2017 Sec 1 Green Book

Table 1. Table of Embryologic Origin of Head and Neck Structures

Derived from the Branchial Apparatus (Simplified)

Cleft

Arch

Pouch

1st

External

auditory

canal

Mandible, incus,

malleus, muscles of

mastication

Eustachian tube,

tympanic

cavity, mastoid

2nd Cervical sinus

of His

Part of hyoid bone,

styloid process,

stapes, muscles of

facial expression,

stapedius muscle,

posterior belly of

digastric muscle,

cranial nerve VII

and VIII

Palatine tonsil

3rd Cervical sinus

of His

Part of hyoid bone,

superior constrictor

muscle,

stylopharyngeus

muscle, cranial

nerve IX, internal

carotid artery

Inferior

parathyroid

gland, thymus,

pyriform fossa

4th Cervical sinus

of His

Cuneiform cartilage,

superior laryngeal

nerve, aortic arch

and right subclavian

artery, thyroid gland

Superior

parathyroid

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

auditory canal.

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.

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).

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.

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

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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