We included 13 studies that evaluated the use of telecytology for thyroid FNAB assessment, accounting for a total of 3856 thyroid cases [2, 13, 14, 20, 23, 32,33,34,35,36,37,38,39]; four studies [34,35,36] did not focus exclusively on thyroid nodules, but also assessed samples from other organs (such as lymph nodes, lung, liver, pancreas, head and neck, and salivary glands). Ten studies were retrospective [2, 13, 23, 32,33,34,35,36,37,38], two were prospective [14, 39], and one consisted of two different phases: the first being retrospective, the second prospective [20]. Five studies were conducted in the USA [32,33,34, 37, 39], three in Greece [13, 23, 38], two in Turkey [20, 36], one in Colombia [35], one in Portugal [2], and one in Brazil [14]. All the studies were published between 2009 and 2022, with eight of them published after 2018 [13, 14, 20, 34,35,36,37, 39].

Five studies used real-time microscopy [14, 32,33,34, 39], four used static images [13, 23, 36, 38], three used virtual slide technology/whole slide images (WSI) [2, 20, 35], and one used both real-time and virtual slide technologies [37]. In one study [23] the slides were transmitted to a password-protected account where the cytopathologists could view them, one used a hospital website [39], two of them used NetCame software [32, 33], one used Caseviewer [20], one used Skype [14], one used WhatsApp [36], one used a Cloud-based portal software [35], three used a Web Browser [13, 34, 38], one used an NDP server [2], and one did not define the modality of transmission [37].

Twelve studies examined the diagnostic concordance of TC diagnosis with final cyto-pathological diagnosis [2, 13, 14, 20, 23, 32,33,34,35,36,37,38], seven analyzed TC application on ROSE for preliminary adequacy assessment of the samples [14, 20, 32,33,34, 37, 39], four evaluated TC image quality [13, 14, 35, 38], two examined the use of TC in preliminary diagnosis [20, 32] and two evaluated the use of TC in acquiring a second opinion [13, 35]. Four studies reported the diagnostic time when TC was used: Khurana et al. [33] estimated 4 to 6 min for each slide pass using real-time microscopy; Yao et al. [37] reported that the average time spent per slide was 270 s (about 4.5 min) using VisionTek Digital Microscope (VDM) real-time microscopy and 122 s (about 2 min) for single Z stack digital scan (SZDS) virtual microscopy, compared to 113 s (about 2 min) for conventional light cytology; Sahin et al. [36] reported an average time of 4.25 min for image capture of thyroid FNAB and 2.14 min from image transfer to diagnosis using static images; Mosquera-Zamudio et al. [35] reported that the average time spent to read and interpret a case (including relevant metadata of the patient) was 6.2 min using virtual microscopy.

A comprehensive view of the characteristics of the included studies is provided in Table 3S in the Online resource. Table 1 summarizes the main results of this review.

Twelve studies reported data on concordance rates [2, 13, 14, 20, 23, 32,33,34,35,36,37,38]: four studies used static images [13,