Introduction
Head and Neck imaging is often considered a “black box” by many residents, and salivary gland masses are particularly tricky due to the wide range of benign and malignant pathologies that can look similar. Mischaracterizing a mass can lead to inappropriate biopsy or surgical delay.
This guide provides a comprehensive framework and an exclusive mnemonic to simplify the Salivary Gland Mass Differential Diagnosis. Master this system to confidently characterize masses in the parotid, submandibular, and minor salivary glands.
The 70/30/10 Rule: Location and Malignancy Risk
The first step in interpretation is understanding the base risk by location:
Gland | Benign (%) | Malignant (%) | Key Takeaway |
Parotid | 70% (Most common) | 30% | 70% are benign, but 70% of malignant salivary tumors occur here. |
Submandibular | 50% | 50% | High risk! Any mass here has a 50% chance of malignancy. |
Minor Salivary | 10% | 90% | Extremely high risk! Assume malignancy until proven otherwise. |
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The Parotid Mnemonic: “PAPA WANTS CHEMO”
The parotid gland is the most common site, and this mnemonic covers the most frequent pathologies in order of their typical appearance.
Letter | Pathology | Key Imaging Features |
P | Pleomorphic Adenoma (PA) | Most common benign tumor. Well-defined, T2 bright on MRI, sometimes lobulated, often has a capsule. |
A | Adenoid Cystic Carcinoma (ACC) | High-grade malignancy. Shows perineural spread (key feature!), irregular margins, often T2-dark. |
P | Papillary Cystadenoma Lymphomatosum (Warthin Tumor) | Second most common benign tumor. Typically bilateral/multifocal, often located in the tail/superficial lobe. Cystic component is common. |
A | Abscess/Inflammation | Poorly defined margins, surrounding fat stranding, ↑ enhancement, often associated with a painful history. |
W | Warthin Tumor (Repeat) | Reminder of its high prevalence. Look for the classic cystic/multilocular appearance. |
A | Acinic Cell Carcinoma | Malignancy. Often well-defined, making it look deceptively benign. Look for indistinct margins or lymphadenopathy. |
N | Nerve Sheath Tumor (Schwannoma) | T2 bright, may involve the facial nerve. Shows “split fat” sign or target sign on MRI. |
T | Tumor in Lymph Node (Metastasis) | Check for malignancy (e.g., Squamous Cell Carcinoma) outside the gland causing nodal metastasis within parotid nodes. |
S | Sjögren Syndrome | Diffuse parotid enlargement, often bilateral, with multiple small, T2-bright cysts (lymphoid infiltration). |
C | Mucoepidermoid Carcinoma | Most common primary malignancy. Tends to be cystic/heterogeneous, but high-grade lesions are solid. |
H | Hemangioma/Lymphangioma | Vascular or lymphatic malformation. Usually present in children. |
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Focus Area: Signs of Malignancy (The Red Flags)
When reviewing any salivary gland mass, use this quick checklist to raise suspicion for malignancy and recommend prompt action.
- Perineural Spread: The single greatest red flag. Look for signal change and enlargement along cranial nerves (especially V3 and VII), indicating Adenoid Cystic Carcinoma (ACC).
- Irregular or Infiltrative Margins: Loss of the clear, defined capsule seen in benign tumors like Pleomorphic Adenoma.
- Extracapsular Extension (ECE): Tumor extending outside the gland and into the surrounding soft tissues (fat, muscle).
- Involvement of the Deep Lobe/Minor Glands: Submandibular and Minor salivary glands have a much higher rate of malignancy.
- Pathologic Cervical Lymphadenopathy: Enlarged, rounded, enhancing nodes with central necrosis are highly suggestive of metastasis.
🚨 On-Call Action Point: If a patient presents with a parotid mass and new onset facial nerve palsy, assume malignancy (often high-grade ACC or Mucoepidermoid) until proven otherwise. Communicate this urgency immediately.
Conclusion
The vast majority of parotid masses are benign, but missing an aggressive malignancy can be detrimental. Use the 70/30/10 rule and the PAPA WANTS CHEMO mnemonic to systematically evaluate the key pathologies. When in doubt, look for the malignancy red flags to guide your final recommendation.