Partial superficial parotidectomy for pleomorphic adenoma of the parotid gland

Background

Pleomorphic adenoma is not only the most common benign tumour of superficial lobe of the parotid gland, but also accounts for about 60%–70% of all parotid tumours.1 2 It has a predisposition for middle-aged people and is most prevalent in women of 30–50 years of age.3 It derives the name of a ‘mixed tumour’ as it can comprise of both epithelial and connective tissue components.4 Salivary gland tumours such as the pleomorphic adenoma can be subdivided into mostly three categories—benign, locally aggressive and malignant tumours, which may show metastasis in later stages.5 The aetiology of the tumour is mostly unspecified but it has the potential to turn malignant, which thus forms one of the indications for surgery.5 Minor salivary glands are affected most after the parotid gland . The minor salivary gland tumours commonly occur in the palate (50%), upper lip (27%) and buccal mucosa (17%). Minor salivary gland tumours can show a plethora of symptoms, including dysphagia, hoarseness, dyspnoea and difficulty in chewing.6

The majority of pleomorphic adenomas have been reported to occur in the superficial lobe and presents itself as a swelling on the ramus in front of the auricle. The tumour mostly appears as an irregular firm nodular lesion. However, islands of cystic degeneration may be palpated if they occur superficially. In general, it does not show fixation. In the parotid gland tumours, signs of facial nerve involvement presents when the tumour is large or if it has undergone malignant changes. Hence, rapid enlargement of a tumour nodule could indicate to the possibility of malignant transformation.7

Roentgenographic imaging not only provides vital information about accurate localisation of the lobe in which the tumour is seated, but also provides critical details about the the intraparotid course of facial nerve, and differentiation of malignant tumours.8 Razek in his study of characterising parotid tumours found that dynamic susceptibility contrast-enhanced perfusion-weighted MRI and diffusion-weighted MRI were non-invasive promising methods that were used for differentiation of malignant from benign parotid tumours and for characterisation of some benign parotid tumours.9 He also stated in his later article that multiparametric MRI using pseudocontinuous arterial-spin labelling and diffusion-weighted imaging is useful for differentiating benign parotid tumours from parotid malignancy. Tissue sampling also plays an important role in diagnosis. These procedures mainly involve fine-needle aspiration (FNA) and core needle biopsy. FNA with an approximate sensitivity of 90% can determine malignancy. On the other hand, core needle biopsy is more invasive but has a higher diagnostic accuracy of around 97%.7 Parotid gland surgery has undergone an evolution beginning with a conservative approach of simple enucleation and moving on slowly but surely to a more aggressive course with the advent of superficial parotidectomy. Superficial parotidectomy involves excising all the parts of the gland superficial or lateral to the facial nerve. Partial superficial parotidectomy involves excising only the portion of the gland surrounding the neoplasm, which is much more conservative than total parotidectomy which involves total removal of the deep part of the parotid gland.

This slashed the high recurrence rate after enucleation. At present, the gold standard treatment modality of pleomorphic adenoma includes aggressive surgery with wide local excision extending at least 0.5 cm beyond the normal tumour margins.3

Case presentation

A 32-year-old male patient reported to the department of oral and maxillofacial surgery with the chief report of a swelling on his right cheek region since last 4 months (figure 1A). He reported that the swelling was painless and was increasing in size. He had no significant medical and dental history. He was previously a smoker for 5 years but had quit smoking 2 years ago. On inspection, there was an extraoral swelling 3.1 cm in size antero-posteriorly and 4.5 cm superior-inferiorly. It extended from the tragus region superiorly to the angle of mandible inferiorly. Antero-posteriorly, the swelling extended from the cheek region to the posterior border of the mandible. On palpation, the swelling was firm, non-tender, non-pulsatile, non-fluctuant with diffuse borders and smooth overlying skin. The clinical and radiographic signs and symptoms were indicative of pleomorphic adenoma.

Investigations

A CT scan with contrast was done (figure 1B). Fine needle Aspiration Cytology was done before the procedure. Both the investigations indicated that the lesion was benign pleomorphic adenoma.

Treatment

The patient was advised to undergo partial superficial parotidectomy under general anaesthesia as the lesion was benign without the involvement of the facial nerve. Informed consent was taken and preoperative anaesthetic clearance was done. The ipsilateral face was prepared with an antiseptic solution and the surgical field was draped (figure 2A). The functional integrity of facial nerve was assessed by placing the nerve electrodes on the ipsilateral facial muscles. In our case, the facial nerve function was not compromised. A modified Blair incision was planned in a preauricular crease, which coursed around the ear lobule and then extended into an upper neck crease. The extension was placed two fingers below the lower border of the mandible, to protect the marginal mandibular nerve (figure 2B). The proposed incision was marked and dissection was carried through skin, superficial fascia, deep fascia and platysma. An anterior flap was elevated, which was superficial to the greater auricular nerve and the parotid fascia. A posterior inferior flap elevation, was done with the purpose of exposing the tail of the parotid gland. During elevation of the tail of the parotid, the integrity of the posterior facial vein was kept intact (figure 2C) after dissecting it from the sternocleidomastoid muscle. A wide plane dissection was carried out from the zygoma to the digastric muscle. The gland was carefully retracted anteriorly, which aided in the identification of the facial nerve. After the facial nerve was identified and preserved, the parotid gland superficial to the facial nerve was divided with utmost care (figure 3A). The required portion of the gland was dissected from facial nerve, after following its course peripherally and the specimen removed. The wound was carefully inspected and bleeding sites were cauterised or ligatures were placed. The integrity of the facial nerve was confirmed after the procedure. The first echelon nodes were inspected, because the neck was clinically negative. The wound was irrigated, and closed in layers over a closed suction drain (figure 3B). The specimen (figure 3C) was sent for histopathological examination.

Outcome and follow-up

The drain was removed on the second postoperative day and the skin sutures were removed after 7 days. There were no complications reported after a follow-up of 6 months.