Operative Aspects

Cervical Exploration

At the time of initial cervical exploration, it is generally recommended that ideally all four glands should be identified and the abnormal gland(s) be removed. However, in the reoperative situation, the objective is to locate the abnormal gland and remove it without disturbing (and perhaps devas-cularizing) normal glands. Prolonged attempts to identify

TABLE 58-3. Accuracy of Different Localizing Studies in Various Reported Series2,3 "30

Procedure Accuracy (%)

Noninvasive

Ultrasonography (small part/real time) 44-76

Thallium-technetium subtraction scan 55-61

Technetium 99m sestamibi scanning 58-83

CT 11-79

MRI 57-65

Invasive

Selective venous catheterization and 44-88 sampling

Selective angiography 49-73

Ultrasonography-guided fine-needle 73-82 aspiration

Persistent/recurrent primary HPT

Confirm diagnosis

Evaluate operative , Indications.

No Yes

Observation Assess operative risk

(ASA and Goldman class)

Low risk High risk

Localizing studies, assess operative records, review prior pathology

Ablative or medical therapy

Cervical ± mediastinal exploration

FIGURE 58-1. Algorithm for management of persistent or recurrent primary hyperparathyroidism (HPT). ASA = American Society of Anesthesiologists.

normal parathyroid glands embedded in scarred tissue invariably result in their devascularization and destruction. Re-exploration generally returns the surgeon to the neck unless there is compelling evidence in the preoperative evaluation that the missing gland is located in the mediastinum since the neck remains by far the most common site of previously missed glands; in addition, ectopic glands in the superior mediastinal thymus (the second most common site for a missed gland) can almost always be retrieved via a standard cervical incision.

A generous incision should be made through the previous operative incision if it is appropriately placed, followed by elevation of ample skin flaps. Exposure via the lateral approach by entering a plane lateral to the strap muscles and medial to the sternal head of the sternocleidomastoid muscle can avoid the scarred median tissue. The tracheoesophageal groove and retrothyroid regions, where most of the missed glands reside, can be entered via this previously undissected plane. The initial exploration should be directed toward those target areas as suggested by localization studies, combined with evaluation of previous operative and pathologic findings.

The recurrent laryngeal nerve should be identified whenever possible and traced generously to preserve its integrity once the thyroid gland is reflected medially to expose the retrothyroid area. The commonly found "anomalous" positions of an inferior gland include the posterior or lateral surface of the thyroid gland beneath a thin layer of thyroid capsule, the thyrothymic ligament, and the thymic tongue in the anterosuperior mediastinum. Arrested descent of the inferior parathyroid gland ("parathymus") during embry-ologic development may leave the gland high in the neck, sometimes as far superiorly as the angle of the mandible.

The inferior gland in this location is thus superior to the superior parathyroid gland. A search along the embryologic descent path of the inferior parathyroid gland should be made from the angle of the mandible to the superior mediastinum. The carotid sheath should be opened and explored. The superior mediastinum can be quite thoroughly explored via the cervical incision, removing a major portion of the thymus gland. For suspected abnormal superior glands, the superior thyroid pedicle should be ligated and divided to facilitate exposure of the posterior aspect of the superior thyroid pole. The retroesophageal area should be thoroughly explored by entering this space immediately superior to the inferior thyroid artery. Inserting a finger into this space toward the posterosuperior mediastinum allows for accurate digital palpation of a space where large glands are often missed by an inexperienced surgeon at the initial operation. A superior gland descending in this groove may thus be located inferior to the inferior parathyroid gland.

The contralateral side should be explored in a similar manner if exploration of the first side is negative. If exploration fails after a thorough bilateral search, thyroid lobectomy should be considered on the side of greater suspicion searching for the rare true intrathyroid parathyroid adenoma. Most of these glands can be suspected because of a nodule seen by US. A staged mediastinal exploration can be considered after appropriate mediastinal localization studies have been performed. It is prudent that all suspicious tissue removed be sent for frozen section and that an intraoperative dialogue (correlating the operative findings and histopathol-ogy) with an experienced pathologist ensue; this dialogue is crucial.

Mediastinal Exploration

The surgeon should be satisfied that a thorough and complete cervical re-exploration has been performed before proceeding to mediastinal exploration unless there is compelling evidence from preoperative localization studies that the missing gland is located in the mediastinum. The mediastinum is entered by a partial or complete sternal split or via a thoracoscopic approach. Once the mediastinum is opened, the search for die parathyroid should begin with the thymus gland. Most mediastinal parathyroid glands are located intrathymically at the level of innominate vein in the anterior superior mediastinum. A small number are situated low in the anterosuperior mediastinum between the thymus and pleura, adjacent to the great vessels along the aortic arch or in the aorticopulmonary window. Occasionally, a missing superior gland may be located in the posterosuperior mediastinum in the retroesophageal space, posterior to the carina, or in the right subpulmonary artery space.

Intraoperative Localization

Several intraoperative localization tests, including intraoperative US, methylene blue staining, intraoperative venous sampling for PTH measurement, and gamma probe examination have been described in the reoperative situation. Intraoperative US performed by an experienced radiologist can help guide dissection.26 It images more abnormal glands than preoperative US and may help locate an intrathyroid or retrothyroid parathyroid gland encased in scar tissue or an ectopic gland within the carotid sheath. The use of intraoperative methylene blue injection has not been as helpful in reoperative cases as in initial operations because of the relative nonspecificity of the test.3 The rapid intraoperative PTH assay enables the surgeon to perform selective venous sampling intraoperatively and to localize and lateralize an abnormal gland by detecting an increase in PTH level on the side of the tumor. In addition, this technique enables the surgeon to confidently confirm the adequate removal of hyperfunctioning tissue, especially in multiple-gland disease, and improve the overall surgical success rate.32 Minimally invasive radio-guided parathyroidectomy using the gamma probe allows a directed dissection with a small incision and is associated with a high success rate in patients with positive sestamibi scans requiring reoperation.33

Cryopreservation and Autotransplantation

Cryopreservation of a portion of excised parathyroid tissue in the reoperative situation has been regarded as state-of-the-art practice to correct postexploration hypocalcemia. A portion of the parathyroid gland is sliced into pieces and cryopreserved for future delayed autotransplantation in the event that the patient develops permanent hypoparathyroidism postoperatively. Controversy exists whether to perform immediate autotransplantation after removal of all parathyroid tissue in the reoperative situation and thus achieve a 90% success rate when using fresh parathyroid tissue in comparison to a 50% success rate when delayed transplantation is employed.24 However, it is generally advantageous to delay transplantation to observe the biochemical response after operation unless three or four parathyroid glands have already been removed. The presence of a fifth supernumerary gland or the possibility of persistent hypercalcemia makes us cautious about immediate autotransplantation. Although cryopreservation plays an integral role in reoperative parathyroid surgery, the rate of cryopreservation usage is low. and unfortunately not all patients are rendered normocal-cemic after autotransplantation of cryopreserved parathyroid tissue.34

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