Diagnostic Pitfalls in Fine-Needle Aspiration Biopsy of Cervical Lymph Nodes: A Case Report of Simultaneous Dual Primary Malignancies in the Head and Neck Regions Missed on Initial Cytological Examination

Background Synchronous multiple primary malignant tumors of the head and neck are clinically rare, this report describes a case of synchronous dual primary malignancies—papillary thyroid carcinoma and tonsillar squamous cell carcinoma—that were missed due to the inherent limitations of fine-needle aspiration biopsy of cervical lymph nodes. Case presentation The patient presented to the Department of Thyroid and Breast Surgery with multiple enlarged cervical lymph nodes as the chief complaint. The patient underwent ultrasound examination and fine-needle aspiration; the aspiration pathology results indicated a mass in the left lobe of the thyroid suspicious for papillary carcinoma, and the right cervical lymph node was considered to contain cells consistent with papillary thyroid carcinoma. Further examinations, including head and neck CT and laryngoscopy, revealed no significant abnormalities; the patient subsequently underwent extended radical thyroidectomy. Postoperative pathology revealed lymph node metastasis in the right Region II consistent with squamous cell carcinoma. A subsequent PET-CT scan ultimately identified a lesion in the tonsils, and a biopsy confirmed squamous tonsillar squamous cell carcinoma. Conclusions This article aims to enhance clinicians’ ability to diagnose and recognize synchronous multiple primary malignant tumors of the head and neck, avoid misdiagnosis or missed diagnosis resulting from a single-lesion diagnostic mindset, and circumvent diagnostic pitfalls caused by the limitations of imaging techniques.