Benign tumours of salivary glands
Benign tumours of the salivary glands occur more commonly in larger salivary glands. Approximately 80% of tumours in the parotid gland, 50–60% in the submandibular gland, and only about 25% in the minor salivary glands are benign. This indicates a higher risk of malignancy in minor salivary glands. These tumours can affect individuals of all age groups, though the incidence peaks in the sixth decade of life. There is a general female predominance for salivary gland tumours, except for Warthin’s tumours, which occur more frequently in males. Tumours may arise from either epithelial or mesenchymal tissues.
Aetiology. The exact cause of salivary gland tumours is not known. However, some studies suggest the effect of electromagnetic fields because of mobile phone use and infection with human papillomavirus 16 (HPV16) may be linked to the development of these tumours.
Presentation. Most parotid and submandibular gland tumours grow slowly over an extended period without causing symptoms. Benign tumours typically present as smooth, mobile, and painless masses. The following symptoms and signs may indicate malignant transformation:
- Pain
- Paraesthesia (especially adenoid cystic carcinoma)
- Rapid growth
- Facial nerve palsy/other nerve palsy
- Skin involvement
- Fixity
Parotid gland tumours present as swellings in the retromandibular region, in front of the tragus or in the cheek. The deep lobe of the parotid gland and parapharyngeal space tumours displace the tonsil and palate medially and are often impalpable externally. Large parapharyngeal salivary tumours cause stertor, and sleep-disordered breathing may affect speech or Eustachian tube function. Submandibular gland tumours present as swellings in the submandibular triangle. Minor salivary gland tumours of the oral and pharyngeal mucosa present as firm submucosal swellings.
Investigations
- Ultrasound-guided fine-needle aspiration cytology (FNAC).
- Ultrasound is the primary investigation for benign tumours.
- If the FNAC is non-diagnostic, imaging may assist in diagnosis. MR is done because it gives a better tumour–normal salivary gland interface. Irregular capsule, or extracapsular invasion, hypervascularity and imaging features consistent with necrosis suggest malignancy.
1. Pleomorphic adenoma.
Pleomorphic adenoma is the most common benign tumour of the salivary glands, particularly affecting the parotid gland. It typically arises in the superficial lobe of the parotid gland, although a few cases originate from the deep lobe or accessory parotid tissue along Stenson’s duct. It can also occur in the submandibular gland and minor salivary glands. When pleomorphic adenomas involve the deep lobe of the parotid, they may present as parapharyngeal tumours in the oropharynx.
Pleomorphic adenomas grow slowly and are asymptomatic, presenting as smooth, firm, rounded, and mobile masses with a rubbery consistency. They are most common in women in their third or fourth decade of life. Histologically, pleomorphic adenomas are called “mixed tumours” because they contain both epithelial and mesenchymal elements. The stroma can vary, including mucoid, fibroid, vascular, myxochondroid, or chondroid tissue, which influences the tumour’s firmness. The term pleomorphic adenoma is derived from the Greek words, Pleos = many and morphus = form because of the heterogeneous nature of its histologic appearance.
Though encapsulated, pleomorphic adenomas can send pseudopods into surrounding tissue, increasing the risk of recurrence if not fully excised. Surgical removal requires excision of surrounding normal gland tissue, especially in parotid tumours, where superficial parotidectomy is performed while preserving the facial nerve. These tumours can rupture during surgery due to their fragile, mucoid nature, which increases the chance of recurrence. Although pleomorphic adenomas carry a low risk of malignant transformation, their delicate structure and potential for spillage during surgery require careful handling.
Surgery for pleomorphic adenoma involves different surgical procedures & approaches based on the gland affected:
- Submandibular gland: Excision of the entire gland.
- Minor salivary glands: Wide local excision.
- Superficial lobe of parotid gland: Superficial parotidectomy. Depending upon the extent of parotidectomy, it can be further divided into total superficial parotidectomy and partial superficial parotidectomy (the tumour and a cuff of normal tissue). Partial superficial parotidectomy is practised in the UK more commonly.
