Surgical Treatment of Primary Parapharyngeal Space Tumors: A Single-Institution Review of 28 Cases

Surgical Treatment of Primary Parapharyngeal Space Tumors: A Single-Institution Review of 28 Cases Haoliang Chen, MDS,* Guowen Sun, DDS, MD, PhD,y Enyi Tang, MDS,z and Qingang Hu, DDS, MD, PhDx Purpose:

This study evaluated the surgical treatment of tumors arising from the parapharyngeal space (PPS) in a single-center setting.

Materials and Methods:

This retrospective study was conducted with 28 patients who underwent surgery for primary PPS tumors from 2011 to 2018. Patient clinical features, histologic tumor type, surgical approach, complications, and follow-up data were evaluated.

Results:

All patients underwent surgery in this series. The transmandibular approach was most frequently performed (35.7%), followed by the transcervical (28.6%), transparotid (17.9%), and transoral (17.9%) approaches. A surgical navigation system was applied to the surgery of 4 cases with superior PPS tumors. The mean surgical duration of these cases (205.0 minutes) was shorter than that of cases without surgical navigation, and the mean maximum size (MMS) of tumors (5.8 cm) was larger (P < .01). Eleven different tumor types were diagnosed after surgery (78.6% benign and 21.4% malignant). For postoperative complications, there were 10 cases of lower lip numbness, 4 of facial nerve dysfunction, 2 of trismus, and 1 each for the remaining types. During 4- to 81-month follow-up, 27 patients had no recurrence, metastasis, or death and 1 patient was lost to follow-up.

Conclusion:

The histopathologic diagnoses were consistent with those of previous reports. Surgical resection is the main treatment for PPS tumors, with relatively low rates of recurrence and death. For superior PPS tumors, the surgical navigation system can substantially shorten the operative duration and is more suitable for larger tumors. Ó 2019 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 77:1520.e1-1520.e16, 2019

The parapharyngeal space (PPS) is a potential neck compartment in the lateral pharyngeal region. It is described as an inverted pyramid, with the floor of the pyramid at the skull base and the apex at the level of the greater cornu of the hyoid bone.1 A wide spectrum of lesions can arise from this region. PPS tumors are rare, comprising only 0.5 to 1.5% of neoplasms in the head and neck.2-5 Of these tumors,

approximately 80% are benign and 20% are malignant. The most common benign neoplasms are salivary pleomorphic adenomas, followed by paragangliomas and neurogenic tumors. Salivary gland neoplasms are the most common primary malignant tumor.2-6 Thus far, surgical management is still the most critical treatment of PPS tumors.2,3,5,7 Various

Received from Department of Oral and Maxillofacial Surgery,

pital, Medical School of Nanjing University, 30 Zhongyang Road,

Nanjing Stomatological Hospital, Medical School of Nanjing

Nanjing 210008, People’s Republic of China; e-mail: guowensun@

University, Nanjing, China.

yahoo.com

*Resident.

Received October 29 2018

yAssociate Professor. zProfessor and Department Head.

Ó 2019 American Association of Oral and Maxillofacial Surgeons

xProfessor.

0278-2391/19/30258-7

Conflict of Interest Disclosures: None of the authors have any

https://doi.org/10.1016/j.joms.2019.03.001

Accepted March 3 2019

relevant financial relationship(s) with a commercial interest. Address correspondence and reprint requests to Dr Sun: Department of Oral and Maxillofacial Surgery, Nanjing Stomatological Hos-

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surgical approaches have been proposed: transcervical, transparotid, transmandibular, and transoral approaches—separately or combined for more exposure and resection of PPS tumors—with the assistance of an endoscope or a robot.8,9 However, because of the complex anatomic features of the PPS and diverse characteristics of primary PPS tumors, it is still a challenge for head and neck surgeons to treat these lesions, especially superior PPS tumors.2,10 The superior portion of the PPS is extremely close to the skull base. Surgery in this area is particularly difficult because of the narrow surgical field and anatomic complexity. The surgical navigation system has been widely used in maxillofacial operations and has been proved as an effective adjunct to maxillofacial surgery.11,12 It can provide surgeons with precise planning and realtime intraoperative navigation (and reliable ways to avoid vital structures). However, there is little information about its application in PPS tumor surgery. The aim of this study was to examine and analyze the clinical data of patients treated for PPS tumors in the authors’ hospital. In addition, the authors assessed a case series of 4 patients with superior PPS tumors who underwent surgical resection under navigational guidance to evaluate the safety and efficacy of intraoperative navigation.

