Surgical resection is the definitive treatment of patients with HPT. Bilateral neck exploration is currently the gold standard for the surgical treatment of patients with a cervical parathyroid adenoma[6]. In these cases, a focused single gland parathyroid exploration can be performed with other adjuvants as the use of intraoperative PTH[7] however, approximately 16% of patients with HPT have an ectopic parathyroid gland and up to 2% of hyperfunctioning parathyroid adenomas are not accessible by a standard cervical surgical approach[8].
Ectopic localization of the parathyroid glands is attributed to an abnormal migration during embryogenesis or as the result of primary mediastinum development[9]. Because the inferior parathyroid glands undergo more extensive migration during embryogenesis, they are more likely to be found in abnormal ectopic locations[10]. These include the thyroid-thymic ligament, the retro/paraoesophageal space, the mediastinum, intrathymic or intrathyroidal, within the carotid sheath and/or a high-undescended cervical position[11].
The possibility of an ectopic localization is why preoperative localization studies for HPT must be performed in all patients, including neck ultrasound, Computed Tomography (CT) scan, Magnetic Resonance Imaging (MRI) or Single Photon Emission Computed Tomography (SPECT-CT) as Scintigraphy with 99mTc Sestamibi which displays 100% sensitivity and 97.4% positive predictive value for the detection of ectopic parathyroid adenoma[12] in HPT patients. Recent reports also describe the usefulness of 18F-flurocholine in PET for patients with occult adenomas [13]. In our series, all patients had a positive SPECT-CT with a single MEPA, which dictated the surgical approach.
The clinical presentation of a MEPA is commonly more dramatic, they often have a longer standing disease, previous cervical explorations, and a delayed diagnosis. They tend to be more hypercalcemic, with a more pronounced bone reabsorption and kidney stones[4]. Rarely, they present with thoracic bleeding due to a ruptured gland hematoma or with symptoms due to compression of adjacent structures such as stridor or dysphagia[14].
Depending on how deep in the mediastinum the gland is located a transcervical, trans-sternal or thoracic approach is necessary: for glands in the superior mediastinum (above the aortic arch) the transcervical approach is the procedure of election, as the upper mediastinum is easily reached through a retrosternal dissection. For the medium mediastinum and lower located MEPA, a medium sternotomy or thoracotomy is needed. Nowadays, the video-assisted thoracoscopic approach for the surgical resection of MEPA is the preferred one, because of its numerous benefits over traditional open procedures, which can be associated with significant complications including phrenic and recurrent laryngeal nerve injuries, innominate vein laceration, wound infections, mediastinitis and death [4].
The first report of the use of a thoracoscopic approach to resect a MEPA was described by Prinz et al. in 1994[15]. VATS is a feasible and safe approach for resecting these glands, with an overall success ratio of 98–100%[4]. It has several advantages over traditional open approaches as any other minimally invasive techniques, such as less bleeding, less operative time, less pain, better cosmesis, less intrahospital stay, more rapid recovery[16][9], and allows better visualization of the tumor due to the magnification of structures[17] with the endoscopic lens. According to Masatoshi[18], all glands under the aortic arch can be resected with VATS, but it must be performed by a trained thoracic surgeon with VATS training, a vast anatomy knowledge together with an experienced group of endocrinologist, endocrine surgeons and anesthesiology to avoid potential catastrophic complications[17]. In our case series, all patients were eligible to this approach because of their adenoma localization in the medium or lower anterior mediastinum. All the procedures were successfully performed by a trained thoracic surgeon in thoracoscopic surgery, with only one complication due to bleeding of an accessory inferior bronchial artery that was repaired during surgery without conversion.
Several reports of the use of VATS are described in the literature, however, more randomized, high-quality studies are needed to determine if VATS can be the gold standard approach for MEPA.