparathyroidism, 67, Parathyroid Management in the MEN Syndromes, and 69, Parathyroid Carcinoma). Coexisting thyroid abnormalities that could require concomitant thyroid gland resection should be absent.1,2,4 A more comprehensive list of contraindications to MIP is presented in Table 60-1.
|Absolute Contraindications||Relative Contraindications|
|Known multigland disease such as familial hyperparathyroidism or multiple endocrine neoplasia (MEN) disease||Symptomatic cervical disc disease|
|Concomitant thyroid pathology requiring surgical intervention||Known contralateral nerve injury|
|Discordant concordant imaging||Lithium use or chronic renal failure|
The focused approach of MIP requires a thorough knowledge of cervical anatomy and embryology (see Chapter 2, Applied Embryology of the Thyroid and Parathyroid Glands). Parathyroid gland location follows definite embryologically influenced patterns. Because the superior parathyroid gland shares an embryologic origin with the lateral thyroid tissue in the primordium in the fourth branchial pouch, nondiseased superior parathyroid glands are invariably found close to the dorsum of the upper thyroid lobe. When a superior parathyroid gland becomes heavy, enlarged, and adenomatous, it tends to be found more posteriorly and caudal. If closely associated with the thyroid capsule, the gland will remain in contact with the posterior surface of the thyroid, in continuity with the thyroid tissue. The pedicle of the superior parathyroid gland is located lateral and posterior/dorsal to the oblique course of the recurrent laryngeal nerve (RLN).
The inferior parathyroid gland shares its embryologic origin with the thymus, and both arise from the third branchial complex. An enlarged inferior parathyroid gland usually remains in proximity of the lower pole of the thyroid, often just lateral or just posterior to the lower pole. If the enlarged inferior parathyroid gland becomes heavy or caudal embryologic migration is excessive, it may descend into the thyrothymic ligament. The enlarged gland may also be present deeper within the thymus and may reside in the mediastinum.
Experienced surgeons use the RLN as an important landmark for identifying parathyroid glands. The inferior parathyroid gland is consistently anterior or ventral to the RLN, whereas the pedicle to the superior parathyroid gland is always posterior or dorsal to the RLN.
Enlarged superior parathyroid glands are almost always found in specific sites; these are, in order of frequency of occurrence, (1) the dorsum of the upper pole of the thyroid, (2) the paraesophageal space behind the thyroid parenchyma (a less common location is the retropharyngeal space), and (3) the descent in the paraesophageal space inferior to the inferior pole of the thyroid.
An enlarged inferior parathyroid gland most commonly rests at the lower pole of the thyroid, within the thyrothymic ligament or in the superior-most portion of the cervical thymic tongue. Occasionally, the inferior parathyroid gland descends within the thymus into the upper mediastinum.
A common misconception is that a parathyroid gland located high in the neck is always a superior gland and that one located low in the neck is an inferior gland. In fact, a superior enlarged parathyroid gland may descend caudally and be located near the lower pole of the thyroid or even below the inferior pole of the thyroid. In this situation, the gland frequently is suspended by a long vascular pedicle from the inferior thyroid artery. The superior gland in this case may actually be “inferior” to the inferior gland based. Surgeons must always pay attention to the location of the gland relative to the course of the RLN. Enlarged superior glands that have descended caudally still retain their normal position posterior or dorsal to the RLN, whereas enlarged inferior glands always remain anterior or ventral to the RLN. The importance of this positioning is that the superior gland will be dorsal in the neck and in proximity to the deeper tracheoesophageal region.
The relationship of an enlarged parathyroid gland to the thyroid capsule is also critical to the potential position of a diseased gland. When located within the fibrous thyroid capsule, the diseased parathyroid gland expands but remains within the confines of the surgical capsule of the thyroid. When located external to the thyroid capsule, enlarged parathyroid glands may become subject to gravity and the repetitive forces of deglutition and become displaced posteriorly behind the gland in the tracheoesophageal region. A summary of anatomic “pearls” for MIP is presented in Table 60-2.
Standardizing parathyroid nomenclature offers a universal, consistent language to communicate the precise locations of enlarged parathyroid glands among members of the multidisciplinary team, which includes radiologists, surgeons, anesthesiologists, endocrinologists, pathologists, ultrasonographers, and nuclear medicine physicians.7 One such classification system was developed and used at our institution to allow a systematic approach to the most frequently encountered positions of enlarged parathyroid glands. This clinically useful classification scheme encompasses information about the parathyroid gland’s pedicle and the surrounding structures, and it incorporates the relation of the RLN to the glands as discussed previously. Based on the premise that superior glands have a pedicle that originates lateral to the RLN and that inferior glands have a pedicle that originates medial to this nerve, the system takes into account natural descent patterns (both embryologic and acquired): superior glands descend posteriorly in the tracheoesophageal groove, and inferior glands descend anteriorly in the plane of the trachea.
