Definition

Oncocytoma is a benign tumour that does not spread outside the boundaries of normal salivary tissue and is closely related to Warthin's tumour.

Incidence

It is a rare form of salivary tumour accounting for less than 1% of all salivary gland tumours. It occurs almost exclusively in the parotid gland.

Age

Rare in under 50 year olds.

Anatomy & Physiology

Two parotid glands are located in front of the ear over the jaw joints on each side. The Parotid gland consists of a superficial (outer) and a deep (inner) part which are separated by the tree-like terminal branches of the facial nerve, responsible for facial movement. Lymph nodes are present within the gland.

Saliva leaves the gland through Stensen's duct, which pierces the facial muscles and enters the mouth through the cheek opposite the second upper molar tooth. Saliva flow is stimulated by chewing and the presence of food in the mouth, particularly sour substances. The stimulus is mediated via parasympathetic nerve fibres carried on the auriculotemporal nerve to the parotid gland.

Causes

The cause is unknown.

Symptoms/Signs

They present as a painless lump in the parotid (in front of or below the ear). Occasionally if the tumour is large and involving the deep lobe, there may be a significant intra-oral component pushing the tonsil towards the midline for parotid tumours.

Weakness of the facial nerve is not a feature of this condition but suggests a possible malignant tumour or may be as a result of technically difficult surgical removal.

Complications of Disorder

Slow progressive enlargement is the main complication. Malignant change is exceedingly rare. Incomplete removal or damage to the capsule during excision makes eventual recurrence and local spread likely.

Tests

The primary objective of tests should be to exclude other causes of parotid/submandibular lumps that require treatments that differ from straightforward surgical excision. For example, parotid lymphomas do not require surgery, but malignant tumours will require more radical surgery.

Fine needle aspiration cytology involves inserting a fine bore needle into the lump and aspirating some of its contents into a syringe, with the sample then examined by a cytologist. Although interpretation of salivary cytology can be very difficult, positive results can be a helpful guide to treatment planning. Availability of high quality cytology services is variable. Incisional biopsies of the parotid are usually avoided because of the high risk of damaging the facial nerve. Sometimes the only way of obtaining a reliable diagnosis is to take out the superficial lobe with careful identification of the relevant nerves.

The secondary objective of tests is to establish the size of the problem and its relationship to neighbouring structures. Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) can both be helpful in this context but neither technique can necessarily precisely delineate the facial nerve. Both techniques may also show characteristic features of this tumour.

For small, mobile lumps in the salivary glands preoperative investigations are not mandatory and may not alter the practical treatment plan.

Other tests may need to be arranged to assess fitness for surgery and these may vary according to the patient's medical condition.

Treatment

No medical treatments are available. Superficial lobe oncocytomas of the parotid are treated by superficial parotidectomy. Deep lobe oncocytomas tumours are treated by total conservative parotidectomy. Recurrent oncocytomas treated with total conservative parotidectomy, but if there is a recurrence around the facial nerve branches, these may need to be sacrificed.

Outcome/Prognosis

For completely exc