Abstract
The conventional treatment for benign tumours arising in the submandibular gland (SMG) has always involved whole gland excision with the tumour. In light of developments in parotid gland functional surgery, this prospective study was performed to evaluate the effectiveness and safety of partial sialoadenectomy (PS) for benign tumours in comparison with conventional total sialoadenectomy (TS). Thirty-one consecutive patients with a preoperative diagnosis of benign tumour in the SMG were included in the study from December 2008 to December 2010. Eleven patients were treated with PS and 20 patients underwent conventional TS. Salivary gland function and surgery-related complications were assessed. No difference in resting saliva flow was found between the two groups before the operation, while this was significantly higher in the PS group than in the TS group at 1 year after surgery ( P = 0.009). With regard to complications, there was less deformity in facial appearance in the PS group. There was no recurrence in any of the 31 patients during the follow-up period (range 41–82 months). It is believed that this modification to SMG surgery is consistent with the idea of functional and minimal invasive salivary gland surgery. This technique represents a good choice for the management of benign tumours of the SMG for appropriately selected cases.
Saliva is a very import fluid for oral health. It protects the oral mucosa, prevents dental carries, and maintains the functions of mastication and speech. The submandibular gland (SMG) is mostly responsible for resting salivary flow, accounting for 60–65% of the resting whole saliva. The conventional treatment for benign tumours arising in the SMG has been extirpation of the entire gland along with the tumour. As a result, the affected SMG is lost and the resting saliva decreases.
The partial parotidectomy is well accepted and widely used for the treatment of benign tumours in the superficial parotid gland. Compared with the conventional total superficial parotidectomy, the advantages of the partial superficial parotidectomy include a shorter operation time, reduced facial deformity and incidence of Frey syndrome, and the preservation of most of the gland’s function.
In light of the success of the partial parotidectomy technique, it was hypothesized that a partial sialoadenectomy might be possible for the treatment of benign tumours in the SMG. Normally, retaining the integrity of the vascular and ductal system of the remaining SMG is crucial for a successful treatment outcome. A previous study by this research group on the microanatomy of the human SMG, performed by perfusing methacrylate to form resin casts of the blood vessels and ducts, showed a tree-like structure with structures of blood vessels and ducts similar at each level in the lobules. This characteristic tree-like structure provides a solid anatomical basis for the partial submandibular sialoadenectomy. Moreover, the research groups of Roh and Park and Ruan et al. each reported a series of 20 patients with pleomorphic adenoma in the SMG treated with gland-preserving surgery. The results showed similar advantages to the partial parotidectomy, including preservation of salivation, reduced surgical morbidity and operating time, and good cosmetic appearance, but without compromising local control.
The purposes of this comparative study were to further investigate the feasibility, safety, advantages, indications, and contraindications of the partial sialoadenectomy for the treatment of benign tumours in the SMG.
Patients and methods
This study was approved by the ethics committee for human experiments of Peking University School and Hospital of Stomatology.
Patients
Thirty-one patients with a preoperative diagnosis of benign tumour of the SMG, attending the department of oral and maxillofacial surgery of the study hospital for treatment between December 2008 and December 2010, were included in this study. All patients provided signed informed consent for the operation.
Before surgery, all patients underwent ultrasound or computed tomography (CT) examination. The imaging appearances of the tumours were consistent with benign solid tumours. A preoperative diagnosis of primary benign tumour of the SMG was achieved based on the combination of case history, clinical examination, and imaging evaluation. Any patient with signs of malignancy or a cyst was excluded from the study.
CT scan
CT scans were performed using an 8-slice scanner (BrightSpeed; GE Medical Systems Waukesha, Wisconsin, USA) with patients in the supine position and the canthomeatal line perpendicular to the floor. The CT scans were carried out with a rotation time of 1 s, pitch of 1.375:1, collimation of 1.25 mm, voltage of 120 kV to 140 kV, and automatic exposure control. Axial images of the parotid and SMGs with a slice thickness of 1.25 mm were reconstructed using a soft tissue algorithm. The diagnosis of a benign tumour of the SMG was based on the judgement of an experienced radiologist and a maxillofacial surgeon.
Treatment assignment
The patients were divided into two groups based mainly on the location of the tumours, according to their appearance on CT. Patients in whom the tumours were located in the lateral part of the SMG (including superficial, posterior, and deeper, but not anterior) and far away from Wharton’s duct ( Figs 1 and 2a ) were assigned to the partial sialoadenectomy (PS) group. The other cases were assigned to the conventional total sialoadenectomy (TS) group.
Surgical procedures
The transcervical approach was used for all patients. An incision was made in the natural skin crease overlying the SMG, which was 2.5–3.0 cm below the lower border of the mandible.
In the conventional TS group, standard excision of the SMG and tumour was performed as usual. In the PS group, the routine procedure for exposure of the SMG was performed. The facial artery and vein were preserved when the tumour was located in the superficial part of the gland. When the tumour was located in the posterior or the deeper parts of the gland, close to the proximal facial artery and vein, the facial artery and vein were ligated proximally and cut, while the distal facial vessels were carefully preserved. Therefore, the gland was supplied via retrograde flow through the distal facial vessels. The whole tumour was carefully dissected with a safe tumour-free margin of surrounding normal gland tissue of more than 0.5 cm ( Fig. 2 b, d). During dissection of the surrounding normal gland tissues, a lobectomy was performed if possible in order to maintain the relative integrity of the remaining SMG and prevent salivary fistula. Wharton’s duct and the lingual nerve were not exposed.
