Fig. 5.1
The viscero-vertebral angle approach
Fig. 5.2
Mediastinal parathyroid adenoma within middle posterior compartment demonstrated in fusion imaging
The most problematic preoperative scenario to confront is that in which localization fails to identify any suspicious putative site suggestive of parathyroid abnormality. It is in this situation where re-operative surgery for hyperparathyroidism is potentially the least successful and the most morbid. Failure to localize usually mandates a bilateral cervical exploration that comprehensively and methodically addresses all potential sites that may harbor a missing gland or glands. A properly constructed initial operative note that accurately documents remaining histologically identified parathyroid glands and regions explored is of utmost importance and potential value for the re-operative surgeon. An orderly systematic approach to re-exploration is necessary in these circumstances to locate the missing gland(s) and limit morbidity. The order in which regions are approached may vary according to the surgeon; however, it is important that all potential areas be accessed to increase the chance of success and avoid a failed re-exploration. The author’s preference is to approach each side explored through the VVA via a lateral to medial orientation. Regions are then addressed in the following manner: the anterior superior mediastinum is dissected first, with careful attention to the thyrothymic ligament and tracheoesophageal groove region adjacent to the recurrent nerve. Cervical thymectomy, if not performed at initial surgery, is completed at this time. Dissection then turns to the retropharyngeal, retroesophageal region where blunt dissection within the prevertebral space will allow for digital exploration superiorly above the cricoid cartilage and larynx and inferiorly into the posterior mediastinum. Enlarged glands in this anatomic plane may often be felt by digital palpation before they are seen using these maneuvers. Next, the thyroid lobe is mobilized, possibly truncating the superior vascular pedicle to allow rotation of the thyroid gland anteromedially so that the posterior capsule may be thoroughly examined for a folded, lobulated parathyroid gland under cover of the capsular fascia. Using this technique, the thyroid lobe is palpated for any nodular densities, which may be suspicious for an intrathyroidal or subcapsular parathyroid gland. The carotid sheath is then opened from the superior mediastinum to the hyoid bone, inspecting and palpating for nodular structures within the sheath. Failing identification on the side explored first, the dissection proceeds contralaterally in the same manner, with orderly inspection of all regions noted above. In the event that a bilateral exploration fails to identify the offending gland, thyroid lobotomy/lobectomy may be performed on the side suspected of harboring the offending gland. It is in this situation where surgeon-performed ultrasound , pre- or intraoperatively, may be of the most benefit to help avoid unnecessary thyroid removal.
In the event that all maneuvers described are unsuccessful in identifying the abnormal missing gland, the procedure is terminated and further measures undertaken to the gland’s position by imaging or angioinvasive techniques . Mediastinal dissection is not advisable in the immediate setting, owing to lack of localization and length of time required after a thorough bilateral re-exploration. It should be emphasized that re-exploration should not be undertaken unless there is a reasonable potential for success based on localization studies and/or previous documentation which identifies the putative missing gland.
Intraoperative Assessment of Parathyroid Hormone
Intraoperative assessment of parathyroid hormone (IOPTH) represents a useful adjunct in the performance of parathyroid reoperation, both for single and multiple gland disease entities. The usefulness of biochemically confirming the removal of hyperfunctional parathyroid tissue by applying IOPTH becomes apparent when one considers the previous operative procedure(s) performed by the initial surgeon with respect to what was identified/removed and whether normal glands were identified and histopathologically confirmed. The utilization of IOPTH allows the surgeon to determine the physiologic effect of removal of the putative abnormal gland, indicating removal of all hyperfunctional parathyroid tissue provided the appropriate criteria (>50% decline in PTH) is achieved intraoperatively. Should this decrement not be achieved, further exploration proceeds until IOPTH confirms removal of all hyperfunctional tissue.
Thus, the application of IOPTH in re-exploration potentially limits the extent to which surgical dissection is required in the previously operated neck, thereby limiting the possibility of injury to the recurrent laryngeal nerve and iatrogenic hypoparathyroidism due to manipulation/biopsy of normal glands. Another capability of IOPTH is through intraoperative sampling of blood from the internal jugular veins simultaneously in order to determine a gradient difference in PTH levels, thereby indicating on which neck side a hyperfunctional gland resides (Fig. 5.4). This technique may also be employed to potentially identify an ectopically located undescended inferior parathyroid adenoma , or so-called parathymus, which was not identified at the time of initial exploration (Fig. 5.5). Ultimately, the use of IOPTH in all parathyroid explorations provides a measure of biochemical confidence that will serve to limit the extent of surgical dissection and reduce the potential for morbidity.
