43(5):606-609,2002 CLINICAL SCIENCES Diagnostic Relevance of Fine Needle Aspiration Cytology for Follicular Lesions of the Thyroid: Retrospective Study Neven Mateša, Irena Tabain, Nina Dabeliæ, Vlado Petric 1 , Zvonko Kusiæ Department of Oncology and Nuclear Medicine; and 1 Department of Otorhinolaryngology and Head and Neck Surgery, Sisters of Mercy University Hospital, Zagreb, Croatia Aim. To determine diagnostic relevance of cytologic subclassification of follicular lesions of the thyroid and its role in the therapeutic approach. Methods. We performed a retrospective analysis of the data of patients who underwent thyroid surgery at the Sisters of Mercy University Hospital, Zagreb, between March 1995 and February 2001, and had a report of preoperative fine needle aspiration (FNA) biopsy of thyroid follicular lesion, which comprises cellular follicular lesion, “suspicious for follicular neoplasm,” or follicular neoplasm. Results. Out of 110 patients with preoperative FNA biopsy diagnosis of follicular lesion, 86 (78%) had a lesion corre- sponding histologically to a neoplasm. However, a malignant tumor was found in only 6% of the patients. In the diag- nostic categories of cellular follicular lesion and lesion “suspicious for follicular neoplasm,” the rate of malignancy was even lower, 3% and 4%, respectively. We found significant difference between FNA and histologic findings in distin- guishing non-neoplastic from neoplastic thyroid lesions in the category of cellular follicular lesion and follicular neo- plasm. Conclusion. Due to the low malignancy rate in patients with FNA biopsy diagnoses of cellular follicular lesion or lesion “suspicious for follicular neoplasm” of the thyroid, we suggest close clinical follow-up of such patients, rather than im- mediate surgical intervention. Key words: adenocarcinoma, follicular; biopsy, needle; thyroid diseases; thyroid neoplasms Fine-needle aspiration biopsy of the thyroid is a rapid, minimally invasive, and cost-effective first line procedure in the evaluation of thyroid nodules (1). The main goal of thyroid fine-needle aspiration is to distinguish nodules that require surgery from those that do not, thereby decreasing the number of diag- nostic surgical procedures (2-6). However, fine-nee- dle aspiration of the thyroid gives indeterminate re- sults for neoplasm in 5-29% of patients (7) and surgi- cal excision, with its attendant high cost and potential morbidity, is usually required to fully evaluate such patients. The most controversial is the management of pa- tients with follicular lesions of the thyroid. The diag- nosis of follicular thyroid carcinoma can be made only by histopathological identification of cellular in- filtration into blood vessels or follicle capsule, or by detection of distant metastasis. Cytologic diagnosis has its limitations because cytologic findings in aspi- rates from adenomatoid nodules, follicular adeno- mas, well-differentiated follicular carcinomas, and papillary carcinomas of the follicular variant or with a prominent follicular component are often very similar (4,8-12). We report our experience with fine-needle aspi- ration biopsy specimens classified as “cellular folli- cular lesion,” “suspicious for follicular neoplasm,” or “follicular neoplasm” of the thyroid during a 6-year period. Our aim was to determine the diagnostic rele- vance of cytologic subclassification of thyroid follicu- lar lesions in relation to the therapeutic approach. Patients and Methods Patients We performed a retrospective search of data of all patients who underwent thyroid surgery at the our hospital between March 1995 and February 2001 and had records of preoperative fine-needle aspiration of the thyroid. Fine-needle aspiration diag- noses included cellular follicular lesion, “suspicious for follicular neoplasm,” or follicular neoplasm of the thyroid. There were 19 men and 91 women. The mean age of pati- ents was 47.2 ± 12.8 years (median 47; range 17-76 years) (Table 1). Methods Routine percutaneous fine-needle aspiration biopsy was preformed under ultrasound control by cytopathologist using a 23-gauge needle attached to a 10-mL syringe. Aspirated material was smeared onto glass slides, air-fixed, stained by May-Grün- 606 www.cmj.hr