HOW I DO IT
Keywords: Facial nerve, operation, parotid tumour, superficial parotidectomy
J.R.Coll.Surg.Edinb., 46, February 2001, 104-107
The surgical procedure of superficial parotidectomy is commonly used in the treatment of superficial parotid tumours. It is essential that, where possible, the facial nerve should be preserved, so its identification and careful dissection is of paramount importance.
There are two basic techniques for the identification and dissection of the facial nerve. One is the forward or anterograde dissection, where the approach to the main trunk is taken as an early step, tracing it to the bifurcation and peripheral branches. The other technique is the retrograde dissection, where the peripheral branches are identified first, then proximally to the bifurcation or main trunk. This retrograde dissection of the facial nerve is the more popular in China. In the past 40 years, we have used this technique in around 2000 cases, presenting with superficial parotid tumour, in the Peking University School of Stomatology, with encouraging results.
The indications for superficial parotidectomy are as follows:
Local anaesthesia with 1% Lidocain (containing adrenaline if possible) is satisfactory and used in most cases. Subcutaneous injection of the anaesthetic is administered over the whole operative field. After elevation of the skin flap, anaesthetic is injected into the superficial gland before the gland is incised. In this way the anaesthetic infiltrates the gland evenly without gland spillage as the periparotid fascia forms a snug envelope and encompasses the gland. If the anaesthetic is injected after gland incision, the anaesthetic will spill out of the gland, lessening the anaesthetic effect.
A modified Blair incision is used (Figure 1). The preauricular incision is made in the preauricular crease. The skin flap is raised to the superior, anterior and inferior borders of the gland. There are two techniques that can be utilised to raise the skin flap. One is to raise the flap over the periparotid fascia. The advantage of this technique is less bleeding and a clear operating field. The other technique is to raise the flap under the periparotid fascia. The fascia is included in the skin flap and the gland tissues are exposed. The periparotid fascia can then act as a barrier to the parasympathetic fibres innervating the salivary and sweat glands, thereby, reducing the incidence of Frey’s syndrome. The disadvantage of this technique, however, is more bleeding peri-operatively. The latter may be overcome if the flap is raised by using cutting diathermy. Blunt dissection with a haemostat should be used when the anterior border of the gland is to be exposed because the distal branches of the facial nerve emanate from the gland on to the masseter muscle.
Figure 1: The modified Blair incision
Dissection of the facial nerve and resection of the gland
The posterior branch of the great auricular nerve should be preserved unless the tumour involves the nerve or the nerve adheres to the tumour. The great auricular nerve, therefore, is identified and its posterior branch is preserved before the dissection of the facial nerve is commenced (Figure 2). This approach serves to diminish the loss of sensation to the earlobe.
Figure 2: The posterior branch of great auricular nerve (arrow) is preserved
The procedure of dissection of the facial nerve is the same as that used in the resection of the gland. Stensen’s Duct is used as a landmark for the identification of the buccal branches of the facial nerve. The skin flap is pulled by a retractor to expose the protrusion of the anterior border of the gland, where Stensen’s duct emanates from the gland onto the masseter muscle. The accessory gland may be found superior to the duct (Figure 3). There are two ways of handling the duct. The facial nerve lies across the duct in most cases, and the duct should be preserved during the dissection of the nerve; the duct, however, is ligated and cut if the facial nerve is below the duct. The duct is then traced towards the direction of the mouth in order to remove the remnants.
Figure 3: Relationship among (1) the buccal branch of the facial nerve, (2) the accessory gland and (3) parotid duct
The retromandibular vein is used as a landmark for the identification of the marginal mandibular branch, and the zygomatic arch for the zygomatic branch of the facial nerve.
Once a nerve branch is identified, dissection proceeds using fine-tipped haemostats to create tunnels in the parotid tissue immediately above the nerve. The bridges of parotid tissue over-lying the nerve are gently cut with a size 14 # scalpel. The cutting should stop immediately if suspected nerve or blood vessels are found in the bridges. The dissection should displace the parotid upwards and downwards, and hence, avoiding too deep and narrow tunnelling. Great care should be exercised to avoid inadvertent entry into the tumour during preservation of the facial nerve. As the bifurcation and main trunk of the facial nerve is exposed, the gland is resected at the posterior border. The parotidectomy should be excised with the tumour ‘en bloc’ (Figure 4).
