Keywords
carotid endarterectomy - mandibular sagittal split osteotomy - mandibular subluxation - neck tumors - split osteotomy - upper neck region
Introduction
The management of difficult-to-access tumors in the upper neck region that extend to the external skull base, along with pathologies of the distal internal carotid artery (ICA), poses a significant challenge for surgeons dealing with this pathology. Despite advancements in endovascular surgery and radiosurgery, there is still a pertinent need to develop and explore combined and extended direct approaches for addressing the pathology of the upper third of the neck. This area of interest attracts the attention of various surgical specialties, including vascular surgeons, neurosurgeons, maxillofacial surgeons, and head and neck surgeons.
Accessing this type of pathology is challenging due to the anatomical position of the mandibular angle and its ramus, which serve as the bony “gateway” to the neurovascular bundle of the lateral neck region. Various techniques have been employed to open this “gateway.” These include the use of endoscopic techniques to create a “tunnel access” without compromising the integrity of the bone structures,[1]
[2] as well as the formation of subplatysmal flaps.[3] Additionally, the method of mandibular subluxation, involving anterior movement of the mandible without bone structure damage, has been extensively utilized for a certain period of time.[4]
[5]
The most invasive yet effective approaches for creating a wide surgical corridor involve mandibular osteotomy. Several methods have been proposed and utilized, including double osteotomy of the mandible with superior and anterior fragment removal,[6] lateral osteotomy with bone fragment subluxation,[6] vertical osteotomy of the mandibular ramus with anterior transposition of the temporomandibular joint (TMJ),[7]
[8]
[9] and median osteotomy with anterior half-mandibular subluxation.[10] These osteotomy techniques are typically performed through the extraoral approach, which presents a higher risk of wound contamination with oral flora. Vertical osteotomies may carry a risk of postoperative malocclusion, and there is a potential for trauma to the marginal branch of the facial nerve and the inferior alveolar nerve in certain cases.
Intraoral mandibular sagittal split osteotomy (MSSO) was first proposed by Trauner and Obwegeser in 1957. In our practice, we have begun to utilize this type of osteotomy as part of the approach to complex neck pathology. Presently, MSSO is commonly employed in maxillofacial orthognathic surgery and has demonstrated reliability with minimal risk of complications.
Materials and Methods
The objective of this study is to assess the effectiveness of a multidisciplinary approach involving neurosurgeons and maxillofacial surgeons, along with the utilization of intraoral MSSO, for the management of carotid artery pathology and accompanying tumors located in the upper third of the neck.
A retrospective analysis was conducted at Moscow State Medical University named after A.I. Evdokimov, Moscow, of patients who underwent intraoral MSSO for surgical treatment of benign neck tumors and distal ICA pathologies between 2020 and 2022. Prior to MSSO, all patients underwent contrast-enhanced MRI and MRI angiography or CT angiography to determine the indications for surgery, plan tumor resection, and evaluate the location of the common carotid artery (CCA) bifurcation and carotid endarterectomy (CEA) plaque. The primary indication for MSSO was tumor positioning above Blaisdell's line (a line connecting the angle of the mandible with the tip of the mastoid process) or the presence of an atherosclerotic plaque in the ICA above the lower border of the C2 vertebra ([Fig. 1A]). Prior to surgery, all patients underwent orthopantomography and/or CT scans to assess and identify contraindications to MSSO. The contraindications included mandibular tumors, dystopia of the third mandibular molar, and acute inflammatory changes.
Fig. 1 (A) Topographic and anatomical location of the Blaisdell line. Technique for performing intercortical osteotomy: (B, C) the stage of splitting, (D) moving the part mandible, and (E, F) temporary fixation with screws.
In order to evaluate the anterior abduction of the mandible prior to and following osteotomy, the projection of the posterior edge of the mandibular ramus onto the skin was determined. The measurement ML, representing the distance above the lower edge of the mandible by 2 cm, was recorded as the distance between the posterior edge of the ramus before and after osteotomy ([Fig. 2]).
Fig. 2 Intraoperative photographs. Radiography of the mandible in the lateral projection (A) before and (B) after osteotomy (arrows indicate the projection of the angle of the mandible). (C, D) Intraoperative marking: 1, line of skin incision; 2, projection of the ramus to the abduction of the mandible; 3, projection of the ramus after mandible abduction; 4, tip of the mastoid process; 5, angle of the mandible.
