Various arrangements of pharyngeal flap in soft palate reconstruction after cancer treatment

The pharyngeal flap (PF) is useful for reconstruction of soft palate defects, but effective arrangements of PF for various types of soft palate defects are controversial. Here, we classify three types of soft palate defects and discuss the arrangements of PF and their functional prognosis.


| INTRODUCTION
Reconstruction of soft palate defects associated with head and neck cancer treatment is critical for velopharyngeal function.Postoperative velopharyngeal insufficiency (VPI) can significantly reduce a patient's quality of life due to difficulty in eating and speaking.Various types of soft palate defects can occur after head and neck cancer treatment, including partial-thickness defects involving the mucosa and musculature, full-thickness defects extending from the oral cavity to the nasal cavity, and full-thickness defects of the soft palate, including the palatopharyngeal arch.Depending on the condition of each defect, reconstructive methods must be considered to maintain velopharyngeal function after surgery.
The closure of palatal defects has been achieved using prostheses and autologous tissue grafts.Prosthesis closure is minimally invasive because it does not require harvesting of the grafted tissue, and it is possible to regain relatively good function for defects in the hard or anterior soft palate.However, if the defect extends posteriorly to the soft palate, watertight closure is difficult, and its applicability is limited because of discomfort while wearing the prosthesis.Autologous tissue grafts can provide reliable closure of the defect and do not require daily management, although they are associated with donorsite morbidity.2][3] Previous reports on algorithmic approaches to palatal reconstruction have recommended a reconstruction ladder and selecting types of skin flaps according to defect size, 4,5 without making specific reference to methods of nasal lining or velopharyngeal narrowing and their indications, which are important for maintaining velopharyngeal function.We focus on the amount of muscle remaining in the soft palate after resection to determine whether the postoperative function of the soft palate will be maintained.From this perspective, we postulate that VPI is more likely to occur in cases where the resection extends posteriorly to the midpoint of the sagittal direction of the soft palate (defined as half the length from the posterior edge of the hard palate to the palatopharyngeal arch, hereafter referred to as the midpoint of the soft palate).
In this study, we present our experience using a pharyngeal flap to effectively narrow the velopharyngeal space for various types of defects after soft palate resection.The concept, technical aspects, and functional outcomes of palatal reconstruction to narrow the velopharyngeal space using pharyngeal flap will be analyzed.

| MATERIALS AND METHODS
This retrospective study was conducted at Okayama University Hospital, Okayama University, from June 2014 to March 2023.Ethical approval was granted by the Institutional Review Board of Okayama University Graduate School of Medicine (No. 2208-035).Informed consent was obtained from all participants via an opt-out option on the study website.Eligible patients were those with tumors confined to the palate and defects posterior to the midpoint of the soft palate due to tumor resection or radiotherapy, excluding defects confined to the hard palate or those involving resection of the lateral or posterior wall of the pharynx.Defects were classified into three types (Figure 1).Type 1 was a partial-thickness soft palate defect (only mucosal and muscular layer defects), Type 2 was a full-thickness soft palate defect (palatopharyngeal arch remaining), and Type 3 was a full-thickness soft palate defect (resection including the palatopharyngeal arch).After at least six postoperative months had passed, velopharyngeal function was evaluated using videoendoscopy, video fluorography, patient speech (Hirose standard), and swallowing function.Postoperative assessment of the patient's speech and swallowing function was performed via interview between the patient and their doctor.

| Techniques
The pharyngeal flaps were superior-based and harvested at the maximum width of the posterior wall of the pharynx.The length of the pharyngeal flap to be harvested should be the maximum length that can be harvested orally for Types 1 and 3, and a necessary and sufficient length that can be sutured to the remaining palatopharyngeal arch for Type 2. The arrangements of pharyngeal flap and skin flaps are discussed as follows.Type 1 involved harvesting the pharyngeal flap, creating a slit in the soft palate slightly posterior to the border between the soft and hard palates, moving the pharyngeal flap from the nasal to the oral side through the slit, and covering as much of the soft palate mucosal defect as possible with a pharyngeal flap (Figure 2).A polyglycolic acid sheet was applied to the raw surface that could not be covered using the pharyngeal flap due to a large mucosal defect, which protected the raw surface and promoted mucosal epithelialization.In Type 2, the pharyngeal flap was sewn so that the remaining palatopharyngeal arch was pulled against the posterior wall of the pharynx, and a free flap was placed in the defect on the oral side (Figure 3).In Type 3, the tip of the pharyngeal flap was sewn to the posterior or lateral edge of the remaining palatal defect, and a free flap was placed in the defect on the oral side (Figure 4).In the free flap reconstruction, the vascular pedicle of the skin flap was moved from the retromolar area to the cervical region via the submandibular tunnel and a vascular anastomosis was performed.Postoperatively, a nasogastric tube was inserted for the purpose of wound rest and tube feeding was provided until oral intake could be re-established.Nasopharyngeal airways for maintaining the lateral pharyngeal port were not inserted.

