B. Anomalies Due to Abnormal Site of Attachment
6. The surface opening of stomodeum forms the oral
N.B. Developmental enigma of upper lip: The upper lip develops from three sources: the median part, the philtrum from globular process derived from frontonasal processes and lateral parts from two maxillary processes.
• The mesodermal basis of lateral parts of the upper lip is derived from the mesenchyme of the maxillary processes, and skin over these parts is derived from ectoderm cover- ing these processes.
• The mesodermal basis of the median part of the upper lip (philtrum) is derived from the mesenchyme of the
Ophthalmic nerve
Maxillary nerve Mandibular nerve
Fig. 12.4 Embryological basis of the sensory innervations of the face. Note area derived from the frontonasal process is supplied by ophthalmic nerve (yellow color), area derived from maxil- lary processes by maxillary nerve (green color), and area derived from mandibular processes by mandibular nerve (blue color).
Embryological basis of innervation of structures in the region of head and face (Fig. 12.4)
● The structures derived from frontonasal process are supplied by ophthalmic nerve (V1).
● The structures derived from maxillary processes are supplied by maxillary nerve (V2).
● The structures derived from mandibular processes are supplied by the mandibular nerve.
The details are given in Table 12.1.
Table 12.1 Correlation of nerve supply of various components of face and their source of development
Component
of face Develops from Nerves Forehead Frontonasal process Ophthalmic
division of Vth nerve (V1)
Nose Frontonasal process Ophthalmic division of Vth nerve (V1) Cheek
(a) Upper part (b) Lower part
Maxillary process Mandibular process
Maxillary division of Vth nerve (V2) Mandibular division of Vth nerve (V3) Upper lip Fusion of maxillary
processes of two sides with the frontonasal process*
Maxillary division of Vth nerve (V2)
Lower lip Fusion of mandibular processes of two sides
Mandibular division of Vth nerve (V3)
*The skin of the philtrum of the upper lip is derived from skin overlying the maxillary processes; hence it is supplied by the maxillary nerve.
Development of Nasolacrimal Duct and Sac (Fig. 12.5)
The line of fusion of maxillary and lateral nasal pro- cesses presents a groove called nasolacrimal groove.
This groove is lined by surface ectoderm.
The ectoderm in floor of this groove proliferates to form a solid epithelial cord (ectodermal cord).
Later on this epithelial cord is detached from the sur- face ectoderm and gets canalized to form nasolacrimal duct.
Upper end of nasolacrimal duct widens to form the lacrimal sac. The nasolacrimal duct becomes com- pletely patent only after birth. The nasolacrimal duct communicates secondarily with the nasal cavity at its caudal end and with the conjunctival sac at its cephalic end. In adults the nasolacrimal duct runs from medial angle of the eye to inferior meatus of the nasal cavity.
Development of Nose
The nose consists of external nose and nasal cavities.
Nasolacrimal duct Lateral nasal process Nasolacrimal groove/furrow Maxillary process Mandibular process Nasal pit opening
into stomodeum
Solid ectodermal cord
Fig. 12.5 Development of nasolacrimal duct.
Primitive oral cavity Primitive
palate
Developing forebrain
Oronasal membrane Primitive oropharynx Primitive nasal cavity
Oral cavity
Secondary palate Definitive choanae (arrow)
Oropharynx Tongue
Nasal conchae Nasal pit
Stomodeum
Foregut
Tongue Primitive choanae (arrow) Primitive (primary) palate
A B
C D
Anterior nares
Fig. 12.7 Development of the nasal cavity.
Bridge of nose Frontonasal process
Sides and alae of nose
Dorsum and tip of nose Fused medial nasal processes
Lateral nasal process
Tip of nose Ala of nose
Fig. 12.6 Derivation of external nose.
Development of External Nose (Fig. 12.6)
The external nose develops from five facial processes, viz., frontonasal process, two medial nasal processes, and two lateral nasal processes as follows:
● The frontonasal process forms the bridge of the nose.
● Two fused medial nasal processes form dorsum and tip of the nose.
● Two lateral nasal processes form sides and alae of the nose.
Development of Nasal Cavities (Figs 12.7 and 12.8)
The nasal cavities develop from ectodermal nasal pits.