During the surgery, intraoperative measurements of the width of the surgical approach were obtained based on the anatomical landmarks in the surgical wound after the performance of the osteotomy. The measurement MM, representing the distance from the tip of the mastoid process to the angle of the mandible, was taken into consideration. An analysis of early postoperative outcomes was conducted at 14 days following the surgery, and follow-up examination after 3 and 6 months.
Surgical Technique
The MSSO was performed following the standard Obwegeser–Dal Pont technique ([Fig. 1B]). An incision was made in the mucous membrane in the retromolar region, extending along the transitional fold to the premolars of the mandible. The vestibular side of the mandibular ramus, the body of the mandible, and subsequently the oral surface of the mandibular ramus were sequentially exposed. The mandibular foramen, along with the neurovascular bundle entering it, was visualized. The cortical layer above the mandibular foramen was cut using a reciprocating saw or a piezo instrument. The cortical plate was then incised along the external edge of the mandibular ramus, following an oblique line that extended between the sixth and seventh molars. The incision then proceeded perpendicularly downward toward the lower surface of the mandible. The mandibular mobilized fragment was carefully split, ensuring the protection of the mandibular nerve to prevent any potential damage ([Fig. 3A]). Subsequently, the mobilized fragment of the mandible was moved anteriorly as far as possible and temporarily fixed in their new position with a screw to the body of the mandible ([Fig. 3B, C]).
Fig. 3 Intraoperative photographs of the stages of intercortical osteotomy. (A) Splitting of the mandible after osteotomy. (B) Mobilization of the osteotomized fragment. (C) Temporary fixation of anteriorly displaced fragment. (D) Final fixation with a titanium plate.
The second stage involved accessing the neck pathology. Intraoperative ultrasound was used to determine the level of CCA bifurcation. For CEA, an incision was made along the anterior edge of the sternocleidomastoid line, specifically in the projection of the CCA bifurcation. In tumor cases, a skin incision was made along the natural folds in an oblique anteroposterior direction, 1.5 cm below the lower border of the mandible, extending toward the mastoid process. Soft tissue dissection was then performed including carotid sheath opening, sequentially dissecting and exposing the internal jugular vein, facial vein, ICA, external carotid artery, as well as the vagus and hypoglossal nerves. From the CCA bifurcation to the skull base, the ICA and its branches were dissected while visualizing and separating the tumor from all vascular and neural structures. To expose the distal ICA, it is necessary to find and divide the posterior belly of the digastric muscle, the stylohyoid muscle, and open styloid diaphragm. In cases of tumor invasion of vascular and neural structures, the affected areas were resected and primary vascular prostheses or neural plastic surgery was performed. Ligating and transecting the occipital artery, as well as suturing and securing the stylohyoid muscle and posterior belly of the digastric muscle, were commonly performed before wound closure. After tumor removal, a meticulous revision and hemostasis were conducted.
Subsequently, utilizing the intraoral technique, the dentitions were evaluated to ensure their proper alignment and fixed in place with ligatures. The osteotomized fragments were then assessed along the incision line and fixed using titanium plates while simultaneously checking the jaw occlusion ([Fig. 3D]). If necessary, a drainage system was placed in the wound. Postoperatively, X-ray imaging was performed to confirm proper bone fixation and stability.
Statistical Analysis
Calculations of means and standard deviations, as well as absolute and relative frequencies for quantitative traits, were performed. The analysis was conducted in Excel (Microsoft Office).
Results
Among the 12 patients who underwent MSSO between 2020 and 2022 ([Table 1]), 11 had benign tumors and 1 had a high bifurcation of the CCA with ICA stenosis. The majority of the study group consisted of women (n = 9, 75%) with a mean age of 51.2 ± 12.4 years. The predominant complaints included neck swelling and a sensation of a foreign body, reported by 41.7% of patients (n = 5). Most of the tumors exhibited slow growth, and 83% of patients did not present with neurological symptoms. Only two patients experienced dysphonia and dysphagia. Objective clinical signs of genetic diseases such as von Hippel-Lindau and type 1 neurofibromatosis were not detected upon examination. One patient with atherosclerotic pathology of the distal ICA had symptomatic right ICA stenosis of 85% and had experienced an ipsilateral stroke 4 months prior to admission.
