Main MRI Feature of Pleomorphic Adenoma of Major Salivary Glands
The main MRI feature of pleomorphic adenoma is marked T2 hyperintensity with well-circumscribed borders and homogeneous solid contrast enhancement. 1, 2
Key Imaging Characteristics
T2-Weighted Signal Characteristics
- Marked hyperintensity on T2-weighted images is the hallmark feature, reflecting the abundant myxochondroid stroma that characterizes pleomorphic adenomas 2
- A hypointense rim may be visible on T2 sequences, representing the fibrous capsule surrounding the tumor 2
- The homogeneous T2 hyperintensity has a positive predictive value of 95% or greater when combined with FNAB diagnosis 1
Morphological Features
- Well-circumscribed, lobulated borders are characteristic and help distinguish pleomorphic adenomas from malignant lesions 1, 2
- The lesions typically appear as well-defined masses with occasional lobulated contours on both CT and MRI 2
Contrast Enhancement Pattern
- Solid, homogeneous contrast enhancement is typical after gadolinium administration 1
- This enhancement pattern, combined with T2 hyperintensity and well-circumscribed borders, demonstrates a PPV of 95% or greater in patients with FNAB-confirmed pleomorphic adenoma 1
Important Caveats
Signal Variability
- Not all pleomorphic adenomas show uniform T2 hyperintensity - intratumoral signal intensity can vary based on cellular density, proportion of epithelial versus stromal components, and the specific type of stromal elements present 2
- Secondary histological changes can alter the typical appearance, including fibrosis, lipometaplasia, ossification, cystic degeneration, and infarction 2
- These atypical features can create diagnostic difficulty and overlap with other salivary gland tumors 2
Optimal Imaging Protocol
- Combined pre- and post-contrast MRI provides the best diagnostic accuracy for identifying and delineating pleomorphic adenomas 3
- MRI is the preferred modality over CT and ultrasound for major salivary gland tumors due to superior soft tissue contrast resolution 3
- Advanced MRI techniques including diffusion-weighted imaging may improve diagnostic accuracy, though these are not consistently used in routine practice 3
Clinical Integration
- When characteristic MRI features (homogeneous T2 hyperintensity, well-circumscribed borders, solid enhancement) are combined with FNAB showing typical cytological features (fibrillary stroma, mesenchymal elements, plasmacytoid myoepithelial cells, epithelial cells forming ducts, absence of nuclear atypia), the diagnostic confidence for pleomorphic adenoma approaches 98% 1