| RESULTS
This study included eight patients, four men and four women, ranging in age from 34 to 72 years (mean age 54.1 years).The primary disease was palate cancer in seven patients and upper gingival cancer in one patient.The tumor histology was adenoid cystic carcinoma in two patients, adenocarcinoma in three patients, squamous cell carcinoma (SCC) in two patients, and mucoepidermoid carcinoma in one patient.Human papillomavirus status was negative for both SCC patients.Five patients underwent primary reconstruction after tumor resection, two underwent secondary reconstruction, and one underwent secondary reconstruction for a soft palate defect after radiation therapy.The types of defects were Type  2).In a patient with a Type 1 defect and partial necrosis of the pharyngeal flap, postoperative scar contracture of the soft palate mucosal defect on the oral side resulted in anterior displacement of the soft palate.However, no VPI occurred because of the placed pharyngeal flap.

| DISCUSSION
The soft palate is composed of several muscles, but the levator veli palatini (LVP) and palatopharyngeus (PP) are largely responsible for velopharyngeal function. 6,7During eating and speaking, these muscles are contracted, and they move backward in the soft palate, separating the velopharyngeal space.Therefore, postoperative function after tumor resection depends on the amount of remaining soft palate muscle.Kuehn et al. divided the soft palate into 10 sagittal segments and histologically examined the distribution of soft palate muscles.They reported that most of the muscle groups that make up the soft palate (including the LVP, PP, and musculus uvulae muscles) develop in the middle third of the soft palate. 8,9Boorman et al. reported that the LVP, corresponding to 40% of the soft palate length, is distributed in the middle of the soft palate. 10In addition, the palatal dimple, which is a mixture of LVP and PP muscle fibers and is considered to be the maximal motor region of the soft palate, is located between the middle and posterior third of the soft palate in normal subjects. 10,11Therefore, we believe that if the soft palate is resected posterior to the midpoint, the residual muscle volume will be markedly reduced, resulting in dysfunction.
Reconstructive techniques for extensive defects of the soft palate have been reported, including simple placement of a skin flap on the oral side, 1 placement of a skin flap on the oral side and a skin graft implanted on the raw surface of the nasal side, 4,12 double-folded radial forearm flap, 3,[13][14][15][16][17][18] local flap with a pharyngeal flap, [19][20][21] pharyngeal flap in combination with a free flap, [22][23][24][25] and dynamic reconstruction using a radial forearm flap. 3,24,26,27The ideal reconstruction of the soft palate is a three-layered reconstruction of the nasal cavity, oral mucosa, and muscularis between them.However, this is difficult to achieve in clinical practice, and reconstruction methods remain subject to debate because of the various types of defects observed after tumor resection.Abbreviations: AC, adenocarcinoma; ACC, adenoid cystic carcinoma; ALT, anterolateral thigh flap; Ca, cancer; HPV, human papillomavirus; MEC, mucoepidermoid carcinoma; Pre-op, preoperative; SCC, squamous cell carcinoma.

