After substantial experimental and preclinical investigations regarding the potential to reach the thyroid region transorally by different study groups since 2006 [11,12,13] and the worldwide first transoral parathyroid resection in 2010 [13], clinical proof of concept for transoral surgery via the vestibular approach was given by Anuwong, who published the first 60 transoral operations in patients who underwent scarless thyroidectomy via the lower vestibule of the mouth with excellent outcomes [14]. Sasanakietkul et al. published the first series of transoral transvestibular parathyroid operations (TOEPVAs) with promising results [6]. Moreover, several reports regarding the use of the TOEPVA have been published, and the results have been good. However, the number of cases is still limited [6,7,8,9, 15, 30].

Our data are in line with other reports confirming that TOEPVA can be performed in selected patients with localized primary hyperparathyroidism [6,7,8,9, 15, 30]. Results, complication rates, and success rates are comparable with and equal to focused conventional parathyroid surgery. Like in focused open and other remote-access techniques, definite preoperative diagnosis of pHPT, assurance of single-gland disease, and exclusion of contraindications, in addition to reliable localization of the suspected parathyroid adenoma, are of utmost importance.

In addition to a thorough diagnosis of pHPT and definite localization of the suspected solitary gland, selection of the “right” patient is of utmost importance.

Ideally, ultrasound is the first-line imaging procedure, performed using a 12–15-MHz linear probe with a specificity of more than 90% for detecting a single adenoma. However, the sensitivity is between 27% and 95% due to the investigator dependence [16].

Surgeon-directed US should always be the preferred practice for visualizing the gland and evaluating its position in relation to the surrounding anatomic structures. In addition, thyroid pathologies can be detected, evaluated, or excluded. Once a suspected parathyroid adenoma is detected by US, as in open minimally invasive parathyroid surgery, to increase safety regarding the correct localization of the suspected gland, additional preoperative imaging can be performed. In our series, patients only underwent TOEPVA with positive US imaging, and only 2 patients underwent US alone to avoid unsuccessful transoral exploration and possible conversion to open surgery because all patients clearly expressed their wish to avoid a visible scar on the neck. However, given the experience over the past decade regarding success rates in other focused approaches, no further localization procedures are necessary if a suspected gland is detected by US and if the family history is inconspicuous regarding Multiple Endocrine Neoplasia (MEN) or familial primary HPT. Like other groups, the authors emphasize that surgeon-directed US should be iterated once anesthesia has been induced and the patient has finally been positioned in the operating room [17].

If further localization is necessary, technetium99m sestamibi scintigraphy should be performed in combination with SPECT, which helps to increase the accuracy of localization, with a sensitivity of approximately 70% and a positive predictive value of 78% to 100% [18]. Notably, the accuracy of nuclear imaging is diminished in patients suffering from multinodular goiter or an intrathyroidal parathyroid adenoma.

In conventional minimally invasive video-assisted parathyroid surgery, discordant preoperative localization or non-visualization of the gland on nuclear imaging does not necessarily lead to BCE if US reveals a suspected gland, because bilateral exploration of the neck can also be performed by video-assisted surgery and enlargement of the skin incision can easily be performed. However, the authors suggest that in cases of discordant preoperative localization and patients still interested in TOEPVA, additional imaging is inevitable, although it is also technically possible to perform bilateral exploration transorally.

Potential additional imaging procedures differ between hospitals and centers.

Even though not used in our series, one option is a so-called 4D CT scan.

Multiphase CT images were acquired in three phases (precontrast, arterial, and venous) along with the fourth phase, which represents the change in perfusion over time. Four-dimensional CT has a sensitivity of 85%, provides optimal anatomical detail in the neck, and may help in detecting multigland disease, while the increase in external radiation is small [19, 20].

Instead of CT or MRI, 18F-fluorocholine PET was used in 4 patients, all of whom had positive results. 18F-fluorocholine PET is rarely available and expensive (Fig. 4). The FSD indicates the functional status of the suspected gland in combination with its localization, with a high sensitivity of up to 94% and an overall accuracy of 95% [21,22,23,24,25].

a, b 18F‑choline positron-emission tomography scan of a left lower parathyroid adenoma in a 65-year-old female with primary hyperparathyroidism. PT Parathyroid adenoma

If two noninvasive imaging modalities are concordant, the positive predictive value in identifying the suspected gland is up to 99% [26].

In principle, if US clearly reveals a parathyroid adenoma, no other localization procedure is necessary in open and minimally invasive parathyroid surgery. Data currently available regarding TOEPVA do not ultimately show that TOPEVA can also be safely performed with only one localization procedure. However, in the case of non-detection of the suspected gland on one side, it is also possible to perform bilateral exploration transorally before conversion to open surgery.

Like in TOETVA, “correct” patients should also be highly motivated toward a “scarless” approach, and patients must be informed that cosmesis is the only veritable advantage of transoral surgery.

However, in most patients, especially in dedicated white individuals, wound healing occurs without any problems and is negligible after a skin incision of less than 2 cm is made [5, 15].

A small incision with potentially excellent long-term outcomes does not prevent a definite discrepancy in the perception of scars between surgeons and these patients, which leads to serious patient considerations regarding scar revision years after surgery in up to 10% of patients [5, 26, 27].

This finding is in line with reports that emphasize the significant negative effect of a cervical incision on health-related quality of life (HRQOL). The impact of a cervical incision on HRQOL was found to be similar to the impact of vitiligo, psoriasis, or severe atopic dermatitis [5, 27].

The presence of a scar in the visible area of the neck impairs patients’ ability to maintain healthcare privacy. In this context, Liao et al. demonstrated attentional bias toward the neck instead of the face or eyes during a conversation due to the presence of a scar after open thyroid/parathyroid surgery [28].

Furthermore, worldwide consideration of potential wound healing problems may lead to a more differentiated appraisal. In African countries, for example, the incidence of keloid development after skin incision is up to 15%, and in some countries, a scar on the neck is historically related to a negative social standing [4].

Various remote-access approaches to the thyroid have been proposed to prevent scarring. Remote-access surgery includes areolar, axillary, or combined areolar/axillary (ABBA) incisions as well as the retroauricular approach, which can effectively minimize the cosmetic burden in some patients. On the one hand, improved cosmesis but unfamiliar dissection planes, longer routes to the central neck, and novel complications have led to further investigations focusing on so-called natural-orifice approaches. The use of TOETVA as popularized by Anuwong has gained acceptance because it is safe and has a short learning curve [29]. He also proposed the transoral endoscopic parathyroidectomy vestibular approach (TOEPVA), which is like TOETVA.

As in other series, the success and complication rates of the current study are comparable to those of the conventional minimally invasive and open techniques [6,7,8,9, 15, 30].

Surgeons interested in performing transoral parathyroid surgery should be well experienced in parathyroid surgery and familiar with embryological and anatomical characteristics, as in conventional parathyroid surgery [30,31,32]. In addition, experience with laparoscopic instrumentation is beneficial. The transoral technique should be trained in cadaveric courses and should be frequently offered in specialized centers. Subsequent first transoral operations in the clinical setting should ideally be performed with the assistance of an experienced transoral surgeon.

The study is limited by the low number of patients, the high number of centers participating, and its retrospective design.