24. Craniofacial Anomalies / Craniofacial Surgery
General Information & Nomenclature
- The skeleton has an axial and a perpendicular part. The perpendicular part includes bones of fins, wings or limbs and the axial skeleton consists of the vertebral column, the skull and the ribs as well as the sternum.
- According to a hypothesis the skull is a modified vertebra in that it encloses neural tissue with entry and exit points for blood vessels and nerves. By way of evolutional economics in higher animals, the important sensory organs are located very near the cranial cavity and are in fact appendages or extensions of the brain.
- By common usage the word skull includes the mandible, the word cranium is used for the rest of the bones, the word calvarium is given to that bony part which encloses the brain and the vault is what you see of the calvarium from the top. The cranial base is that part on which the brain rests.
- The visible part of the calvarium is formed by two unpaired and two paired bones. The frontal bone is in the front, the occipital bone is at the back and they are unpaired. The parietal bones superiolaterally and the temporal bones inferio-laterally are paired. Theoretically the frontal bone is also in two parts with the inter-frontal suture between them fusing very early (before two years).
- Generally all the bones of the skull develop in a membrane and later articulate with each other by synchondrosis (cartilage). Developmental growth occurs mainly at the junctions of the calvarial bones called sutures. The cranial base however ossifies from cartilage (mainly the sphenoid) and its growth is also sutural.Sridhar from Chennai adds: In the process of formation of bone in a membrane, islands of bone form in various future units of the calvarium which will ultimately anatomically become specific bones. These bony islands grow centrifugally and the edges of the islands are called osteogenic fronts. When the fronts come to abut against each other, at what will be formally called sutures in the future, if the brain is expanding in size, reabsorption of newly laid bone will occur to allow the expansion and this process will continue till the brain has attained its ultimate size around 7 years when the process of reabsorption will cease and it is said that the bones have fused at the sutures. But synchondrosis persists which as pointed above is a cartileginous joint.
- The bones of the skull are somewhat malleable and are able to withstand blows from the exterior up to a limit and also adjust to raised intra-cranial pressure from within. The skull also withstands the tension generated by the action of muscles which are attached to the bones of the face and also by those muscles which straddle across on to the neck.
- The suture between the frontal bone and the two parietal bones, in a semi-circle, is the coronal suture though in some pathological conditions each half or a part of the suture can behave differently vis-à-vis sutural growth. This can occur in all sutures and is the cause of a variety of sutural stenosis.
- The suture between the parietal bones front to back is the sagittal suture which ends at the occipital bone and is perpendicular to a transverse suture between the single occipital bone and the two parietal bones. This is called the Lambdoid suture and the point at its centrewhere it meets the sagittal suture is called the Lambda. Similarly the junction of the sagittal suture with the coronal suture and beyond between the frontal bones goes by the name metopic suture most of which closes very early.
- In the area at the junction of sagittal, metopic and coronal sutures a non-osseous gap of about 2.5 cm. transverse to 4 cm. anterio-posterior called the anterior fontanelle is seen up to two years of age closing slowly after birth. This gap allows for rapid growth of the brain during that period and is a safeguard against pressure during the passage of the fetus through the birth canal. Much smaller similar fontanelles posteriorly and laterally are also present and close by 6 months (two on each side).
- Though separated by sutures during growth the whole calvarium acts as one single bone plate and grows centrifugally and this is caused by the growth of the brain and includes the growth at the junctions between the sphenoid and several other bones.
- When the vault is removed the sphenoid bone is seen to straddle the base. It has a lesser and a greater wing and articulates with the occipital bone at the back the frontal bone in front, the temporal and parietal bone laterally in addition it articulates with the zygoma anterio-laterally, the ethmoid in front and the palatine bone below. Because of its articulation with the palatine bone it is in close proximity to the palatine process of the maxilla.
- The anatomical and developmental proximity of these articulations means that the abnormalities in the calvarial structure during growth will have a bearing on facial growth and to a lesser extent any abnormalities of developmental growth in the facial region may also impact on adjacent calvarial structures. The Sphenoid though not visible is also subject to torsional effects on this count.
- A brief note on embryology is given below to explain some craniofacial anomalies.
- While a living creature after its birth is subject to millions of environmental influences which shape the creatures’ life, prior to the creatures’ birth, its embryological development is fully programmed in advance by way of a genetic code and is deterministic unless stray incidences of genetic mutations or environmental damage vitiate the programmed development and lead to abnormalities.
- In the human scenario for e.g. the superior of cephalad ascent of the notochord (which forms the vertebral column) and the inferior or caudal descent up to a point of the tissue that will form the brain, the skull, the face and its various parts is an example of this programming.
