ACS is characterized by prominent malformed ears with auricular clefts, mandibular condyle aplasia or hypoplasia, and a number of other features that are secondary to the auricular and oral abnormalities. In its most severe form, there is severe micrognathia and a characteristically round facial appearance with prominent cheeks.

The first branchial arch is the first of six branchial arches and is the embryological origin of most of the structures of the face. A wide variety of congenital conditions may arise from its contents. Understanding of the anatomic formation of this region is important in understanding abnormalities in development which aids in formation of a precise diagnoses and lists of differentials.

The 1st BA, also called the first pharyngeal arch and mandibular arch, is the first of six BAs that develops in fetal life. The BAs develop in the 4th and 5th weeks of development. The 1st BA is located between the stomodeum and the first pharyngeal groove. This arch divides into a maxillary and a mandibular process. The maxillary process becomes the maxilla and palate.

HFM is a common birth defect involving 1st and 2nd BA derivatives. The phenotype is highly variable. There may be cardiac, vertebral, and CNS defects, in addition to craniofacial anomalies. The features of HFM include unilateral deformity of the external ear and small ipsilateral half of the face with epibulbar dermoid and vertebral anomalies. Coloboma of the upper eyelid is frequent. The ear deformities range from preauricular tags of cartilagenous masses, to atresia of the external auditory canal, anomalies in the size and shape of the external auricle, and even to anotia. This syndrome is sometimes called oculoauriculovertebral dysplasia or Goldenhar Syndrome.

A 1st BCC is a cystic mass that arise in the parotid, posterior submandibular space or preauricular region. It is a remnant of the 1st branchial cleft due to incomplete closure in utero.

1.  To review the normal CT anatomy of the 1st branchial arch (BA) and associated structures with embryological correlation.

2.  To illustrate the imaging findings in classic syndromes affecting the first BA and associated structures.

3.  To discuss the list of differential diagnosis when examining malformations of the first BA and associated structures.

Failure of fusion between any of the facial structures results in a cleft which may be unilateral or bilateral. The two most common types of facial cleft are cleft lip which results from failure of the maxillary swellings to fuse with the intermaxillary process, and cleft palate, which results from the failure of the palatine shelves to fuse in the midline.

The 1st BA consists of a maxillary process and a mandibular process. The mesenchyme of the maxillary process gives rise to the maxilla, zygomatic bone and part of the temporal bone through membranous ossification. The mandible is also formed by membranous ossification of mesenchymal tissue surrounding Meckel’s cartilage. The 1st BA also contributed to formation of the ossicles.

Treacher Collins syndrome is a disorder of craniofacial development. The features include antimongoloid slant of the eyes, coloboma of the lid, micrognathia, microtia and other deformity of the ears, hypoplastic zygomatic arches, and macrostomia. Conductive hearing loss and cleft palate are often present.

Also called DiGeorge syndrome, VCFS is caused by a 1.5 to 3.0-Mb hemizygous deletion of chromosome 22q11.2. The syndrome consists of cleft palate, cardiac anomalies, typical facies, and learning disabilities. Less frequent features included microcephaly, mental retardation, short stature, slender hands and digits, minor auricular anomalies, and inguinal hernia. VCFS is the most frequent clefting syndrome, accounting for 8.1% of children with palatal clefts seen in their center. Cardiac anomalies were found in 82% including isolated ventricular septal defect and tetrology of Fallot.

1.  Digilio MC, Marino B, Capolino R, Dallapiccola B. Clinical manifestations of Deletion 22q11.2 syndrome (DiGeorge/Velo-Cardio-Facial syndrome). Images Paediatr Cardiol 2005; 23:23-34. 2.  Dixon MJ. Treacher Collins syndrome. Hum Mol Genet 1996; 5 Spec No:1391-1396. 3.  Gladwin AJ, Dixon J, Loftus SK, et al. Treacher Collins syndrome may result from insertions, deletions or splicing mutations, which introduce a termination codon into the gene. Hum Mol Genet

1996; 5:1533-1538. 4.  Gorlin RJ, Jue KL, Jacobsen U, Goldschmidt E. Oculoauriculovertebral Dysplasia. J Pediatr 1963; 63:991-999 5.  Larsen WJ. Human embryology. New York: Churchill Livingstone, 1993. 6.  Moore KL, Dalley AF. Clinically oriented anatomy. Philadelphia: Lippincott Williams & Wilkins, 1999. 7.  Sadler TW, Langman J. Langman's medical embryology. In. 10th ed. Philadelphia: Lippincott Williams & Wilkins, 2006; xiii, 371 p. 8.  Sheffield LJ, Reiss JA, Strohm K, Gilding M. A genetic follow-up study of 64 patients with the Pierre Robin complex. Am J Med Genet 1987; 28:25-36. 9.  Shprintzen RJ, Goldberg RB, Young D, Wolford L. The velo-cardio-facial syndrome: a clinical and genetic analysis. Pediatrics 1981; 67:167-172. 10.  Shprintzen RJ, Wang F, Goldberg R, Marion R. The expanded velo-cardio-facial syndrome (VCF): additional features of the most common clefting syndrome. Am. J. Hum. Genet. 1985; 37:A77. 11.  Som PM, Curtin HD. Head and neck imaging. St. Louis, Mo.: Mosby, 2003. 12.  Storm AL, Johnson JM, Lammer E, Green GE, Cunniff C. Auriculo-condylar syndrome is associated with highly variable ear and mandibular defects in multiple kindreds. Am J Med Genet A 2005;

138:141-145.

13d 13e 13f 13g

A 2nd BCC is the most common BCC accounting for >90% of all BCC anomalies. It is considered a failure of closure of the cervical sinus. Typically painless mass along the sternocleidomastoid (SCM), but may become infected.

16c

16d

4 3 5

6 7 8

10a 10b 10c

10d 10e 10f 10g

9a

9b

11a 9d

13a 13b 13c

15a 15b 15c

15d

16a 16b

Mandibular symphysis

Ramus of mandible

Mental tubercle

Maxilla

Intermaxillary suture

Mental foramen

Body of mandible

Angle of mandible

1

TMJ

9c

11a 11b 11c

12a 12b 12c 12d

14a 14b 14c

14d 14e 14f

Condylar process

Coronoid process Body of

mandible

Zygomatic arch

Orbitomeatal plane

Ramus of mandible

TMJ

Angle of mandible

Clinical Finding

Affected individuals

Facial anomaly

100%

Congenital heart defect

82%

Speech / Learning difficulties

80%

Neonatal hypocalcemia

73%

T-Cell deficiency

69%

Skeletal anomaly

32%

Palatal anomaly

31%

Asymmetric crying face

21%

Renal malformations

15%

Genital anomaly

11%

2