The nasal pits deepen dorsally during the sixth week of intrauterine life to form nasal sacs. Each nasal sac grows dorsoventrally to developing forebrain to form primitive nasal cavity. Dorsal end of primitive nasal cavity is separated from oral cavity by oronasal mem- brane. At the end of sixth week this membrane rup- tures to form primitive choanae and as a result the nasal cavity communicates with the primitive oral cav- ity. The primitive choanae lie at the junction of primi- tive nasal and oral cavities, immediately behind primary palate. Later with further growth of primitive nasal cavity (definitive nasal cavity) and formation of secondary palate the definitive choanae lie at junction of the nasal cavity and the nasopharynx.
External openings of the nasal pits persist as exter- nal nares. While these changes are occurring the fol- lowing events take place:
1. Superior, middle, and inferior nasal conchae develop as curved elevations from the lateral wall of the nasal cavity.
2. Ectoderm lining the roof of the nasal cavity becomes specialized to form olfactory epithe- lium, which provides origin of olfactory nerves (Fig. 12.8).
The development of various components of the nose is summarized in Table 12.2.
Development of Paranasal Air Sinuses
The paranasal air sinuses develop as diverticulae from the walls of the nasal cavities. They grow into sur- rounding bones, viz., maxilla, ethmoid, frontal, and sphenoid, and become air filled. They are named after the name of the bone that they invade, viz., maxillary air sinus in maxillary bone, frontal air sinus in frontal bone, ethmoid air sinus in ethmoid bone, and sphenoid air sinuses in sphenoid bone. The primitive openings of diverticulae persist as orifices of the adult sinuses. The lining of paranasal air sinuses is ectodermal as that of the nasal cavity.
All the sinuses begin to develop before birth except frontal air sinuses, which begin to develop after birth.
Maxillary air sinuses are first to develop, and they appear as shallow groove on the medial surface of each maxilla during the third month of intrauterine life.
The frontal air sinuses develop by fifth or sixth post- natal year.
The paranasal air sinuses reach their maximum size at puberty and subserve following functions:
1. Contribute to definitive shape of face 2. Reduce weight of skull
3. Add resonance to the voice.
Other Developmental Events
Lens placode: The sites of development of lens plac- odes indicate the sites of development of the eyes in the region of the face. Here, only a brief account of their development is given. The development of the eye is described in detail in Chapter 24.
The surface ectoderm at the sites of development of eyes thickens to form lens placodes—primordia of eye lenses.
The formation of lens placode is induced by underlying developing optic vesicle from the forebrain. The devel- oping eyeballs produce bulges at these sites. These bulges at first lie in angles between the maxillary and lateral nasal processes, but later due to narrowing of maxillary processes they come forwards.
Intermaxillary Segment of Face
Due to medial growth of the maxillary processes the two medial nasal processes fuse to form intermaxillary segment of face.
Olfactory bulbs Nasal septum
Frontonasal process
Maxillary process
Palatal
shelf Tongue Fusion of palatal
shelves and frontonasal process
Eye
Nasolacrymal duct
Nasal cavity Olfactory nerves
Developing eye
Fig. 12.8 Formation of the nasal septum and palatine shelves.
Table 12.2 Development of the various components of the nose and their source of development
Components Develop from
• Dorsum and tip of nose Frontonasal process
• Nasal cavities Nasal sacs formed by
elongation of nasal pits
• Nasal septum Frontonasal process
• Nostrils (anterior nares) Nasal pits
• Choanae (posterior nares) Rupture of oronasal membrane (in the second month)
The intermaxillary segment of face consists of three components:
1. Labial component that forms the philtrum of the upper lip.
2. Upper jaw component (alveolar process) that carries four incisor teeth.
3. Palatal component that forms triangular primary palate (also called premaxilla).
Development of Palate
Embryologically the palate consists of two parts: pri- mary palate and secondary palate. The primary pal- ate develops from the frontonasal process and secondary palate develops from the maxillary processes.
Development of palate begins in the sixth week and completes by the end of the twelfth week. The palate develops in two stages:
1. Development of primary palate 2. Development of secondary palate.
Development of Primary Palate (Fig. 12.9) The primary palate is formed by fusion of two medial nasal processes of the frontonasal process. The fusion of these processes (at a deeper level) forms a wedge-shaped mass of mesenchyme opposite upper jaw carrying four incisor teeth called primary palate. It ossifies to form premaxilla.
