S2 - Craniofacial Malformations & Cleft Lip and Palate Flashcards
(39 cards)
What are the different stages of embryonic craniofacial development? Which syndromes are associated with each stage and 3 categories?
1) Germ layer formation - FAS
2) Neural tube formation - Anencephaly
3) Migration of neural crest cells - Hemifacial microsomia, Treacher Collins syndrome
4) Organ system formation - Cleft Lip
4a) Primary palate - Cleft Palate
4b) Secondary palate
5) Final differentiation of tissues - Crouzon’s Syndrome (craniosynostosis), Achrondoplasia
1-3 are neural crest problems (day 17-28), 4 is lack of fusion (week 4-8) , 5 is suture problems (day 50-birth)
What is a teratogen. What are some examples and their result?
substance which interferes w normal development
Aspirin, cigarette smoke, Dilantin (phenytoin) → Cleft lip/palate
Zika virus, x-radiation → microcephaly
Others: ethyl alcohol, Rubella, Valium (diazepam), excess Vit D, Thalidomide
Name Neural Crest problems
FAS, Treacher Collins Syndrome, Hemifacial (craniofacial) microsomia, Anencephaly
Which stage of embyronic development would alcohol cause FAS
germ layer formation (17 days)
What is FAS caused by
exposure to alcohol (maternal use) during early development
causes preventable alcohol related birth defects - craniofacial malformation in early pregnancy, impaired cognitive and behavioural development in late stage pregnancy
→ microcephaly (small head), smooth philtrum, thin upper lip, epicanthal folds, low nasal bridge, short midface, minor ear abnormalities
Prevalence of FAS in Australia
0.06% in Australia, increase to 1.5% in remote FNQ
as high as 12% in some communities in Australia
estimated 38% Australian women drink while pregnant* (1st trimester), reduces to less than 7% after 1st trimester therefore craniofacial malformations are more common than neurological deficits
*why? they may not necessarily know they are pregnant, FAS affects in early weeks of pregnancy
Dental/orthodontic implications of FAS
- midface deficiency
- retrognathic md
- cleft lip and/or palate
- enamel hypoplasia (possibly)
few studies on dental effects, FAS is a spectrum, dont find all effects in all children
Which stage of embryonic development can Treacher Collins Syndrome occur
Migration of neural crest cells (19-28days)
Characteristics of Treacher Collins Syndrome
aka mandibulofacial dysostosis
- microtia (77%) or anotia
- conductive deafness (50%)
- zygoma deficiency (80%)
- mandibular hypoplasia (78%)
- cleft palate (30%) plus other associated facial clefting
Cause of TCS
3 gene mutations (1 present in 90% cases)
largely autosomal dominant (if parent carries 1 gene, likelihood is high)
mutation affects neural crest cells resulting in an overall lack of mesenchymal cells → causes lack of tissue in lateral parts of face
What is hemifacial (craniofacial) microsomia and cause?
mainly unilateral, 10-15% bilateral
defect of 1st and 2nd brachial arch
probably congenital but not inherited
might be associated with bleed of stapedial artery
(hypothesis: in early embryogenesis, mx and md artery feed the 1st brachial arch, facial feeds 2nd, normally these arteries are supplied by internal carotid, then stapedial artery breaks down and switches to external carotid - if there is bleeding when stapedial artery deteriorates can have defect on that side)
Given blood supply to 1st and 2nd brachial artery are disrupted in hemifacial microsomia, which structures would be affected? Name characteristics. What is the OMENS classification.
1st arch - mx and md, mm. mastication
2nd arch - mm. facial expression
- MAINLY mandibular and ear defects (usually absence of part of md)
- facial nerve weakness
- can also get maxillary hypoplasia
- signficant facial assymetry
OMENS says structures affected, way of classifying severity: orbits, mandible, ear, facial nerve, soft tissue/muscle deficiency
How may the mandibular defect in hemifacial microsomia range?
in mild form, all md structures present but one side slightly smaller
in severe form, whole ramus and condyle may be absent
What is craniosynostosis? Is it a syndome?
early closure of skull sutures
can be subdivided into syndromic and non-syndromic (80%)
Describe non-syndromic craniosynostosis
80% not associated with syndrome
very rare
head shape altered
Describe syndromic craniosynostosis. Name 4 clinical features
over 150 syndromes involving craniosynostosis
Crouzon’s syndrome (most common)
Apert’s syndrome (2nd most common)
clinical features differ but include:
- cranial vault deformities
- midface deficiency
- cleft palate
- hand and foot syndactyly (webbing)
Risk of increased intracranial pressure in non-syndromic vs syndromic craniosynostosis
non-syndromic: rare but can happen
syndromic: (happens because soft tissues continue to grow outward but supporting hard tissues cant catch up) cranial vault expansion may be required in early childhood, now usually do distraction osteogenesis
- can cause problems with neural development
- eyelids cant close - eye exposure can cause corneal abrasions, scarring and blindness
- compromised airways (maxilla cant come forward)
- feeding problems
Distraction osteogenesis is one of the most signficant changes in management of craniofacial syndrome. Why?
can achieve 1mm/day bone growth (14mm in 2 weeks which would be rly difficult w surgery)
no need for bone grafting
(surgeon does osteotomy, distractor device put in and turned daily)
Distraction osteogenesis is one of the most signficant changes in management of craniofacial syndrome. Why?
can achieve alot of bone growth, 1mm/day (14mm in 2 weeks which would be rly difficult w surgery)
no need for bone grafting
(surgeon does osteotomy, distractor device put in and turned daily)
Difference between syndrome and sequence
Syndrome - pattern of anomalies that occur tgt in a predictable fashion due to a single aetiology
Sequence - group of anomalies that generally stem from single major anomaly that alters development of surrounding structures e.g. Pierre robin sequence - small mandible cause other issues such as airway obstruction
What is Pierre Robin Sequence caused by? How does it present/why
micrognathia (small md) caused by posture in utero → elevation of tongue obstructs upper airway and causes cleft lip and palate and breathing problems
(*fetus chin against chest, stopping md from coming forward, tongue trapped and moves upward - fusion of palatal shelves requires for the tongue to be descended → cleft)
Facial development summary (for lip formation)
face formed between 4-10th week of pregnancy by fusion of 5 facial swellings:
- unpaired frontonasal process (frontal prominence)
- pair of maxillary swellings
- pair of md swellings
the mx and md swellings constitute dorsal and ventral regions respectively of 1st pharyngeal(brachial) arch, and give rise to upper and lower jaws
frontal prominence is part of forebrain (pink in pic), comes down to form median and lateral nasal process which fuse tgt
at around week 6, maxillary process fuse against median nasal process forming the lip and primary palate
*rmb: mx and md BOTH form from 1st brachial arch
Philtrum and part of alveolus holding upper centrals are formed by what?
forebrain, NOT 1st brachial arch
Cleft lip vs palate in terms of formation
separate processes that can happen tgt or alone, happen at different times and fusion of different structure
cleft lip = when median nasal process and maxillary process dont fuse - lips and primary palate
cleft palate = when secondary palatal shelves dont fuse
