What causes parotid gland enlargement?

Causes of Parotid Gland Enlargement

Parotid gland enlargement occurs primarily due to inflammatory, autoimmune, infectious, obstructive, or neoplastic processes, with Sjögren's syndrome being the most common autoimmune cause of bilateral enlargement. 1, 2

Inflammatory and Autoimmune Causes

Sjögren's Syndrome

• Primary manifestation includes bilateral parotid gland enlargement
• MRI typically shows multiple areas of low-intensity signal mixed with foci of high-intensity signal (multicystic appearance) 2
• Diagnostic criteria include:
  • Focal lymphocytic sialadenitis (FLS) in labial salivary gland biopsies 1
  • Positive autoimmune blood tests
  • Xerostomia (dry mouth) and xerophthalmia (dry eyes)
• Carries increased risk of non-Hodgkin lymphoma development 3

Sialadenitis (Inflammation of Salivary Glands)

• Can be acute or chronic
• Bacterial causes (most commonly Staphylococcus aureus - 80% of cases) 4
• Viral causes:
  • Mumps (globally most common in children)
  • Juvenile recurrent parotitis (in vaccinated populations) 5

Sialadenosis

• Chronic asymptomatic enlargement due to systemic disease 5
• Non-inflammatory, non-neoplastic enlargement

Obstructive Causes

Sialolithiasis (Salivary Stones)

• Accounts for up to 50% of salivary gland disorders 5
• More common in submandibular glands (>80%) due to:
  • Mucinous secretions high in calcium and phosphate salts
  • Long duct that flows against gravity 5
• Associated with salivary stasis and inflammation caused by:
  • Dehydration
  • Malnutrition
  • Medications
  • Chronic illness

Other Obstructive Causes

• Ductal stenosis
• Trauma
• Mucoceles 5

Neoplastic Causes

Benign Tumors

• Most parotid tumors are benign (approximately 80%)
• Pleomorphic adenoma is the most common benign tumor
• Surgical approach for benign tumors:
  • Partial superficial parotidectomy for appropriately located T1 or T2 low-grade tumors 1
  • Facial nerve preservation when a dissection plane can be created 1

Malignant Tumors

• Comprise approximately 20% of parotid tumors
• High-grade or advanced-stage tumors require at least superficial parotidectomy 1
• Risk factors for malignancy include:
  • Numbness
  • Trismus (limited jaw opening)
  • Fixation
  • Facial weakness 1

Systemic Disease Associations

HIV Infection

• Can present with parotid gland enlargement with or without facial paralysis
• Radiologic signs include intraparotid or submandibular gland cysts with focal intraparotid mass lesions 6

Multiple Endocrine Neoplasia (MEN) Syndromes

• MEN1, MEN4, and CDC73-related (Hyperparathyroid-Jaw Tumor) syndromes can involve the parotid glands 1
• Often associated with primary hyperparathyroidism

Sarcoidosis

• Parotid involvement is a "probable" clinical feature supporting diagnosis
• Presents as symmetrical parotid enlargement 1

Diagnostic Approach

Imaging

• MRI with and without IV contrast is the preferred imaging modality for comprehensive evaluation of:
  • Full extent of masses
  • Deep vs. superficial lobe involvement
  • Perineural spread
  • Extension into surrounding structures 1, 7
• Ultrasound is useful for initial assessment and guiding fine-needle aspiration 7
• CT with IV contrast is commonly used for suspected acute inflammation and better visualizes sialoliths 1

Histopathological Evaluation

• Often required to exclude malignancy, as imaging alone cannot reliably determine if a parotid lesion is benign or malignant 1
• Focal lymphocytic sialadenitis (FLS) should be determined prior to focus score calculation in Sjögren's syndrome 1

Management Considerations

Conservative Management

• For inflammatory conditions:
  • Treat underlying etiology
  • Optimize predisposing factors
  • Control pain
  • Increase salivary flow with sialagogues and hydration
  • Apply massage, warm compresses
  • Maintain oral hygiene
  • Adjust medications 5

Surgical Management

• Indications for parotidectomy in Sjögren's syndrome:
  • Recurrent parotitis refractory to medical management
  • Salivary gland malignancy
  • Severe, refractory pain 3
• Surgical complications include:
  • Facial nerve injury (transient or permanent)
  • Post-operative pain
  • Persistent inflammation of remnant tissue
  • Frey syndrome
  • Facial scarring 3

Sialendoscopy

• Gland-sparing technique for treating obstructive and non-obstructive disorders 5

Clinical Pearls and Pitfalls

• Bilateral parotid enlargement is more commonly associated with inflammatory or systemic conditions, while unilateral enlargement raises suspicion for neoplasm
• Histologic confirmation is usually required to exclude malignancy, even with suggestive imaging findings 1
• Failure to recognize HIV-associated parotid enlargement may lead to inappropriate or unnecessary interventions 6
• Conservative approaches should be considered as first-line management for bacterial parotitis in Sjögren's syndrome before resorting to antibiotics 4