Some of the operations that now form the armamentarium of craniofacial surgery have been performed by different specialist groups for many years. Craniectomy and, to a degree, cranial remodelling in craniosynostosis, has been carried out by neurosurgeons for a long time. Similarly, major osteotomies on the facial skeleton have been undertaken by plastic and maxillofacial surgeons in the past and are nothing new: Gillies carried out a le Fort III facial osteotomy in 1942. It is the integration of techniques in a team approach which has made craniofacial surgery a subspecialty. A craniofacial team should comprise a nucleus of reconstructive plastic surgeon, neurosurgeon, anaesthetist, and ophthalmologist. Help should also be readily available from other specialities, such as maxillofacial surgery and otolaryngology.

This joint approach allows safer and comprehensive reconstruction of difficult deformities and defects which would previously only have been treated in a superficial way to camouflage the problem.

The development of craniofacial surgery has depended not only on teamwork, but also on a number of other advances in surgical technology. Computerized tomographic imaging has made it possible for surgeons to visualize and better understand the deformities on which they work. New knowledge of the biology of bone grafts, the introduction of miniplating systems for bone fixation, and advances in anaesthesia have all added momentum to the growth of craniofacial surgery.

The common thread which runs through craniofacial surgery is that it is surgery of, and adjacent to, the skull base. This interface between neurosurgery, plastic and maxillofacial surgery, ear, nose and throat surgery, and ophthalmology was a relative surgical ‘no man's land’ until joint efforts were made to develop techniques to tackle some of the problems involving this anatomical area. As methods have evolved many conditions in and around the orbits, the vault of the skull, and the facial skeleton and soft tissues have also been addressed by craniofacial surgery, and the scope of the specialty has widened. Techniques and knowledge have been applied to the management of deformities such as Treacher-Collins syndrome, hemifacial microsomia, cleft lip and palate, and trauma of the orbit and face, where the skull base itself is not involved in the surgical procedures. The broad scope of modern craniofacial surgery is shown in Table 1 705. Three main groups of conditions are treated—congenital deformities, trauma, and tumours involving the craniofacial region.

Many conditions dealt with by craniofacial surgeons are rare. This is particularly true of the more difficult congenital abnormalities. It makes sense, therefore, for a few centres to undertake this work, so that a team's expertise and safety can be maintained; one centre for 10 to 20 million population is probably advisable. Many of the techniques of craniofacial surgery can also be useful to surgeons working outside craniofacial units, particularly in the areas of trauma and tumours. These will be discussed further in this chapter.

Radiographic imaging should be undertaken to define the deformity or defect and to ascertain whether intracranial abnormalities coexist. A thorough assessment of fitness for major surgery is always required, and preparation of blood for transfusion, preoperative baseline visual testing, dental assessment, and psychological preparation may also be appropriate. A team of medical and paramedical personnel who may or may not be involved in the actual surgery is needed for adequate preoperative preparation. Decisions may need to be made about the best timing for surgery. In the growing child, for example, some procedures may have a limiting effect on further growth, whereas others may promote more normal growth. The whole area of surgery on the craniofacial soft tissues and skeleton during growth is a very complex one. The psychological benefits of early surgical treatment of deformity in children, if any, are not known as yet.

This has all the hazards associated with anaesthesia for neurosurgical procedures, but other factors are often present, such as difficult airway problems. In small children blood loss can be relatively massive, and unless precautions are taken, hypothermia may occur. Craniofacial surgery is no more for the ‘occasional’ anaesthetist than it is for the ‘occasional’ surgeon—a high level of expertise is needed to provide good operating conditions for the surgical team and to maintain the safety of the patient.

These include the bicoronal incision across the top of the scalp, other scalp incisions, and incisions in the face, for example in the lower eyelid to give exposure to the orbital floor. All of the cranio-orbital skeleton can be exposed through the bicoronal approach by turning down the forehead scalp flap, and using subperiosteal dissection as the supraorbital margin is approached (Fig. 1) 2870. By dissecting in this plane into the orbits the eyes and other orbital contents are protected within a sleeve of periosteum attached anteriorly only at the lacrimal sac at its junction with the nasolacrimal duct, but the orbital skeleton is widely exposed. The nasal and zygomatic areas can be similarly exposed by subperiosteal dissection. Laterally, care needs to be taken to avoid facial nerve branches, particularly the frontal branch. The supraorbital nerves are preserved intact by their careful removal from any bony tunnel or notch. Exposure of the skull base within the cranium is achieved by an appropriately placed craniotomy followed by extradural dissection to delineate the area of bone required.

