DEVELOPMENT OF FACE, PARANASAL SINUSES, ASSOCIATED STRUCTURES & ANOMOLIES

DR.ASHWIN K HAREKAL1ST MDSDEPT OF ORAL AND MAXILLOFACIAL SURGERY

CONTENTS• Introduction• Phases Of Development• Formation Of Germ Layers• Formation Of The Pharyngeal Arches• Development Of Face• Development Of Lips• Development Of Cheeks• Development Of Nose• Development Of Eye• Development Of External Ears• Development Of Paranasal Sinuses• Development Of Mandible• Development Of Maxilla• Anomalies Associated With Each

INTRODUCTION Every individual spends the first nine months of its life within the womb or uterus of its mother. During this period, it develops from a small one- celled structure to an organism having billions

of cells Numerous tissue are formed and come to function in a perfect harmony The most spectacular changes occur in the first 2 months of IUL; the unborn acquires its main

organs and just begins to be recognizable as HUMAN . During these 2 months ,we call the develo- ping individual an embryoo From the 3rd month until birth we call it a fetus

INTRODUCTION

Human development is a continuous process that does not stop at birth. Begins when an oocyte (ovum) from the female is fertilized by a sperm

(spermatozoon) from a male. Fertilization takes place when one spermatozoon enters an ovum. The fused ovum

and sperm form the zygote Development involves changes from a single cell, the zygote into a multicellular human being.

PHASES OF DEVELOPMENT

Embryogenesis is divided into three distinct phases during the 280 days of gestation.

Pre-implantation period:the first 7 days

Embryonic period:the next 7 weeks

Fetal period:the next 7 months

PRE-IMPLANTATION PERIOD

Cleavage: within 24 hours after fertilization, the zygote initiates a rapid series of mitotic cell divisions

no increase in size of the embryo. The zygote is subdivided into many small daughter cells called as the

Blastomeres.

• After morula formation, compaction occurs.

• Centrally placed blastomeres are called as the inner cell mass.

• Blastomeres at the periphery are called as the trophoblast.

• Inner cell mass forms the embryo proper hence called as the embryoblasts.

• Trophoblast forms the fetal component of the placenta.

• on the 7th day, the blastocyst which develops from the morula, implants in the decidual layer of the uterine wall.

CLEAVAGE, BLASTULATION, GASTRULATION, AND NEURULATION

THE EMBRYONIC PERIOD

From the end of 1st week to the 8th week

PRESOMITE

• 8-21 days postconception

• germ layers & the fetal membranes are formed

SOMITE

• 21-31 days postconception

• Basic pattern of the main body systems & organs are established

POSTSOMITE

• 32-56 days postconception

• formation of body’s external features

THE FOETAL PERIOD Longest phase. 8th week to term. Identified by 1st appearance of ossification centers and the earliest

movements by the fetus. Organogenesis occurs. Rapid expansion of the basic structures already formed.

FORMATION OF GERM LAYERS Blastocyst develops to form various structures that support the embryo &

helps it to acquire nutrition. Embryonic disc is formed. 3 layers: Endoderm Ectoderm Mesoderm All the tissues of the body are derived from these layers.

Some cell of the inner cell mass differentiate into flattened cell that comes to line its free sueface.this layer is hypoblast.

The remaining cell of the inner cell mass become columnar .these cell form the epiblast. The embryo is now in the form of a disc having 2 layers.

A space appears between the epiblast and the trophoblast.This is the amniotic cavity filled by amniotic fluid. The roof of this cavity is formed by amniogenic cell derived from the trophoblast,while its floor is formed by the epiblast

Flattened cell arising from the hypoblast or according to some from trophoblast spread and line the inside of the blastocystic cavity .this lining of flattened cell is called Heuser’s membrane.this cavity is called the primary yolk sac

The cell of the trophoblast give origin to a mass of cells called the extra-embryonic mesoderm(primary mesodem).

These cell comes to lie in between the trophoblast and the flattened endodermal cells lining the yolk sac,thus seprating from each other

These cell also seprate the wall of the amniotic cavity from the trophoblast.this mesoderm is called the extra-embryonic mesoderm

Small cavity appear in the extra-embryonic mesoderm.gradually, these join together to form a larger space and ultimately one large cavity is formed.this cavity is called extra embryonic coelom.

Its clearly seen that the extra embryonic coelom does not extend into the part of the extra embryonic mesoderm which attaches the wall of the amniotoc cavity to the trophoblast. This is called a structure called the connecting stalk.

At this stage two very important structure are formed chorion and amnion

This both play a important role in child birth(parturition).

