OBJECTIVE: To systematically review published studies on the prevalence of the thyroid foramen (TF), perform a meta-analysis to generate pooled prevalence estimates, and identify factors associated with its presence.
METHODS: A systematic literature search was conducted in Google Scholar, PubMed, and Journal Storage databases. Studies reporting the prevalence of the thyroid foramen were included without language or date restrictions. Quality assessment was performed using AQUA tool. A random-effects meta-analysis was performed with subgroup analyses. Heterogeneity was assessed using Higgins\' I2 statistics, and publication bias was evaluated using funnel plots and Egger\'s test.
RESULTS: Out of 271 entries, 38 studies met the inclusion criteria, comprising 3,030 subjects from various continents. The overall TF prevalence was 24.5% (95% CI: 19.2-29.8%, I2 = 93.44%), with unilateral TF present in 16.9% and bilateral TF in 6.2%. Prevalence was highest in North America (31.4%,) and lowest in Africa (12.3%). No significant prevalence difference was found between adults and younger populations (p = 0.15). Publication bias, or the small-study effect, was detected (p < 0.01).
CONCLUSIONS: This meta-analysis reveals a 24.5% overall prevalence of TF, with significant heterogeneity primarily explained by geographical differences. The TF\'s clinical relevance necessitates awareness among surgeons and radiologists to avoid complications during laryngeal surgeries and prevent misdiagnosis in imaging studies.

The presence of a thyroid foramen in the thyroid cartilage of the larynx is not uncommon. It may be occluded by a fibrous layer, or it may be an abnormal path for the neurovascular bundle of the larynx. The superior laryngeal nerve and the superior laryngeal vessels are the most common contents of the thyroid foramen. During the observation of the skeleton of a 32-year-old female, we found a completely ossified laryngeal framework with bilateral double thyroid foramina. Three of the foramina were circular, and one was oval in shape. This is a very rare anatomical variation. Deep knowledge of the thyroid cartilage anatomy is mandatory during laryngeal and thyroid surgery. The meticulous dissection of laryngeal vessels and nerves is of paramount importance to control bleeding and avoid postoperative neurological sequelae due to nerve injury. The surgeon should be aware that in the whole length of the oblique line of the thyroid cartilage, a thyroid foramen may be detected.

The ancient Greek physicians skipped the description of thyroid gland probablydue to their difficultly to understand the anatomy and the existence of this organ.Although the ancient physicians had described the disease bronchocele (Greek:Βρογχοκήλη), this disease did not correspond exactly to goitre. The first officialdescription of this gland was made by Andreas Vesalius (1514-1564). Thomas Wharton (1614-1673) in his work Adenographia was the one who coined the term \'Glandulae thyreoidea\'.

This study presents an analytic review about the trait of the thyroid foramen. A detailed description about the demographics, frequency, embryology, morphometry, possible content, topography, clinical and surgical considerations is provided. The overall frequency was 28.3% in adults, 15% in children and neonates, 40.6% in embryos and fetuses. The content of the thyroid foramina was a neurovascular bundle in 41.2% of studies. An equal number of studies define a nerve as the common content, while only in 17.6% the usual content was a vessel. Interestingly, in 11.8% the content was just connective tissue or a pit. An updated classification is presented taking into account all the possible content that can cross through a thyroid foramen. The variant is of high interest for surgeons intervening in the larynx due to potential complications such as local bleeding and unwanted neural impairment. The oblique line of the thyroid lamina acts as the best topographical landmark to identify any aberrant anatomy related to a thyroid foramen.