Materials and Methods This retrospective study included 28 patients with PPS tumors who were treated from November 2011 to June 2018 at the Nanjing Stomatological Hospital of the Medical School of Nanjing University (Nanjing, China). All patients who underwent surgical treatment were enrolled in this study. Tumors originating from the deep lobe of the parotid gland were included only when fully located in the PPS. Patients with metastatic neoplasms and tumors originating from other regions involving the PPS were excluded. This study was approved by the ethics committee of the Nanjing Stomatological Hospital of the Medical School of Nanjing University. All patients’ medical records were retrospectively evaluated for demographics, clinical features, characteristics of the PPS mass, histologic diagnosis, surgical approaches, complications, and outcomes. In addition to routine preoperative examinations, including electrocardiography, chest radiography, and hematologic laboratory examination, computed tomographic (CT) or magnetic resonance imaging (MRI) scans were used to confirm the location and size of the tumor as a preoperative diagnosis. In particular, the following aspects were evaluated: tumor shape, tumor margin,

and the association of tumor location with the major vasculature and surrounding tissue. According to the classification proposed in previous studies,10,13,14 the PPS was divided into 3 portions: superior (between the skull base and the line joining the inferior borders of the lateral pterygoid muscle), middle (between the line joining the inferior borders of the lateral pterygoid muscles and the line joining the mandibular angle), and inferior (between the line joining the inferior borders of the mandibular angle and the plane of the hyoid). Then, the tumor’s vertical position in each case was noted on the coronal view of preoperative CT or MRI scans. The surgical approach was determined by the tumor’s location, its dimensions, its relation to surrounding anatomic structures (carotid artery, jugular vein, cranial nerves), and the degree of suspicion of malignancy. The surgical navigation system (AccuNavi-A, Shanghai, China) was applied in 4 cases to explore the safety and efficacy of surgical navigation technology in the treatment of tumors involving the superior part of the PPS. CT scan data of the 4 cases, including tumors, skull base, and surrounding soft tissue, were uploaded into the Windows-based computer workstation of the AccuNavi-A system. Then, surgeons performed preoperative planning and simulated surgery using the software. To achieve intraoperative navigation, the digital reference frame, as a coordinate to mark the position of the patient, was fixed rigidly to the patient’s forehead to reflect the infrared light of the camera. The patient and the reconstructed CT images were matched with the reference points, including the skull bony landmarks and tooth cusps.15,16 The pointing device was used to pinpoint the reference points twice to make sure the patient and the virtual images were accurately matched. The pointing device was visible on the computer screen in real time. Anatomic landmarks were pinpointed intraoperatively to constantly judge the distance between the resection margins and the skull base. Follow-up data were obtained through personal interviews, examinations, and telephone conversations with patients or family members. SPSS 18.0 (SPSS Inc, Chicago, IL) was used for data analysis to describe and analyze the clinical features, diagnoses, surgical approaches, and treatment outcomes of patients with PPS tumors.

Results CLINICAL SYMPTOMS

Twenty-eight patients (11 men and 17 women) with PPS masses were included in this series. Mean age at the time of surgery was 53 years (range, 23 to 79 years).

