Salivary duct carcinomas are a subtype of primary salivary gland tumor. Salivary duct carcinomas show high rates of metastasis and recurrence.
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Epidemiology
Salivary duct carcinomas represent 5-10% of salivary gland malignancies and can arise de novo or out of a pleomorphic adenoma 1,2. They typically arise in males during the 6th or 7th decades 3.
Clinical presentation
Clinical presentation can vary depending on disease severity, but patients most often present with a parotid or neck mass. While frequently painless, some patients presenting with salivary duct carcinoma have also reported pain. In advanced disease, patients may present with facial nerve involvement resulting in weakness or paralysis 4,5.
Metastatic spread affects 30% of patients at presentation and 50-60% patients following diagnosis. Metastatic disease can present as dyspnea (lung metastases), bone pain (bone metastases), or right upper quadrant pain (liver metastases) 6,7.
Pathology
Although radiological and molecular studies are helpful, a definite diagnosis of salivary gland carcinoma requires histological studies.
Histology
Microscopically, salivary gland duct carcinomas resemble breast ductal carcinoma, containing ducts with comedonecrosis 8. Tumor cells have prominent nucleoli with moderate to abundant eosinophilic cytoplasm 8,9.
Location
Previous studies indicate tumor localization most frequently to the parotid glands, followed by the submandibular glands and buccal space 5.
Radiographic features
Ultrasound
Salivary duct carcinomas have been sparingly described on ultrasound with features of a malignant salivary gland tumor including ill-defined borders, hypervascularity, heterogeneous echotexture and calcifications 21.
CT / MRI
CT and MR studies prove beneficial in determining localization and severity of disease 5,16-20. These tumors most commonly appear as a solid mass with ill-defined borders and heterogenous enhancement patterns. Compared with other salivary gland malignancies, salivary gland carcinomas are associated with invasion into adjacent tissue, including fat, muscle, and skin 10.
Nuclear medicine
Salivary duct carcinomas are highly 18F-FDG avid, thus, PET may provide clinically relevant information for neck node investigation and surgical planning 11,12. Notably, sensitivity and negative predictive values are significantly higher for 18F-FDG PET compared to CT 11.
Treatment and prognosis
Management of salivary duct carcinoma is based on retrospective studies. Surgical resection of the tumor followed by radiotherapy is a frequent therapeutic choice 2,13. Surgery including ipsilateral neck dissection has also been used in some patients 14, although less frequently than resection of the tumor alone.
Salivary duct carcinoma is an aggressive malignancy with a high rate of local recurrence. Median overall survival is 79 months, with a five-year disease-specific survival of 64% 3.
Differential diagnosis
Due to the nonspecific radiological appearance of salivary duct carcinoma, the differential diagnosis should include primary parotid neoplasms, metastatic intraparotid lymph nodes, and more common salivary tumors such as myoepithelial carcinoma 15. A heterogenous enhancement pattern with cribriform necrosis and invasion into adjacent tissue is more indicative of salivary duct carcinoma.