Introduction: Patients undergoing a total thyroidectomy for multinodular goiter typically have a long clinical history of the disease. They often come to surgery for compression symptoms, with no suspicion of neoplastic disease. For these patients, the incidence of microcarcinomas is high, even though we know that this does not affect subsequent therapies and long-term survival. On the other hand, when a true incidental carcinoma is present, the patient requires specific therapy and long-term follow-up. The purpose of the study was to identify the incidence of incidental carcinomas in the high prevalence region of goiter, the clinical-pathological characteristics of the tumor, and the therapeutic implications. Method: This is a retrospective study, from January 2010 to December 2020, on a case series of 1435 total thyroidectomies for goiters. All patients had a preoperative diagnosis of a benign disease. Gender, mean age, and mean duration from the initial diagnosis of goiter were evaluated along with the number and frequency of fine needle aspirations carried out. On the basis of the histological examination, the incidence of incidental carcinoma was then assessed (diameter ≥ 10 mm) as well as the incidence of microcarcinoma (diameter < 10 mm), the pathological characteristics (multifocality, capsular invasion), and the subsequent prescribed therapies. Results: Patients with incidental carcinoma numbered 41 (2.8%%), 34 women and 7 men. The mean age was 53.5 years, while the patients diagnosed with microcarcinoma were 88 (6.1%). The mean duration of the disease from initial diagnosis was 7.8 years. On average, these patients underwent 1.8 fine needle aspirations during the course of the disease, almost exclusively in the first four years. The mean diameter of the tumor was 1.35 cm (±0.3). Multifocality was present in six patients, while only one patient presented capsular invasion. The chi-square test delivered a significant dependence on gender in terms of the incidental diagnosis after Yates correction (chi-stat = 5.064; p = 0.024), highlighting a higher incidence in the female population. All patients underwent subsequent metabolic radiotherapy. The mean follow-up was 6.3 years and in the 35 patients examined, none displayed any recurrence of the disease. Conclusions: Incidental carcinoma is not uncommon in patients who have undergone total thyroidectomy for goiters. It must be differentiated from microcarcinoma for its therapeutic implications and the follow-up of the patient. Statistical analysis has shown that the only significant variable is gender. In a goiter area, the careful monitoring of patients is required to highlight suspicious clinical–instrumental aspects that may appear even several years after the initial diagnosis.
