Ultrasound of the Neck for Parotid Mass Evaluation
Order a high-frequency ultrasound of the neck (typically 12 MHz or higher) with color Doppler imaging as the initial imaging modality for evaluating a potential parotid mass. 1, 2
Why Ultrasound First
Ultrasound is the recommended first-line imaging study because it effectively localizes whether the mass is truly within the parotid gland versus extraparotid, identifies features suspicious for malignancy, and can guide fine-needle aspiration biopsy if needed 1, 2. The American College of Radiology specifically endorses ultrasound for its ability to distinguish parotid from extraparotid masses and characterize suspicious features 1.
Key Technical Specifications
- Request high-frequency ultrasound (12 MHz or higher) rather than standard ultrasound, as this provides superior resolution for parotid gland evaluation 3, 4
- Include color Doppler imaging to assess vascular characteristics, which helps differentiate benign from malignant lesions 3, 5, 4
Important Limitations to Recognize
Ultrasound has significant limitations for deep lobe parotid lesions, which are not well visualized compared to superficial lobe masses 1. If the clinical examination or initial ultrasound suggests deep lobe involvement, you should proceed directly to MRI with and without IV contrast, which is the preferred comprehensive imaging modality 2, 6.
When to Upgrade to MRI
Proceed to MRI with and without IV contrast if:
- Deep lobe involvement is suspected on clinical exam or ultrasound 1, 2
- Cranial neuropathy is present (particularly facial nerve involvement) 1
- Additional palpable neck nodes are identified 1
- Ultrasound findings are indeterminate or show concerning features requiring better characterization 2
Critical Caveat About Diagnosis
Imaging alone—whether ultrasound, CT, or MRI—cannot definitively distinguish benign from malignant parotid masses 1, 2. Histologic confirmation through fine-needle aspiration biopsy (FNAB) is essential for definitive diagnosis 2. Ultrasound has relatively low sensitivity (39-60%) for detecting malignancy, though specificity is higher (90-95%) 7, 3, 5.
Ultrasound Features Suggesting Malignancy
While not definitive, these features warrant heightened concern:
- Heterogeneous echotexture 3, 5
- Indistinct or irregular margins 3, 5
- Increased vascularity on color Doppler 3
- Regional lymph node enlargement 5
Alternative Imaging Considerations
CT with IV contrast can be used when MRI is contraindicated and is particularly useful for evaluating bony involvement or sialoliths 2, 8. However, it is not the preferred initial study for soft tissue characterization 1, 2.
Avoid ordering MRA, CTA, FDG-PET/CT, or angiography as initial imaging—these have no established role in evaluating a new parotid mass 1.