Transparapharyngeal Space Transposition of a Submental Flap for Nasopharyngeal Reconstruction After Endoscopic Transoral Skull Base Surgery: An Anatomical Study and Clinical Case Series

Abstract

Background: Large defects after endoscopic transoral skull base surgery remain difficult to reconstruct, particularly in previously irradiated fields. The submental flap is widely used in head and neck reconstruction, but its application in endoscopic skull base surgery has rarely been described.

Methods: Eight fresh cadaveric heads underwent endoscopic transoral skull base dissection to evaluate harvesting, arc of rotation, and transparapharyngeal transposition of the submental flap. Clinical feasibility was then assessed in 30 consecutive patients who underwent submental flap reconstruction for nasopharyngeal skull base defects after endoscopic transoral surgery, with or without a combined transnasal approach.

Results: When dissected to the origin of the facial artery, the flap measured 11.3 ± 1.0 cm in length and 4.1 ± 0.8 cm in width. Anatomically, the flap adequately covered the ipsilateral inferior petrous apex, nasopharynx, lower clivus, parapharyngeal space, and Eustachian tube region. Clinically, all flaps reached the target defect. Total flap necrosis occurred in 5 of 30 patients (16.7%), and all were salvaged with temporalis muscle flap reconstruction; no carotid blowout occurred during follow-up.

Discussion: The submental flap provides vascularized tissue with a favorable arc of rotation and can address selected lateral and inferior skull base defects beyond the reach of standard intranasal flaps.

Conclusion: The submental flap is a feasible complementary reconstructive option after endoscopic transoral skull base surgery in carefully selected patients, especially when carotid coverage is required. Meticulous patient selection, flap handling, and postoperative surveillance remain essential.

Keywords

endoscopic skull base surgery / nasopharyngeal carcinoma / skull base reconstruction

1 Introduction

The reconstruction of large skull base defects remains a major challenge in skull base surgery. Several pedicled regional flaps are available for endoscopic reconstruction. Among these, the Hadad-Bassagasteguy (HB) flap is well established for endoscopic skull base repair^[1]. More recently, our group reported the use of the temporalis muscle flap as an effective option for reconstruction after endoscopic transoral skull base surgery^[2,^3]. However, these flaps may be unavailable when the tumor invades the donor site or when the vascular supply has been compromised by prior surgery or radiotherapy.

The submental flap, first described by Martin and colleagues^[4], is a reliable and cosmetically favorable option for head and neck reconstruction. Although its use in conventional open head and neck surgery is well documented^[5], its application to endoscopic skull base reconstruction has rarely been described. In the present study, the emphasis is not merely on the submental flap itself, but on its transparapharyngeal transposition as a regional vascularized option for lateral and inferior nasopharyngeal-central skull base defects, particularly when internal carotid artery (ICA) coverage is required. Therefore, the aim of this study was to investigate the surgical anatomy of the submental flap in endoscopic transoral skull base surgery and to evaluate its clinical application in patients undergoing reconstruction after expanded nasopharyngectomy.

2 Materials and Methods

2.1 Study design

Eight fresh cadaveric heads were used in an anatomical study conducted in the Otorhinolaryngology Anatomy Laboratory of the Eye & ENT Hospital, Fudan University, to evaluate the feasibility of transposing the submental flap through the parapharyngeal space to the skull base. In all specimens, the common carotid arteries, vertebral arteries, and internal jugular veins were isolated and cannulated. The arterial and venous systems were injected with red and blue silicone, respectively. The specimens were then placed in 75% alcohol for subsequent dissection using 0° and 45° endoscopes (Karl Storz GmbH & Co., Tuttlingen, Germany). The submental flap was harvested using a conventional open technique, and the feasibility of its transposition through the parapharyngeal space to the skull base was assessed.

After the surgical procedure had been established, the submental flap was used to reconstruct nasopharyngeal skull base defects in 30 patients who underwent endoscopic transoral skull base surgery. The anatomical and clinical components of the study were approved by the Research Ethics Committee of the Eye & ENT Hospital, Fudan University (approval date: January 26, 2021; approval No. 2020123-1).

2.2 Harvesting the submental flap

The submental flap was harvested using a conventional open technique (Fig. 1). An elliptical skin paddle was designed over the midline submental region. Flap width was determined using a pinch test to allow primary closure of the donor site. For longer defects or when additional reach was required, the skin paddle could be extended laterally as needed. In selected cases, dissection was extended to the origin of the facial artery to maximize pedicle length.

2.3 Endoscopic exposure of the skull base

Comprehensive exposure of the skull base, including the anterior skull base, sellar region, nasopharynx, clivus, petroclival region, and parapharyngeal space, was achieved through an endoscopic transoral approach, either alone or in combination with an endoscopic transnasal approach^[6].