Development of Secondary Palate (Fig. 12.10)
It is the main part of definitive palate. It is formed by fusion of two shelf-like outgrowths called palatine shelves from inner aspects of the maxillary processes.
The palatine shelves appear in the sixth week of devel- opment. Initially they grow downward and medially on each side of and below the tongue. Later, during the seventh and eighth week they assume horizontal posi- tion above the tongue and fuse with each other to form the secondary palate.
Intermaxillary segment
Maxillary processes
Premaxilla (primary palate) Palatine shelf Philtrum of upper lip
Alveolar process of upper jaw with four incisor teeth
Fig. 12.9 Intermaxillary segment and maxillary processes. Note that intermaxillary segment gives rise to: (a) philtrum of the upper lip, (b) median part of maxillary bone with its four incisor teeth, and (c) triangular primary palate.
Nasal septum Nasal cavity Maxillary process Palatine shelf
Fusion of palatine shelves and nasal septum
Frontonasal process
Primitive palate Maxillary processes
Secondary palate Hard
palate Soft palate
Uvula
Fig. 12.10 Development of definitive palate. Note derivation of its various parts from different sources. Figure in the inset (on the left side) shows separation of nasal cavities from each other and from the oral cavity.
The secondary palate is the primordium of most of hard part and whole of soft part of the adult palate.
Once the palatine shelves are fused the ossification extends from the maxillae and palatine bones into these shelves to form the hard palate. The posterior parts of these processes that extend posteriorly beyond the nasal septum fail to ossify and form the soft palate, includ- ing its soft conical projection—uvula.
Development of Permanent Palate
Anteriorly the secondary palate fuses with the primary palate by a Y-shaped suture and each limb of Y passes between the lateral incisor and canine teeth. Junction between the primitive and secondary palates is repre- sented in adults by incisive fossa into which opens two incisive foramina.
The nasal septum grows down and joins superior aspect of anterior three-fourth of the hard palate in the midline.
The nasal septum develops as a downgrowth from the frontonasal process. The fusion between nasal septum and secondary palate begins anteriorly during the ninth week and is completed posteriorly by the twelfth week.
The anterior three-fourth of permanent palate ossifies in membrane and forms the hard palate.
Table 12.3 Development of various components of the adult palate
Component Source of development (i.e., develops from) 1. Hard palate
(a) In front of incisive fossa (premaxilla) carrying four incisor teeth (b) Behind the incisive fossa
Fused medial nasal processes of frontonasal process
Fusion of palatine shelves (palatal processes) of maxillary processes of two sides
2. Soft palate Unossified part of fused palatine shelves (palatal processes) of two maxillary processes, which extend posteriorly beyond the nasal septum
The posterior one-fourth of the permanent palate that fails to join with the nasal septum and fails to ossify as well forms the soft palate. The soft palate hangs as a curtain to form the posterior margin of the hard palate.
The components of adult palate and their sources of development are summarized in Table 12.3.
1. Cleft lip: It commonly occurs in the upper lip. The incidence of cleft lip is 1 in 1000 births and 60–80% of children involved are males. The cleft upper lip presents three varieties (Fig. 12.11).
(a) Unilateral cleft lip: It occurs due to failure of fusion of maxil- lary process with the medial nasal process of the same side.
(b) Bilateral cleft lip: It occurs due to failure of fusion of maxil- lary processes with the frontonasal process.
(c) Central cleft lip/hair lip: It occurs due to failure of develop- ment of philtrum of the upper lip from the frontonasal process.
Very rarely the two mandibular processes may fail to fuse in the midline to cause cleft lower lip.
2. Oblique facial cleft (also called orbitofacial fissure Fig. 12.12): It is a rare congenital anomaly of the face, which occurs when maxillary process fails to fuse with the lateral nasal process. The fissure extends from medial angle of the eye to the upper lip.
Consequently, the nasolacrimal duct is exposed to the exterior.
This anomaly is usually bilateral.
3. Microstomia (small mouth) and macrostomia (large mouth):
Lateral angles of oral fissure are formed at the junction of the maxillary and mandibular processes. Initially the lateral angle of mouth extends much laterally close to auricle. Subsequently in normal conditions the angles of mouth gradually shift medially by fusion between the maxillary and mandibular processes till normal adult position is reached. The excessive fusion of these processes lead to microstomia and arrest of this fusion leads to macrostomia.
