What causes enlargement of lymph nodes in the parotid gland?

Causes of Intraparotid Lymph Node Enlargement

Intraparotid lymph node enlargement occurs due to malignant processes (lymphoma, metastatic disease), infectious/inflammatory conditions (bacterial lymphadenitis, viral infections), and autoimmune diseases (particularly Sjögren's syndrome), with lymphoma being the most critical diagnosis to exclude. 1, 2

Malignant Causes

Lymphoma

• MALT (mucosa-associated lymphoid tissue) lymphoma is the most common lymphoma affecting the parotid gland, arising directly from glandular parenchyma or from intraparotid/periparotid lymph nodes 3, 4
• Follicular lymphoma and diffuse large B-cell lymphoma are the next most common histologic subtypes after MALT 4
• Most parotid lymphomas present at low stages (IE/IIE according to Ann Arbor staging, 76.5% of cases) 4
• Patients with Sjögren's syndrome have up to 6% annual risk of developing B-cell lymphomas, including MALT lymphomas, making this association critically important 5, 6
• Lymphoma typically presents as painless, soft masses, though pain occurs in 4.8% and B symptoms (fever, night sweats, weight loss) in 2.2% of cases 4
• Post-transplant lymphoproliferative disorders can also affect parotid lymph nodes 2

Metastatic Disease

• Metastatic squamous cell carcinoma from head and neck primary sites can involve intraparotid lymph nodes 7
• Cutaneous malignancies (melanoma, squamous cell carcinoma) may metastasize to parotid lymph nodes 7
• Physical examination features suggesting malignancy include: fixation to adjacent tissues, firm consistency, size >1.5 cm, and ulceration of overlying skin 7

Infectious and Inflammatory Causes

Bacterial Infections

• Bacterial cervical/parotid lymphadenitis can cause lymph node enlargement that mimics malignancy 2
• Purulent material may be aspirated in some cases of infectious lymphadenopathy 8

Viral Infections

• Epstein-Barr virus (infectious mononucleosis) causes reactive lymph node hyperplasia 2
• HIV-related lymphadenopathy presents as benign hyperplastic lymphadenopathy, particularly in intravenous drug users 2, 8
• Measles, adenovirus, and enterovirus can cause reactive lymphadenopathy 2

Autoimmune Causes

Sjögren's Syndrome

• Sjögren's syndrome is the most important autoimmune disease causing parotid lymph node enlargement, affecting up to 70% of patients with parotid MALT lymphoma 4, 5
• Presents with recurrent, indolent swelling of parotid glands, often bilateral 5, 6
• MRI demonstrates multiple areas of low-intensity signal mixed with foci of high-intensity signal 6
• Prognostic factors for lymphoma development include elevated ESR and hypergammaglobulinemia 5
• Germinal center formation in labial salivary glands correlates with increased lymphoma risk 7
• Persistent salivary gland swelling, lymphadenopathy, low complements (C3 or C4), monoclonal gammopathy, and cryoglobulins are high-risk features for lymphoma development 7

Other Autoimmune Conditions

• Sarcoidosis can cause parotid lymphadenopathy 2
• Drug hypersensitivity reactions may cause reactive lymph node enlargement 2

Benign Reactive Hyperplasia

• Benign reactive lymph nodes with follicular hyperplasia can appear enlarged and mimic malignancy 2
• Lymphoepithelial hyperplasia presents as benign hyperplastic lymphadenopathy, particularly in HIV-positive patients 8

Critical Diagnostic Thresholds

Size criteria for concern:

• Lymph nodes >1.5 cm in short axis diameter require workup for potential malignancy 7, 2
• Nodes ≤15 mm are typically reactive, while nodes >25 mm are usually pathologic 2

Imaging features suggesting malignancy:

• Loss of fatty hilum 2
• Round shape rather than oval 2
• Heterogeneous echogenicity on ultrasound 2
• Central necrosis 2
• PET-avid parotitis (standardized uptake value ≥4.7) accompanied by lung nodules suggests lymphoma 7

Common Pitfalls

• Do not rely on size alone: Normal-sized nodes can harbor microscopic metastases, and enlarged nodes may be hyperplastic rather than neoplastic 2
• In Sjögren's syndrome, distinguishing recurrent inflammatory swelling from lymphoma is clinically difficult—persistent unilateral swelling despite immunosuppressive therapy warrants biopsy 5
• Absence of symptoms does not exclude malignancy—90% of parotid lymphomas are asymptomatic 4
• Parotid lymphadenopathy in intravenous drug users may represent early manifestation of HIV/AIDS-related complex 8