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Fig 5. Axial T1-weighted (A) and axial fat-suppressed T2-weighted (B) MR images of a child with a Work type II first branchial cleft anomaly. The images demonstrate a well-defined, thin-walled cystic structure in the right parotid gland. On the axial T2-weighted image (B), the cyst content reveals debris in the dependent portion of the lesion, possibly due to prior infection, inflammation, or trauma.

Fig 6. Axial T1-weighted (A), axial fat-suppressed T2-weighted (B), and sagittal T1-weighted (C) MR images of a child with a Bailey type II second branchial cleft anomaly. The images demonstrate a well-defined, thin-walled cystic structure situated in the lateral neck. The axial images (A, B) demonstrate the classic location of the cyst lateral to the carotid space. The sagittal image (C) shows the other classical location landmarks of the cyst, positioned along the anterior surface of the sternocleidomastoid muscle and posterior to the submandibular space.

the anterior superior mediastinum. 12,27 Thymopharyngeal duct anomalies have a high preference for the left side of the neck; however, midline and right-sided anomalies are seen. 21 Cervical thymic cysts arise along the tract of the thymopha- ryngeal duct. The etiology of these cysts is controversial. One of the prevailing theories for the pathogenesis is the congen- ital persistence of thymopharyngeal duct remnants as origin of the lesions. A less favored hypothesis is that the cysts re- sult from acquired progressive cystic degeneration of thymic elements (corpuscles, epithelium reticulum). 3 US imaging may show a large unilocular or multilocular cystic structure anterior or deep to the SCM muscle with downward extension parallel to the SCM muscle. A characteristic imaging finding during US examination is rapid enlargement of the lesion during Val- salva maneuver. The typical location of the cyst adjacent to the carotid space and the degree of extension into the superior me- diastinum are better appreciated on MR imaging (Fig 7). The T1 signal of the cyst varies from hypointense to hyperintense, depending on the protein content of the cyst material or prior intracystic hemorrhage. 3,12 Ectopic or residual thymic tissue can occur as solitary thy- mopharyngeal duct anomaly or in association with cervical thymic cyst formation. On imaging, ectopic thymic tissue has imaging features identical to normal positioned thymic tissue

identified as sinus tracts or sinus tract complications (eg, abscess) and are in general left-sided lesions. The left thyroid lobe is a preferred location. In this specific location, a fourth branchial cleft cyst can be confused with thyroglossal duct cysts or thyroid cysts. Furthermore, the imaging features of a fourth branchial cleft cyst can appear similar to an external or mixed laryngo- cele. The position of the branchial cleft anomaly in reference to the laryngeal nerve differentiates fourth from third branchial cleft anomalies. Anomalies derived from the fourth branchial cleft are typically located below the laryngeal nerve. 12,24,26 Thymopharyngeal Duct Anomalies Thymopharyngeal duct anomalies are very rare congenital anomalies. These lesions show a slight male predominance and frequently present in the first decade of life as this is the age of maximal thymic activity and size. A common presentation is that of a slow growing asymptomatic neck lesion with symp- toms of mass effect and compression (eg, dysphagia, dyspnea, pain, and hoarseness) of adjacent structures in 10% of cases. During embryonic development, the thymus derives from the third branchial pouch. Subsequent descending migration of the thymus into the mediastinum is facilitated through the thy- mopharyngeal duct. The course of the duct extends from the level of the mandibular angle, lateral to the thyroid gland, into

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