- In the head and face the matter is remarkable because the developing nervous tissue is responsible for the development and growth of the cranial and maxillofacial skeleton both as a genetic biological stimulus as well as by volume enlargement.
- For example, if the brain fails to develop, microcephaly will result. If the two parts of the forebrain (prosencephalon) do not separate, and grow laterally, there will be consequences on the development of the face which too will not develop bilaterally and result in a baby whose eyes are closer to each other than normal (hypotelorism) or in extreme cases a Cyclops like baby with a central eye.
- The word bilateral development in the above paragraph is important because most anomalies occur due to
- Failure of separation bilaterally (as in above)
- Improper separation or fusion leaving behind gaps (for e.g. encephalocele)
- Or amalgamation of the two separate units with formation of excess tissue in between leading to the orbital cavities being spaced abnormally far apart (hypertelorism) or, in severe forms, a double face.
- To go in to some details in the early embryo there is a neural plate on both sides of which form folds (the bilateral aspect of development). These folds roll over and invaginate to form a tube called the neural tube in to which develops into the brain and spinal cord. The roll over of the folds leads the adjacent tissue to heap over the tube to form the neural crest. This neuro-ectodermal crest grows and travels downwards bilaterally on each side of which develop segmental neuroectodermal prominences and therefore corresponding clefts (branchial arches). Mesoderm migrates in to these and proliferates to form several craniofacial units which then join to form the face together with the central part of the neuro–ectodermal crest (the area of the frontal suture, the ethmoids, the midline of the nose and the philtral column). In addition to problems of fusion the neuroectodermal and mesenchymal development might also suffer hypoplasia on account of defective genes leading to a variety of conditions which might be just about apparent at birth but will become grossly obvious as the rest of the face grows normally.
Anomalies in this region have been divided into four types only for convenience in arranging the chapters that follow:
- Anomalies pertinent to the embryology described above in which a variety of clefts or other abnormalities occur some of which have been explained above. This part will be treated in a separate section.
- Where cranial sutures unite prematurely and / or are absent and retard growth of the bones perpendicular to either side of the suture.
- Where early fusion of cranial sutures is accompanied by other abnormalities in the nearby skeleton or in discontinuous parts.
- Where anomalies occur in the cranio-facial skeleton without sutural abnormalities.Note: It is granted that several of these conditions overlap because of their genetic origin.
- In order to understand the subject some terms need to be explained.
- Syndrome:When a series of clinical cases show the same group of anomalies in parts of the body at a distance from each other (discontinuous) they constitute a syndrome. It is reasonable to assume that this has as its basis a specific genetic mutation for example, Apert’s syndrome is characterized by early closure of coronal sutures (also sometimes the Lambdoid) with flattening of the skull in the anterio-posterior direction, cleft palate, severe syndactaly and less than normal IQ notwithstanding early release of high intra-cranial pressure caused due to cranial stenosis. A congenital heart defect might also be present.
- Sequence (formerly called a syndrome): When a group of anomalies occur in adjacent parts and influence each other the word Sequence is now used in preference to a syndrome. For example, in oligo–hydramnious when the neck remains flexed with little space for extension, the tongue continues to occupy the space between the vertical palatine processes preventing their progress to a horizontal position and later their fusion, a U shaped cleft palate results. In the absence of the tongues’ propelling force in its normal position behind the mandible, the mandible fails to develop (retrognathia or microgenia) and this sequence is named after Pierre Robin.
- Malformation result from an intrinsically abnormal developmental process (e.g. cleft lip)
- Deformation results from mechanical causes which prevent the normal progression of embryological events. The Pierre Robin sequence mentioned above belongs to this category. In more severe mechanical obstructions like tight amniotic bands an actual disruption might occur in the embryological tissue for e.g. in random deep facial and cranial clefts. These are different from clefts caused by failure of fusion.
- Teratogenic events: a disease such as German measles or a deficiency of folic acid can have a focal destructive consequence. Some drugs are also responsible for producing teratogenic events.
- Sutural stenosis: Though the word stenosis is in common usage and is generally considered to result from a premature fusion of a suture a view is emerging that except at the metopic junction stenosis results because a suture in fact does not exist and therefore affects growth. Growth is obstructed in a direction perpendicular to the suture.
- Scaphocephaly:In abnormalities caused by early fusion or an absent sagittal suture, the growth of the skull is restricted in the transverse axis but continues unabated in the direction of the sagittal suture. The skull is therefore abnormally long, resembles a boat and is therefore called scaphocephaly(Scapho = boat in Greek).