2.4 Transparapharyngeal space transposition of the submental flap

The anatomical continuity among the parapharyngeal space, skull base, and submandibular space permitted creation of a tunnel connecting the skull base defect to the donor site. The tunnel was developed in the prestyloid compartment to avoid injury to the styloid muscle group and reduce the risk of damage to the ICA in the poststyloid compartment.

After identification of the posterior belly of the digastric muscle, the surgeon protected the vital structures, including the facial artery, submental artery, and hypoglossal nerve when identified. Blunt finger dissection was then performed along the medial border of the posterior belly of the digastric muscle toward the styloid process and skull base. Additional loculations between the medial pterygoid muscle and the superior pharyngeal constrictor were released. The direction of dissection through the parapharyngeal space toward the skull base was guided by the mandibular angle and medial pterygoid muscle.

To create sufficient space for transposition of the flap into the nasopharynx, the medial pterygoid plate was removed and the eustachian tube was sacrificed when necessary. A gauze strip was sutured to the superior edge of the flap, passed through the tunnel into the nasopharynx, and retrieved through the nasal cavity. The portion of the flap traversing the tunnel was de-epithelialized before transposition. The exposed ICA before flap placement is shown in Fig. 2a. The donor site was closed primarily in layers. Under endoscopic visualization, the flap was positioned over the skull base defect and secured with surgicel and iodoform gauze (Fig. 2b). The iodoform gauze was removed 2 weeks after surgery. In all cases, a nasogastric tube was used for postoperative feeding for 10 days or until there was no evidence of wound dehiscence or fistula.

2.5 Patients

Patients who underwent reconstruction with a pedicled submental flap after endoscopic transoral skull base surgery between January 2022 and December 2023 were retrospectively reviewed. This study included consecutive eligible patients treated during the study period. Substantial defects were defined as nasopharyngeal-central skull base defects requiring vascularized tissue coverage because of exposed critical structures, devitalized irradiated tissue, denuded skull base bone, or extension into the parapharyngeal space, lower clivus, or petrous region. Tumor extent was assessed using computed tomography (CT) and magnetic resonance imaging (MRI), with positron emission tomography-CT performed when necessary. After lesion resection, a submental flap was used for reconstruction of the nasopharyngeal defect. The primary outcomes were flap survival/necrosis, wound healing, and protection of critical structures such as the ICA. Secondary outcomes included reoperation, postoperative complications, and follow-up status. Patients with incomplete essential clinical records or inadequate follow-up were excluded. All patients underwent mandatory postoperative follow-up for at least 24 months. The clinical component of this study is reported in accordance with the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement statement for observational studies.

2.6 Statistical analysis

Statistical analyses were descriptive. Continuous variables are presented as mean ± standard deviation or median (range), as appropriate, and categorical variables are presented as number (percentage). Because this study was a single-arm case series with a modest sample size and only five flap-necrosis events, no inferential between-group comparisons or multivariable analyses were performed. Analyses were based on available data; no missing values were imputed.

3 Results

3.1 Anatomical study

When dissected to the origin of the facial artery, the submental flap had a mean length of 11.3 ± 1.0 cm. The widest part of the flap measured 4.1 ± 0.8 cm. The flap could reconstruct defects involving the ipsilateral inferior exocranial surface of the petrous apex, the nasopharynx, and the lower clivus, and it could provide coverage of the parapharyngeal, petrous, and paraclival segments of the ICA.

3.2 Clinical application

The submental flap was used in 30 patients with substantial nasopharyngeal defects after an endoscopic transoral approach, either alone or in combination with an endoscopic transnasal approach (Table 1). Lesions involved the nasopharynx, parapharyngeal space, and/or skull base. The mean age at surgery was 55.3 years. Twenty-seven patients (90.0%) had received prior radiotherapy, whereas 3 (10.0%) had not; the 3 non-irradiated patients had 2 clear cell carcinomas and 1 adenoid cystic carcinoma. Detailed retrospective records did not completely capture whether cervical irradiation had been administered in all irradiated patients. The submental skin was supple and showed no obvious scarring or induration. During follow-up, 25 flaps (83.3%) survived, whereas flap necrosis occurred in 5 patients (16.7%).

3.3 Flap-related complications and salvage management

Flap necrosis occurred in 5 of 30 patients (16.7%), and all 5 events were total necroses. These patients underwent salvage reconstruction with a temporalis muscle flap. Based on retrospective review of the clinical records, the main contributing factors appeared to include local surgical-site infection and insufficient distal perfusion of the submental flap. Although flap necrosis occurred in these patients, no carotid blowout or major hemorrhagic event was observed during follow-up.

