Surgery of salivary gland disease

The most common indication for removal of the sublingual salivary gland is in the management of a ranula, which is a mucous extravasation/retention cyst of the gland. Neoplasms of the sublingual gland occur only rarely but nearly all tumours at this site will be malignant. In this situation sur­gery is the same as that for any other malignancy in the floor of the mouth — resection with a clear margin often involving the mandible and when necessary en bloc with a neck dissection. Before an incision is made it is helpful to infiltrate the floor of the mouth with a local anaesthetic containing a vasoconstrictor. For simple excision of the sublingual gland, a linear incision is made in the floor of the mouth parallel to and just lateral to the submandibular duct, with care taken not to extend the incision more posteriorly than the first molar tooth so as to avoid damage to the lingual nerve (Fig. 42.16). The incision should open the cavity of the ranula and allow the mucinous contents to he aspirated. The submandibular duct is now carefully identified and retracted medially. Stay sutures passed through the margins of the mucosa are helpful to aid retraction. Using blunt dissection with scissors the lingual nerve is identified. The sublingual gland which lies adjacent to the inner cortex of the mandible is then mobilised and its multiple ducts which drain into the submandibular duct are divided carefully in order nor to damage the duct itself. The anterolateral part of the sublingual gland may be attached to the periosteum of the mandible by fibrous tissue and this must be divided carefully. Following removal of the gland, the mucosa of the floor of the mouth is loosely closed with two or three plain gut sutures. When sublingual gland excision is necessary for a tumour, it should be removed with a wide margin including a rim resection of the mandible (Fig. 42.17).

Complications

Damage to the lingual nerve posteriorly or the submandi­bular duct medially is avoided by careful surgical technique. Meticulous haemostasis is required to avoid a postoperative haematoma in the floor of the mouth.

 

Submandibular gland excision

The patient is positioned supine on the operating table with moderate neck extension and the chin rotated to the opposite side. It is helpful to have head-up tilt on the operating table as this reduces venous engorgement. Following routine skin preparation and draping the incision is mapped out. The line should run within a skin crease in the neck at least 3 cm below the lower border of the mandible in order to avoid risk of damaging the mandibular branch of the facial nerve as it loops down below the lower border of the mandible. The incision should be approximately 7 cm long. The incision line is then infiltrated with conventional dental local anaesthetic solution containing 2 per cent lignocaine and 1:80 000 adrenaline. This results in some vasoconstriction which limits capillary ooze and helps to define tissue planes.

The incision is made with either a number 15 blade or a fine cutting diathermy whilst the assistant puts tension across the incision line. The incision is made directly down to platysma. The subcutaneous fat is stripped with firm pressure and a swab from the underlying muscle for approximately 1 cm on each side of the incision as this facilitates a layered closure later. The underlying platysma is then incised to the full extent of the skin incision again with either a blade or cutting diathermy. The assistant can now retract the wound margins using ‘cat paws’ or Allis forceps applied to the cur edge of the platysma muscle (never the skin edges!).

The underlying investing layer of the deep cervical fascia is next divided, preferably with scissors, after the fascia is first tented outwards with toothed forceps. Often the fascia consists of a series of separate laminae like an onion skin but occasionally it is composed of a single thicker sheet. Again the fascia should be divided along the full length of the incision to avoid the operative field becoming ever smaller.

Posteriorly, the fascial incision approaches the angular tract where the deep cervical fascia splits to form the investing layer that has just been incised and the deeper layer that forms the floor of the submandibular triangle containing the submandibular gland.

The mandibular branch of the facial nerve normally runs on the deep aspect of the investing layer of fascia although occasionally it lies between the platysma and the fascia. Great care must be taken to protect the mandibular branch.

The anterior facial vein which lies in the connective tissue overlying the submandibular gland -is clamped, divided and tied. The loose connective tissue is separated with scissors to expose the submandibular gland. The dissection from now on continues on the capsular surface of the gland. For chroni­cally infected glands there is frequently extensive fibrosis, and care and patience are required to maintain this plane. For all tumours contained within the submandibular gland capsule, this plane is safe as it forms an effective barrier. For malignant tumours that have infiltrated beyond the capsule, a full submandibular clearance, usually as part of a neck dissection, and often including the periosteum of the lower and inner aspect of the mandible, is needed.

