A Review of Salivary Gland Malignancies: Common Histologic Types, Anatomic Considerations, and Imaging Strategies

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Key points

  • Most parotid neoplasms (approximately 4/5) are not malignant. Most sublingual neoplasms (approximately 4/5) are malignant. Approximately half of the minor salivary and submandibular neoplasms are malignant.

  • The parotid gland has lymph nodes within its fascia, which makes it an important site in both primary and secondary malignancy evaluation.

  • In addition to local aggressive features, important directions of spread for parotid malignancy include routes along the cranial nerves (CNs), most

Tumor epidemiology and presentation

Salivary gland malignancies are a rare group of heterogeneous neoplasms arising along the aerodigestive tract and its major secretory structures. They represent less than 8% of head and neck tumors and a total of less than 2500 new cases per year in the United States. Both viral and environmental factors have been implicated as potential causes of neoplasia.1

These tumors can present in various clinical scenarios. Major salivary gland malignancy typically manifests as a palpable abnormality to a

Tumor histology

According to the World Health Organization (WHO), there are more than 25 types of distinct salivary gland tumors. New histologic and biochemical techniques allow for identification of different molecular and genetic subtypes (including hallmark translocations), which can help direct targeted therapy. The WHO updated their 20057 Classification of Head and Neck Tumours with a new list of salivary gland malignancies in 2017.8 The most common salivary malignancies (Box 1) still include

Imaging and staging of salivary gland malignancies

Major salivary gland malignancies have a separate, dedicated American Joint Committee on Cancer (AJCC) tumor-node-metastasis (TNM) staging system. Minor salivary gland malignancies are staged according to the local site of origin. AJCC TNM classifications for malignancies of the paranasal sinuses/nasal cavity, nasopharynx, oral cavity, oropharynx, hypopharynx, or larynx (with subsites) are used. Proper radiologic assessment of salivary gland malignancies requires having familiarity with the

Adenocarcinoma

Adenocarcinomas most commonly occur in the minor salivary glands of the palate and can be treated with surgical resection if caught early. Care must be taken to ensure clear margins because there is a risk of perineural extension and (less commonly) osseous invasion. Histologic progression25 and transformation are also risks.8 These adenocarcinomas were previously described as polymorphous low-grade adenocarcinoma. They stain positive for S100 on pathology,26 have gene rearrangements of PRKD,

Summary

Salivary gland malignancies represent a wide range of tumors from the indolent to the aggressive. The smaller the gland, the higher the malignant risk with (up to) 90% of sublingual gland tumors malignant. The most common location for a malignant tumor is the parotid gland because there are so many more parotid tumors overall. Patients may present with localized swelling, facial pain (suggesting trigeminal involvement), or facial paralysis (suggesting facial nerve involvement). CT and MR

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