Malignant tumours of salivary gland
Introduction
Malignant tumours of the salivary glands are classified primarily into epithelial tumours, mesenchymal tumours and haematolymphoid tumours like lymphomas. Epithelial tumours account for the majority (95%) of malignant salivary gland tumours, but are infrequently encountered and exhibit considerable heterogeneity in microscopic appearance and clinical behaviour. These tumours arise from both major (parotid, submandibular, sublingual) and minor salivary glands, the latter being unencapsulated seromucinous glands and distributed across the upper aerodigestive tract. The smaller the salivary gland, more likely is the tumour to be malignant.
Incidence
The incidence of salivary gland malignancies ranges from 7 to 12 cases per million person-years in the western world. Risk factors include environmental exposures, low-dose ionizing radiation, aflatoxins, smoking (linked to Warthin’s tumour), and Epstein-Barr virus (associated with undifferentiated carcinoma).
Clinical presentation
Malignant parotid tumours may present as rapidly enlarging masses with pain, facial nerve dysfunction, fixation with surrounding structures or cervical lymphadenopathy. Submandibular tumours usually present as slow-growing masses under the jaw or in the floor of the mouth. While minor salivary gland tumours are often present as painless submucosal swelling or ulcer in the oral cavity (mainly hard palate) and oropharynx. Imaging, particularly MRI (superior) and CT, plays a crucial role in diagnosis and assessing tumour characteristics for surgical planning. Ultrasound-guided fine-needle aspiration cytology (FNAC) is advisable. Incisional or punch-biopsy for minor salivary gland tumours is the standard of care.
Treatment
- Parotid Gland – The primary treatment is surgical excision, which offers the best chance of cure. For small tumours in the superficial parotid lobe, superficial parotidectomy is often sufficient, especially with the use of post-operative radiotherapy to control microscopic disease. Larger tumours (>4 cm), those in the deep lobe, or those involving the facial nerve (VIIN) require more extensive procedures like total or radical parotidectomy. Facial nerve branches are only removed if they are pre-operatively paralyzed or invaded by the tumour. It should be followed by immediate cable grafting. For cases with N+ neck disease, a comprehensive neck dissection is necessary, with removal of non-lymphatic structures (nerve XI, jugular vein or sternocleidomastoid muscle) if invaded. The N0 neck is treated with surgery or radiotherapy, depending on risk factors for occult neck disease.
- Submandibular Gland – Submandibular gland excision is accompanied by selective neck dissection and indication for post-operative radiotherapy follows that for parotid gland malignancy.
- Minor salivary gland – It requires wide local excision with clear margins and radiotherapy to improve survival for N+ patients.
Mucoepidermoid carcinoma – Mucoepidermoid carcinoma is the most common malignant tumour of the salivary glands, primarily affecting women. While some pathologists classify it as a mucoepidermoid tumour rather than true cancer, mucoepidermoid carcinoma poses serious risks due to its ability to invade nearby structures, including the facial nerve, and metastasize. Histologically, the tumour is composed of mucin-producing and squamous cells, with its aggressiveness increasing in proportion to the number of squamous cells. Mucoepidermoid carcinoma is categorized as low or high grade, with low-grade tumours having a more favourable prognosis and a five-year survival rate of 90%, while high-grade tumours are more aggressive and have a five-year survival rate of only 30%. Symptoms like pain, facial paralysis, and skin fixation often indicate high-grade tumours, which are more common in adults. Conversely, low-grade mucoepidermoid carcinoma is typically seen in children. In minor salivary glands, mucoepidermoid carcinoma behaves more aggressively, resembling adenoid cystic carcinoma, while in major glands, it can mimic pleomorphic adenoma.
Treatment for low-grade tumours typically involves superficial or total parotidectomy with facial nerve preservation. High-grade tumours may require total parotidectomy, and if the facial nerve is involved, it may be sacrificed. Radical neck dissection may also be performed due to the high risk of microscopic tumour spread. Recurrence rates are around 25%, and factors like bone invasion and advanced stage worsen the prognosis. Females and younger patients generally have better outcomes.