These are performed by making cuts in the bones of the craniofacial skeleton and moving the separated segment to the desired position where it is fixed. In order to carry out osteotomies on the skull base and adjacent areas safely, good exposure of the bone is needed, with gentle retraction of orbital contents and brain and dura away from the area in question.

These are frequently used in craniofacial procedures to repair defects left by the movement of skeletal segments or after excision of bone. The most readily available donor site for bone grafts is the cranium itself. Following a craniotomy, the bone flap is split through the diploe and bone grafts used from the inner table. If no craniotomy is needed cranial bone grafts can be taken from the outer table. This donor site is painless by comparison with iliac crest or rib grafts, and there is some evidence that grafts taken from bone which develops in membrane, such as the cranium, will undergo less postoperative resorption than grafts taken from bone of endochondral origin. If insufficient bone is available from the cranium because it is too thin, or if a large amount is needed, bone grafts from other sites may also be needed. Bone grafts and mobilized skeletal segments are fixed into position by wires or miniplates and screws.

In infants under 1 year of age large craniectomies usually reossify quite readily from the osteogenic dura, and grafts are not needed to fill defects.

Bone and soft tissue are used to form a barrier if the nasal cavity, nasopharynx, or paranasal sinuses are opened into communication with the cranium. Absence of such a barrier is associated with a risk of ascending infection into the intracranial cavity, early or late after surgery. Bone grafts are obtained as above. Soft tissues can take the form of free pericranial grafts, vascularized flaps of local tissues such as galea or temporalis muscle and fascia, or tissues brought to the area from elsewhere in the body and vascularized by microvascular anastomoses.

Careful monitoring of blood and fluid losses is required: replacement is particularly important in small children. Other management takes the form of general supportive measures and airway management, antibiotic cover, anticonvulsant prophylaxis if the cranium has been opened, and after considerable brain retraction, steroids to minimize cerebral oedema. Appropriate intensive care facilities, ready access to CT scanning in the event of neurosurgical complications, and the easy availability of team members should they be needed, are all essential for safe postoperative care of these patients.

The potential problems which can develop during and after surgery are listed in Table 2 706. Many of these can be fatal unless they are attended to promptly. Even with constant vigilance by experienced teams there is occasional mortality of around 1 per cent and an incidence of serious complications of about 10 per cent if all operations in the scope of craniofacial surgery are included. Some groups of patients have a higher risk of complications: this is particularly true of those undergoing radical resections of large tumours around the skull base, and some children with complex syndromal craniofacial deformities such as Apert's syndrome.

These conditions are the result of premature closure (synostosis) of the sutures between bones in the cranial vault or base by ossification. Depending on the site of synostosis, a deformity of the skull often occurs as the growing brain pushes on the bones, which can still grow at the sutures. So-called ‘simple’ craniosynostoses involve only one or two sutures in the vault; complex cases involve multiple sutures in the vault and skull base. There is a genetic background to many of these conditions, in particular the syndromal complex craniofacial synostoses (sometimes called craniofacial dysostoses). These syndromes often include deformities of the limbs, such as syndactyly in Apert's syndrome. The exact biochemical mechanisms underlying expression of the phenotype in these syndromes is, to date, unknown.

The chief clinical features of craniosynostoses are deformity, and raised intracranial pressure, which affects a significant number of infants with these problems. Mental development in some conditions such as Apert's syndrome may be delayed for reasons as yet not understood, as well as due to any effects of raised intracranial pressure.

Treatment is initially directed at early release of the brain from restriction of growth by craniectomy or cranial remodelling. This lowers raised intracranial pressure. Such procedures should be performed during the first year of life for maximum benefit. Simple craniectomies are not usually undertaken; these have been replaced by more complex operations to remodel the cranium and attempt to increase the intracranial volume. Secondary procedures may be required for the correction of residual or recurrent deformities.

These conditions affect only one or two of the cranial sutures. Unimpaired growth at normal unfused sutures causes a cranial deformity to develop with growth. The deformity is usually characteristic, depending on which suture is fused (Fig. 2) 2871. In only a small proportion of children is intracranial pressure increased. There may be imbalance of the extraocular muscles in association with an orbital deformity in some children. The growth of the midface and lower face is usually normal. Untreated, the deformity will persist into adult life.