The anterior pole of the superficial lobe of the submandi­bular gland is first mobilised and retracted upwards with Allis forceps (Fig. 42.18). This reveals the posterior belly of the digastric muscle which is then gently retracted downwards with a small Langenbeck retractor. This exposes the facial artery which emerges from behind the stylohyoid muscle and passes upwards and forwards to enter the deep surface of the

submandibular gland. The artery is then clamped, divided and tied. Great care must be taken to secure the proximal ligature. As the vessel is divided it retracts out of sight and, if the ligature slips, the bleeding end of the vessel can be very difficult to identify.

The course of the facial artery is variable. Often it deeply penetrates the substance of the gland to emerge again at its upper border. Sometimes the artery lies in a groove in the deep aspect of the gland. The dissection in the plane of the submandibular gland capsule continues to mobilise the anterior pole of the superficial lobe of the gland, which is then gently retracted posteriorly. During this dissection a number of small arteries and veins will be identified entering the gland. These should be carefully clamped, divided and tied or diathermised according to their size. As the dissection con­tinues posteriorly along the lower border of the mandible, the facial artery and anterior facial vein are encountered as they hook around the mandible. The vessels are again clamped, divided and ligated at this point.

At this stage in the operation, the anterior pole of the superficial lobe of the gland can be retracted posteriorly to reveal the groove between the superficial and deep lobes of the submandibular gland. The posterior border of the mylohyoid muscle lies within this groove. It is gently freed with scissors and then retracted forwards with a Langenbeck retractor. The deep lobe of the submandibular gland can now be mobilised either with a finger or by opening the blades of the scissors applied to the surface of the gland. On the deep aspect of the deep lobe, one or two small veins may be encountered running from the gland through the underlying hyoglossus into the lingual veins. If these veins are not tied or adequately diathermised, troublesome bleeding may be encountered.

The submandibular salivary gland can now be pulled downwards revealing the V-shaped lingual nerve. The apex of the V is the point at which parasympathetic secreto motor fibres tether the lingual nerve to the salivary gland. It is very important to identify carefully the V of the lingual nerve and its parasympathetic fibres as the latter must be transected to free the gland (Fig. 42.19). As these fibres are cut, the lingual nerve springs forwards. Finally the submandibular duct is clamped, divided and tied as far forward as possible with just enough left to drain the major sublingual gland which empties into the duct. A thin layer of loose connective tissue remains in the gland bed overlying the hypoglossal nerve.

The wound is inspected for any bleeding points, a vacuum drain inserted and the wound closed in layers using a subcuti­cular suture to close the skin. The wound edges are rein­forced with skin closure tapes.

 

Complications

 

Three cranial nerves are at risk during removal of the sub­mandibular salivary gland  the mandibular branch of the facial nerve, the lingual nerve (a branch of the third division of the trigeminal nerve) and the hypoglossal nerve.

When chronic infection and subsequent fibrosis have occurred, it is sometimes difficult to identify the lingual nerve and the deep aspect of the deep lobe may be attached to the hypoglossal nerve. At these stages of the operation, the surgeon must be convinced that these structures have been identified before using any sharp dissection.

Meticulous haemostasis is required throughout the opera­tion as many of the vessels entering and leaving the sub­mandibular gland are only apparent when the gland is under traction and as soon as they are divided the vessels retract into the adjacent muscle planes.

 

Parotidectomy

Treatment of parotid tumours is by superficial parotidectomy for all benign tumours in the superficial lobe and total parotidectomy for all benign deep lobe and dumb-bell tumours. Such tumours including deep lobe tumours should never be approached from the pharyngeal aspect. The facial nerve is preserved in all cases.

The prognosis for malignant parotid tumours is poor. There is little evidence that radical parotidectomy, which includes sacrificing the entire facial nerve, adds significantly to the patient’s survival. It does, however, considerably increase the morbidity. For this reason, superficial or total parotidectomy for malignant tumours is undertaken with preservation of those branches of the facial nerve not macroscopically invaded by tumour. This is followed in all cases of malignant parotid tumours by radical radiotherapy.