| Pharyngeal flap elevation and its effect in soft palate reconstruction
The pharyngeal flap was first described as an inferiorly based flap by Schoenborn in 1875.However, he later modified it to a superiorly based flap because of the short length of the inferiorly based flap and its tendency to contract and pull the soft palate downward. 28As the velopharynx becomes narrower as one proceeds in a cephalad direction and the essential element of a pharyngeal flap is effective obturation, a superiorly based flap should be more effective. 29Therefore, it is now a common practice to treat VPI with a superior-based pharyngeal flap. 30he role of the pharyngeal flap in soft palate reconstruction after head and neck cancer treatment is to line the nasal cavity and narrow the velopharyngeal space.Penfold et al. and Brown et al. reported good postoperative function for extensive full-thickness soft palate defects, including the palatopharyngeal arch, nasal lining by the pharyngeal flap, and oral coverage by the forearm flap. 22,23Following this report, we used a pharyngeal flap for defects involving posterior resection of the soft palate.Although the pharyngeal flap can be used as a nasal liner for small defects of the soft palate, in clinical practice, soft palate defects vary widely, and it is difficult to completely line the nasal side with the pharyngeal flap alone.Therefore, the effect of the pharyngeal flap in soft palate reconstruction is twofold.First, per our classification, in Type 2 defects, it prevents flaring of the velopharyngeal space due to anterior deviation of the remaining palatopharyngeal arch.Second, in Type 1 and 3 defects, it physically narrows the velopharyngeal space.In our experience, the ideal width of a pharyngeal flap is approximately 20-25 mm, which matches that of the posterior pharyngeal wall.Although it is possible to harvest the pharyngeal flap including the lateral wall of the pharynx, it is better to preserve the lateral wall of the pharynx for smooth postoperative nasal breathing and velopharyngeal function.In addition, regarding the length of the pharyngeal flap to be harvested, Type 1 and Type 3 are harvested greater in length, $40 mm, while Type 2 is harvested only long enough to bridge the velopharyngeal space, $25 mm, to minimize donor site morbidity of the posterior pharyngeal wall.When only the soft palate mucosa and muscularis are resected, as is done in Type 1, the soft palate defect is very thin and mobile; therefore, reconstruction with a skin flap and skin grafts is difficult.However, if a defect remains on the raw surface, significant postoperative scar contracture occurs, and velopharyngeal dysfunction is inevitable.Indeed, in our case, the shape of the soft palate was greatly deformed because of scar contracture in an area not covered by the pharyngeal flap.However, VPI did not occur, and video-endoscopy observations showed that the pharyngeal flap bridged the velopharyngeal space, and the lateral pharyngeal port was firmly closed by the movement of the lateral wall during swallowing.Narrowing the velopharyngeal space with a pharyngeal flap can be effective for Type 1 defects, and Gart et al. reported a similar approach for VPI after cleft palate surgery. 31ne concern is that the oral side of the pharyngeal flap remains on the raw surface, which may enlarge the lateral pharyngeal port due to scar contracture.In our study, postoperative video-endoscopy observation of the velopharyngeal space showed no significant constriction of the pharyngeal flap bridging the velopharyngeal space.In all cases, the lateral pharyngeal port was closed with good movement of the lateral pharyngeal wall.Shapiro et al. performed reconstruction in three patients with total soft palate defects using only a pharyngeal flap, leaving the oral side as a raw surface, and reported no postoperative functional problems. 19They also reported that the lateral pharyngeal port can be closed without any problem if the movement of the cephalic wall is normal, and normal speech and swallowing can be maintained. 19Furthermore, according to Trier, as long as the lateral pharyngeal wall motion can provide valving of the ports on either side of the pharyngeal flap, adequate velopharyngeal closure can be readily achieved, provided the velopharyngeal sphincter or sphincters are capable of closure. 29In addition, in the present cohort, age was not considered in the surgical indications, but the mean age of the patients was 54.1 years, which reflects a relatively young age group.Patient age is important for postoperative function, and it is not clear whether similar results would be achieved in older patients.However, this procedure physically narrows the velopharyngeal space using a pharyngeal flap, and if the velopharyngeal space is appropriately narrowed, we believe that postoperative function will be maintained regardless of the age of the patient.

| Flap selection in soft palate reconstruction
In previous reports on soft palate reconstruction, when a skin flap was transferred only to the oral side and the nasal side was left as a raw surface, the flaring velopharyngeal space due to scar contracture in the raw surface area was a problem. 1 Therefore, thin skin flaps, mainly radial forearm flaps, have been used for soft palate reconstruction to provide lining on the oral and nasal sides.However, the radial forearm flap involves sacrifice of the radial artery and requires skin grafting to the donor site, and results in postoperative aesthetic outcomes.In contrast, in soft palate reconstruction using a pharyngeal flap, the velopharyngeal space is physically narrowed by the pharyngeal flap, and the pharyngeal mucosa can be used as a lining on the nasal side.This eliminates the need for lining on the nasal side and simplifies complicated surgical techniques such as a double-folded flap.As a result, relatively thicker skin flaps such as the ALT flap can be selected.The ALT flap, which has a long vascular stem and allows primary closure of the donor site, can be raised as a pure fasciocutaneous flap to reduce donor site morbidity. 32However, whether or not ALT can be used depends on the thickness of the thigh, and if the thickness of the subcutaneous fat exceeds 15 mm, the use of a radial forearm flap must be considered.
This study has a few limitations.First, the number of included patients was small.Palatal tumors in soft palate reconstruction after head and neck cancer treatment are rare; thus, studies published to date have mainly been case reports, and a multicenter study is desirable to ensure a sample size sufficient to draw any conclusions.Second, only one case of radiation therapy was included in our study.Radiation therapy impairs blood flow in the pharyngeal flap and delays wound healing around the reconstructed area and at the site of pharyngeal flap harvesting.In our case, remucosalization of the site of pharyngeal flap harvesting took $3 months.In cases where preoperative radiotherapy was administered, the irradiation field should be confirmed, and postoperative wound complications should be carefully monitored.Third, in this study, the Hirose standard scores and swallowing function were used to assess postoperative function; however, these were subjective findings of the patient and their doctor.To compensate for this, objective imaging evaluations were performed using VF and VE, but a more detailed and objective method of functional assessment is desirable.
In conclusion, we reported functional reconstruction using either a pharyngeal flap alone or a pharyngeal flap and free flap for various types of soft palate defects caused by head and neck cancer treatment.In soft palate reconstruction, we focused on maintaining velopharyngeal function after surgery.By physically narrowing the velopharyngeal space with a pharyngeal flap and closing the velopharyngeal space mainly by movement of the lateral wall of the pharynx, good function was maintained in various types of soft palate defects.Although soft palate defects are relatively rare, and no functional and standardized surgical techniques have been established, we believe that soft palate reconstruction using a pharyngeal flap is a useful technique because it is a relatively simple and reliable technique to narrow the velopharyngeal space.

