Advanced oral tongue squamous cell carcinoma (OTSCC) represents a challenge for head and neck surgeons. The goal of surgery is to achieve oncological radicality while ensuring acceptable functional results in terms of speech and swallowing. In advanced tumors (cT3-T4a), the disease can spread through the lingual septum and along the intrinsic transverse muscle to involve the contralateral hemi-tongue (1). An anatomic-based approach, performed according to preoperative imaging and intraoperative findings, allows for complete and oncologically safe resection, preserving structures not involved in the disease.

In advanced OTSCC, one of the main adverse features in predicting postoperative swallowing impairment is the involvement of the base of the tongue (BOT). The key role of the BOT in maintaining an acceptable swallowing function was already demonstrated in the literature by the experience of Chen et al. in robotic surgery (2, 3). We postulated that to maintain an acceptable swallowing function, it is paramount to preserve a functional unit made by the hyoglossus and styloglossus muscles together with their innervation, for which the term hyo-styloglossus unit (HSU) was coined (Figure 1).

The study aims to describe the surgical approach to advanced cT4a tumors that extend beyond the lingual septum to the contralateral hemi-tongue involving the genioglossus muscle while sparing the hyoglossus and styloglossus muscle of the contralateral side. The procedure of the subtotal glossectomy sparing the HSU (EG Type B) is described step by step, focusing on the surgical anatomy. In addition, preliminary functional results in terms of swallowing and quality of life (QoL) are presented.

A retrospective review of patients who underwent EG Type B for advanced OTSCC between January 2019 and November 2022 was conducted in the Department of Otolaryngology-Head and Neck Surgery in “Ospedale Centrale” of Bolzano (4).

All patients underwent preoperative MRI with gadolinium, which is a fundamental decision-making tool to depict the invasion of key anatomical structures.

Based on the clinical presentation and MRI, the indications for subtotal glossectomy with preservation of the HSU are as follows: ○

advanced cT3-cT4a OTSCC extended beyond the lingual septum and involving the contralateral hemi-tongue (Figure 2);

Six patients (five males and one female, with a median age of 49.2 years) were included in the study. Two patients were active smokers, whereas none had a history of alcohol abuse. All patients were affected by advanced tongue squamous cell carcinoma pT3 or pT4a. Data about patients, surgery, and follow-up are summarized in Table 1. The types of consistencies of foods and liquids are categorized according to the International Dysphagia Diet Standardisation Initiative (IDDSI) Framework of 2016 (10).

Regarding the swallowing results, five out of the six patients reached a full oral diet within 1-year follow-up, with a score of 6 on the FOIS. One patient with severe neurocognitive disorder continued to be fed through a percutaneous gastrostomy, since sufficient oral intake was not reached. Information regarding swallowing function and the patient's QoL is summarized in Tables 2, 3.

The primary goal of tumor ablation in OTSCC is to remove the entire tumor along with a “margin” of normal tissue. Inadequate clearance of tumor cells results in increased risks of local and regional recurrences, as well as decreased long-term survival rates (11, 12).

The extrinsic muscles of the tongue can be divided into a peripheral group including palatoglossus, styloglossus, and hyoglossus muscles, which are located laterally, and the genioglossus muscle, located in a deeper plane, which gives rise to fibers running to the periphery, the dorsal surface, and the apex of the tongue (13). Local tumor spread first involves the intrinsic musculature following the direction of muscle fibers, the genioglossus muscle in case of an anterior tumor, or the hyoglossus and styloglossus muscles in case of a posterior tumor. In the case of macroscopic infiltration of the extrinsic musculature of the tongue, CTS is indicated, with the aim of removing the entire oncological compartment with the pathways of tumor spread. These include the tumor, within the entire hemi-tongue and related floor of the mouth and the neck lymph nodes in continuity with the so-called tumor-node tract (TNT) (5, 12).

