Medullary thyroid carcinoma is a rare tumor (5% of all cases).FNA biopsy is one of the main methods for diagnosing thyroid pathologies, including medullary carcinoma. However, in some cases, false-negative indicators of FNA biopsy significantly complicate treatment tactics, in particular the choice of the extent of surgery.

From 2022 -2023, 117 patients with thyroid cancer were operated on. The ages of 108 female,9 male patients ranged from 19 to 73 years. All patients underwent FNA biopsy before surgery. Follicular neoplasia was detected in 36 cases. The size of the nodules varied from 0.6 to 5.0 cm. The presence of nodules in both lobes of the thyroid was observed in 21 cases. A solid nodule was in one of the gland lobes in 15 cases.

Thyroidectomy was planned for all patients with nodules larger than 2.0 cm and a preliminary diagnosis of follicular neoplasia. Hemithyroidectomy was planned for patients with unilateral glandular lesions with microcarcinomas (nodules up to 1 cm). The results of the intraoperative frozen section, however, revealed a suspicion of thyroid gland medullary neoplasia in 5 patients. Thyroidectomy was performed on all of these patients.

The preoperative diagnosis of follicular carcinoma made on the basis of FNA biopsy and ultrasound is not a reliable indicator for choosing the extent of surgery. To optimize the preoperative diagnosis process, all patients with follicular neoplasia must have serum calcitonin levels measured, which is a tumor marker of MTC. When serum calcitonin levels are low, a washout fluid calcitonin assay (FNA-CT) is recommended.