Cystic change in metastatic lymph nodes: a common diagnostic pitfall in fine-needle aspiration cytology

Fine-needle aspiration cytology (FNAC) of cystic metastases is a challenging diagnostic category and has been investigated in a limited number of malignancies and sites. The present study retrospectively reviewed 1,211 FNAC of superficial masses, including lymph nodes (1,102 aspirates), benign cystic lesions (64 aspirates), and lymphocysts (45 aspirates) with the aim of determining the tumors that cause cystic change in metastases. Cytology results from 1,102 lymph node aspirations were suspicious or positive for malignancy in 541 specimens (49.1%), benign in 230 (20.9%), and unsatisfactory in 331 (30%). There were 28 malignant aspirates demonstrating cystic change (5.2%). The tumor type that most frequently caused cystic change was thyroid papillary carcinoma (42.8% of cases), followed by squamous cell carcinoma (primary in the head and neck region 30.8% and in the skin 24%), tumors of unknown origin (6.3%), serous papillary carcinoma of the ovary or endometrium (4.8%), and malignant melanoma (2.1%). Cystic change was observed most commonly in the head and neck region lymph nodes (60%). The most challenging lesions to assess using FNAC were metastatic lymph nodes showing cystic change, accounting for six of the 16 false-negative diagnoses and one false-positive diagnosis. The results of this study suggest that cystic change in metastatic lymph nodes occurs in certain types of tumors and is an important cause of diagnostic error. FNAC should be repeated in case of suspicious hypocellular cystic aspirations, especially in patients with known malignancy.