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Table 1. INCIDENCE AND FREQUENCY OF CLINICAL SYMPTOMS

Clinical Symptoms

n

%

Pain Foreign body sensation of pharynx Dysphagia Unilateral facial weakness Dyspnea Blurred vision Numbness Headache Dizziness Asymptomatic

9 6 3 3 2 2 1 1 1 10

23.7 15.8 7.9 7.9 5.3 5.3 2.6 2.6 2.6 26.3

Note: One patient could have at least 1 of these symptoms. Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

The average time from onset to treatment was 18.2 months (range, 2 days to 20 years). The main clinical symptoms and signs of patients are presented in Tables 1 and 2, respectively. The most common symptoms were pain (23.7%), followed by foreign body sensation (15.8%) and dysphagia (7.9%), and the most frequent clinical signs were neck mass (59.2%), followed by oropharyngeal mass (8.7%) and parotid mass (3.9%).

IMAGING EXAMINATION

Preoperative CT or MRI images were used to evaluate the location of each tumor. All cases were divided into 3 groups based on the vertical location of the tumor in the coronal plane (superior, middle, and inferior PPS tumors) according to the classification proposed by Prasad et al.13 Tumors were located in the inferior part of the PPS in 14 cases, the middle part in 4 cases, and the superior part in 10 cases. The size of each tumor was measured on CT or MRI images. The mean of maximum size (MMS) of all 28

Table 2. INCIDENCE AND FREQUENCY OF CLINICAL SIGNS

Clinical Signs

n

%

Oropharyngeal mass Parotid mass Neck mass Hemiprosoplegia

16 6 5 3

53.3 20.0 16.7 10.0

Note: One patient could have at least 1 of these signs. Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

tumors was 4.29 cm. The MMSs of tumors in the 3 parts were 3.28, 5.43, and 5.24 cm, respectively. HISTOPATHOLOGIC DIAGNOSES

All tumors were submitted for histopathologic examination after surgery. The results are presented in Table 3. In this series, 11 different tumor types were diagnosed, including 6 benign tumor types and 5 malignant tumor types. Overall frequencies of benign and malignant tumors were 78.6 and 21.4%, respectively, which are in accordance with previous reports.2-4,7,17 Of the 22 cases with benign tumors, the most frequent type was pleomorphic adenoma (35.6%), which also was the most common type of salivary gland tumor (57.2%). Schwannoma was the only neurogenic tumor type observed in this series (21.4%). For the 6 cases with malignant tumors, the most frequent type was mucoepidermoid carcinoma (10.7%). SURGICAL APPROACHES

Tumor resection was performed in all cases. The transmandibular approach (35.7%) was applied most frequently in this series, followed by the transcervical approach (28.6%). The surgical approaches and MMSs of tumors are presented in Table 4. Of the 10 tumors in the superior part of the PPS, 6 were resected by mandibulotomy. The transoral approach was used in the 5 cases with lesions located in the inferior part of the PPS. The specific association between surgical approach and the vertical position of the tumor is presented in Figure 1.

Table 3. HISTOPATHOLOGIC DIAGNOSES

Histopathologic Type

n

%

Salivary gland tumors Pleomorphic adenoma Basal cell adenoma Mucoepidermoid carcinoma Carcinoma ex pleomorphic adenoma Adenoid cystic carcinoma Neurogenic tumors Schwannoma Miscellaneous lesions Vascular malformation (hemangioma) Solitary fibrous tumor Low differentiated carcinoma Branchial cyst Lymphnoditis Total

16 10 1 3 1 1 6 6 6 2 1 1 1 1 28

57.2 35.6 3.6 10.8 3.6 3.6 21.4 21.4 21.4 7.1 3.6 3.6 3.6 3.6 100

Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

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Table 4. SURGICAL APPROACHES AND TUMOR SIZE

Surgical Approach Transoral Transcervical Transparotid Transmandibular Total

n 5 8 5 10 28

%

Table 5. SURGICAL DURATION AND TUMOR SIZE IN SUPERIOR PARAPHARYNGEAL SPACE TUMORS

MMS (cm)

17.9 28.6 17.9 35.7 100

2.6 3.5 5.2 5.3 4.2

Time MMS (cm) (minutes) P Value

Surgical Approach

n

Intraoperative navigation No navigation Total

4

5.8

205.0

6 10

4.9 5.4

237.2 323.6

<.01

Abbreviation: MMS, mean of maximum tumor size. Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

