All cases were correlated with clinical observations. Each case was reviewed by 3 radiologists, and extension of the thyroid gland into the mediastinum or cranially behind or along the sides of the pharynx was noted. Standard definitions of the mediastinum and its compartments were also used. The maximal size of a normal thyroid gland and the limits of the normal thyroid bed were defined on the basis of established anatomic measurements. Methods We used a 28-month period, to retrospectively identify 190 cases of neck goiters that underwent computed tomographic imaging. Objectives To analyze the distribution of thyroid goiters into the mediastinum and/or behind or along the sides of the pharynx, and to review the anatomy of the spaces in the neck that explains these extensions. Shared Decision Making and Communication.Scientific Discovery and the Future of Medicine.Health Care Economics, Insurance, Payment.Clinical Implications of Basic Neuroscience.Challenges in Clinical Electrocardiography.Once behind the esophagus, it can then grow caudally into the posterior mediastinum or cranially into the retropharyngeal space, both of which are areas of the common visceral space. The thyroid gland can also grow posteriorly into the retrovisceral space. The gland can extend caudally and anteriorly into the pretracheal space and substernal region. The arrows indicate the 3 directions of growth that the thyroid gland can take. The inside of the space is seen via a cutaway in the fascia. B, The actual space is represented without the visceral contents. The common fascia around the cervical esophagus (visceral fascia) is also seen as it extends around the pharyngeal constrictor muscles extending up to the skull base. The fascia around the inferior thyroid artery is also seen as it divides the lower portion of the visceral compartment into anterior pretracheal and posterior retrovisceral spaces. A, Through a cutaway in the fascia, the thyroid gland and trachea are seen within the visceral compartment. The fifth arch only exists transiently, and no human structures are derived from the fifth arch.Oblique drawings of the neck from the left side. The cranial nerve supply to the sixth arch structures is the recurrent laryngeal branch of CN X (vagus nerve). The cranial nerve supply to the fourth arch structures is the superior laryngeal branch of CN X (vagus nerve). The muscles derived from the sixth arch include the intrinsic muscles of the larynx (except the cricothyroid). The muscles derived from the fourth arch include the pharyngeal constrictors and the cricothyroid. The fourth and sixth arches give rise to various cartilages including the thyroid, cricoid, arytenoids, corniculate and cuneiform. They are comprised of cartilage support (serving as a precursor to skeletal elements), arterial supply (from the aortic arch system) and cranial nerve supply. They are all derived from mesoderm and appear early in the third to fourth gestational week, and differentiate into terminal structures by the seventh to eighth gestational week. The pharyngeal arches (also known as branchial arches) are a fundamental aspect of vertebrate head and neck development.
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