Treatment is best carried out during the first year of life if possible, and is aimed at excising the fused suture and correcting any cranial deformity which may be present. If the sagittal suture is affected operation within the first 2 months of life is worthwhile: simple craniectomy is usually sufficient treatment at this stage. If, however, the coronal sutures are affected on one or both sides surgery needs to be delayed. Not only is the suture excised but the forehead is remodelled and advanced by removal of the frontal bone and supraorbital bony skeleton and refixing these skeletal segments in a symmetrical, advanced position. Such surgery is carried out through a bicoronal incision. In small infants this can result in considerable blood loss and loss of heat.

Correction of simple craniosynostoses during the first year of life usually allows satisfactory subsequent growth of the cranium, and no further treatment is needed in the majority of cases.

These conditions are usually caused by genetic abnormalities and involve several cranial sutures. As well as the cranial vault sutures being involved, those in the skull base and the growth centres between the cranial base and the facial skeleton are often affected. This results in deformity of the midface as well as the cranium. Shallow orbital cavities result in proptosis of the eyes, underdeveloped nasal passages and nasopharynx cause airway problems, and a dish face deformity is associated with malocclusion of the teeth. Typical examples are Apert's and Crouzon's syndromes, which are autosomal dominant conditions (Fig. 4) 2874. The incidence of raised intracranial pressure is higher in these syndromes than in simple craniosynostoses. A proportion of patients with some conditions, such as Apert's syndrome, have mental retardation.

In most of these conditions the cranial part of the synostosis affects both coronal sutures. Surgical correction in infancy aims to advance the frontal bone and supraorbital area as far as possible, (usually about 2 cm) through a bicoronal incision. This has the effect of releasing the fused coronal sutures, correcting the recessed frontal bone and supraorbital region, and increasing the anteroposterior dimensions of the anterior cranial fossa. It probably also increases the intracranial volume. Whether early surgery improves the potential for mental development is not known. It does, however, lower raised intracranial pressure to normal levels. Since a high intracranial pressure during development and growth of the brain carries a poor outlook for mental development, early surgery would appear to be worthwhile. It has added benefits of improving the appearance of the anterior cranium and supraorbital region.

The recessed midfacial skeleton often needs to be advanced at a later date, although this is sometimes undertaken in young children if there are pressing indications, such as excessive proptosis such that the eyelids do not close over the eyes causing exposure, inadequate nasal airways for nasal breathing, or cosmetic deformity caused by the dish face. If the surgery is being performed simply for cosmetic reasons it is usually left until late childhood.

Facial advancement is usually undertaken with osteotomy at the Le Fort III level, which is a separation of the facial skeleton from the cranial base (Fig. 5) 2875. It can be combined with frontal advancement as a frontofacial monoblock advancement procedure, but this has a high incidence of complications such as infection. The procedure is, therefore, often split into two separate operations, one to advance the forehead and a second to advance the face. In this way communication between the intracranial cavity and the nasal cavity and nasopharynx can be avoided and the complication rate lowered. Facial advancement in children needs to be repeated, or some further orthognathic procedure needs to be carried out at the end of growth, to obtain optimal dental occlusion. This further surgery however may not be at the Le Fort III level and a lower level advancement, such as a Le Fort I procedure, may be sufficient. Repeating facial advancement at the same level is made difficult by the scarring of the previous operation.

Facial advancement in children is a major operation, with considerable blood loss; postoperative airway complications are always to be feared. These procedures are usually carried out in specialized centres ( Fig. 6(a) 2876, (b)).

Many children with craniofacial synostosis syndromes have abnormalities of the hands and feet. Complex syndactylia present in Apert's syndrome for example frequently needs to be corrected in a number of staged operations. Abnormal nails on the feet may also need surgical attention. These children also need attention from orthoptists and ophthalmic surgeons for squints caused by extraocular muscle imbalance, from orthodontists to correct malocclusion and other dental problems, and management by otolaryngologists for airway and ear abnormalities. They, most of all, need the expertise of a whole treatment team.

