2017 Sec 1 Green Book

Table 1. Table of Embryologic Origin of Head and Neck Structures Derived from the Branchial Apparatus (Simplified)

auditory canal. 3 The sinus tract often runs parallel to the exter- nal auditory canal (Fig 4). The imaging appearance of a Work type II cyst (periparotid cyst) is that of a cystic structure super- ficial to, in, or deep to the parotid gland (Fig 5). In case of in- volvement of the deep lobe of the parotid gland, extension into the parapharyngeal space or even the posterior submandibu- lar space may occur. There are no reliable imaging features to differentiate Work type II branchial cleft cysts from other cystic parotid lesion. 3,12 Surgical removal of first branchial cleft anomalies requires familiarity with the complex and intimate relationship of these lesions with the facial nerve. 23 Second branchial cleft anomalies (75-95% of branchial ap- paratus anomalies) occur along the second branchial cleft tract extending from the oropharyngeal mucosa in the tonsillar fossa, coursing lateral in between the glossopharyngeal and hypoglos- sal nerve through the carotid bifurcation region and descend- ing lateral to the common carotid artery to the supraclavicu- lar region. 12,24 The lesion often manifests as an asymptomatic slowly enlarging mass in childhood or early adulthood and may be painful if secondarily infected. The Bailey classification dis- tinguishes four subtypes of second branchial cleft cysts. Only the Baily type III cyst is of clinical relevance (Fig 6), because the cyst may show the pathognomonic imaging finding of a small extension of the cyst between the proximal internal/external carotid artery close to the common carotid artery bifurcation (beak sign). 3 Third branchial cleft cysts are rare anomalies, but remain the second most common congenital lesion of the posterior cervical space after lymphatic malformations. 12,25 They arise in the third branchial cleft tract coursing from the piriform sinus, through the thyrohyoid membrane and subsequently posterior to the common or internal carotid artery between the glossopharyn- geal and hypoglossal nerve. The tract of the third branchial cyst is located above the course of the laryngeal nerve, a discrimina- tive feature for differentiating these cysts from fourth branchial cleft anomalies. 12 On imaging, the anomaly is identified as a thin-walled unilocular cystic structure located anterior or deep to the sternocleidomastoid (SCM) muscle. 3,26 Fourth branchial apparatus anomalies are extremely rare and arise in the fourth branchial cleft tract coursing from the piriform sinus, through the thyrohyoid membrane and descend- ing into the mediastinum along the tracheoesophageal groove. On imaging, lesions involving the fourth branchial cleft tract are

Cleft

Arch

Pouch

1st

External

Mandible, incus,

Eustachian tube, tympanic cavity, mastoid

auditory canal

malleus, muscles of mastication Part of hyoid bone, styloid process, stapes, muscles of facial expression, stapedius muscle, posterior belly of digastric muscle, cranial nerve VII and VIII Part of hyoid bone, superior constrictor muscle, stylopharyngeus muscle, cranial nerve IX, internal carotid artery Cuneiform cartilage, superior laryngeal nerve, aortic arch

2nd Cervical sinus of His

Palatine tonsil

3rd Cervical sinus of His

Inferior

parathyroid gland, thymus, pyriform fossa

4th Cervical sinus of His

Superior

parathyroid gland

and right subclavian artery, thyroid gland

5th Rudimentary Laryngeal cartilage, laryngeal

Thyroid cells

6th

muscles, inferior pharyngeal constrictors, cranial nerve XI, recurrent laryngeal nerve

triangle. 12,21 The lesions often present as a mass or swelling in the periauricular or mandibular region, with a history of recur- rent infection/inflammation likely due to the presence of a sinus tract. The Work classification of first branchial cleft cysts de- scribes two subtypes. The Work type I cyst (periauricular cyst) is located close to the external auditory canal. On imaging, a cystic structure around the pinna anterior, inferior, or poste- rior to the external auditory canal is identified. The structure may beak toward the bony-cartilaginous junction of the external

Fig 4. Axial (A) and sagittal (B) fat-suppressed T2-weighted MR images of a child with a Work type I first branchial cleft anomaly. The images demonstrate a cystic structure in the left pinna region anterior to the external auditory canal. The sinus tract runs parallel to the external auditory canal.

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