The lingual septum represents a barrier to contralateral spread, but it is not uncommon in advanced stages (cT3-cT4a) for it to be overcome. In those cases, the extension of the resection to the contralateral tongue may affect the postoperative tongue functionality and thus the patient's quality of life. The defect resulting from EG Type B requires reconstruction that includes free flaps to adequately restore bulk and prevent ankyloglossia (13). Radical surgical treatment often affects all oral functions, such as speech and swallowing physiology (13, 14). In the oral preparatory phase, there can be alterations related to tongue motility for bolus preparation and formation and, in the oral phase, alterations related to bolus transportation and bolus control. In the pharyngeal phase, alteration of swallow initiation, posterior tongue propulsion, hyolaryngeal excursion, bolus propulsion, post-swallow pharyngeal residue, and risk of penetration and aspiration can be observed (15, 16). Advanced tumor (T) stage, extraoral surgical approach, the incremental volume of glossectomy defect, and adjuvant radiotherapy correlate significantly with poor swallowing outcomes (17, 18).

Grammatica et al. investigated the long-term functional outcomes in patients treated by CTS and reconstructed by free flaps and demonstrated that CTS does not significantly affect speech and swallowing (5). However, the study included only patients who underwent ipsilateral CTS.

The important role of the BOT in the propulsion of food makes its removal of particular concern, even if tongue base resections are becoming increasingly common in the modern era of transoral robotic surgical approaches (2, 3).

In this scenario, the pivotal concept of HSU in the maintenance of an acceptable residual swallowing function should be highlighted. The HSU can be compared to the cricoarytenoid unit in partial OPHL laryngectomies, where preservation of one arytenoid with the underlying portion of the cricoid plate and the recurrent nerve allows normal motility of the arytenoid (functioning cricoarytenoid unit) (19, 20). A concept similar to HSU has been described in the works of Gawryszuk et al. in the field of radiotherapy (21, 22). They introduced a concept rooted in anatomy and physiology known as functional swallowing units (FSU), aiming to enhance comprehension of radiation-induced dysphagia.

Preserving HSU is one of the main goals of the EG Type B also in the case of bilateral involvement of the genioglossus muscles. This unit must only be sacrificed if there is a direct invasion of the hyoglossus muscle bilaterally, so in this case, the approach should be converted to total glossectomy.

The importance of preserving the HSU in advanced tongue tumors is supported by our encouraging results in terms of swallowing and QoL. Though the number of patients is limited, it is noteworthy that all patients but one resumed a regular oral food intake of liquid and solid of different consistencies, and did not develop aspiration pneumonia. All patients, except one, can swallow liquids and foods of different consistencies using the swallowing technics learned during rehabilitation. The long-term results regarding the impact of dysphagia on their QoL demonstrated that all patients present good day-to-day functioning and QoL.

In our series, only one patient with severe comorbidities was not reconstructed with a free microvascular flap but in a sub-optimal way with a major pectoralis flap. Furthermore, he was affected by a severe cognitive disorder that prevented swallowing rehabilitation. This was the only patient in our case series that was not able to resume a full oral diet and a percutaneous endoscopic gastrostomy was performed and maintained. This experience confirms that patients who are candidates for surgery should be carefully selected, including only those who are suitable for a highly demolitive procedure, microvascular reconstruction, and an intensive swallow rehabilitation program. Therefore, patients should be appropriately counseled on the risks of this strong demolitive surgery with emphasis placed on intensive swallow rehabilitation in the posttreatment setting (2, 13).

Regarding the oncological outcomes, as shown in Table 1, all patients thus far are disease-free except for one who passed away due to other reasons. These results demonstrate that preserving the HSU, which we have observed to be both functional and essential for swallowing, does not compromise oncological safety.

Further studies are needed to confirm the preliminary functional results shown in the present study.

In our experience, the minimal functional unit that allows an acceptable swallowing result is the so-called functional unit of the BOT, which includes the hyoglossus and styloglossus muscles innervated by the hypoglossal nerve (HSU).

The importance of preserving this functional unit is corroborated by the highly encouraging results we observed in terms of both swallowing and QoL.