Table 1
General characteristics of the study group
|
Group characteristics
|
Index
|
|
Average age (y)
|
51.2 ± 12.4
|
|
Sex (F/M)
|
9/3
|
|
Tumor/ICA stenosis
|
11/1
|
|
Neurological status was normal before surgery
|
10/12 (83.3%)
|
|
Jaw abduction (mm)—ML
|
17.2 ± 1.6
|
|
Width of the surgical approach (mm)—MM
|
48.7 ± 3.5
|
|
Total removal of the lesion
|
9/11 (82%)
|
Abbreviations: ML, mandible luxation; MM, mandible mastoid.
To prevent the communication of wound cavities, all osteotomies were carried out exclusively through an intraoral approach. The mandibular osteotomy on the affected side enabled an average anterior movement of the mandible of 17.2 ± 1.6 mm, as measured by the distance ML ([Fig. 4]).
Fig. 4 Intraoperative photograph. After performing the osteotomy, the mandibular fragments were successfully advanced by an average of 16 mm.
The average duration of the osteotomy procedure was 23 ± 5.2 minutes. The width of the surgical approach, denoted by the distance between the tip of the mastoid process and the anteriorly displaced angle of the mandible, averaged 48.7 ± 3.5 mm. In all cases, the initial step involved locating and dissecting the internal and external carotid arteries to ensure their protection. The subsequent step involved accessing the tumor through the transection of the stylohyoid and posterior belly of the digastric muscles. Additionally, the occipital artery was transected in 10 cases.
CEA was performed using the eversion method. For schwannomas involving the sympathetic trunk or hypoglossal nerve, the endocapsular removal technique was utilized to decompress the tumor and minimize the risk of neural structure damage.
The histological types of the identified formations included 4 patients with schwannoma (G 1), 2 patients with paraganglioma (G 1), 3 patients with pleomorphic adenoma, and 1 patient with a retention cyst.
Postoperative Complications
Two complications were observed following MSSO, accounting for 18% of cases, during the early postoperative period (within the first 14 days after surgery). These complications included soft tissue hematoma in the buccal and submandibular regions, as well as malocclusion necessitating plate refixation ([Table 2]). Numbness in the area innervated by the inferior alveolar nerve was experienced by all patients during the early postoperative period. This numbness is attributed to the stretching of the nerve during mandible fragment retraction, wherein anatomical preservation of the nerve coincides with temporary dysfunction. Patients were informed of these expected transient consequences prior to surgery. A mechanical injury of the inferior alveolar nerve occurred in one case, directly associated with the procedure-related complications. Nonetheless, single-stage microscopic neurorrhaphy typically results in complete recovery of nerve function. During follow-up after 3 and 6 months, 11 patients had complete recovery of sensitivity, and 1 patient had partial recovery. There were no reports of strokes or deaths among any of the patients.
Table 2
Results of surgical treatment
|
No.