Figure 4: (left) The superficial lobe is removed; (right) The specimen of superficial lobe and tumour
Several points should be emphasised to avoid mechanical damage to the facial nerve:
Preservation of the parotid duct
The parotid duct is resected by the traditional technique of superficial parotidectomy. The parotid remnant atrophies spontaneously. It is reported and found in our own experience, that the facial nerve is above the parotid duct in most cases.2 It is possible, therefore, to preserve the duct during resection of the superficial lobe of the parotid gland. The advantage of this is that the saliva secreted from the parotid remnant will be discharged into the mouth through the duct and partial function of the gland may be preserved. It should be emphasized that the interlobular ducts, encountered during the dissection, should be ligated carefully in order to prevent the establishment of a salivary fistula (Figure 5).
Figure 5: Ligation of interlobular duct
Completion of the procedure
After removal of the superficial parotid gland and the tumour, the cut surface of the parotid remnant should be sutured by absorbable sutures. This achieves haemostasis, and also prevents the development of a salivary fistula. If the duct and function of the parotid remnant are to be preserved, deep sutures should be avoided in order to prevent obstruction of the duct. The wound is irrigated with saline and the integrity of the facial nerve is checked. If the nerve has been disrupted, an end to end anastomosis of the nerve is carried out. Closed suction drainage is advisable, and the suction tube should be placed away from the dissected facial nerve to prevent damage to the nerve. Further anaesthetic is injected into both sides of the incision. The skin flap is replaced; the platysma muscle and subcutaneous tissues are closed with absorbable sutures. Finally, the skin incision is closed using 5-0 non-absorbable sutures.
Closed suction drainage with external pressure by gauge is maintained for 48 or 72 hours and, thereafter, a thin layer of gauze is placed on the wound. The sutures are removed one week after operation.
Facial nerve weakness
Mechanical damage to the facial nerve should be avoided in most cases if the aforementioned procedures are followed. The facial nerve may be compressed by a large tumour, or be in close proximity to a tumour. In these cases, the facial nerve will inevitably be damaged (to a variable degree) if the nerve is peeled from the capsule of the tumour. In general, the function of the damaged facial nerve will recover in three months if the nerve itself is not disrupted. During this period, treatment, including injection of Vitamin B1, B12, and the functional training of facial muscles, may serve to accelerate the recovery of facial nerve weakness.
This is a rare complication. In most cases the secondary bleeding is from the damaged retromandibular vein or its branches. The postoperative swelling of the face will be diminished if the retromandibular vein is preserved. The branches of the vein should be ligated carefully to prevent secondary bleeding. If the retromandibular vein is damaged, the upper and lower ends of the damaged vein should be ligated. If significant secondary bleeding occurs, the wound should be reopened, the haematoma removed, the wound irrigated with saline, the active bleeding point identified and the damaged vein ligated.
Local saliva accumulation or salivary fistula
This is caused by continuous secretion of the parotid remnant and obstruction to the outflow of the secretions. The obstruction of the suction tube may be one of the causes so a regular check of the suction drainage system is necessary. If the drainage tube is obstructed irrigation with saline from the outport of the tube into the wound may clean the blood clots obstructing the holes of the inner tube. Suction is then reconnected and checked for flow. Should there be a large collection of saliva in the wound it can be eliminated by aspiration with a syringe and the wound is then compressed with gauze. Spicy and acidic foods should be avoided. Administration of atropine, 0.3 mg three times a day, is suggested 30 minutes before meals to decrease saliva secretion.
Loss of sensation to the earlobe
This is generally due to damage to the great auricular nerve. If possible, the nerve should be preserved. The patient will gradually adapt to the situation and the peripheral sensory nerve fibres will regenerate. The loss of earlobe sensation will gradually improve.
Frey’s syndrome, also termed gustatory sweating syndrome, results from damage to the parasympathetic fibres, which regenerate in a misdirected manner to innervate the sweat glands in the skin overlying the nerve. Stimuli that normally promote parotid gland secretion result in facial sweating. The transfer of the sternocleidomastoid muscle, to preserve the periparotid fascia within the skin flap, might prevent this complication. Most patients with Frey’s syndrome require nothing more than education about the pathophysiology and reassurance that it is a not unusual side-effect of parotidectomy.3 No special treatment is necessary for most patients though application of topical glycopyrrolate is reported to be effective.4
Copyright date: 17th February 2001
Correspondence: Professor Guangyan Yu, Department of Oral and Maxillofacial Surgery, Peking University School of Stomatology, Beijing, 100081, P. R. China
©2001 The Royal College of Surgeons of Edinburgh, J.R.Coll.Surg.Edinb