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Hemifacial Microsomia in Pediatric Patients: Asymmetric Abnormal Development of the First and Second Branchial Arches

¹ Department of Radiology, Children's Hospital & Regional Medical Center, 4800 Sand Point Way N.E., CH-69, Seattle, WA 98105.
² Department of Otolaryngology, University of Washington, 1959 N.E. Pacific St., Seattle, WA 98195.
³ Children's Craniofacial Center, Children's Hospital & Regional Medical Center, Seattle, WA 98105.

View larger version (29K): [in a new window]   Fig. 1A. —Drawings illustrate migration of neural crest cells and development of branchial arches. Neural crest cells (NC) form as neural plate folds and meets in midline to form neural tube (NT). These cells then migrate throughout body to form diverse structures of head, neck, and body.

View larger version (24K): [in a new window]   Fig. 1B. —Drawings illustrate migration of neural crest cells and development of branchial arches. Branchial arches develop in craniocaudal sequence. First branchial arch (I) begins to form at approximately day 22 of gestation; second (II) and third (III) arches, at day 24 of gestation; and fourth (IV) and sixth (VI) arches, at day 29 of gestation.

View larger version (34K): [in a new window]   Fig. 2A. —Drawings illustrate branchial arch and membrane anatomy at approximately 5 weeks' gestation. First (I), second (II), third (III), fourth (IV), and sixth (VI) branchial arches are shown. Plane of section through branchial arches corresponds to interrupted line in Figure 1B. Area outlined by rectangle illustrates cross-sectional anatomy of one branchial arch.

View larger version (47K): [in a new window]   Fig. 2B. —Drawings illustrate branchial arch and membrane anatomy at approximately 5 weeks' gestation. Each arch contains arch-specific cartilage (C), muscle anlage (M), artery (A), and cranial nerve (CN). Inner branchial pouch (FBP) is lined by endoderm (EN), and outer branchial cleft (groove) (FBC) is lined by ectoderm (EC). Branchial membrane (FBM) consists of endodermal cells of branchial pouch, ectodermal cells of branchial cleft, and intervening mesoderm.

View larger version (36K): [in a new window]   Fig. 3A. —Drawings show first branchial arch derivatives. Arch dermal mesenchyme forms mandible, maxilla, zygomatic temporal bone, and squamous temporal bone (ST) through direct ossification. First-arch cartilage derivatives include malleus (M); incus (I); alisphenoid (greater wing of sphenoid); and small fibrous core in mandible, which is called Meckel's cartilage (MC).

View larger version (133K): [in a new window]   Fig. 4A. —Facial bones in 4-year-old girl with left hemifacial microsomia. Three-dimensional CT reconstruction shows hypoplastic, malformed left mandibular body, ramus, and condyle (arrow) that does articulate with glenoid fossa (type 2A mandible). Zygomatic arch (arrowhead) is incomplete, and maxilla and squamous temporal bone are small. Note bony atresia of external auditory canal.

View larger version (138K): [in a new window]   Fig. 4B. —Facial bones in 4-year-old girl with left hemifacial microsomia. Three-dimensional CT reconstruction of contralateral side with normal appearance of mandible, maxilla, zygomatic arch, squamous temporal bone, external auditory canal, and temporomandibular joint (arrow).

View larger version (94K): [in a new window]   Fig. 5A. —Temporal bone in 4-year-old boy with left hemifacial microsomia. Coronal CT scan obtained through right temporal bone shows normal malleus (arrow), tympanic cavity, external auditory canal, and pinna.

View larger version (106K): [in a new window]   Fig. 5B. —Temporal bone in 4-year-old boy with left hemifacial microsomia. Coronal CT scan obtained through left temporal bone shows fused, malformed malleus and incus (arrow), which are displaced and fused to lateral wall of tympanic cavity. Note bony and soft-tissue atresia of external auditory canal. Pinna is small and malformed.

View larger version (113K): [in a new window]   Fig. 5C. —Temporal bone in 4-year-old boy with left hemifacial microsomia. Axial CT scan obtained through right temporal bone shows normal malleoincudal articulation (straight arrow) and tensor tympani muscle (wavy arrow). Inner ear structures are normal.

View larger version (94K): [in a new window]   Fig. 5D. —Temporal bone in 4-year-old boy with left hemifacial microsomia. Axial CT scan obtained through left temporal bone shows fusion of malleus and incus (arrowhead), small tensor tympani muscle (arrow), and malformed pinna. Inner ear structures are normal.