With the appearance of the extra-embryonic mesoderm and later the extra embryonic coelom,the yolk sac becomes much smaller and is called the secondary yolk sac.

Embryo is a circular disc composed of 2 layers upper layer (towards amniotic cavity)-epiblast lower layer (towards yolk sac) -hypoblast

We soon see that,at one circular area near the margin of the disc,the cuboidal cell of the endoderm becomes columnar.its called prochordal plate.

After the formation of prochordal plate, some of the epiblasts cells lying along the central axis near the tail end, proliferate to form an elevation, which becomes the primitive streak.

In starting primitive streak is an oval swelling but as the elongation take place it become linear structure.

Cells which proliferate in the region of primitive streak pass sideways , between epiblast and hypoblast These cells form intra embryonic

mesoderm(secondary mesoderm) Some cells from the primitive streak

displace hypoblast and form the endoderm.thus endoderm and mesoderm are derived from epiblast

Remaining cells of epiblast form ectoderm

Hence, a disc of 3 layers- ectoderm, endoderm and mesoderm are seen

Formation of primitive streak, endoderm and intra embryonic mesoderm- GASTRULATION

We have seen that when the embryonic disc is formed it s suspended from the tropoblast by the connecting stalk

This connecting stalk is very broad as compared to the size of embryo

As the embryonic disc enlarges in size the coonecting stalk becomes smaller and its attachment becomes confined to the region of the tail end of the embryonic disc

Some intraembryonic mesoderm passes through this

FATE OF THE GERM LAYERS FORMED AT GASTRULATION

ECTODERM• Nervous system & sense

organs• Outer layer of skin

(epidermis) & its associated structures like the hair, nail

• Pituitary gland

MESODERM• Notocord• Skeleton• Muscles• Circulatory system• Respiratory system• Urinary system• Inner layer of skin

(dermis)• Outer layers of

digestive tube

ENDODERM• Inner linings of the

digestive tube

FORMATION OF THE PHARYNGEAL ARCHES The forgut is bounded ventrally by

the pericardium and dorsally by the developing brain.

At this stage,head is represented by bulging caused by developing brain,while the pericardium may be considered as occupying the region of the future thorax.

This elongation is mainly due to appearance of a series of mesodermal thickening in the wall of the cranial most part of the foregut

CONT…..

The pharyngeal apparatus consists of: Pharyngeal arches Pharyngeal pouches Pharyngeal clefts Pharyngeal membranes

Pharyngeal arches appear in the 4th and 5th week of development and contribute to the characteristic external appearance of the embryo.

They are rod- like thickenings of mesoderm present in the wall of foregut.

They contribute extensively to the formation of the face, nasal cavity, mouth, larynx, pharynx and neck.

STRUCTURE TO BE SEEN IN PHARYNGEAL ARCH

o SKELETAL ELEMENTS o STRIATED MUSCLE o ARTERIAL ARCH VENTRAL AORTA DORSAL AORTA

DERIVATIVES OF THE SKELETAL COMPONENT The derivative of the first arch is called

meckel’s cartilage. The incus and the malleus of the

middle ear are derived from itz dorsal end

The vental part is surrounded by the developing mandible and its resorbed.

Cartilage of the second arch forms the Stapes Styloid process Stylohyoid ligament Smaller cornu of the hyoid bone Superior part of the hyoid bone

Cartilage of the third arch forms the greater cornu of hyoid bone lower part of the body of the hyoid

bone

The cartilage of the larynx are derived from the fourth and sixth arch with the possible contribution from the fifth arch,but their exact derivation is controversial

FATE OF ECTODERMAL CLEFT

o Epithelial linning of the external Acoustic

meatus o cervical sinus

FATE OF ENDODERMAL POUCHES

First pouch formation of the tongue inner and the middle earo Second pouch ventral part of this pouch

contributes to the formation of tonsil

dorsal part in the formation of tubotympanic recess

o Third pouch inferior parathyroid gland and

thymuso Fourth pouch superior parathyroid gland and

thyroid gland

DEVELOPMENT OF THE FACE

Formation of the fronto-nasal process After the formation of head fold, the developing

brain & pericardium form two prominent bulgings on the ventral aspect of the embryo.

Bulgings are separated by the stomatodeum floor is formed by the buccopharyngeal membrane separates it from the fore gut. Soon the mesoderm covering the developing

forebrain proliferates and form the downward projection it overlap the upper part of the stomadeum

This downward projection is called the frontonasal process.