3.4 Illustrative case

A 58-year-old man had undergone chemoradiotherapy for nasopharyngeal carcinoma 15 months previously. He presented with headache, and contrast-enhanced MRI demonstrated a lesion involving the right nasopharynx and skull base. Complete lesion removal was achieved through a combined endoscopic transoral and transnasal approach. The resulting defect was reconstructed and the ICA protected with a submental flap. Histopathology showed radiation-induced osteonecrosis. Contrast-enhanced MRI obtained on postoperative day 3 confirmed complete resection, and nasal endoscopy performed 6 weeks after surgery showed satisfactory flap integration and healing (Fig. 3).

4 Discussion

This study demonstrated that the submental flap can be transposed through the parapharyngeal space to reconstruct selected nasopharyngeal and central skull base defects after endoscopic transoral surgery. The anatomical study clarified the available arc of rotation and the boundaries of coverage, while the clinical series showed that the flap could be delivered reliably to the defect and provide vascularized tissue over critical structures, particularly the ICA. In this setting, the flap offers a practical complement to intranasal reconstructive options, especially in previously irradiated patients and in defects extending laterally or inferiorly beyond the reach of a conventional nasoseptal flap.

From a reconstructive standpoint, the submental flap should be considered a complementary regional option rather than a replacement for established techniques. The nasoseptal flap remains preferred for small-to-moderate midline endonasal defects. In contrast, the submental flap may be particularly useful for substantial lateral or inferior nasopharyngeal-central skull base defects, especially when robust vascularized coverage of an exposed ICA is required or when standard intranasal options are unavailable or insufficient. Temporalis muscle flap or free-flap reconstruction may be more appropriate when wider tissue bulk is needed.

The submental flap can be extended toward the contralateral mandibular angle according to the size and location of the defect. When the pedicle is dissected back to the origin of the facial artery, an additional 1–2 cm of length can be gained^[7].

In the present series of 30 patients, the flap provided adequate coverage for the ipsilateral inferior exocranial surface of the petrous apex, the nasopharynx, and the lower clivus. More importantly, it covered the parapharyngeal, petrous, and paraclival segments of the ICA. Because the procedure does not require harvesting of the temporalis muscle, it avoids temporal hollowing and does not directly affect the muscles of mastication. However, the submental flap is less suitable for anterior skull base defects because a substantial portion of the flap length may be lost during passage through the parapharyngeal tunnel.

When using the submental flap, several risks should be recognized. One is possible injury to the marginal mandibular branch of the facial nerve^[8]. In addition, when preoperative imaging suggests metastatic lymph nodes in the submental region, flap harvest should be approached with caution or avoided^[9]. If indicated oncologically, complete lymph node dissection should be performed before flap use is considered.

The submental flap is attractive because it leaves a relatively concealed scar, has low donor-site morbidity, offers a good color and contour match, and provides a wide arc of rotation with a relatively short operative time. Nevertheless, prior radiotherapy may adversely affect flap viability^[10]. In the present series, 27 of 30 patients had received radiotherapy, and flap necrosis occurred in 5 patients. Flap necrosis in this cohort appeared to be multifactorial. The main observed contributing factors were local surgical-site infection and compromised distal flap perfusion. In previously irradiated patients, impaired tissue vascularity and wound-healing capacity may have further increased vulnerability to flap compromise. Given the limited number of events and the retrospective design, these findings should be interpreted as descriptive clinical observations rather than validated independent predictors.

The absence of carotid rupture despite flap failure may be related to careful perioperative vascular assessment, appropriate ICA management in selected cases, close postoperative surveillance, and timely salvage reconstruction before progression to catastrophic vascular complications.

This study has several limitations. First, it was a retrospective single-center case series without a control group, which limits causal inference and external generalizability. Second, the sample size was modest, and the heterogeneity of pathology and defect extent precluded meaningful subgroup analysis and reliable multivariable modeling of flap necrosis risk. Third, detailed retrospective records did not completely capture whether cervical irradiation had been administered in all irradiated patients. Fourth, although the flap provides robust vascularized coverage, the use of hair-bearing submental skin may cause postoperative discomfort in some patients. Finally, functional outcomes and patient-reported quality-of-life measures were not systematically collected. Larger comparative studies are needed to define the optimal indications for this flap relative to other regional and free-flap reconstructive strategies.

5 Conclusion

The submental flap is a useful complementary option for reconstruction of selected skull base defects after endoscopic transoral skull base surgery, particularly in patients with local recurrent nasopharyngeal carcinoma or osteoradionecrosis when vascularized carotid coverage is required. Prospective comparative studies are warranted to further define its indications, safety, and long-term outcomes.

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