Dept. of Radiology, UNC Chapel Hill Branchial Cleft Cysts David M. Chaky, MD Dept. of Radiology, UNC Chapel Hill

Introduction The embryologic model is used to explain the origins of all branchial apparatus anomalies. The most accepted theory proposes that vestigial remnants result from incomplete obliteration of the branchial apparatus or buried cell rests, and, thus, if cells are trapped  in the branchial apparatus during  the embryologic stage, they can  form branchial cysts later in life.

The branchial apparatus consists of a series of  6 mesodermal arches separated from each other externally by ectodermal-lined branchial clefts (grooves) and internally by endodermal- lined pharyngeal pouches. By the end of the 4th week of gestation, 4 well-defined pairs of branchial arches are visible externally; the 5th and 6th arches are small and cannot be seen on the embryonic surface.

Embryology and Anatomy Branchial System: 6 pairs of pharyngeal arches separated by endodermally lined pouches and ectodermally lined clefts. Each arch consists of a nerve, artery, and cartilaginous structures. The remaining neck musculature gains contributions from cervical somites.

Common Lateral Neck Masses in Infancy Branchial cleft anomalies Laryngoceles Dermoid and Teratoid Cysts Sternocleidomastoid Pseudotumor of Infancy (fibromatosis colli) Plunging ranulas Adenopathy

First Branchial Cleft Cysts Imaging Findings Best diagnostic clue: Cystic mass around pinna and EAC (type I) or extending from EAC to angle of mandible (type II) Well-circumscribed, non enhancing or rim-enhancing, low-density mass If infected, may have thick enhancing rim or be dense internally Top Differential Diagnoses *Benign Lymphoepithelial Cysts *Venolymphatic Malformation (VLM) *Suppurative Adenopathy/Abscess *Nontuberculous Mycobacterial Adenitis

First Branchial Cleft Cysts Type I Ectodermal Duplication anomaly of the EAC with squamous epithelium only. Parallel to the EAC Pretragal, post auricular Connection with TM or Malleus>Incus Surgical Excision

First Branchial Cleft Cysts Type II Squamous epithelium and other ectodermal components Anterior neck, superior to hyoid bone. Courses over the mandible and through the parotid in variable position to the Facial Nerve. Terminates near the EAC bony-cartilaginous junction. Surgical excision- superficial parotidectomy

First Branchial Cleft Cyst, Type 2

First Branchial Cleft Cysts Accounts for 8% of all branchial apparatus remnants Most common location for 1st BCC to terminate is in EAC between its cartilaginous & bony portions

Second Branchial Cleft Cysts Most Common (90%) branchial anomaly Painless, fluctuant mass in anterior triangle Inferior-middle 2/3 junction of SCM, deep to platysma, lateral to IX, X, XII, between the internal and external carotid and terminate in the tonsillar fossa Surgical treatment may include tonsillectomy

Second Branchial Cleft Cysts Imaging Findings Low density cyst with non enhancing wall & surrounding soft tissues, unless infected If infected, wall is thicker & enhances with surrounding soft tissues appearing "dirty" (cellulitis) or internally dense Top Differential Diagnoses Lymphangioma Thymic cyst Suppurative jugulodigastic node Cystic vagal schwannoma Cystic malignant adenopathy (ALWAYS CONSIDER THIS POSSIBILITY IN ADULTS!)

Second Branchial Cleft Cysts

Second Branchial Cleft Cysts * Epidemiology: 2nd BCC account for > 90% of all branchial cleft anomalies in teens and adults, 66-75% in children * Most common signs/symptoms: Painless, compressible lateral neck mass in child or young adult * Neck mass often chronic, recurrent, increasing in size with upper respiratory tract infection * Beware an adult with first presentation of "2nd BCC” * Mass may be metastatic node from head & neck SCCa primary tumor

Third Branchial Cleft Cysts Rare (<2%) Similar external presentation to 2nd BCC Internal opening is at the pyriform sinus, then courses cephalad to the superior laryngeal nerve through the thyrohyoid membrane, medial to IX, lateral to X, XII, posterior to internal carotid Surgical approach must visualize recurrent layngeal nerves- Thyroidectomy incision

Third Branchial Cleft Cysts

Third Branchial Cleft Cysts Imaging Findings *Best diagnostic clue: Unilocular thin-walled cyst in posterior cervical space (posterior triangle) *May occur anywhere along course of 3rd branchial cleft or pouch Top Differential Diagnoses * 2nd branchial cleft cyst * 4th branchial cyst * Lymphangioma * Infrahyoid thyroglossal duct cyst * Suppurative adenopathy * External laryngocele * Cystic-necrotic lymph node

Fourth Branchial Cleft Cysts Courses from pyriform sinus apex caudal to superior laryngeal nerve, to emerge near the cricothryoid joint, and descend superficial to the recurrent laryngeal nerve.

Fourth Branchial Cleft Cysts

Fourth Branchial Cleft Cysts Imaging Findings * Best diagnostic clue: Unilocular thin-walled cyst in superior lateral aspect of LEFT thyroid lobe with associated thyroiditis * May occur anywhere from LEFT pyriform sinus apex to thyroid lobe * Morphology: Unilocular & thin-walled unless infected Top Differential Diagnoses * Thyroglossal duct cyst * Thymic cyst * 3rd branchial cleft cyst * Lymphangioma * Thyroid colloid cyst * Parathyroid cyst * Thyroid abscess

Fourth Branchial Cleft Cysts Clinical Issues, may present as: * Recurrent neck abscesses * Recurrent suppurative thyroiditis * Imaging diagnosis of left thyroid lobe abscess in pediatric patient should strongly suggest diagnosis of infected 4th BCC