This system not only offers a concise, reliable means of communicating the exact location of enlarged parathyroid glands but also can facilitate surgical planning and selection of approach. The gland’s letter designation has therefore implications for placement of the incision, patient positioning, the scope of the operation, and the degree of anesthesia. For example, precise information about the expected location of the adenoma allows for better planning by the anesthesiologist, who can determine the type of anesthesia needed based on operative complexity, depth of dissection, and projected duration of the procedure. Knowledge of the adenoma’s location also helps operating room personnel to anticipate technical requirements, such as the need for nerve monitoring devices, sternotomy or thymectomy instrumentation, or intraoperative ultrasonography equipment. Common descriptors of adenoma location also facilitate communications between physicians, for example, in reviewing the report of an operation performed by another surgeon, particularly if reoperation is being planned, and in documenting an excised gland’s exact location for the pathologist. In addition to describing common locations of glands, the alphabetic letters A through G are used as reminders of locations to explore when a diseased gland cannot be identified intraoperatively.
A common nomenclature also facilitates communications among institutions in situations such as registering patients for clinical trials and reporting results in the medical literature. At MD Anderson Cancer Center, this nomenclature provides our primary terminology for use in imaging reports and has been expanded and incorporated into our anesthesia, nursing care, operative, and pathology reports. We have found that this system greatly improves communication, removes ambiguity, and obviates lengthy descriptions of parathyroid gland locations.
Type A. Adherent to the posterior thyroid parenchyma. A type A parathyroid gland is in the expected location of a normal parathyroid gland and is in apposition to the posterior surface of the thyroid parenchyma. The gland may be compressed within the capsule of the thyroid.
Type B. Behind the thyroid parenchyma. A type B gland is a superior gland that is exophytic to the thyroid parenchyma and has fallen posteriorly into the tracheoesophageal groove. There is minimal or no contact between the gland and the posterior surface of the thyroid tissue. On coronal views, the gland is posteriorly located near the esophagus. An undescended gland high in the neck near the carotid bifurcation or mandible also may be classified as a type B gland.
Type C. Caudal to the thyroid parenchyma, a type C gland is a superior gland that has descended posteriorly and caudally into the tracheoesophageal groove. On anterior images, a type C gland is inferior to the inferior pole of the thyroid parenchyma. The type C gland is posterior to and in many cases inferior to the oblique angle of the RLN. Glands in the carotid sheath are either type B or C glands, depending on their craniocaudal relationship to the inferior pole of the thyroid gland (cranial, type B, caudal, type C).
Type D. Directly over the RLN in the middle region of the posterior surface of the thyroid tissue. The dissection of the type D gland can be “difficult” or “dangerous” because of this gland’s proximity to the RLN. The gland lies in the middle region of the posterior surface of the thyroid parenchyma, near the junction of the RLN and the inferior thyroid artery. The embryologic origin of a type D parathyroid adenoma may be that of either a superior or inferior gland. The distinction is made intraoperatively based on the gland’s relationship to the RLN and the pedicle of the gland. Usually, the position of the pedicle cannot be determined on preoperative imaging studies.
Type E. The type E gland is an inferior gland proximal to the inferior pole of the thyroid parenchyma. This gland is more closely aligned with the same anterior-posterior plane of the thyroid tissue and the trachea (as opposed to more posterior glands that relate to the esophagus). The type E adenoma has a pedicle that is medial and anterior to the RLN and is the easiest to resect because of its superficial location relative to the depth of the cervical region.
Type F. The type F gland is an inferior gland that has descended into the thyrothymic ligament or superior thymus. This gland may be in the anterior mediastinum. On anterior-posterior imaging views, the type F gland is in the coronal plane of the thymus. It has “fallen” into the thyrothymic ligament, is below the inferior pole of the thyroid, and is usually superficial or immediately lateral to the trachea. A type F gland is frequently referred to as an ectopic gland, and its resection usually involves transcervical delivery of the thyrothymic ligament or superior portion of the thymus.
Type G. The type G gland is a rare, gauche gland. This gland is an intrathyroidal parathyroid gland that has thyroid tissue circumferentially around it. Resection of a type G gland may require thyroid lobectomy, as the gland “got caught” within the thyroid tissue.