- Brachycephaly:When the whole of the coronal suture is fused, the anterio-posterior growth of the skull is retarded but the temporo-parietal width remains unaffected and is therefore greater in comparison. This results in a short head and therefore called brachycephaly(brachy=short, Greek).
- Plagiocephaly: Denotes a twisted head. This occurs classically when only one half of the coronal suture is affected. This results in only one ipsilateral segment of the skull not growing anterio–posteriorly but because the other half (contralateral) grows normally not only does the forehead on that side appear prominent but it also gives a twisted appearance to the head (Plagio=oblique in Greek). This condition can occur when other sutural abnormalities are either hemi-cranial or at different points and asymmetrical. Alternatively, if normal growth is obstructed by pressure within the uterus or immediately after birth due to bad positioning, the condition is common particularly in the posterior half of the cranium and can be treated by giving a proper position to counter balance the earlier pressure points. This kind of plagiocephaly is not sutural in origin. Plagiocephaly can therefore be (external) deformational or sutural which is also called synostotic.
Anatomic feature Unicoronal synostosis plagiocephaly Frontal deformational plagiocephaly Ipsilateral superior orbital rim Up and high Down Nasal root Ipsilateral Midline Chin deviation Contralateral Ipsilateral Ipsilateral cheek Forward Backward Ipsilateral palpebral fissure Wide , low Narrow ,high Ipsilateral Ear Anterior and high Posterior and low
- Trigonocephaly: Occurs when a restriction of growth results from an early fusion of the metopic suture affecting lateral growth but allows unimpeded growth anterio–posteriorlyleadingto a triangular shaped head instead of a normal convex forehead.
- Microcephaly: Probably does not arise from a cranio–stenotic event but is usually simply a result of the failure of the brain to grow.
Note: Multiple, random, small sutural abnormalities may occur rarely which may even involve the temporal or sphenoidal bone sutures and are a class by themselves, do not have a fixed pattern or a specific nomenclature. This is covered under a general term called craniofacial dysostosis which is the subject of the next chapter.
- Hemi facial microsomia was a term originally applied to a group of patients who showed concomitant hypoplastic deformities of the ear and the mandible on one side. The condition is since then known to occur bilaterally and might also have hypoplastic deformation of the maxilla, the frontal bone, the orbit, the pterygoid plate of the sphenoid, the mastoid process of the temporal bone, the zygoma, the middle ear canal, masticatory muscles, the palate, the pharynx, the floor of the nose, the facial nerve and the soft tissue around the cranio-facial skeleton.
Note: Originally described on one side of the face and called hemi-facial microsomia. When it occurs on both sides it is called bilateral hemi-facial microsomia because the two sides might have pathological changes of a different degree. The term in common usage now isCranio-facial microsomia.
- Hypertelorism: Occurs when the anterio-posterior growth is stunted due to abnormalities in the coronal suture but the lateral growth continues to occur, the orbits are pushed laterally in a flattened retruded forehead. The average distance between the dacryons of the two orbits is 28 mm in adult males and 25 mm in adult females (on an average).Note: Mukund Jagannathan from Mumbai very pertinently points out that the classic hyperteloric face will occur because of clefts occurring in the midline (the middle of the neuroectoderm) with or without herniation of intra-cranial contents. If there is a cleft lateral to the mid-line (with or without intra-cranial herniation), a unilateral hyperteloric orbit will result. In the child the distance between two dacryons is 16 mm, the dacryons then growing apart to reach their normal width in girls by the age of 15 to 17 and in boys between 18 and 20.Hypotelorism has already been mentioned in 13d.
- Telecanthus: Is said to be present when the orbits are a normal distance apart but the distance between the two medial canthal ligaments is more than normal. Normally this is between 24-39 mm in Caucasians and is equal to the breadth of the eyeball at its equator and therefore the area between the two lateral canthii is divided in to three equal parts. The equators of the two eyeballs and the distance between the two medial canthii.
Sketch contributed by Prof. Ramesh Sharma, Chandigarh
- Exorbitism: Resultswhen the orbits are shallow in all dimensions. The eye therefore cannot be accommodated within this space as it grows normally and gets proptosed.
- Exophthalmos: Increase in the size of the soft tissue around the eye within a normal orbit causes the eyeball to bulge and is denoted by the term exophthalmos. This can occur in hyperthyroidism but maybe due to inflammation or a neoplasm characterized by a scleral show on all sides of the cornea.
This chapter has been a combined effort of Ravin Thatte, Sridhar Krishnamurthy, Mukund Jagannathan, Nitin Mokal and Jyotsna Murthy.