Discussion
The paraglottic space is a potential space containing adipose tissue and blood vessels, bordered laterally immediately adjacent to the thyroid cartilage, medially adjacent to the thyroarytenoid muscle and bordered dorsally to the piriformis sinus [3]. The paraglottic space can be easily exposed if the thyroid cartilage plate is cut obliquely during the operation and the posterior part of the thyroid cartilage plate is pulled outward (such as the description of the previous surgical method). The advantages of the paraglottic space approach are as follows. ①The paraglottic space is a natural anatomical space, and the tissue is easily separated through the paraglottic space approach with less intraoperative blood loss and a clear surgical field. ②The hypopharynx is easier to separate from the larynx and the highly wrinkled pharyngeal cavity is easily planarised to fully expose the tumour and removing the tumour in a 3D way under the full dissociation of the mucous membrane through the paraglottic space approach. The tumour is not squeezes in the process of surgical resection, which is in line with the principle of tumour resection. ③The surgical field of view via the paraglottic space approach is well exposed. Combined with the preoperative narrow band imaging examination, the tumour can be accurately removed under direct vision, and the normal hypopharyngeal mucosa can be preserved as much as possible, which is conducive to pharyngeal cavity reconstruction and function preservation.
How to improve the retention rate of laryngeal function without affecting the survival rate of patients has become the focus of clinical attention. Relevant scholars also confirmed the feasibility of laryngeal function-preserving surgery for pyriform sinus carcinoma and provided a pathological basis [4-6].The National Comprehensive Cancer Network guidelines point out that surgery is feasible for patients with T1+N positive and T2−3Nx hypopharyngeal cancer to preserve the laryngeal structure, and partial laryngectomy (open or laser) combined with postoperative radiotherapy can be considered. These patients are expected to preserve laryngeal function. Although a part of pyriform fossa carcinoma belongs to T4, only the posterior edge of the thyroid cartilage, a small part of the cricoid cartilage, or the entrance of the cervical esophagus are involved. After tumor resection, most of the larynx can be preserved, the pectoralis major myocutaneous flap can be used to reconstruct the pharyngeal cavity, and the preservation of laryngeal function can be realised.
The paraglottic space of stage T1–T2 pyriform sinus carcinoma is rarely invaded. It is the best indication for this surgical approach. In addition, the paraglottic space approach can be used if the T3–T4 lesion does not involve the paraglottic space, because most cases of the vocal cord fixation is caused by tumour compression and not by tumour invasion of the paraglottic space [7]. For the carcinoma of the lateral wall of the piriform sinus, the tumour rarely invades the larynx because of its anatomical position. The approach through the paraglottic space can fully separate the hypopharynx and larynx, that is, the entire tumour can be directly exposed from the ventral side. The surgical field of view is wide, and the tumour can be accurately removed. For the primary tumour in the medial wall of the pyriform sinus, the transglottic approach can firstly complete the resection of the deep cutting edge of the tumour when entering the pharyngeal cavity, then separate the tumour from the larynx by pulling the thyroid cartilage plate outward and remove the tumour under direct vision. Preoperative cervical enhanced CT and electronic laryngoscopic examination can effectively determine the presence or absence of paraglottic space and laryngeal cartilage involvement. If the paraglottic space is involved, in the actual surgical operation, we can first enter through the paraglottic space approach, separate the hypopharynx and larynx and then combine the lateral pharyngeal approach, and observe the scope of tumour invasion in multiple planes. Supraglottic hemilaryngopharygectomy, partial pharyngectomy or total laryngectomy is performed according to the actual extent of tumour invasion.
In addition, the incidence of pharyngeal fistula in this study was 4.3%, which was considerably lower than those in other studies[6,8]. As mentioned above, the paraglottic space approach can retain more normal hypopharyngeal mucosa, dissociate the pharynx from the larynx, effectively reduce the suture tension during pharyngeal reconstruction and prevent mucosal avulsion during pharyngeal movement. In addition, the lifting of the uninvaded lateral thyroid lobe to strengthen the pharyngeal wall is another main reason to reduce the occurrence of pharyngeal fistula. The lateral thyroid lobe has good blood circulation and large tissue volume, which can be used as the strengthening plane of the new pharyngeal cavity.