The transcervical approach was the most common approach used in cases with neurogenic tumors. In the group of salivary gland tumor cases, the transmandibular approach was used most frequently, followed by the transcervical and transparotid approaches. During the operation of salivary gland tumors, the facial nerve and its branches were carefully identified, elevated, and preserved, especially the marginal mandibular branch. Most benign tumors were excised en bloc to avoid tumor spillage. For malignant tumors, the surgical margin was expanded as wide as possible because of carcinoma invasion. For example, in the case of low differentiated carcinoma, the facial nerve, total parotid lobe, and affected side of the mandible were sacrificed to prevent tumor recurrence. In addition to the common approaches, the surgical navigation system was applied in the surgery of 4 patients whose tumors were in the superior part of the PPS. The technical precision of the system was approximately 1.0 mm. During the operation, agreement between the surgical results and the preoperative plans was constantly checked. Surgeons could identify the vital landmarks near the skull

Abbreviation: MMS, mean of maximum tumor size. Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

base region and recognize the relation between tumors and the surrounding anatomic structures under the guidance of real-time navigation. Of the 10 cases with superior PPS tumors, the mean surgical duration and MMS of tumors were 237.2 minutes and 4.9 cm for cases without navigation guidance versus 205.0 minutes and 5.8 cm in the intraoperative realtime navigation group. Statistical analysis results are presented in Table 5. POSTOPERATIVE COMPLICATIONS

Complications caused by surgical treatment were found in 19 patients. Table 6 presents a summary of the main postoperative complications observed in this series. Lower lip numbness was observed in 10 cases because of the mandibulotomy. Four cases were complicated by facial nerve palsy, which was the most frequent complication encountered in cases using the transparotid approach. The facial nerve function of all these patients recovered to normal after 3 to 6 months of follow-up. Trismus was observed in 2 patients (1 with mucoepidermoid carcinoma and 1 with solitary fibrous tumor), but their symptoms were relieved after postoperative functional training within 1 year at most. One patient with carotid mixed

Table 6. INCIDENCE OF POSTOPERATIVE COMPLICATIONS

Symptoms

n

%

Numbness of lower lip Facial nerve palsy Trismus Hemorrhage Cerebral infarction Pneumonia

10 4 2 1 1 1

52.6 21.1 10.5 5.3 5.3 5.3

FIGURE 1. Surgical approach and vertical position of tumor.

Note: One patient could have at least 1 of these symptoms.

Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

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FIGURE 2. A, B, Preoperative physical examination showed no neck swelling or mass. C, Preoperative axial computed tomogram of branchial cyst (arrow). (Fig 2 continued on next page.) Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

hemangioma developed cerebral infarction and pneumonia after the surgery. The patient’s internal carotid was tightly adhered to by the lesion and could not be anastomosed or grafted by the vascular surgeons. In addition, the case of another patient with schwannoma was complicated by hemorrhage caused by a carotid cavernous fistula that developed 11 days after the surgery. FOLLOW-UP DATA

Of the 22 patients in the benign tumor group, only the patient with postoperative cerebral infarction and pneumonia underwent further treatment postoperatively. One patient was lost to follow-up. The remaining 21 patients were followed for 4 to 81 months, with no recurrence. In the malignant tu-

mor group, 1 patient with low differentiated carcinoma underwent postoperative chemoradiotherapy in the oncology department. One patient with adenoid cystic carcinoma was advised to receive postoperative treatment, but refused. Fortunately, no recurrence and metastasis were observed in all patients during the 14to 77-month follow-up.

