2017 Sec 1 Green Book

Fig 7. Sagittal T2-weighted fetal MR images of a fetus with a cervical thymic cyst (A-C). The images show a well-defined, thin-walled, unilocular cystic structure in the left lateral neck. The images demonstrate the typical location of the cyst (A) adjacent to the carotid space (B) and the continuity with the mediastinal thymus (C).

relatively large and starts to involute by the end of the sixth year. Congenital laryngeal anomalies typically manifest with respiratory difficulties or dysphagia during the neonatal time period. 6,12 Laryngoceles are air-filled dilated laryngeal saccules com- municating with the cavity of the larynx. They may arise from congenital anomalous large saccules with a potential subsequent narrow ventricular orifice and demonstrate progressive expan- sion with increased intraluminal laryngeal pressure (eg, crying). Acquired laryngoceles are often associated with laryngeal carci- noma causing (partial) occlusion of the ventricular orifice. 12,28,29 Saccular cysts are saccular dilatations filled with mucus and develop secondary to atresia of the orifice of the ventricle (con- genital) or obstruction of the ventricular orifice due to mucus retention (acquired). 6,28 Both laryngoceles as well as saccular cysts demonstrate sim- ilar modes of potential distension and expansion through struc- turally weak areas of the larynx. They may extend beyond the superior border of the thyroid cartilage but remain confined to the larynx (internal type). In contrast, the dilated laryngeal sac- cules can penetrate the thyrohyoid membrane and extend into the supraglottic subcutaneous tissues of the neck (external type). The component superficial to the thyrohyoid membrane is typ- ically dilated, while the saccular portion inside the membrane is normal in size. The combined type shows abnormal dilatation of the saccule on both sides of the thyrohyoid membrane. 12,28,42 The external type as well as the combined type will result in a neck mass. On imaging, a well-defined mass in the lateral

and may be identified anywhere along the course of the thy- mopharyngeal duct. US may reveal the typical “starry sky” appearance of thymic tissue in an aberrant location. If solid components are identified in cervical thymic cysts, this will probably represent additional ectopic thymic tissue. These focal elements of ectopic thymic tissue demonstrate mild enhance- ment on postcontrast MR imaging sequences. 3,21 In 50% of cases of thymopharyngeal duct anomalies, either cervical thymic cysts or ectopic thymic tissue, a connection can be identified between the anomaly and the mediastinal thymic tissue by direct extension, also referred to as cervical extension of the thymus, or through a fibrous cord (representing a remnant of the thymopharyngeal duct). 12 Laryngeal Anomalies Laryngeal anomalies are uncommon congenital or acquired malformations that rarely present during childhood and are more commonly seen in adults. Laryngoceles and saccular cysts arise from the saccule, or appendix, of the laryngeal ventricle. The orifice of the laryngeal ventricle (of Morgagni) is located between the false and true vocal cords. The laryngeal saccule originates from the roof of the laryngeal ventricle and extends superiorly bounded by the false vocal cord and aryepiglottic fold medially and by the thyroid cartilage laterally. Because of the numerous amount of mucous glands in the saccule, it has been hypothesized that it provides lubrication of the vo- cal cords. 12 From birth to the sixth year of life, the saccule is

Fig 8. Axial CT image in soft tissue window (A) and lung window (B) and coronal CT image in soft tissue window (C) of a child with a laryngocele. The images show an air-filled well-defined mass in the lateral aspect of the superior paralaryngeal space (A, B) in keeping with a dilated laryngeal saccule. Note that the mass extends beyond the superior border of the thyroid cartilage (C) but remains confined to the larynx and therefore represents an internal type laryngocele.

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