In recent years, a growing number of studies have examined the relationship between thyroid pathophysiology and intestinal microbiota composition. The reciprocal influence between these two entities has been proven so extensive that some authors coined the term "gut-thyroid axis". However, since some papers reported conflicting results, several aspects of this correlation need to be clarified. This systematic review was conceived to achieve more robust information about: 1)the characteristics of gut microbiota composition in patients with the more common morphological, functional and autoimmune disorders of the thyroid; 2)the influence of gut microbial composition on micronutrients that are essential for the maintenance of thyroid homeostasis; 3)the effect of probiotics, prebiotics and synbiotics, some of the most popular over-the-counter products, on thyroid balance; 4)the opportunity to use specific dietary advice. The literature evaluation was made by three authors independently. A five steps strategy was a priori adopted. After duplicates removal, 1106 records were initially found and 38 reviews were finally included in the analysis. The systematic reviews of reviews found that: 1) some significant variations characterize the gut microbiota composition in patients with thyroid disorders. However, geographical clustering of most of the studies prevents drawing definitive conclusions on this topic; 2) the available knowledge about the effect of probiotics and synbiotics are not strong enough to suggest the routine use of these compounds in patients with thyroid disorders; 3) specific elimination nutrition should not be routine suggested to patients, which, instead have to be checked for possible micronutrients and vitamins deficiency, often owed to gastrointestinal autoimmune comorbidities.

Background: Solitary fibrous tumors are uncommon fibroblastic neoplasms. These tumors are characterized by the recurrent NAB2-STAT6 gene fusion, which is a hallmark of solitary fibrous tumors (SFTs), particularly those arising in the thoracic cavity. While SFTs are mostly found in the abdomen and pleura, they can occur in various locations, including the head and neck region (6% of cases of SFTs). Solitary fibrous tumors of the thyroid (SFTTs) are extremely rare, accounting for only 0.1% of all thyroid tumors. The gold standard imaging modality for thyroid tumors is ultrasonography, even though distinctive characteristics for these types of neoplasms are absent, making pre-operative diagnosis more challenging. Aim: The aim of this study is to perform a systematic literature review and to describe our case by analyzing the main clinical features, histological diagnostic features and treatments of this rare tumor, in order to clarify the behavior and molecular characteristics of SFTTs. Methods: A comprehensive systematic literature review was conducted according to the PRISMA guidelines for SFTTs. We searched the PubMed and EMBASE databases for articles published up to November 2025. The inclusion criteria include confirmed diagnosis of SFTT, while articles describing unrelated neoplasms or articles that were not in English were excluded. A standardized form was used to extract information on the imaging characteristics, histological diagnosis, treatment and outcome. Results: As of 2025, a total of 43 articles were selected, with 61 reported cases of SFTT in the English literature. Pre-operative diagnosis of SFTT is controversial and usually requires immunohistochemical confirmation. In our case, molecular analysis identified, for the first time, a NAB2ex6–STAT6ex17 fusion, contributing to the molecular characterization of this rare tumor. Conclusions: SFTTs are rare and difficult to diagnose; thus, they require a multidisciplinary approach for accurate diagnosis and management. The combination of imaging, cytology, histopathology, and molecular testing is essential in distinguishing SFTTs from other thyroid malignancies. Surgical excision remains the mainstay of treatment, and long-term follow-up is recommended due to the potential risk of recurrence or metastasis.