A craniofacial cleft can be defined as a zone of dysplasia or an abnormality of development producing a zone of hypoplasia or absence of the skeleton or the soft tissues, or both. Clefts are usually surrounded by hypoplastic tissues. The most typical cleft is that of the lip and palate. Craniofacial clefts, however, tend to occur at a higher level in the craniofacial skeleton. Tessier has classified these by relating them to the orbit anatomically, and numbering them as they progress periorbitally. This classification system, while not related to the developmental fault behind the deformity, is useful because it describes the anatomy of the cleft quite accurately.

With growth, the deformity of patients with a craniofacial cleft tends to remain the same, although in some there is the potential for the condition to worsen.

The most typical craniofacial cleft is the group of midline or paramedian clefting syndromes which result in hypertelorism, or widening of the distance between the orbits with a wide, abnormal nose in the middle of the face. This condition was one of those to receive early attention in the development of craniofacial surgery because of the serious deformity. It is possible to reduce the wide distance between the orbits since, although the orbits are angulated away from one another in a lateral direction, their apices usually show a fairly normal separation. The anterior parts of the orbits containing the globes can therefore be rotated closer together by appropriate osteotomies and resection of central bone and tissues. The apices of the orbits containing the optic nerves, the third, fourth and sixth cranial nerves and the origins of the extraocular rectus muscles can be left undisturbed. This surgery is undertaken through a bicoronal incision: the orbits can be moved either by a periorbital osteotomy and movement of the orbit as a ‘box’, or by facial bipartition, in which the orbits and hemifacial skeletons are moved as single units closer to each other with resection of a wedge-shaped piece of the central facial skeleton to narrow the nose. Nasal reconstruction is frequently necessary in these patients (Figs. 7, 8) 2877,2878.

Many clefting syndromes, in particular hypertelorism, are corrected for aesthetic rather than functional reasons ( Fig. 9(a) 2879, (b)). Visual disturbances such as the lack of stereoscopic vision are not improved by such surgery. If clefts involve the eyelids, surgery can help with cover of the eye and does, therefore, have functional implications.

Operations to correct hypertelorism or orbital dystopia are major operations in children and, because of the rarity of these conditions, should be carried out in specialized units. In such units the incidence of serious complications is about 10 to 12 per cent, and there is a mortality rate of 1 to 2 per cent. Major surgery round the orbital skeleton has potential complications of visual loss, postoperative extraocular muscle disturbance, infection of bone which may lead to loss of skeletal segments, and major intracranial problems such as infection or haemorrhage.

Assessments of the aesthetic outcome of such operations have rarely been undertaken. The few studies that have been published indicate that such surgery is worthwhile, but that these patients still look deformed after their operation and cannot usually be made normal. The psychological benefits of undertaking surgery early in childhood have not been investigated adequately.

Encephaloceles are hernias of cerebral tissue and the covering meninges through a bony defect in the cranium. Around the craniofacial region this defect can occur between the frontal and nasal bones, between the nasal bones and ethmoids, or through the skull base further posteriorly. Encephaloceles can be corrected by craniofacial exposure and reconstruction with excision of the usually abnormal, herniated brain, and repair of the dura and cranial base or cranium and of the overlying soft tissues. If carried out within the first year of life, subsequent growth of many of these children is satisfactory and nothing further needs to be done. Some patients present later and with extensive deformity due to distorted growth of the affected area of the craniofacial region. These need more major repositioning of the orbital or facial skeleton in addition to treatment of the encephalocele itself.

There are other congenital anomalies of the craniofacial region which may not need joint neurosurgical/transcranial procedures for their correction, but which benefit considerably from the techniques of craniofacial surgery. These include Treacher-Collins syndrome and hemifacial microsomia, both of which affect the mid and lower facial skeleton and soft tissues.

The facial skeleton in Treacher - Collins syndrome is hypoplastic or cleft in the area of the malar bones (Fig. 11) 2882. This can be repaired during childhood using vascularized or free bone grafts to augment the skeleton in those areas. Other soft tissue components of the deformity such as the colobomas of the lower eyelid may need correction simultaneously. The complex upper and lower jaw deformity which exists in these patients can also be corrected, but best results are obtained if this is left until adolescence.

Hemifacial microsomia is an asymmetrical hypoplasia of the face centred round the structures derived from the first and second branchial arches. It usually consists of hypoplasia of the external ear, of the vertical ramus of the mandible, and of the temporomandibular joint on the affected side; the overlying soft tissues may also be hypoplastic. Surgery can be carried out during childhood to improve the appearance but will need to be repeated in adolescence ( Fig. 12(a) 2883, (b) ). Skeletal surgery on the mandible and maxilla is usually necessary, many patients requiring soft tissue augmentation of the cheek tissues, as well as some kind of reconstruction of the abnormal pinna. This can be done using autogenous cartilage graft from the costal margin; alternatively, a prosthetic ear can be fitted to osteo-integrated implants in the bone.

