To Freeze or Not to Freeze? Recommendations for Intraoperative Examination and Gross Prosection of Thyroid Glands

[Frozen section in oncologic endocrine surgery]

BACKGROUND

The aim of the present study is to discuss the benefits of intraoperative frozen sections (FS) for the surgical management of endocrine tumors.

METHODS

A systematic search of the literature of the last ten years on FS in the field of oncologic endocrine surgery was carried out and a discussion based on the available evidence and experience of the authors is provided.

RESULTS

A group of publications focused on the role of intraoperative FS in thyroid surgery in identifying the malignant potential of thyroid nodules. The detection of lymph node metastasis and extrathyroidal growth in differentiated thyroid cancer (DTC) were also two other topical groups as well as the diagnosis of lymph node involvement based on stromal desmoplasia in medullary thyroid cancer (MTC). A further group investigated the possibilities of deep learning to overcome technical problems and another investigated the cost-benefit analyses. There is no relevant literature on the role of FS in the surgical treatment of parathyroid and adrenal cancers.

DISCUSSION

The synthesis of the available evidence suggests that FS investigations of the thyroid glands should be restricted to Bethesda V nodules. The technical limitations in the exclusion of vascular and capsular invasion make the FS unsuitable for follicular neoplasms and oncocytic lesions. The Delphi lymph node seems to be suitable for investigation using FS and when positive represents an indication for lymphadenectomy in cN0 patients. Larger studies are necessary in the future to confirm if the absence of desmoplasia with an intact tumor capsule can reliably justify omitting lymph node resection in MTC, independent of the calcitonin level. The costs and benefits depend on the individual context so that generalization is difficult. Deep learning models could generally improve the performance of FS analysis in the future.

CONCLUSION

In thyroid surgery awareness of the technical limitations of FS is crucial for correct implementation and thus to optimize its performance. A preoperative fine needle biopsy and surgical experience help in selecting the nodules that can benefit from FS. Deep image learning could help to overcome current problems in the future. In adrenal and parathyroid oncologic surgery FS do not play a relevant role.

The Role of Frozen Section Examination in Thyroid Surgery

In endocrine pathology, frozen section (FS) examination is most commonly used for the intraoperative evaluation of thyroid and parathyroid tumors, as well as cervical lymph nodes. In the past, frozen section was considered a fundamental tool in thyroid surgery. However, with advancements in preoperative ultrasound and fine-needle aspiration biopsy (FNAB), there have been increasing queries about its routine use due to the improved preoperative diagnosis. Nowadays, while the use of FS during thyroidectomy has decreased, it is still used as an additional method for different purposes intraoperatively. FS may not always provide definitive results. If FS will alter the surgical plan or extent, it should be applied. Routine FS is not recommended for evaluating thyroid nodules. But in addition to FNAB, if FS results may change the operation plan or extent, they can be utilized. FS should not be applied for thyroid lesions smaller than 1 cm, and the entire lesion should not be frozen for FS. For the assessment of thyroid nodules, the use of FS is recommended based on the Bethesda categories of FNAB. In Bethesda I category nodules, FS may contribute to distinguishing between malignant and benign lesions and guide surgical treatment. In Bethesda II nodules, where the malignancy rate is low, the performance of FNAB and FS can be compared, but it's not recommended due to the lack of a significant contribution to the surgical strategy. The sensitivity of FS in Bethesda III and IV nodules is low; its contribution to the diagnosis is limited, and it does not provide an apparent benefit to treatment; therefore, it is not recommended. In Bethesda V nodules, FS can effectively confirm the malignancy diagnosis, contribute to the surgical strategy, and reduce the possibility of completion thyroidectomy, and accordingly, it is recommended for use. Nonetheless, in Bethesda V nodules with a benign FS report, the malignancy rate remains high, so it should not be used to rule out malignancy. In Bethesda VI nodules, the performance of FS is lower or comparable to FNAB and does not significantly contribute to the treatment strategy; hence, it is not recommended. Particularly in patients with papillary thyroid cancer, intraoperative FS can be effective in detecting extrathyroidal extension and can assist the surgeon in determining the extent of thyroid surgery and central neck dissection. FS has high sensitivity and specificity in evaluating the lymphatic status of the central region intraoperatively and can be used to determine the extent of central compartment node dissection. During thyroidectomy, FS examination can be used in recognizing parathyroid tissue and distinguishing it from fatty tissue, thymus, thyroid, lymph nodes, especially in differentiating metastatic lymph nodes.