It will now be readily appreciated that the face is derived from the following structure

frontonasal process 1st pharangeal arch (mandibular

arch)o Each mandibular arch form the lateral

wall of the stomadaeumo This arch gives abud from its dorsal end

that is maxillary process o The mandibular process grow ventro-

medially

1 Frontonasal prominence

2 Maxillary prominences

3 Mandibular prominences

Stomatodeum

The ectoderm overlying the frontonasal process soon show bilateral localised…

They are called nasal placode The formation of this nasal placode

is induced by underlying forebrain The placodes sink below the

surface to form nasal pits The pits are continous with

stomadaeum below There are 2 process medial nasal process lateral nasal process

DEVELOPMENT OF LIPS Lower lip The mandibular processes of 2 sides grow towards each other

& fuse in midline. Form the lower margin of the stomatodeum. Fused mandibular process give rise to lower lip and lower jaw

UPPER LIP Each maxillary process now grow medially and fuses first

with lateral nasal process then with medial nasal process. The 2 nasal process also fuse with each other, thus cutting off

the nasal pits from the stomatomedum.

• Maxillary process further grows, whereas the frontonasal process becomes narrower from side to side, causing the external nares to come closer.

• Upper lip is formed by the :• Mesodermal basis of the lateral part of the lips is

formed by the maxillary process. The overlying skin is derived from the ectoderm covering this process.

• The mesodermal basis of the median part of the lip, philtrum, is formed by the frontonasal process. The ectoderm of the maxillary process overgrows & meet in the midline.

• Thus, entire upper lip is supplied by the maxillary nerve.

DEVELOPMENT OF CHEEKS After formation of upper & lower lip, the

Stomatodeum is very broad. It is bounded above by Maxillary Process & below

by Mandibular Process. These processes undergo progressive fusion with each other to form Cheeks.

The fusion of Maxillary Process with Lateral Nasal Process occurs not only in the region of lip but extends from the stomatodeum to the median angle of the developing eye.

This line of fusion is marked by a groove called Naso-optic furrow or Nasolacrimal sulcus.

A strip of ectoderm becomes buried along this furrow & gives rise to the Nasolacrimal Duct.

DEVELOPMENT OF NOSE Nose is formed by the contribution of - Frontonasal & medial and lateral nasal processes. External nares are formed when the nasal pits are cut off

from the stomatodeum by the fusion of the maxillary process with the medial nasal process.

External nares approach each other. Frontonasal process becomes progressively narrower &

forms the nasal septum. Mesoderm becomes heaped up in the medial plane to form

the prominence of the nose…. As the nose become prominent the external nares project

downwards instead of forwards

DEVELOPMENT OF EYE

• Region of eye is 1st seen as ectodermal thickenings, lens placode, which appears lateral & cranial to the nasal placode.

• Sinks below the surface & cut off from surface ectoderm.

• Developing eyeball produces a bulging. • Bulgings are at first seen laterally & lie in the

angles between the maxillary& lateral nasal processes.

• After narrowing of the frontonasal process they lie forward.

DEVELOPMENT OF EXTERNAL EARS

• It is formed around dorsal part of first ectodermal cleft.

• A series of mesodermal thickenings (tubercles or hillocks) appear on mandibular and hyoid arches where they adjoin this cleft.

• Pinna or auricles is formed by fusion of these thickenings.

• The pinna lies caudal to the developing jaw • It is pushes upward and backward to it

original position due to enlargement of the mandibular process

DEVELOPMENT OF PALATE

Maxillary process not only form the upper lip but also extend backward on either side of the stomadaeum

From the maxillary process a plate like shelf grow medially

This is called palatal process 3 components from which the

palate will be formed -2 palatal process -primitive palate formed from

FNP

Palate forms from 3 components fusing with each other--

1) 2 Palatal processes, fuse in midline. Thier fusion begin anterior and proceeds backward.

2) each palatal process fuses with posterior margin of primitive palate.

The medial edge of the palatal process fuse with free lower edge of the nasal septum…

At later stage mesoderm in palate undergoes intramembranous ossification to form hard palate. Ossification does not extend into posterior most portion which remains as Soft palate.

The part of palate derived from FNP is Premaxilla which carries incisors.

DEVELOPMENTAL ANOMALIES OF THE FACE Hare lip upper lip of the hare normally has a cleft. Due to non- fusion of one or both of Maxillary Process

with Median nasal Process. Can be of various degrees & can be unilateral or bilateral.

Defective development of lowermost part of Frontonasal Process may give rise to Midline defect of upper lip.

When 2 Mandibular Process do not fuse with each other the lower lip shows midline defect , this cleft may extend into the jaw.

