The thyroid foramen: a systematic review and surgical considerations.

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.

The incidence of the foramen thyroideum in Turkish population.

This study was undertaken to investigate the incidence and characteristics of the foramen thyroideum (FT) in Turkish population. A total of 50 cadaver specimens were dissected which were a randomly selected sample of population from the criminal laboratory of the Republic of Turkey's Ministry of Justice (Istanbul). Larynges were dissected with a surgical SMZ 10 Nikon stereomicroscope. Six of the 50 specimens dissected had distinctly identifiable foramina with neurovascular component. One specimen had bilateral foramina, five specimens had unilateral foramina, and two had it in the left side, three in the right. One specimen had a double foramen in the left side. All of them were male and contained neurovascular components. Our data showed 12% incidence of FT in Turkish population.

Anatomical study of meandering and functions of human intralaryngeal artery.

In recent years, partial laryngectomy and partial reconstruction are increasingly intended for conservation of functions of phonation and swallowing. In partial reconstruction, it is important to comprehend morphological characteristics of the blood vessels distributed in the larynx, but there have been only few reports discussing detailed information about them. Previous reports on laryngeal blood vessels have shown that branches of some arteries show remarkable "meandering". In the present study, we devised a method for objectively determining the morphological nature, "meandering" and assessed functions of the arteries. Intralaryngeal arteries were excised from the larynx of cadavers prepared for practice in anatomy, and images of the "meandering" artery were analyzed with NIH Image. The extent of "meandering" was expressed mainly as the ratio of the total length of the blood vessel to the distance between the starting point and the end point of meandering. The results showed that there was a significant difference in the extent of meandering between superior posterior and medial posterior branches of superior laryngeal artery. These arteries, which were distributed in the arytenoid region, were found to be of primary importance in partial laryngectomy and partial reconstruction of the larynx.

An external landmark for the anterior commissure.

OBJECTIVE: The ability to predict the level of the true vocal cords based on external landmarks is crucial to the success of many laryngeal surgical procedures. This study examines the reliability of one such landmark on the thyroid cartilage. METHODS: Twenty-four cadaver larynges were examined. A pin was placed through the landmark, best described as a small diamond shaped area of color change and surface depression along the anterior midline of each thyroid cartilage through which travels a very small unnamed artery. The endolaryngeal position of the pin was checked with a flexible nasopharyngoscope. RESULTS: In all 24 cadavers, the pin entered the larynx at the anterior commissure, just above or at the level of the true vocal cords. CONCLUSIONS: This external landmark reliably predicts the position of the true vocal cords. It serves as a useful adjunct to existing external landmarks used to direct thyroid cartilage cuts in laryngeal procedures.

Vascularization and cartilage mineralization of the thyroid cartilage of Munich minipigs and domestic pigs.

Thyroid cartilages of Munich minipigs and domestic pigs were investigated by polychrome sequential labeling, radiography, intravascular injections, histologic examination and scanning electron microscopy in order to gain further insight into the process of vascularization and cartilage mineralization. The relationship between vascularization and cartilage mineralization has only been studied in chondroepiphyses of long bones. Vessels branch off the perichondrial vascular network and enter parts of the thyroid cartilage with a large transverse diameter. Cartilage canals, which are perichondral invaginations, contain an arteriole, a venule, a capillary network and connective tissue. The capillaries form a glomerulus-like structure deep in the matrix of the cartilage. Neighbouring cartilage canals do not display any anastomoses. Cartilage mineralization occurs in large areas of the thyroid cartilage. It is only found in the interterritorial extracellular matrix. Mineralization of the cartilage is evident in areas supplied with cartilage canals as well as in non-supplied areas. Mineralized interterritorial matrix is composed of circular structures of different sizes fusing to form plaques. In scanning electron microscopy circular structures appear as globules. It is possible to visualize the dynamic process of cartilage mineralization with polychrome sequential labeling; it proceeds up to 4 microm per week. Distribution of cartilage canals reveals their nutritional role for the cartilage. According to investigations in chondroepiphyses, cartilage mineralization starts adjacent to the glomerular end of cartilage canals. In contrast, no correlation between cartilage vascularization and the beginning of cartilage mineralization of the thyroid cartilage of Munich minipigs and of domestic pigs has been found.

Tracheal transplantation: defining the vascular territory of the canine cranial thyroid artery.

The management of long-segment tracheal stenosis remains an unsolved clinical problem that has significant implications for the survival of some patients and the quality of life of others. However, recent advances in microvascular tissue transfer may allow tracheal transplantation to be used as a treatment option. Studies in dogs have demonstrated that the reanastomosis of the cranial thyroid artery (CTA) after the transplantation of a short segment of trachea sustains cartilage viability. However, the distal perfusion zone of the CTA within the canine trachea has not been described. Hence it is unclear what length of trachea can be safely harvested, with use of the CTA as the donor artery, without risking ischemia of the distal trachea. This study determined the perfusion territory of the CTA by use of latex or dye infusion via the thyroid branches of the CTA. Findings in five perfusion-fixed cadaver mongrel dogs (8 to 12 kg) were studied. In each dog, both common carotid arteries were dissected and the CTAs identified. The right CTA was ligated and the left common carotid artery was ligated cranial to the CTA. The left common carotid artery was perfused for 10 minutes under 100 mm Hg pressure with black india ink/saline solution (20:1000 ml) or with blue latex solution. Perfusion territories were determined by grossly and microscopically measuring the region of stain in the endolaryngeal and endotracheal airways. The results demonstrated that up to 18 ipsilateral rings of the canine trachea are perfused after injection of dye under physiologic pressure into the CTA. Contralateral staining was also noted, but to a lesser degree. These results suggest that the canine CTA may perfuse, on average, a 16- to 17-ring tracheal segment.

[Morphologic studies of the beginning of vascularization and ossification in human thyroid cartilage]. / Morphologische Untersuchungen zum Beginn von Vaskularisation und Knochenbildung im menschildren Schildknorpel.

In contrast to the cartilaginous preformed bones of the skeleton, ossification of human thyroid cartilage begins at the end of the second decade of life. The process continues until an advanced age and shows sex differences. An in-growth of blood vessels by cartilage canals is a prerequisite for ossification. The aim of the study was to investigate the temporal and spatial appearance of cartilage canals in thyroid cartilage. Extracellular matrices of cells in cartilage canals were characterized immunohistochemically. Corrosion casts indicated that the cricothyroid branch of the superior thyroid artery was involved in vascularization of the thyroid cartilage. The first cartilage canals were detectable at the end of puberty, always lying at certain distances to almost ossified areas of the thyroid cartilage. The extracellular matrix localized at the border of the cartilage canals reacted with antibodies against type I collagen and type III procollagen, as well as with antibodies against type II collagen. This finding suggests that these cells are intermediate between fibroblasts and chondrocytes.

Tracheal reconstruction with pedicled thyroid cartilage.

Limited areas of tracheal stenosis have been repaired with a variety of techniques. More extensive upper tracheal defects present a greater challenge with less predictable success. The following is the description of yet another technique for reconstruction of extensive upper tracheal defects. We report on the use of a muscle-pedicled thyroid alar graft which carries its own blood supply and perichondrial covering, supplies a large, conveniently shaped graft, requires one operative site and one operative sitting, and has proven advantageous even in the comprised patient.