2 and
Type 3 in three patients each and Type 1 in two patients.The defect sizes ranged from 25 (width) Â 40 (depth) to 40 Â 60 mm.All pharyngeal flaps were harvested at the maximum width of the posterior wall of the pharynx (20-27 mm), and ranged in length from 25 to 40 mm.The free flaps used in Type 2 and Type 3 reconstructions were all anterolateral thigh flaps (ALT), with sizes ranging from 35 Â 55 mm to 70 Â 60 mm.The patient characteristics are summarized inTable1.In oneF I G U R E 2 Reconstruction schematic diagram and case presentation for Type 1. (A) Schematic showing the placement of the transferred tissue during Type 1 (Pt.8) reconstruction.(B) Resection of the mucosa and muscle layers.Extensive partial-thickness defects were observed in the soft palate.(C) A 23 Â 40 mm pharyngeal flap was elevated and moved to the oral side through the slit created in the median soft palate.The pharyngeal flap was sutured to the defect on the oral side, leaving the raw surface of the lateral soft palate.(d) Six months postoperatively, the soft palate is displaced anteriorly due to scar contracture; however, the velopharyngeal space is narrowed by the pharyngeal flap, and there are no functional problems.[Color figure can be viewed at wileyonlinelibrary.com] case of Type 1 reconstruction, partial necrosis of the pharyngeal flap occurred, which was treated conservatively.No other complications, such as infection or fistula formation, were observed.Postoperative oral intake was started 7-15 days (mean 9.5 days) after surgery, and the postoperative hospital stay ranged from 13 to 22 days (mean 16.0 days).Videoendoscopic (VE) and video fluorography (VF) evaluation of swallowing revealed no F I G U R E 4 Reconstruction schematic diagram and case presentation for Type 3. (A) Schematic showing the placement of the transferred tissue during Type 3 (Pt.1) reconstruction.(B) Full-thickness defects of the soft palate including the palatopharyngeal arch.The size of the defect was 30 mm Â 40 mm.(C) The 20 Â 40 mm pharyngeal flap is elevated.(D) The tip of the pharyngeal flap is sutured to the posterior end of the hard palate, and the oral side is covered with an anterolateral thigh flap.[Color figure can be viewed at wileyonlinelibrary.com]F I G U R E 3 Reconstruction schematic diagram and case presentation for Type 2. (A) Schematic showing the placement of the transferred tissue during Type 2 (Pt.2) reconstruction.(B,C) Full-thickness defect from the hard palate to the soft palate after tumor resection (the palatopharyngeal arch remains).The size of the defect was 40 mm Â 60 mm.(D) A 25 Â 30 mm pharyngeal flap is elevated and sutured to the edge of the remaining palatopharyngeal arch, and the oral side is covered with an anterolateral thigh flap.[Color figure can be viewed at wileyonlinelibrary.com] regurgitation into the nasal cavity during swallowing in any patient, and good velopharyngeal function was maintained.Postoperative VE and VF findings for each type are shown in Videos S1, S2, and S3.All patients scored 10 points on the Hirose standard and had excellent swallowing function (Table

T A B L E 1
Patient characteristics.
T A B L E 2 Summary of functional results.