Oblique facial cleft Non fusion of Maxillary Process & Lateral Nasal Process gives rise to a cleft from

median angle of eye to mouth. The nasolacrimal duct is not formed. Macrostomia: Inadequate fusion of Maxillary & Mandibular Process- wide mouth Microstomia: Too much fusion –small mouth

Nose : bifid. May be associated with median cleft lip. One half of the nose may be absent. Proboscis: Rarely nose forms a cylindrical projection on forehead. This

anomaly is associated with Cyclops. ( fusion of 2 eyes). One half of the face may be underdeveloped or overdeveloped. Congenital tumours : may attempt at duplication of some parts. Hypertelorism: Eyes widely separated.

Mandibulo-facial dysostosis / Treacher Collins syndrome- First arch syndrome The entire arch is underdeveloped on one or both sides affecting lower eyelid, maxilla, mandible & external ear. cheek prominence is absent, ear may be displaced ventrally & caudally. Cleft palate Genetic condition ( autosomal dominant)

DEVELOPMENT OF NASAL CAVITY

Formed by extension of nasal pits. Initially, nasal pits are in open communication with

the stomatodeum. Soon medial & lateral nasal processes fuse to form a

partition between them, the primitive plate. Nasal pits deepens to form nasal sacs, which

expands both dorsally & caudally. dorsal part is 1st separated from the stomatodeum by

a thin membrane, bucconasal membrane.

• This soon breaks down, leading to the opening on the face, anterior or external nares & on the stomatodeum, posterior nasal aperture.

• The two nasal sacs are separated by the frontonasal process, which eventually forms the nasal septum.

• lateral nasal process forms the lateral wall of nose.

• Nasal conchae appear as elevations on the lateral wall

ANOMOLIES OF NASAL CAVITY

There may be atresia of the cavity at external nares, at posterior nasal aperture, or in cavity proper. May be unilateral or bilateral.

Congenital defects in cribriform plate of ethmoid bone may lead to communication between cranial cavity and nose.

Septum may be deviated or absent. Nasal cavity may communicate with mouth.

DEVELOPMENT OF PARANASAL SINUSES PNS appear as diverticula from nasal cavity Maxillary and sphenoidal sinus begins to

develop before birth. Frontal and ethmoidal sinuses develop after

birth. Enlargement of paranasal sinuses is associated with overall enlargement of the facial skeleton.

The 4 sets of paranasal sinuses begin their development at the end of the 3rd month of IUL as outpouchings of the mucous membrane of the middle & superior nasal meatus.

Primary pneumatization: The early nasal sinuses expands into the cartilage walls & roof of the nasal fossae by growth of mucous membrane sacs into the respective bones

Secondary pneumatization: the sinuses enlarge into bone and always retain communication with the nasal fossae through ostia.

MAXILLARY SINUS

Largest sinus & radiographically identifiable 1st to develop around 10th week of IUL Develops from the evagination from primitive ethmoid infundibulum in lateral walls of middle

meatus At birth, maxilla is filled with decidous tooth germs, which are very close to orbital floor. The maxillary sinus averages 7mm in AP length & 4mm in Height and width at this stage. It expands approx 3mm in AP dimension and 2mm vertically each year.

Pneumatization of maxilla commences just below the orbital floor. Downward growth of maxillary sinus leaves the ostium in a position unfavourable for gravitational

drainage. The maxillary sinus expands not only downward but also forwards and backwards. sinus enlarges by the resorption of all walls of the maxilla, except medial wall. It undergoes lateral expansion & by the end of 1st year extends beneath the orbit as far as infra orbital

canal. By end of 2nd year sinus has reached half of adult size. During 3rd & 4th year there is very conspicuous

growth in width. At 7th year dimension is – AP- 27 mm height- 17mm width-18mm By 12th year maxillary sinus extends to same level as nasal floor and is surgically accessible by Inferior

Meatus.

SPHENOID SINUS

Starts developing at 4 months IUL, by constricting the posterosuperior portion of the spheno-ethmoid recess.

The recess is between the sphenoidal conchae (bone of bertin) & the sphenoid body.

No primary pneumatization takes place. Secondary pneumatization occurs at 6-7 years into the

presphenoid & later the basisphenoid bones. It continues growing in early adulthood & may invade

wings, rarely the pterygoid plates of the sphenoid bone.

ETHMOIDAL SINUS

Ethmoid air cells from the middle & superior meatus & spheno-ethmoid recess invade the nasal capsule in the 4th month IUL.

Secondary pneumatization occurs between birth & at 2 years, as group of 3-15 air cells grow irregularly to form the ethmoid labyrinth.

The most anterior ethmoidal cells grow upward into frontal bone; they may form the frontal sinus.

The air cells may also expand in the sphenoid, lacrimal or the maxillary bones.