Patients with acute craniofacial trauma benefit considerably from the application of craniofacial surgical principles in their management. Procedures carried out jointly by a neurosurgeon and a reconstructive surgeon will improve the postoperative appearance, lessen the need for secondary surgery, result in a lower incidence of dangerous late intracranial infections, and shorten the patient's stay in hospital.

Patients with craniofacial trauma need the usual early attention to airway and respiratory problems. Any acute intracranial complications such as haematomas need to be dealt with urgently and the soft tissues closed. The craniofacial fractures can be treated several days later, when the acute injury to the brain has had some time to settle down, and when there has been time to assess the injury properly with radiographs and CT scans, and full ophthalmic and dental assessment. When all of this information is available a joint procedure can be planned to repair all the fractures at a single procedure and also repair all the basal dural tears and any associated soft tissue problems, such as telecanthus caused by detachment of the medial canthal ligaments from their bony anchorages.

First, the fractures all need to be exposed. Much of this work can be done through a bicoronal incision, avoiding the creation of surgical scars on the face. It may, however, be necessary to use subciliary incisions in the lower eyelids to gain access to the orbital floor and infraorbital margins. This is advisable in trauma patients to avoid excessive retraction of the injured orbital contents. Craniotomy is usually required for repair of the dural tears in the anterior cranial fossa; the craniotomy flap can be split and the inner layer used as bone graft material for the reconstruction. Dural tears are delineated. If the dura cannot be directly sutured, it is patched with pericranium: this can be done extradurally without having to make wide intradural exposures. Reconstruction of bone may be needed in the anterior cranial fossa, the supraorbital region, the nasal or nasoethmoidal region, the malar areas, and orbital floors. When the posterior wall of the frontal sinus is extensively fractured the whole frontal sinus is cranialized by removal of the posterior walls and all the mucosa, with plugging of the fronto-nasal ducts using cancellous bone from the diploe of the craniotomy bone flap. Other facial injuries such as those of soft tissues, and maxillary and mandibular fractures, if present, are then attended to in the same procedure.

The late management of untreated deformities following craniofacial trauma is difficult. The displaced bones and soft tissues tend to become fixed by scar tissue in the deformed position, and correction at a late stage is much more difficult than it is acutely when there is no scar tissue. While considerable improvements can be made in some patients with late corrections the results are never as satisfactory as when early reconstructive surgery is practised. The surgery is difficult and has a higher complication rate and is therefore best carried out in specialized centres.

A variety of tumours and tumour-like conditions affecting the craniofacial region are amenable to surgical resection and reconstruction of the resulting defects using the principles of craniofacial exposure and reconstruction (Table 4) 708.

Bone dysplasias, in particular fibrous dysplasia, are the most common of these. Fibrous dysplasia results in an enlargement of areas of the skeleton, sometimes confined to the craniofacial region or sometimes polyostotic in nature. The enlargement of bone can be progressive or can cease and begin again at a later date. In the craniofacial region fibrous dysplasia usually affects either the maxilla or the supraorbital region. Ideally, surgical correction is aimed at removal of all the affected bone but sometimes this is so extensive that total removal is impossible. Areas of bone which cannot be removed and replaced by reconstruction can then only be managed by shaving and sculpturing procedures. Sometimes however the entire affected area can be removed and replaced by bone graft.

Indications for surgery in fibrous dysplasia are deformity, pain, or encroachment of bony enlargement on foramena such as the optic foramen. If the latter occurs bone needs to be removed from adjacent to the optic canal so that the optic nerve can be decompressed. The results in terms of improvement in appearance can be very well worthwhile in these patients ( Fig. 14(a) 2885, (b)), and visual deterioration caused by optic nerve decompression can often be arrested.