Adenoid cystic carcinoma (cylindroma) – Adenoid cystic carcinoma (ACC), also known as cylindroma, is a slow-growing yet highly aggressive and destructive tumour that commonly affects the head and neck region. It occurs in adults between the ages of 50 and 70, affecting both males and females equally. The most frequent locations for ACC are the parotid, submandibular, and palatal salivary glands, with the sublingual gland being less commonly affected. Despite its slow growth, ACC infiltrates surrounding tissues, including muscles, nerves, and lymphatics, often causing pain and facial nerve paralysis. Metastasis to lymph nodes, lungs, brain, and bones is possible, and local recurrences are common, sometimes occurring up to 10–20 years after surgical removal.
Treatment typically involves a radical parotidectomy with a margin of normal tissue, and radical neck dissection is usually not done as distant metastasis is more common unless histologically proven nodal metastases are present. Postoperative radiation is recommended if the tumour margins are not clear.
Acinic cell carcinoma – Acinic cell carcinoma is a low-grade tumour that resembles a benign mixed tumour. It appears as a small, firm, and movable mass, occasionally occurring bilaterally. It rarely metastasizes, and treatment involves conservative surgery, such as superficial or total parotidectomy.
Adenocarcinoma – Adenocarcinoma, primarily arising in minor salivary glands, is highly aggressive and prone to distant metastasis.
Malignant mixed tumour – There are two varieties of this tumour which can either develop from pre-existing benign mixed tumours or arise de novo (has much shorter history), require radical parotidectomy if malignancy is suspected due to rapid growth or pain. In cases of facial nerve involvement, grafting is performed immediately after nerve sacrifice.
Squamous cell carcinoma – Squamous cell carcinoma grows rapidly, infiltrates tissues, and often ulcerates through the skin. It can metastasize to the neck nodes, and treatment involves radical parotidectomy, possibly extending to surrounding muscles, the mandible, or temporal bone, followed by radiation therapy.
Undifferentiated carcinoma – Undifferentiated carcinoma is a rare yet aggressive tumour that spreads rapidly and causes significant pain, facial paralysis, and skin ulceration. It commonly metastasizes to cervical lymph nodes. Treatment includes wide excision, radical neck surgery, and postoperative radiation.
Lymphoma – Lymphomas affecting the parotid gland are rare and often associated with systemic disease, though primary lymphomas can occur. Treatment follows protocols for other lymphomas.
Sarcoma – Sarcomas, such as rhabdomyosarcoma, rarely arise from the parotid gland. Treatment for sarcoma is based on the specific type and extent of the tumour.
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Reference Textbooks.
- Scott-Brown, Textbook of Otorhinolaryngology-Head and Neck Surgery.
- Cummings, Otolaryngology-Head and Neck Surgery.
- Stell and Maran’s, Textbook of Head and Neck Surgery and Oncology.
- Ballenger’s, Otorhinolaryngology Head And Neck Surgery
- Susan Standring, Gray’s Anatomy.
- Frank H. Netter, Atlas of Human Anatomy.
- B.D. Chaurasiya, Human Anatomy.
- P L Dhingra, Textbook of Diseases of Ear, Nose and Throat.
- Hazarika P, Textbook of Ear Nose Throat And Head Neck Surgery Clinical Practical.
- Mohan Bansal, Textbook of Diseases of Ear, Nose and Throat Head and Neck Surgery.
- Hans Behrbohm, Textbook of Ear, Nose, and Throat Diseases With Head and Neck Surgery.
- Logan Turner, Textbook of Diseases of The Nose, Throat and Ear Head And Neck Surgery.
- Arnold, U. Ganzer, Textbook of Otorhinolaryngology, Head and Neck Surgery.
- Ganong’s Review of Medical Physiology.
Author:
Dr. Rahul Bagla
MBBS (MAMC, Delhi) MS ENT (UCMS, Delhi)
Fellow Rhinoplasty & Facial Plastic Surgery.
Renowned Teaching Faculty
Mail: msrahulbagla@gmail.com
India
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