View larger version (46K): [in a new window]   Fig. 3B. —Drawings show first branchial arch derivatives. Muscle anlage of first branchial arch gives rise to muscles required for mastication—temporal (T), masseter (M), medial and lateral pterygoids (P)—and to anterior belly of digastric muscle (ABD), tensor tympani muscle (TT), mylohyoid muscle (MH), and tensor muscle of velum palatinum.

View larger version (135K): [in a new window]   Fig. 6A. —Muscles of mastication in 7-year-old girl with left hemifacial microsomia. Axial CT scan shows normal right masseter muscle (straight arrow) and medial pterygoid muscle (arrowhead) compared with hypoplastic left medial pterygoid muscle (wavy arrow) and essentially absent masseter muscle. Patient has complex segmentation anomalies of cervical spine resulting in left convex scoliosis and eccentric position of dens relative to anterior arch of C1. These vertebral anomalies, which are traditionally associated with Goldenhar's syndrome, are now generally considered part of spectrum of findings associated with hemifacial microsomia.

View larger version (151K): [in a new window]   Fig. 6B. —Muscles of mastication in 7-year-old girl with left hemifacial microsomia. CT scan shows normal right lateral pterygoid muscle inserting along lateral surface of lateral pterygoid plate (straight arrow). On left, small and poorly formed lateral pterygoid muscle (arrowhead) can be identified by its insertion on hypoplastic lateral pterygoid plate. Lateral pterygoid muscle is difficult to distinguish from medial pterygoid muscle, which inserts into pterygoid fossa. Muscle lying lateral to lateral pterygoid fossa is temporal muscle (wavy arrow), which inserts inferiorly on dysplastic mandible.

View larger version (132K): [in a new window]   Fig. 6C. —Muscles of mastication in 7-year-old girl with left hemifacial microsomia. Axial CT scan obtained through level of temporal fossae shows normal temporal muscle on right (arrowhead) and hypoplasia of contralateral temporal muscle on left (arrow). Left zygomatic arch is incomplete. Note bony atresia of left external auditory canal.

View larger version (88K): [in a new window]   Fig. 7. —Anterior belly of digastric muscle in 4-year-old girl with left hemifacial microsomia. Axial CT scan obtained through floor of mouth shows normal right anterior belly of digastric muscle (arrowhead) and atresia of left anterior digastric muscle. Rounded soft-tissue structure adjacent to anterior digastric muscle is submandibular gland.

View larger version (27K): [in a new window]   Fig. 8A. —Drawings show derivatives of second branchial arch. Cartilage derivatives of second branchial arch include stapes (S), styloid process (SP), stylohyoid ligament (SL), and lesser horns and upper rim of hyoid bone (H).

View larger version (123K): [in a new window]   Fig. 9. —Hyoid bone in 11-year-old girl with left hemifacial microsomia. Axial CT scan obtained through hyoid bone shows absence of left lesser and greater horn of hyoid bone; greater horn is derived from third branchial arch. Normal lesser horn (arrowhead) and greater horn (arrow) are visible on right.

View larger version (50K): [in a new window]   Fig. 8B. —Drawings show derivatives of second branchial arch. Muscle anlage of second branchial arch gives rise to muscles of facial expression including orbicular muscle of mouth (OM) and of eye (OE), nasal muscle (N), levator muscle of upper lip, greater and lesser zygomatic muscles, buccinator muscle (B), auricular muscles (A), and occipitofrontal muscle (OF). Other muscles that originate from second branchial arch are posterior belly of digastric muscle (PBD), stapedius muscle (S), and stylohyoid muscle (SH).

View larger version (115K): [in a new window]   Fig. 10A. —Muscles of facial expression in 13-year-old girl with right hemifacial microsomia. CT scan shows that left orbicular muscle of mouth has normal bulk (arrow), whereas right is atretic.

View larger version (136K): [in a new window]   Fig. 10B. —Muscles of facial expression in 13-year-old girl with right hemifacial microsomia. CT scan shows bulk of left levator muscle of upper lip (straight arrow) and greater zygomatic muscle (arrowhead) compared with atretic right side. Also note atretic right mandibular ramus (wavy arrow).

View larger version (130K): [in a new window]   Fig. 10C. —Muscles of facial expression in 13-year-old girl with right hemifacial microsomia. CT scan shows left orbicularis oculi muscle is normal (arrow), but right orbicularis oculi muscle is barely visible. Note bony atresia of right external auditory canal and malformed, small, and flattened pinna (arrowhead).