|
Gender, age
|
Complaints
|
Dimensions (mm), type of education
|
Relationship with structures (growth zone)
|
ML (mm)
|
MM (mm)
|
Histology
|
Resection volume
|
Complications of removal
|
Complications of osteotomy
|
|
1
|
F, 33
|
Swelling in the neck
|
18.5 × 15 × 38.5, solid
|
From the sympathetic nerve
|
16
|
46
|
Schwannoma, G1
|
Total
|
No
|
Malocclusion, plate refixation
|
|
2
|
F, 56
|
Swelling in the submandibular region
|
71 × 31 × 21, cystic
|
Submandibular and parotid salivary glands
|
19
|
53
|
Retention cyst of the excretory duct of the large salivary gland
|
Subtotally (multiple cysts with a thin wall)
|
No
|
No
|
|
3
|
F, 48
|
Swelling in the submandibular region
|
31 × 26 × 43, solid
|
Pharyngeal process of the parotid salivary gland
|
15
|
44
|
Pleomorphic adenoma of the salivary gland
|
Total
|
Paresis of the muscles of the lower lip (marginal branch)
|
No
|
|
4
|
F, 61
|
No
|
Cystic solid
|
Pharyngeal process of the parotid salivary gland
|
17
|
49
|
Pleomorphic adenoma of the salivary gland
|
Total
|
No
|
No
|
|
5
|
F, 60
|
No
|
30 × 24 × 18, solid
|
From the vagus nerve
|
15
|
42
|
Paraganglioma, G1
|
Total
|
Dysphonia, paresis affecting the left half of the larynx
|
No
|
|
6
|
F, 55
|
Discomfort when swallowing, decreased visual acuity in the right eye
|
31 × 43 × 24, solid
|
From the sympathetic nerve
|
16
|
45
|
Schwannoma, G1
|
Total
|
Horner's syndrome
|
No
|
|
7
|
F, 30
|
Swelling in the submandibular region
|
34 × 33 × 20, solid
|
Tight connection with the hypoglossal nerve
|
21
|
57
|
Schwannoma, G1
|
Total
|
No
|
No
|
|
8
|
F, 52
|
Pain in the TMJ
|
40 × 23 × 19, solid
|
From the sympathetic nerve
|
17
|
48
|
Schwannoma, G1
|
Total
|
Paresis of the soft palate, Horner's syndrome
|
Soft tissue hematoma
|
|
9
|
F, 33
|
Neck pain when turning head
|
2-sided, 65 × 45 × 38, solid, relapse
|
Carotid body. Overgrown with ICA and cranial nerves IX, X, XI, XII with growth at the skull base
|
17
|
49
|
Paraganglioma, G1
|
Total
|
Thrombosis of the ICA shunt, insufficiency of cranial nerves IX, X, XI, and the XII
|
No
|
|
10
|
M, 64
|
CVA by ischemic type in the basin of the right middle cerebral artery (MCA)
|
Stenosis of the right ICA up to 85%
|
–
|
15
|
46
|
–
|
Total (eversion CEA)
|
Paresis of the hypoglossal nerve
|
No
|
|
11
|
M, 59
|
Swelling in the submandibular region
|
Solid, 41 × 32 × 35 mm
|
Schwannoma of the hypoglossal nerve
|
20
|
55
|
Schwannoma, G1
|
Removal of a component on the neck (stage 1)
|
Paralysis of the hypoglossal nerve, paresis of the facial nerve (traction)
|
No
|
|
12
|
M, 63
|
Swallowing disorder
|
41 × 42 × 37 solid
|
Pharyngeal process of the parotid gland
|
18
|
50
|
Pleomorphic adenoma
|
Total
|
No
|
No
|
Abbreviations: CEA, carotid endarterectomy; ICA. internal carotid artery; TMJ, temporomandibular joint.
Clinical Case
A 63-year-old patient presented with complaints of dysphagia and was admitted to the hospital. An MRI examination revealed a solid parapharyngeal tumor measuring 41 × 42 × 37 mm, exhibiting irregular contours and a cellular structure. Following the MSSO technique described earlier ([Fig. 5C–E]), microsurgical removal of the tumor was successfully performed. The tumor was excised in fragments, preserving healthy tissues, including the pharyngeal process of the parotid salivary gland. The wound drainage was removed on the first postoperative day, and no neurological complications were observed. Postoperative MRI with contrast enhancement displayed no residual tumor fragments ([Fig. 5G, H]). CT data indicated satisfactory fixation of the fragments with a titanium plate ([Fig. 5E]). The patient's hospital stay duration was 5 days.
Fig. 5 Clinical observation no. 1. (A, B) Preoperative MR images; (C) intraoperative photograph showing osteotomy and temporary fixation; (D) intraoperative photograph of the skin incision marked along the natural fold; (E) tumor removal intraoperative photograph; (F) 3D CT reconstruction control of the mandibula; (G, H) Postoperative MR images.
Discussion
The selection of the method for mandibular movement to extend the surgical approach for upper third neck lesions remains individualized and nonstandardized due to the potential risks of complications and the need for collaboration with other specialists. In this study, we have presented one option for addressing this challenge—performing MSSO.
The anatomical topography of the CCA bifurcation can vary significantly, ranging from the level of the C7 vertebra to the C2 vertebra, with the most common projection observed at the C3–C4 level. While a “low” bifurcation may be advantageous for CEA, accessing the upper cranial regions necessitates extensive dissection of cranial nerves and muscles, working in a narrow and deep surgical corridor, and often manipulating the angle of the mandible to achieve anterior retraction.