Report of Cases CASE 1

A 61-year-old man complained of left-sided pharyngeal pain. CT scan visualized a low-density cystic mass 6.5 cm in maximum diameter extending to the superior portion of the PPS. Because this tumor was very large and its position was very high, en bloc

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FIGURE 2 (cont’d). D, Preoperative sagittal computed tomogram showed the mass (arrow) in the superior part of the parapharyngeal space and extending to the skull base. (Fig 2 continued on next page.) Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

removal without mandibulotomy was unrealistic. Therefore, a transmandibular approach was selected for this tumor. The navigation system also was applied during surgery to protect the skull base from injury. This patient had no postoperative complications. The histologic diagnosis was branchial cyst (Fig 2).

CASE 2

A 42-year-old man complained of neck and rightsided pharyngeal swelling. Preoperative CT scan displayed a tumor in the deep portion of the parotid gland extending to the superior portion of the PPS. The maximum size of this tumor was 6.1 cm, so a transmandibular approach was selected to acquire more exposure and direct access. The navigation system was used to recognize the critical landmark of the skull base. This patient had no postoperative complications. The histologic diagnosis was pleomorphic adenoma (Fig 3).

Discussion The PPS is a central region connecting many compartments in the head and neck. It is regarded as a ‘‘danger space’’ because it contains several vital anatomic structures. Traditionally, the PPS has been divided into the prestyloid and post-styloid compartments by the tensor veli palatini muscle and styloid process.1,2,6 The prestyloid space contains the deep parotid lobe and minor salivary glands. The poststyloid space contains cranial nerves IX, X, XI, and XII, the cervical sympathetic chain, the internal jugular vein, the internal carotid artery, and lymph nodes.5 This kind of division is mainly visualized on axial CT or MRI scans. In recent decades, a new compartmentalization of this complex area has been proposed for the selection of appropriate surgical approaches. Shahinian et al,14 Kanzaki and Nameki,10 and Prasad et al13 proposed that the PPS could be divided into 3 compartments based on coronal CT or MRI views. In the present study, cases were divided into superior,

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FIGURE 2 (cont’d). E, Design of operative incision. F, Transmandibular approach was applied to achieve direct access to the lesion (arrow). (Fig 2 continued on next page.) Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

middle, and inferior groups according to this compartmentalization. No matter how this region is divided, the ultimate aim is to determine the optimal surgical approaches based on anatomic and radiographic analyses. To date, there are 5 common approaches to resect PPS tumors: transoral, transcervical, transparotid, infratemporal fossa, and mandibulotomy.2-5,7,17-20 However, radical resection of PPS tumors remains a challenge

for surgeons because the surgical field is narrow and close to vital structures. There is still no expert consensus on how to optimize the surgical removal of these tumors. The aim of this study was to describe the relation between the location of PPS tumors and the optimum surgical approach for their removal and to share the authors’ experience in the surgery of superior PPS tumors using intraoperative navigation.

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FIGURE 2 (cont’d). G, H, The navigation system was used to detect the superior bound of the lesion and its relation to the skull base. (Fig 2 continued on next page.) Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

In large studies, the transoral approach is usually reserved for small circumscribed tumors.7,19,21 The greatest advantage of this approach is avoidance of surgical scars left on the skin. Nevertheless, this approach has been considered insufficiently safe because of the narrowness of the surgical field, the risk of damaging vital blood vessels, and the potential for incomplete tumor extirpation.7,19 Bozza et al22 proposed that the transoral approach can be used to resect PPS tumors smaller than 3 cm in diam-

eter individually. In their clinic, the authors used this approach to perform intracapsular resection in 5 cases without recurrence. The mean diameter was 2.6 cm, and all were located in the inferior part of the PPS. With the increase of applications of minimally invasive surgical approaches in head and neck surgery, transoral robotic surgery has been successfully performed on PPS tumors.8,9,23 Salivary gland tumors account for 40 to 50% of PPS lesions, and most are located in the prestyloid PPS.5

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FIGURE 2 (cont’d). I, The branchial cyst was completely resected. J, Postoperative axial computed tomogram. K, Postoperative coronal computed tomogram. Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