4. Cleft palate: The defective fusion of various segments of palate gives rise to clefts in the palate. These vary considerably in degree, leading to varieties of cleft palate as follows:
(a) Complete cleft palate (Fig. 12.13)
– Unilateral complete cleft palate occurs if maxillary pro- cess on one side does not fuse with the premaxilla. It is always associated with the cleft lip on the same side.
Clinical Correlation
A B
C D
Fig. 12.11 Types of cleft lip. A. Unilateral cleft upper lip. B. Bilateral cleft of the upper lip. C. Median cleft of the upper lip (hair lip). D. Cleft lower lip.
– Bilateral complete cleft palate occurs if both the maxillary processes fail to fuse with the premaxilla. In this type, secondary palate is divided into two equal halves by a median cleft with an anterior V-shaped cleft separating the premaxilla completely.
(b) Incomplete or partial cleft palate (Fig. 12.14): The follow- ing types may occur.
– Bifid uvula: Cleft involving only uvula. It is of no clinical importance.
– Cleft of the soft palate: Involving uvula and adjoining part of the soft palate.
– Cleft of the soft palate: Involving uvula, whole of the soft palate, and extends into the hard palate.
Clinical photographs of cleft lip and cleft palate are shown in Fig. 12.15.
A B
Philtrum
Premaxilla
Fig. 12.13 Complete cleft palate. A. Unilateral. B. Bilateral.
B A
Fig. 12.15 Congenital anomalies of cleft lip and cleft palate. A. Infant with unilateral cleft lip and cleft palate. B. Infant with bilateral cleft lip and cleft palate.
A B C
Hard palate
Soft palate Cleft Philtrum
Premaxilla Hard palate
Soft palate
Uvula
Fig. 12.14 Incomplete/partial cleft palate. A. Bifida uvula. B. Cleft of the soft palate involving uvula and joining part of the soft palate. C. Cleft of the soft palate extending into the hard palate.
Oblique facial cleft
Fig. 12.12 Oblique facial cleft.
CLINICAL PROBLEM SOLUTIONS
1. The unilateral cleft lip is a gap between the philtrum and lateral part of the upper lip. It occurs when the maxillary process of first pharyngeal arch fails to fuse with the medial nasal process of the same side. It is often associated with cleft palate because the palate develops from same sources as that of the upper lip. The symptoms of the cleft lip and cleft palate are:
(a) Disfigurement (b) Inability to suckle
(c) Interference with the speech, particularly with the formation of consonants, viz., D, T, and G (d) Distortion of teeth
2. The philtrum, alveolar arch bearing incisor teeth, and primary palate develop from frontonasal process (intermaxil- lary segments) whereas the lateral part of the upper lip, associated alveolar arch, and secondary palate develop from the maxillary processes (palatine shelves) of the first pharyngeal arches.
The cleft lip occurs due to nonfusion of frontonasal and maxillary processes; therefore it often involves alveolar arch and palate due to a common source of development.
CLINICAL PROBLEMS
1. A baby was born with unilateral cleft lip extending through alveolar process of the maxilla into the palate. What is the embryological basis of this anomaly and discuss symptoms from which the child suffers?
2. The cleft lip is often associated with the cleft palate. Give the embryological basis.
3. Although the upper lip develops from two different sources: frontonasal process and maxillary processes, but gen- eral sensory innervation is provided only by nerves of maxillary processes (i.e., maxillary nerves). Why? Give the embryological basis.
4. The clefts of the lip and palate are the most common congenital anomalies. Can they be recognized/identified before birth by ultrasonography?
5. An epileptic mother who was treated with an anticonvulsant drug phenytoin during her pregnancy gave birth to a male child with cleft lip associated with cleft palate. Tell if there is any evidence to suggest that this drug increases the incidence of these anomalies.
GOLDEN FACTS TO REMEMBER
Nasolacrimal duct and sac develops from Epithelial cord derived from ectodermal lining of the floor of nasolacrimal groove
Most common craniofacial congenital anomalies Clefts of lip and palate
Critical period of palate development End of sixth week to beginning of ninth week
Most common cleft lip Unilateral cleft of upper lip
Most rare cleft lip Median cleft of lower lip
Commonest cause of cleft lip with or without cleft palate
Multifactorial inheritance (i.e., combination of genetic and environmental factors)
Commonest congenital anomaly of face Unilateral cleft of upper lip