HEMIFACIAL MICROSOMIA- Basics

Hemifacial microsomia is the second congenital malformation in prevalence, after cleft lip and palate, and is described as a congenital alteration of the first and second branchial arches.

Hemifacial microsomia (HFM) corresponds to a spectrum of congenital craniofacial malformations characterized by hypoplasia of tissues embryologically originating from the first and second branchial arches.

PATHOGENESIS :

Explained by different theories.

1. Poswillo's theory - Vascular disruption causing bleeding during embryologic formation of the stapedial artery, accompanied with alterations in the development of the first and the second branchial arches. 

2. Johnston's theory-  An alteration in the migration of cells of the neural crest towards the formation of the trigeminal ganglion. This lack in migration, and therefore the absence of interaction between mesenchyme and neural crest cells, has been associated with other problems observed in HFM patients, such as microdontia and hypodontia, cleft palate and heart problems.

3. Other authors suggest this relationship between lack of migration of cells of the neural crest and HFM because in the absence of these cells there is less vascular endothelial growth factor (VEGF). This growth factor promotes the proliferation of Meckel cartilage, and the absence of VEGF creates a correlation with mandibular hypoplasia.

CLASSIFICATION: 

Pruzansky's classification of HFM

Grade I	Smaller mandible than the preserved normal side
Grade II	on the affected mandible; condyle, ramus, and sigmoid notch identifiable, but grossly distorted in size and shape
Grade III	affected mandible is grossly distorted, loss or agenesis of ramus, condyle and TMJ.

CLINICAL FEATURES

 

1. Jaw and TMJ: asymmetrical mandibular development for hypoplasia, absence of mandibular structures (condyle and ramus), absence or ankylosis of temporomandibular joint (TMJ). 

 

2. Orbit: orbital dystopia (bad position), epibulbar dermoid, anophthalmia/microphthalmia, blepharoptosis, retinal or choroidal coloboma, among other less frequent anomalies.

 

3. Ears: microtia, anotia, loss of hearing, disorders of the middle ear.

 

4. Cranial nerves: involvement of facial nerve and, in more severe cases, of the tgminal and hypoglossal nerves.

 

5. Dental: agenesis, dental hypoplasias, microdontia, and malocclusions. Delayed tooth development in HFM patients type IIB and III, with the most alterations in posterior teeth.

 

6. Maxillofacial: labio-palatal fissure,macrostomia, hypoplasia of the facial thirds, occlusal plane inclination (highly variable in angle), hypoplasia of masticatory muscles, velopharyngeal insufficiency.

 

7. Extracranial changes: primarily in kidney, lungs, heart, gastrointestinal, skeletal, and central nervous system (CNS).

 

DIAGNOSIS 

 

Although diagnosis is mainly clinical, various complementary tests allow a better analysis of this pathology. Panoramic radiography (OPG) an initial analysis of the structures of mandibular and maxillofacial structures, evaluating both sides in the same image. A lateral cephalometry allows evaluating, through cephalometric analysis, the relations between maxilla and mandible, allows observing the degree of asymmetry and mandibular deviation. An occlusal x-ray offers a clear view of the palatal vault in case of labio-palatal fissure. 

CT scan /3D CT scan of head and neck is very reliable to understand the exact location and extent of the disease.