Therefore, the transparotid approach is a common approach in the operation of PPS tumors. It works well for patients with prestyloid tumors or deep-lobe parotid neoplasms extending into the PPS. To acquire an adequate surgical field, it is necessary to pull up the facial nerve, resect part of the superficial or deep lobe of the parotid, and retract the mandibular angle forward.7 Some reports also have reported that the transparotid approach can be applied to primary tumors arising from the post-styloid space and superior portion of the PPS.7,17,19 This approach was applied to 5 cases, and the MMS of the tumors was 5.2 cm. Of these cases, 3 were in the superior portion. In the authors’ experience, the key to this kind of surgery is protecting the facial nerve and the superficial lobe of the parotid as much as possible. In addition, it can not only decrease the chance of the occurrence of Frey syndrome but also avoid soft tissue collapse of the parotid region after surgery. The transcervical approach is considered the first choice for most PPS tumors. Its advantage is that it

can achieve adequate exposure of the tumors and the vital blood vessels and nerves around them. Thus, it might be indicated for large tumors (benign and malignant), particularly for malignant tumors, whose margins are hard to determine unless visualized or palpated by surgeons.2,7 However, some researchers have debated that this approach is suitable only for benign tumors and a few circumscribed malignant neoplasms, especially those located in the superior part of the PPS, because of obstruction of the mandible. In this series, this approach was performed in 8 cases. One case was situated in the superior part of the PPS, and 7 cases were in the middle or inferior portion of the PPS. The MMS of the tumors was 3.5 cm. The authors consider that the transcervical approach can be applied to almost all benign PPS lesions because of the satisfactory exposure and surgical safety. However, for most malignant tumors, a safe resection margin and prevention of recurrence should take precedence. Therefore, the transmandibular

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FIGURE 3. A, Preoperative physical examination showed neck swelling below the right mandibular angle (arrow). B, Examination of the oral cavity showed right-sided pharyngeal swelling (arrow). (Fig 3 continued on next page.) Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

approach or combined approaches might be more secure. Although there are various types of mandibulotomy, all aim toward a wider surgical vision, more exposure, and greater surgical security. Tandon et al24 suggested that the transmandibular approach should be considered for selected patients, including those with tumors larger than 8 cm in diameter, lesions invading the skull base region, or neoplasms squeezing the internal carotid artery inside. There also are suggestions that mandibulotomy is unnecessary for tumors smaller than 4 cm in diameter. In the present retrospective study, the transmandibular approach was applied in 10 cases in which the MMS

was 5.3 cm. Six were in the superior part of the PPS. One patient with low differentiated carcinoma underwent partial mandibulectomy because of extensive infiltration. In addition to these approaches, various modified surgical approaches have been proposed in recent years.13,25,26 Whatever approach is chosen, the focus is always the same, namely identification and exposure of the lesions, complete resection, recurrence prevention, protection of vital blood vessels and nerves, and minimization of functional and esthetic damage caused by surgery. For these reasons, the authors advocate using the surgical navigation system in surgeries of superior PPS tumors.

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FIGURE 3 (cont’d). C, Preoperative axial computed tomogram of pleomorphic adenoma (arrow). D, Preoperative coronal computed tomogram of tumor (arrow) showed the lesion extending to the skull base and leading to bone absorption of the pterygoid process. (Fig 3 continued on next page.) Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

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FIGURE 3 (cont’d). E, Design of operative incision. F, Intraoperative image of removal through a transmandibular approach. (Fig 3 continued on next page.) Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

Surgical navigation systems have been widely used in maxillofacial surgeries for decades, such as resecting ankylosis in bony ankylosis of the temporomandibular joint, osseous tumor resection, fracture reduction, and removal of a foreign body.11,12 However, there is currently little information about its application in the surgical treatment of PPS tumors, especially those in the superior part of the region. In this region, surgery becomes extremely difficult because of the lack of anatomic landmarks and narrow surgical field.27 For some large superior PPS tumors, the skull base can be invaded. Therefore, it has a high risk of nerve, blood vessel, and skull base injuries, leading to cranial nerve damage, severe bleeding, dura

mater exposure, and possibly death. How to resect this kind of tumor safely and accurately depends mainly on the surgeons’ personal experience. However, the computer-assisted navigation system based on CT scan provides the surgeon with precise planning and intraoperative guidance, and most important is that the system can keep the image in good agreement with the anatomic structures in real time.15,28 In this series, there were 10 cases of superior PPS lesions. The surgical navigation system was used in 4. The mean surgical duration and MMS with the common approaches were 237.2 minutes and 4.9 cm versus 205.0 minutes and 5.8 cm in the group that received intraoperative navigation. This result