Similarly, ‘supraradical’ surgery for adenoid cystic carcinomas is nor advocated. This tumour, although probably always fatal in the long term, is compatible with a useful 10-year survival rate. It is difficult, therefore, to justify extensive mutilating surgery without offering a cure. Adenoid cystic carcinomas whose macroscopic margins remain within the parotid are treated by total parotidectomy followed by radical radiotherapy. For more extensive tumours, radical dissection with as wide a margin as is anatomically appropriate whilst being compatible with reasonable rehabilitation followed by radical radiotherapy will ensure excellent local control of tumour. The radiotherapy field should include the skull base in order to control the perineural tumour extensions.

For any malignant parotid tumours with skin involvement, facial nerve weakness, mandibular invasion, extension into the infratemporal fossa or lymph node metastasis, radical resection often in continuity with radical neck dissection must be undertaken with reconstruction with the use of appropriate flaps and followed by radical postoperative radiotherapy.

 

Surgical technique

 

Whenever the facility is available and the patient fir, hypotensive anaesthesia is used, as this considerably reduces oozing and thus makes it easier to trace the facial nerve fibres. The incision line is infiltrated with lignocaine hydrochloride and 1:80 000 adrenaline and the incision made with a knife or fine cutting diathermy. Following a preauricular incision extending downwards to continue in a suitable skin crease in the neck, the skin flap is raised in the plane of the pre parotid fascia and then held forward by suturing the margins for the flap to the adjacent towels. The blood-free plane anterior to the external auditory meatus is opened up by blunt dissection and this leads the surgeon down to the base of skull just superficial to the styloid process and the stylomastoid foramen. This plane is then gently opened up in an inferior direction by blunt dissection until the trunk of the facial nerve is seen. With large posterior tumours this plane may be difficult to open up. In this situation it is helpful to identify the posterior belly of the digastric muscle in the cervical extension of the incision. The anterior border of the sternocleidomastoid muscle is mobilised and retracted inferiorly to display the digastric muscle beneath it (Fig. 42.20). This manoeuvre necessitates sectioning the great auricular nerve. The posterior belly of the digastric is traced upwards and backwards to its insertion on to the mastoid, which lies immediately below the stylomastoid foramen, thus leading the operator to the facial nerve from below.

There are four anatomical landmarks leading to the identification of the trunk of the facial nerve as it leaves the stylomastoid foramen (Fig. 42.21).

1.       The cartilaginous external auditory meatus forms a pointer’ at its anterior, inferior border indicating the direction of the nerve trunk.

2.       Just deep to the cartilaginous pointer is a reliable bony landmark formed by the curve of the bony external meatus and its abutment with the mastoid process. This forms a palpable groove leading directly to the stylomastoid foramen. Unfortunately this groove is filled with fibrofatty lobules that often mimic the trunk of the facial nerve which can lie as much as 1 cm deep to this landmark.

3.       The anterior, superior aspect of the posterior belly of the digastric muscle is inserted just behind the stylomastoid foramen.

4.       The styloid process itself can be palpated superficial to the stylomastoid foramen and just superior to it. The nerve is always lateral to this plane and passes obliquely across the styloid process. A branch of the postauricular artery is usually encountered just lateral to the nerve.

 

Once the facial nerve trunk has been identified the super­ficial lobe of the parotid can he exteriorised by opening up the plane in which the branches of the facial nerve run between the two lobes by blunt dissection. Initially, as it leaves the stylomastoid foramen, the trunk of the facial nerve turns abruptly to become more superficial and also divides into the larger zygomaticofacial trunk and smaller cervicofacial trunk. The five main branches of the nerve are then followed peripherally through the parotid until the superficial lobe is completely freed. This part of the operation is performed using fine scissors, opened up in the plane of the facial nerve branches, with care always taken to identify the nerve fibre before dividing parotid tissue (Fig. 42.22).

During the lower part of the dissection, branches of the posterior facial vein will be encountered immediately deep to the marginal mandibular branch. Great care must be taken when vascular clamps are applied to these branches to avoid damaging the facial nerve.

If the superficial partotidectomy is being performed for chronic infection, the duct should be tied off as far forward as possible to prevent recurrent ascending infection from the oral cavity.