- Deep lobe of parotid gland: Total conservative parotidectomy.
- Recurrence of pleomorphic adenoma: Higher malignancy risk; Facial nerve preservation with resection of all remaining tissue, with radiotherapy reducing further recurrence. Selective neck dissection (level 1-3) is also advised for submandibular gland recurrences.
- Parapharyngeal space tumours: Cervico-parotid or transmandibulotomy approach.
2. Warthin’s tumour.
Warthin’s tumour, also known as papillary cystadenoma lymphomatosum, is the second most common benign salivary gland tumour. It accounts for 20% of benign parotid tumours. It is rare outside the parotid gland and primarily affects older adults, with a peak incidence in the fifth to seventh decades. There is a strong association between Warthin’s tumour and smoking, and the tumour predominantly affects males (5:1 ratio). The tumour arises from lymphoid stroma and oncocytic epithelium, suggesting an origin from intra-parotid or peri-parotid lymph nodes, explaining its rarity in the submandibular gland.
Warthin’s tumours present as slow-growing, painless swellings, typically at the lower pole of the parotid gland. They may be bilateral in 10% of cases and sometimes undergo rapid cystic expansion. These tumours are encapsulated, nodular, and can vary from moderately firm to fluctuant on palpation. Histologically, they show both epithelial and lymphoid components.
Treatment generally involves total or partial superficial parotidectomy, though the tumour can be enucleated without risk of recurrence. Warthin’s tumours are not associated with a significant risk of malignant transformation. For older patients or those with slow-growing tumours, conservative management with observation may be a viable option.
3. Oncocytoma (oxyphilic adenoma).
Oncocytomas are rare salivary gland tumours, comprising less than 1% of cases, most commonly arising in the parotid gland. They originate from oncocytes, which are acidophilic cells with eosinophilic, granular cytoplasm. These tumours are typically seen in elderly females in the seventh or eighth decade of life. Oncocytomas usually appear as slow-growing, firm, multi-lobulated masses in the superficial lobe of the parotid and rarely exceed 4-5 cm. Oncocytomas may rarely be bilateral. Treatment typically involves superficial parotidectomy with facial nerve preservation, while submandibular cases require complete sialoadenectomy. While mostly benign, malignant oncocytomas and recurrences have been reported. Oncocytomas show increased uptake of technetium-99.
4. Myoepithelioma.
Myoepithelioma tumours occur solely from the proliferation of myoepithelial cells. They are rare and considered to be variants of pleomorphic adenoma. It commonly presents in 4th decade of life. Both genders are equally affected and all salivary glands can be affected. Management is the same as pleomorphic adenomas.
5. Haemangiomas are the most common benign tumours of the parotid gland in children, particularly affecting females. These tumours are typically present at birth, grow rapidly during the neonatal period, and tend to regress spontaneously over time. In approximately 50% of cases, a cutaneous haemangioma may coexist. Haemangiomas are soft and painless, and their size may increase during crying or straining. The overlying skin can exhibit a bluish discolouration. If spontaneous regression does not occur, surgical excision is recommended.
6. Lymphangiomas are less common and may affect the parotid and submandibular glands. They are soft, cystic on palpation, and do not regress on their own, requiring surgical removal.
——– End of the chapter ——–
Learning resources.
- Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
- Susan Standring, Gray’s Anatomy.
- Stell and Maran’s, Textbook of Head and Neck Surgery and Oncology
- Frank H. Netter, Atlas of Human Anatomy.
- B.D. Chaurasiya, Human Anatomy.
- P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
Author:
Dr. Rahul Bagla
MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Renowned Teaching Faculty
Mail: msrahulbagla@gmail.com
India
Please read. Glomus Tumour. https://www.entlecture.com/glomus-tumour/
Follow our Facebook page: https://www.facebook.com/Dr.Rahul.Bagla.UCMS
Join our Facebook group: https://www.facebook.com/groups/628414274439500