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FIGURE 3 (cont’d). G, H, The navigation system was used to detect the superior bound of the lesion and identify key anatomic landmarks on the skull base. I, Rigid internal fixation of mandibular angle. J, The pleomorphic adenoma was completely resected. (Fig 3 continued on next page.) Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

indicated that when treating superior PPS tumors, the surgical navigation system could be an effective adjunct to the surgery of larger tumors. It also can substantially shorten the operative duration and might be more suitable for larger tumors. During the course of an operation, surgeons could identify vital anatomic structures based on updated information constantly provided by the navigation system about the location of surgical instruments and make sure that the surgical outcome was in agreement with the preoperative planning. The authors’ experience was that, for most superior PPS tumors, the radical resection could be completed by the transcer-

vical or transparotid approach or their combination under the guidance of the navigation system. Moreover, surgeons could add modified adjuvant incisions as needed instead of sacrificing more of the parotid to achieve more exposure. This procedure could lower the risk of salivary fistula and facial paralysis. For lesions involving the skull base region, particularly those with large volume, long vertical length, and high position, the navigation system could actually offer surgeons exact preoperative planning and instant intraoperative 3-dimensional visualization of a tumor’s position, which could help surgeons determine the distance between the lesion and the skull base. It

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FIGURE 3 (cont’d). K, Postoperative axial computed tomogram. Tumor was completely removed (arrow). (Fig 3 continued on next page.) Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

also could assist surgeons in more accurately recognizing the anatomic landmarks around the lesions. It functions like another pair of eyes for surgeons. Thus, surgeons could be more confident in distinguishing a tumor from the surrounding normal structures. The operation can be carried out smoothly and safely. In consequence, the optimum surgical approach will be determined more easily, the difficulty of the surgery will be decreased, the operative duration will be relatively shortened, and, most importantly, surgical injury will be minimized.12,15,28 Despite the many advantages described earlier, some disadvantages remain. For example, the navigation system was expensive and additional time was required for the preoperative planning and simulated operation (approximately 20 to 30 minutes).16 In addition, a professionally trained person is needed to oper-

ate the workstation computer during surgery.29 Moreover, because of the fantastic flexibility of the soft tissue and the characteristic of CT scans, the real position of the soft tissue might deviate from its original position during surgery, which could lead to a measuring error in the intraoperative navigation. Some researchers have reported that MRI-based intraoperative navigation could calibrate the system to avoid this kind of error. However, this technique has not been widely promoted because of its high costs and difficulty for users. In the present study, the navigation system was used in only 4 superior PPS tumor cases. More research is needed to verify the use of this technology in the surgery of PPS tumors. In conclusion, PPS tumors are rare and have atypical clinical manifestations and diverse pathologic types. Surgery is the main treatment for PPS tumors. The

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FIGURE 3 (cont’d). L, Postoperative coronal computed tomogram. Tumor was completely removed (arrow). Chen et al. Surgery for Primary Parapharyngeal Space Tumor. J Oral Maxillofac Surg 2019.

tumor’s histology, size, and anatomic location, which are important factors in the determination of the appropriate surgical approach, should be considered before the surgery. The intraoperative navigation system showed valuable advantages in the surgery of large superior PPS lesions. It could offer surgeons assistance in recognizing the tumor’s location and its relation to the skull base, optimizing the selection of a surgical approach, and avoiding undesired injury of vital anatomic structures. In addition, the application of surgical navigation could shorten the surgical time.

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