FRONTAL SINUS

Starts as mucosal invaginations in the frontal recess of the middle meatus of the nasal fossa at 3-4 months IUL.

Do not invade the frontal bone (secondary pneumatization) until between 6 months & 2 years post-nataly.

They grow upward till puberty . All the para nasal sinus appear to continue

increasing their size into old age.

ANOMOLIES OF PARANASAL SINUSES Absence of development of frontal and sphenoidal sinus is characteristic of

down syndrome (TRISOMY21) and Apert’s syndrome.

If an inter frontal (metopic) suture persists, frontal sinuses are small, or even absent.

DEVELOPMENT OF MANDIBLE

The mandible develops from the fibrous membrane of the meckel’s cartilage

The fibrous membrane of the ventral part of meckel’s cartilage is ossified to form the body of the mandible,which extends from the mandibular foramen to the mental foramen

The cartilage cells disappear later The 1st structure to develop in the lower

jaw region is the mandibular branch of the trigeminal nerve, which is considered to be the initiator of osteogenesis.

• A single ossification center for each half of the mandible arises 6th week IUL.• In the region of the bifurcation of the inferior alveolar nerve & artery into mental and incisive branches.

• The ossifying membrane is lateral to the Meckels’ cartilage & its accompanying neuromascular bundles.

• Ossification spreads from the primary center below & around the inferior alveolar nerve & its incisive branches, upwards to form a trough for developing teeth.

• The spread of the intramembraneous ossification dorsally & ventrally forms the body & ramus of the mandible.

• Meckels cartilage becomes surrounded & invaded by the bone.

• Ossification stops dorsally at a site that forms the mandibular lingula.

• The neuromascular bundle ensures formation of the mandibular & mental foramen.

SECONDARY GROWTH CARTILAGES Further growth of the mandible till birth is influenced by the

formation of three secondary cartilage.

CONDYLE CORONOID

SYMPHYSEAL

Condyle: At 5th week of IUL- area of mesenchymal condensation is seen

above ventral part of developing mandible . At 10th week- develops in a cone shaped cartilage. At 14th week- ossification starts At 4 months – migrates inferiorly and fuses with ramus. Most of cartilage forms bone but its upper end persists acting as

growth & articular cartilage.

Coronoid: At 10-14 weeks of IUL- secondary accessory cartilages appear. This secondary cartilage grows as a result of developing Temporalis muscle. These accessory cartilage becomes incorporated into expanding intramembranous

bone of ramus & disappears before birth. Mental region: On either side of symphysis 1 or 2 small cartilages appear and ossify in 7 month

of IUL to form variable number of mental ossicles in the fibrous tissue of symphysis.

These ossicles becomes incorporated into the body of the mandible. Symphysis ossify after 1 year after birth.

DEVELOPMENTAL ANOMALIES OF MANDIBLE Agnathia: Mandible is grossly deficient or absent Deficiency of neural crest tissue in the lower face Can occur in combination with the absence of the hyoid bone ( i.e. 1st and 2nd arch

syndrome) Lethal combination Multiple defects of the eye and maxilla Well developed low-set ears and auditory ossicles suggest that ischaemic necrosis of

mandible and hyoid bone occurs after the formation of ear

Micrognathia: Small mandible Defective neural crest production, migration, or destruction leads to hypoplastic mandible Pierre Robin Syndrome Cri-du-chat syndrome Progeria Downs syndrome Turners syndrome

Bifid or double condyle: Results from the persistence of septa dividing the fetal cartilage

Macrognathia: Large mandible Prognathism Acromeagly

Congenital hemifacial hyperthrophy: Evident at birth but tends to increase at puberty

DEVELOPMENT OF MAXILLA Develops from the center of ossification in the mesenchyme of the maxillary process.o No primary cartilage existoCenter of ossification is closely associated with the cartilage of the nasal septumoPrimary centre of ossification develop near the division of inferior orbital nerve into the anterior superior nerveo From the center of ossification the bone formation extends posteriorly towards the developing zygoma and anteriorly towards the incissor region.o ossification spreads superiorly to form the central process of maxilla o A bony trough is formed further in infra orbital nerveo From this trough lateral alveolar plate forms for the developing tooth germ

Ossification spreads into the palatine process to form the hard palate

Median alveolar plate develops from the palatal process

Median and lateral alveolar plate form the trough for the tooth germ.

CONCLUSION

REFRENCES Human embryology: 8th edition : Inderbir Singh Larsen’s Human embryology: 4th edition Craniofacial embryology: 4th edition : G.H. Sperber Before we were born: Moore Persaud