Differential Diagnosis for a Left-Sided Neck Mass in Adults

Primary Malignant Etiologies

• The American Academy of Otolaryngology-Head and Neck Surgery recommends considering metastatic squamous cell carcinoma (HNSCC) from primary sites including oral cavity, oropharynx, hypopharynx, nasopharynx, or larynx as a primary malignant etiology for a left-sided neck mass in adults 1, 3
• HPV-positive oropharyngeal cancer (tonsil and base of tongue) often presents as cystic cervical metastases that may be mistaken for branchial cleft cysts 3
• Lymphoma (Hodgkin's and non-Hodgkin's) is a primary malignant etiology for a left-sided neck mass in adults 1, 2
• Thyroid cancer (particularly in women under age 40) is a primary malignant etiology for a left-sided neck mass in adults 1, 4
• Salivary gland malignancies are a primary malignant etiology for a left-sided neck mass in adults 1, 2
• Metastatic cutaneous malignancies (melanoma, squamous cell carcinoma, basal cell carcinoma from scalp, face, or neck) are a primary malignant etiology for a left-sided neck mass in adults 5, 4

Benign Neoplastic Etiologies

• Thyroid nodules or goiter are a benign neoplastic etiology for a left-sided neck mass in adults 6
• Benign salivary gland tumors (pleomorphic adenoma, Warthin's tumor) are a benign neoplastic etiology for a left-sided neck mass in adults 2

Congenital Lesions

• Branchial cleft cysts (second branchial cleft most common, typically anterior to sternocleidomastoid muscle) are a congenital lesion that can present as a left-sided neck mass in adults 3
• Thyroglossal duct cysts (midline, moves with swallowing and tongue protrusion) are a congenital lesion that can present as a left-sided neck mass in adults 7

Infectious/Inflammatory Etiologies

• Mycobacterial infection (tuberculosis or atypical mycobacteria) is an infectious etiology for a left-sided neck mass in adults 6
• Cat-scratch disease (Bartonella henselae) is an infectious etiology for a left-sided neck mass in adults 6
• HIV-related lymphadenopathy is an infectious etiology for a left-sided neck mass in adults 6
• Epstein-Barr virus (EBV) or cytomegalovirus (CMV) infection is an infectious etiology for a left-sided neck mass in adults 6

Autoimmune/Systemic Conditions

• Sarcoidosis is an autoimmune/systemic condition that can present as a left-sided neck mass in adults 6
• Sjögren's syndrome (bilateral parotid enlargement) is an autoimmune/systemic condition that can present as a left-sided neck mass in adults 6
• Systemic lupus erythematosus is an autoimmune/systemic condition that can present as a left-sided neck mass in adults 6

Critical Red Flags for Malignancy

• A mass present ≥2 weeks or of uncertain duration is a critical red flag for malignancy in a left-sided neck mass in adults 5, 8
• Absence of infectious etiology is a critical red flag for malignancy in a left-sided neck mass in adults 5, 8
• Firm texture (malignant nodes lack tissue edema) is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Reduced mobility/fixation to adjacent tissues (suggests capsular invasion) is a critical red flag for malignancy in a left-sided neck mass in adults 5, 3
• Size >1.5 cm is a critical red flag for malignancy in a left-sided neck mass in adults 5, 3
• Nontender (infectious masses are typically tender) is a critical red flag for malignancy in a left-sided neck mass in adults 5, 4
• Ulceration of overlying skin is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Age >40 years is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Tobacco and alcohol use (synergistic risk factors for HNSCC) is a critical red flag for malignancy in a left-sided neck mass in adults 5
• History of prior head and neck malignancy (including skin cancer of scalp, face, or neck) is a critical red flag for malignancy in a left-sided neck mass in adults 5, 4
• Pharyngitis or throat pain (may indicate mucosal ulceration) is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Dysphagia is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Ipsilateral otalgia with normal ear exam (referred pain from pharynx) is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Recent voice change is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Ipsilateral hearing loss (suggests nasopharyngeal malignancy with middle ear effusion) is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Ipsilateral nasal obstruction and epistaxis is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Unexplained weight loss is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Oral cavity or oropharyngeal ulcer is a critical red flag for malignancy in a left-sided neck mass in adults 5
• Tonsil asymmetry is a critical red flag for malignancy in a left-sided neck mass in adults 5, 4

Location-Specific Considerations

• Anterior triangle masses may be due to thyroid pathology, submandibular gland pathology, lymph nodes, or carotid body tumors 4

Common Pitfalls to Avoid

• Never perform open biopsy before complete evaluation, as this violates oncologic principles and may compromise subsequent treatment if malignancy is present 3
• Cystic masses on imaging or FNA should not be assumed benign—HPV-positive oropharyngeal metastases are frequently cystic and mistaken for branchial cleft cysts 3
• Do not routinely prescribe antibiotics unless clear signs of bacterial infection exist, as this delays cancer diagnosis 3
• Normal anatomic structures frequently mistaken for pathologic masses include submandibular glands, hyoid bone, C2 transverse process, and carotid