View larger version (129K): [in a new window]   Fig. 10D. —Muscles of facial expression in 13-year-old girl with right hemifacial microsomia. CT scan shows left frontalis muscle is thin soft-tissue sheet that can be seen over the frontal bone (arrow). Atretic right muscle can barely be detected. Note normal bulk of left temporal muscle in temporal fossa (arrowhead) in contrast to atretic right temporal muscle.

View larger version (14K): [in a new window]   Fig. 11A. —Drawings illustrate development of pinna. Areas with black dots = first branchial arch, areas with white dots = second branchial arch. Pinna originally arises from six swellings, or auricular hillocks (AH), of first (FBA) and second branchial arches (SBA), which flank first branchial cleft (FBC).

View larger version (87K): [in a new window]   Fig. 11B. —Drawings illustrate development of pinna. Areas with black dots = first branchial arch, areas with white dots = second branchial arch. Auricular hillocks fuse and remodel to form structures of immature pinna.

View larger version (88K): [in a new window]   Fig. 11C. —Drawings illustrate development of pinna. Areas with black dots = first branchial arch, areas with white dots = second branchial arch. Pinna is fully formed and predominantly originates from second branchial arch.

View larger version (30K): [in a new window]   Fig. 12A. —Drawings reveal development of external, middle, and inner ear. Gray area = cartilage condensations of neural crest origin, areas with horizontal lines = ectoderm, areas with diagonal lines = endoderm. First branchial cleft (FBC) will become external auditory canal, first branchial pouch (FBP) will become auditory canal (eustachian tube) and tympanic cavity, and otic vesicle (OV) (ectodermal derivative) will give rise to membranous labyrinth. Ossicles (OC) are formed from cartilage condensations of neural crest origin. EA = endolymphatic appendage, AH = auricular hillocks.

View larger version (29K): [in a new window]   Fig. 12B. —Drawings reveal development of external, middle, and inner ear. Gray area = cartilage condensations of neural crest origin, areas with horizontal lines = ectoderm, areas with diagonal lines = endoderm. Medial-developing external auditory canal becomes filled with meatal plug (MP) consisting of proliferating ectodermal cells that subsequently recanalize. Tubotympanic recess (TR) has deepened to form tympanic cavity (TC). Otic vesicle forms endolymphatic duct and sac (ES), early semicircular canals (SC), and cochlear diverticulum (CD). Membranous labyrinth induces surrounding mesenchyme to condense and ultimately form bony labyrinth. S = stapes, I = incus, M = malleus.

View larger version (55K): [in a new window]   Fig. 12C. —Drawings reveal development of external, middle, and inner ear. Gray area = cartilage condensations of neural crest origin, areas with horizontal lines = ectoderm, areas with diagonal lines = endoderm. External auditory canal (EAC) is separated from tympanic cavity (TC) by tympanic membrane (TM), which has inner layer of endoderm, middle layer of mesoderm, and outer layer of ectoderm. Tympanic cavity has expanded around ossicles, leaving endodermal surface layer. Membranous labyrinth and surrounding bony labyrinth are in apposition with tympanic cavity via oval window (OW) and round window (RW). ES = endolymphatic sac, ED = endolymphatic duct, S = saccule, CD = cochlear duct, U = utricle, AT = auditory tube, SSC = superior semicircular canal, LSC = lateral semicircular canal, PSC = posterior semicircular canal, ET = epitympanum.

View larger version (101K): [in a new window]   Fig. 13A. —Abnormal facial nerve course and small tympanic cavity in 5-year-old boy with left hemifacial microsomia. Coronal CT scan obtained through normal right temporal bone shows horizontal segment of facial nerve lying just beneath lateral semicircular canal (white arrowhead). Stapes inserts into unobstructed oval window (black arrowhead).

View larger version (115K): [in a new window]   Fig. 13B. —Abnormal facial nerve course and small tympanic cavity in 5-year-old boy with left hemifacial microsomia. Coronal CT scan obtained through abnormal left temporal bone shows anterior displacement of vertical segment of facial nerve (arrows), which crosses in front of oval window (arrowhead). Tympanic cavity measures less than 3 mm from promontory of cochlea to lateral wall of tympanic cavity. Also note bony atresia of external auditory canal and virtual aplasia of pinna.

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