The other major tumour-like condition is neurofibromatosis affecting the cranio-orbital region. This is a difficult condition to treat, and surgery carries a high complication rate. Although the results are not particularly satisfactory in aesthetic terms ( Fig. 15(a) 2886, (b)), some improvement can be made. Typically, cranio-orbital neurofibromatosis involves a partial absence of the wings of the sphenoid bone, which allows the orbital contents to pulsate because of the unrestrained pressure of the intracranial contents behind through the defect in the posterior orbit. This results in an increasing proptosis, and eventually in loss of vision. There may also be infiltration of the soft tissues of the lateral part of the upper lid and other periorbital areas by neurofibromatous tissue, causing grotesque deformity. As well as repair of the missing bone at the back of the orbit, these soft tissue enlargements may need attention.

Haemangiomas and lymphangiomas are tumour-like conditions which can also be difficult to treat surgically, but in some cases surgery may be well worthwhile. Operative procedures can be made easier and safer in some haemangioma patients by preliminary embolization via radiologically placed intravascular catheters to reduce blood supply. Total removal of the lesion is ideal, but in many cases this is not realistic.

One of the most common benign tumours in the craniofacial region is intraosseous meningioma of the sphenoid wing. This tumour usually presents with proptosis. The involved bone can be removed using craniofacial exposures and the resulting defect replaced by a bone graft (Fig. 16) 2887. A wide variety of other benign tumours occur around the anterior cranial base and orbit: these can be resected and reconstructed, usually with quite acceptable results in terms of aesthetic outcome (Fig. 17) 2888, recurrence rate, and complication rates.

Both epithelial and connective tissue malignancies can affect the craniofacial area. Some of these are amenable to resection using craniofacial exposures and techniques. The large defects created then need to be repaired by bony and soft tissue reconstruction of the skull base, cranium, facial skeleton, and associated soft tissues.

Because of the size of the resulting defects and the importance of separating the intracranial contents from the nasopharynx, nasal cavity, and air sinuses, flap transfers are frequently necessary, and free flap surgery using microvascular anastomosis aids considerably in the reconstruction of these patients. The nature of these tumours and their significant recurrence rate means that such surgery may only be palliative, and its effects on the patient's quality of life need to be borne in mind when planning treatment. However, if surgery can be carried out without major postoperative disability it is often worthwhile, even if the patient is not cured of the tumour. Fungating masses can be removed, odour and pain alleviated, and quality of life improved in some incurable patients.

Full preoperative assessment of the extent of these lesions using modern radiological techniques is necessary to predict the required extent of resection and the likely outcome.

Attempted excision of craniofacial tumours is contraindicated when the major cerebral vessels would need to be sacrificed, where the only remaining seeing eye would need to be sacrificed, where tumour is extensively involving the cavernous sinus, or where it would appear for other reasons that attempted extirpation of the tumour is going to disable the patient to the extent that postoperative quality of life would be severely impaired. Management of these tumours requires extensive preoperative discussion with the patients and their families.

In general, about 50 per cent of patients with malignant tumours of the anterior skull base of sufficient extent to require a craniofacial procedure will survive and remain tumour-free postoperatively. The complication rate of these operations is quite high, however, at around 20 per cent.

It is likely that with more long-term studies, and more information on the psychological effects of surgery for craniofacial deformities, surgeons will be able to predict better which patients are most likely to benefit. Refinements in techniques, improvements in ease and safety, and a better understanding of the nature of the deformities will improve outcome. Concentration of craniofacial surgery into centralized units gives the opportunity for basic research into the cause of some of these problems, and will hopefully provide some answers.

Cohen MM, ed. Craniosynostosis. Diagnosis, Evaluation, and Management. New York: Raven Press, 1986.

Marchac D, ed. Craniofacial Surgery. Berlin: Springer-Verlag, 1987.

Marchac D, Renier D. Craniofacial surgery for Craniosynostosis. Boston: Little, Brown and Company, 1982.

Poole MD. Complications in craniofacial surgery. Br J Plast Surg, 1988; 41: 608 - 13.

Poole MD, Briggs M. Cranio-orbital trauma: a team approach to management. Ann R Coll Surg Engl, 1989; 71: 187 - 94.

Salyer KE. Techniques in Aesthetic Craniofacial Surgery. Philadelphia: JB Lippincott, 1989.

Stricker M, Van der Meulen J, Raphael B, Mazzola R, eds. Craniofacial Malformations. Edinburgh: Churchill Livingstone, 1990.

Tessier P. Anatomical classification of facial, cranio-facial and latero-facial clefts. J Maxillo-facial Surg, 1976; 4: 69 - 92.