If the tumour lies in the deep lobe of the gland a conventional superficial parotidectomy is performed as described. Next, the branches of the facial nerve are mobilised and lifted on nylon tapes to enable the deep lobe to be freed around its margins and removed when the mass is dropped downwards (Fig. 42.23). As this space is wedge shaped with its apex superior, it is almost invariably possible to do this. The deep lobe is covered by a capsule (the deep layer of the deep cervical fascia which splits to envelope the parotid) and is surrounded by the parapharyngeal fat. Thus, it is relatively easy to mobilise the deep lobe by blunt dissection with either scissors or a finger. Only very rarely is it necessary to perform a mandibulotomy to gain access to the deep lobe.

Very rarely most often after recurrent infection with fibrosis or previous radiotherapy — the trunk of the facial nerve cannot be confidently identified. In this situation the peripheral branches of the nerve are identified at the anterior border of the parotid and traced centrally towards the stylomastoid foramen.

Following removal of the parotid gland the blood pressure is returned to normal, all bleeding points are controlled, a vacuum drain is placed and the wound closed in layers. A pressure dressing is then applied for 48 hours.

 

Complications

 

Permanent facial nerve paralysis following superficial or total parotidectomy is rare except when branches of the facial nerve have been deliberately sacrificed. When the facial nerve or its branches are sacrificed as a result of macroscopic tumour involvement, an immediate nerve graft may be undertaken using conventional microneural techniques.

Temporary weakness due to neuropraxia occurs in approximately 30 per cent of operations but recovers rapidly, usually within 6 weeks. Anaesthesia of the skin flap slowly resolves as the sensory nerves regenerate from the periphery.

Anaesthesia of the ear lobe due to sectioning of the great auricular nerve can be troublesome, -particularly in females who find it difficult to wear earrings. Recovery can rake up to 18 months and sometimes is never complete.

Gustatory swearing (Frey’s syndrome) is a regular sequel to parotidectomy occurring in up to 54 per cent of cases. Surgical manoeuvres to treat it once established are not successful and most patients either learn to live with it or alternatively use an antiperspirant containing aluminium chloride.

Spillage of a benign pleomorphic adenoma should not occur if a formal superficial parotidectomy is undertaken. However, there are four circumstances where even with meticulous surgical technique this can happen:

 

  extremely large pleomorphic adenomas occupying the entire superficial lobe making mobilisation of the gland difficult;

  tumours that are intimately associated with branches of the facial nerve requiring very delicate dissection along the capsule of the tumour to release the nerve;

  tumours with lobular extensions extending beneath the mastoid, zygomaric arch or mandible;

  some tumours that are abnormally friable with even routine retraction of the superficial lobe resulting in rupture. If rupture occurs an extremely careful inspection of the wound must be undertaken and the area thoroughly irri­gated. In all such cases postoperative radiotherapy should be undertaken in order to avoid multiple recurrences due to tumour seeding.

Other tare complications such as sialocele or salivary fistuIa occasionally follow parotidectomy. Both complications are managed conservatively and resolve spontaneously after days or weeks. Very rarely a parotid fistula persists despite attempts at surgical closure. In this situation postoperative radiotherapy will destroy the residual functioning acinar tissue and allow the flstula to close.

Radiotherapy

Parotid tumours are often considered to be ‘radioresistant’. This is not true: regression after radiotherapy is usually slow, but this reflects the slow cell turnover time of the majority of these tumours, rather than the inability of radiation to effect a cure. There are many reports of long-term local control of large inoperable tumours by radiotherapy. Nevertheless, the chance of successful radiotherapy does seem lower than in the case of squamous cell carcinoma, and therefore the primary treatment should be surgical wherever possible.

Radiotherapy is of value for the inoperable tumour, and also should be used postoperatively whenever there is a risk of incomplete excision such as rupture of a pleomorphic adenoma. It should also be used prophylactically to radical dosage following excision of any malignant parotid tumour. In cases where reoperation is required for recurrence or where there is gross residual tumour, radiation in high doses increases survival significantly.

Adenoid cystic carcinoma has been reported to be the most, consistently radio responsive tumour type. In view of the propensity of this tumour for later recurrence, it is doubtful whether high local control rates at 3 or 5 years really indicate radio curability.

A wide volume around the tumour should be irradiated, especially in the case of adenoid cystic carcinoma. A dose close to the limits of normal tissue tolerance is necessary.