What are the imaging characteristics of salivary gland neoplasms?

From the Guidelines

Salivary gland neoplasms are best visualized using MRI with IV contrast, which provides superior soft tissue contrast resolution and can accurately depict the anatomy of the floor of the mouth, making it the modality of choice for initial staging of major salivary gland cancer. The imaging characteristics of salivary gland neoplasms vary depending on whether they are benign or malignant. Common imaging modalities used to visualize these neoplasms include ultrasound, CT scans, MRI, and occasionally PET scans. Benign tumors like pleomorphic adenomas typically appear as well-defined, homogeneous masses with smooth margins, while malignant tumors such as mucoepidermoid carcinoma or adenoid cystic carcinoma often show irregular borders, heterogeneous enhancement, and possible invasion of surrounding tissues.

Key Imaging Modalities

• MRI: provides superior soft tissue contrast resolution and is considered the modality of choice for initial staging of major salivary gland cancer 1
• CT scans: useful for evaluating bone erosion and detecting focal intratumoral calcifications, but may not provide as much detail as MRI for soft tissue evaluation 1
• Ultrasound: often used as a first-line imaging tool, especially in children, but may be limited in evaluating the deep extent of masses or involvement of the skull base 1
• PET scans: may be useful in staging regional neck nodal disease and preoperative planning for neck dissection, but is not recommended for distinguishing between benign and malignant tumors due to its limited diagnostic accuracy 1

Imaging Characteristics

• Benign tumors: well-defined, homogeneous masses with smooth margins
• Malignant tumors: irregular borders, heterogeneous enhancement, and possible invasion of surrounding tissues
• Key features to evaluate: size, location, extent of tumor, and involvement of surrounding structures such as nerves and blood vessels

Clinical Recommendations

• A comprehensive evaluation including clinical examination, imaging, and often fine-needle aspiration biopsy is recommended to establish the diagnosis and guide appropriate management 1
• MRI with IV contrast is recommended for initial staging of major salivary gland cancer, especially when there is concern for perineural invasion and/or skull base involvement 1

From the Research

Imaging Characteristics of Salivary Gland Neoplasms

• Salivary gland neoplasms account for less than 3% of all tumors, with most being benign and occurring in the parotid gland 2
• The role of imaging in assessing salivary gland tumors is to define intra-glandular vs. extra-glandular location, detect malignant features, assess local extension and invasion, detect nodal metastases, and systemic involvement 2
• Ultrasound is an ideal tool for initial assessment of lesions in the superficial parotid and submandibular gland, providing excellent resolution and tissue characterization without radiation hazard 2

Imaging Modalities

• MRI is the best imaging modality to evaluate salivary gland tumors, especially for lesions in the deep lobe of the parotid gland, minor salivary glands, and sublingual gland 2, 3
• CT scans are also used to evaluate tumor extent, local invasion, and perineural spread 2, 4
• MR spectroscopy may differentiate malignant and benign salivary gland tumors, as well as distinguish Warthin's tumor from pleomorphic adenoma, but its role in clinical practice is not well established 2
• PET scans and nuclear medicine have limited roles in imaging parotid masses 2

Diagnostic Accuracy

• The positive predictive value (PPV) of fine needle aspiration biopsy (FNAB) diagnosis of pleomorphic adenoma is high, at 97.8% 5
• Characteristic features of pleomorphic adenoma on FNAB and MRI have PPVs of 95% or greater 5
• Multiparametric MR imaging can help distinguish benign and low-grade neoplasms from malignant tumors, but a biopsy is often needed for definitive histopathologic diagnosis 3