The definition of CCA bifurcation levels varies in the literature. Some authors describe a position above the level of the C3–C4 vertebrae, where it may be possible to avoid mandibular manipulations and instead utilize subplatysmal flaps to achieve a wider access.[3] Dissecting the digastric muscle and resecting the styloid process are also options for accessing the distal cervical segment of the ICA. However, this approach requires within a narrow and deep surgical corridor. Most authors define a high bifurcation level as being in the projection of the C2 vertebra or above the Blaisdell line, often necessitating various methods of mandibular lateralization to achieve a wide approach.[11]
[12]
Prolonged stenoses of the ICA, even with a normally located CCA bifurcation, can also present challenges and require extended access. Vang and Hans introduced the concept of high plaques, which are located above the lower surface of the C2 vertebra. Their study analyzed 100 patients with high plaques and concluded that the risk of perioperative stroke and mortality after CEA was similar in both high and low plaque groups. However, the risk of permanent cranial nerve injury was higher in the high plaque group following CEA.[13]
In a study by McNamara et al in 2015, the length between the bifurcation and the base of the skull was examined, highlighting a critical segment of ≤5 cm below the mastoid process. The presence of the CCA bifurcation within this segment was considered high, indicating a prediction of technically challenging dissection and endarterectomy.[14] Correct soft tissue dissection using the trans-styloid diaphragm approach including step-by-step exposure of the posterior belly of the digastric muscle, the stylohyoid muscle, and opening styloid diaphragm is necessary for revealing the greater length of the distal ICA.[15]
Based on our empirical findings, we observed that complex dissection within a narrow surgical window typically commence at the level of the C2 vertebra, necessitating the retraction of mandible fragments to expand the surgical corridor.
The intraoral technique of MSSO with mandibular abduction provides a wide surgical approach for addressing tumors and pathologies in the distal sections of the ICA, yielding satisfactory outcomes.
Compared to other mandibular abduction techniques, MSSO offers several advantages. First, it avoids cosmetic defects caused by neck incisions and eliminates the need for tooth extraction. The intraoral approach also minimizes the risk of contamination from oral flora by isolating the surgical cavities. Studies utilizing MSSO have reported lower incidences of damage to the marginal branch of the facial nerve, mental branch, and inferior alveolar nerve, as well as reduced risk of vascular structure injury.[16] Additionally, the favorable configuration of the mandibular fragments allows for reliable osteosynthesis and decreases the risk of disocclusion.[17] The execution time for MSSO is approximately 23 ± 5.2 minutes, considering its versatile and widespread use in maxillofacial surgery. However, there are limitations to MSSO. It provides a smaller surgical approach to the pathology of the upper third of the neck compared to more radical osteotomy techniques through facial access. Nevertheless, our experience shows that for the tumors presented, the surgical access after MSSO was sufficient. MSSO is less invasive than mandibular subluxation and avoids trauma to adjacent neurovascular structures and TMJ dysfunction.
To prevent hematomas and tissue imbibition in the intervention area, it is necessary to monitor the coagulation profile before and after the surgery, especially in patients who are on continuous aspirin therapy. Postoperatively, it is advisable to place a wound drain in the oral cavity for 24 hours in such patients. Additionally, applying skin tapes to all patients for 3 weeks can help prevent edema and blood imbibition of the soft tissues.
To prevent mechanical trauma to the inferior alveolar nerve, it is important to visualize it during osteotomy. To avoid overstretching the nerve and temporary sensory disturbances postsurgery, do not extend the mandibular fragment to its maximum.
There are studies confirming the close location of the marginal branch of the facial nerve to the angle of the mandible.[18] In order to prevent nerve trauma, it is advisable not to use a monopolar coagulator in this area, to perform a wider detachment of the mucous membrane and to control the position of the reciprocal saw.
To improve the alignment of mandibular fragments, the use of two titanium plates is recommended.
Although our study is based on a small patient group, preliminary conclusions can be drawn regarding the advantages and disadvantages of MSSO and its potential for expanding surgical approaches to the upper third neck region. However, to ensure greater reliability, further research with larger patient groups and longer follow-up periods is warranted.