A frozen section was used to identify the nature of the tumour. During the operation, the tumour and partial SMG tissue or the whole SMG was extirpated as a whole. Investigation of the tumour sample was performed by non-surgical staff on a back table and the entire procedure followed the tumour-free principle. In this way, there was no possibility of tumour capsule rupture and contamination of the surgical bed, thus avoiding tumour seeding. When the frozen section result identified a malignancy, except for malignant lymphoma, the operation would be extended to the removal of the whole SMG. When the frozen section result identified a benign tumour, the operation would be ended with careful enclosure of the surface of the cut gland edge in order to prevent salivary fistula formation postoperatively ( Fig. 2 c).
A drainage rubber or tube was inserted in the surgical bed in all cases after the operation and was removed within 24–48 h postoperative, depending on the amount of exudate from the wound. Complications were evaluated on the first day postoperative and recorded until recovery during follow-up every 3 months.
Collection of whole saliva
Salivary gland function was evaluated by measuring the saliva flow rate before the operation and at 1 year after surgery. Saliva samples were collected at 9:00 to 11:00 a.m., in an air-conditioned room, where the room temperature was kept at 20–24 °C and humidity was kept at 40–70%. Subjects were asked to refrain from eating, drinking, smoking, and brushing their teeth for at least 90 min before collection.
Before collection, the subjects were instructed to rinse their mouths with water and then to rest for 5 min with their eyes open and head tilted slightly forward. By using the spitting method, whole saliva at rest was collected for 5 min into a pre-weighed cup. After 5 min of rest, stimulated whole saliva was collected by smearing 2.5% citric acid solution on the lateral side of the tongue with a swab every 30 s for another 5 min. By defining the specific gravity of saliva as 1 g/ml, flow rates were calculated and recorded in ml/min.
Technetium 99m ( 99m Tc) scintigraphy
Salivary gland function was also evaluated by scintigraphy at 1 year after surgery. 99m Tc scintigraphy using Hawkeye SPECT equipment (Infinia Hawkeye 4, GE Healthcare Waukesha, Wisconsin, USA) was undertaken using a standardized protocol.
The period from stimulation using 2.5% citric acid solution to the minimum value after stimulation within 30 min was considered to be the ‘secretion phase’. The secretion index (SI) was calculated using the following formula: SI = (maximum value before stimulation using citric acid − minimum value after stimulation using citric acid)/(maximum value before stimulation using citric acid − background) × 100%.
Data analyses
SPSS for Windows version 13.0 (SPSS Inc., Chicago, IL, USA) was used for the data analysis. Descriptive data were expressed as the mean ± standard deviation (SD). Fisher’s exact test was used to compare the proportions of complications and Student’s t -test was used to compare the within-group and between-group means. A P -value of less than 0.05 was accepted as statistically significant.
Results
A total of 31 patients were enrolled in the study: the PS group comprised 11 patients, while the conventional TS group comprised 20 patients. The patients’ clinical data are shown in Table 1 . The final diagnosis in all patients was a benign tumour.
| Surgical group | ||
|---|---|---|
| Partial sialoadenectomy | Total sialoadenectomy | |
| Number of patients | 11 | 20 |
| Age, years, mean (range) | 34.8 (17–51) | 56.5 (36–74) |
| Sex | ||
| Male | 4 | 11 |
| Female | 7 | 9 |
| Pathology | ||
| Pleomorphic adenoma | 10 | 18 |
| Basal cell adenoma | 1 | 1 |
| Myoepithelioma | – | 1 |
| Follow-up, months, mean (range) | 67.8 (41–82) | 60.4 (42–80) |
The operations of the 11 patients in the PS group all went smoothly, as designed preoperatively. The frozen section diagnosis of these patients was pleomorphic adenoma in 10 cases and basal cell adenoma in one case. The final diagnosis was confirmed by examination of paraffin-embedded sections.
The whole saliva flow before and after the operation for the two groups of patients are given in Table 2 . There was no difference in the resting saliva flow between the two groups before the operation ( P = 0.798). However, the resting saliva flow rate in the PS group was significantly higher than that in the conventional TS group at 1 year after the operation ( P = 0.009). No difference was found in stimulated saliva flow rate before or after the operation ( P = 0.515, P = 0.187) between the two groups. The postoperative resting saliva flow rate in the TS group was significantly lower than the flow rate preoperative ( P < 0.001).
| Partial sialoadenectomy (PS) | Total sialoadenectomy (TS) | |||
|---|---|---|---|---|
| Preoperative | Postoperative | Preoperative | Postoperative | |
| Resting saliva flow, ml/min | 0.73 ± 0.36 | 0.63 ± 0.30 a | 0.75 ± 0.40 b | 0.39 ± 0.18 a , b |
| Stimulated saliva flow, ml/min | 1.47 ± 0.39 | 1.38 ± 0.47 | 1.43 ± 0.42 | 1.25 ± 0.41 |
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