Orbital hypertelorism

32 Orbital hypertelorism






Introduction


Craniofacial malformations are disorders that affect both the cranium and the face. In faciocraniosynostoses, the facial maldevelopment is associated with craniosynostosis (premature fusion of one or several sutures). In facial clefts, the major anomaly affects the face, and is occasionally associated with a cranial problem. Hypertelorism is not a disease in itself; rather, it is a symptom or associated finding which accompanies some craniofacial conditions. Hypertelorism is defined by the abnormal increase in the interorbital distance (between the bony orbits). The abnormality may be symmetrical or asymmetrical.


In embryonic development, the development of the face occurs early, between the fourth and eighth weeks of gestation. When one observes that the midportion of the face develops immediately anterior to the forebrain, it is obvious that there is a close relationship between the face and the brain. Lateral to this midline prominence, paired elements appear: the nasal placodes and the maxillary processes. These structures merge in the midline whilst the frontonasal prominence is displaced in a cephalic direction. This prominence narrows to form the bridge and roo t of the nose. The developing eyes present as optic vesicles “outpouching” from the brain, and are initially positioned far laterally. The optic vesicles move closer together as the frontonasal prominence narrows. Simultaneously, the tip of the nose is derived from the paired medial elements, as the paired maxillary and mandibular processes fuse to form the lower part of the face. Clefts of the midline craniofacial structure occur when this delicate sequence of events is disrupted.




Basic science and disease process


If the frontonasal prominence remains in its embryonic position, the optic placodes cannot migrate toward the midline, and this results in orbital hypertelorism, often associated with various anomalies of the forehead and nose. It had been said that “the face predicts the brain,” and the importance of the centrofacial anomaly appears to parallel the forebrain defect.1 Conversely, interrupted development of the medial prominence may lead to an absence of midline structures with excessive narrowing, such as cyclopia or ethmocephaly. Hypertelorism alone is a mild degree of this sequence at the orbital level.


The associated maxillary anomalies seen with hypertelorism consist mainly of insufficient anterior growth in the upper maxilla, resulting in maxillary retrusion. Since the face is physiologically underdeveloped in infancy, facial anomalies may be more apparent later in childhood when facial growth is completed.


There is little known of the genetics of craniofacial malformations, likely due to the limited number of cases. As major facial clefts are rare, most of our knowledge of the pathogenesis of these malformations is based on studies of the formation of cleft lip and palate. Nevertheless, the role of heredity is obvious in the more frequent clefts of the lip, palate, and the lateral aspects of the orbit.


Radiation, infection, and maternal metabolic imbalances, which can be involved in cleft lip, have not been reported to be responsible for craniofacial malformations. Drugs and chemicals such as tretinoin, thalidomide, corticosteroids, and even aspirin are known to be responsible for malformations; and, while facial development occurs early in pregnancy,2 mothers may ingest various drugs while unaware of being pregnant. Causal environmental and hereditary factors probably play varying epigenetic roles in the formation of particular malformations.


Various systems of classification have been proposed for craniofacial clefts; two of them are of special value when assessing craniofacial anomalies. These are the “median facial clefts” and the Tessier classification, an orbitocentric cleft classification.



Diagnosis of hypertelorism and patient presentation in facial clefts




Tessier classification of facial clefts


In the Tessier classification,5 the orbit is the reference landmark, common to both the cranium and the face. The clefts, numbered from 0 to 14, rotate around the orbit and follow constant lines through the skeleton and soft tissues (Fig. 32.1). Clefts can be mostly cranial if they run upward from the eyelid (7–14) or mostly facial if they run downward from the palpebral fissure (0–6). They are craniofacial if the upper and lower pathways are connected.



The following combinations can be clinically observed: 0 and 14, 1 and 13, 2 and 12, 3 and 11, and 4 and 10. This concept of additive facial and cranial clefts equaling 14 is helpful when examining the patient and often allows identification of malformation along its entire length, above and below the orbit. The severity of the cleft is highly variable and can range from a slight soft-tissue indentation to a complete open cleft. The soft-tissue and skeletal clefts are, on the whole, superimposable. However, a detailed description of the soft-tissue defect, in relation to the skeletal cleft, is more reliable, because the skeletal landmarks are more consistent. The Tessier classification defines the 0–14 cleft as a midline widening, present in frontonasal dysplasia.


Unilateral and bilateral forms of clefting are found in various combinations, mainly asymmetrical when bilateral. Three-dimensional computed tomography has greatly facilitated diagnosis, whilst magnetic resonance imaging explores the brain, looking for an associated malformation. Stereolithographic models, constructed from computed tomography images, are also available, and may be useful for diagnosis and surgical planning as these malformations are uncommon and rarely identical.


Some isolated facial clefts, such as those affecting the lateral aspect of the face in Treacher–Collins syndrome (bilateral 6, 7, and 8 clefts), do not present any surgical interest for the neurosurgeon. The central and paramedial clefts affecting the face and cranium are of neurosurgical interest, as the cranium is the means of access for surgical correction.



Diagnosis of hypertelorism and patient presentation in faciocraniosynostosis


Hypertelorism is not the main feature of faciocraniosynostosis, and is variable in its presentation.6 When mild, it is frequently left untreated; however, when more noticeable, it can be addressed through a separate surgical step. Depending on the dental occlusion, and particularly the horizontal position of the upper maxillary arch, the treatment of hypertelorism will vary between an orbital shift and a facial bipartition. The timing of treatment is variable according to the pathology; however, in the authors’ experience, skull expansion for craniosynostosis treatment should precede hypertelorism correction.7,8



Crouzon’s syndrome


Described by Crouzon in 1912,9 this syndrome involves only the face and cranium and is not associated with other anomalies elsewhere on the limbs or trunk. The fundamental dysmorphology is an underdeveloped midface presenting with exorbitism secondary to insufficient depth of the orbits, hypoplasia of the malar bones, and a class III malocclusion. Hypertelorism may be present but is usually mild. The nose is short. Brachycephaly is usually present; however, scaphocephaly, plagiocephaly, or even a cloverleaf skull may be present. With an extended classification, the association of facial retrusion and craniosynostosis might be named as a related Crouzon’s anomaly. Commonly, the diagnosis of Crouzon’s syndrome is difficult to make during the first year of life, even if brachycephaly is obvious. It is often difficult to know whether the midface will be affected, even on radiological examination. Midface retrusion and exorbitism appear later in life. In some cases, however, the diagnosis is evident at birth.


Severe maxillary retrusion may produce airway obstruction with mandatory mouth breathing. There is a great variability of expression, and both severe and mild forms can be observed in the same family.


The strategy of treatment of faciocraniosynostosis is either two-staged1012 (fronto-orbital first, then facial advancement later) or a frontofacial monobloc advancement,1315 preferably with distraction.16 Whenever present, the hypertelorism might be corrected around 4–5 years of age, usually with an orbital shift (Fig. 32.2), because in Crouzon’s disease, the maxillary arch is normal (at least in the horizontal dimension).





Apert’s syndrome (acrocephalosyndactyly)


First described by Apert in 1906,17 this syndrome is easy to recognize because of the associated syndactylies of the hands and feet. The severity of syndactyly is scored according to Cohen and Kreiborg.18 Type 1 is syndactyly of the central three digits, type 2 is syndactyly of digits 2–5, and type 3 is syndactyly of all five digits.


The craniofacial involvement is always marked at birth, in contrast with that in Crouzon’s, with brachycephaly (sometimes asymmetrical) associated with facial retrusion. Both coronal sutures are fused, although some rare cases present with unilateral coronal synostosis or without any synostoses (4 cases without synostoses in our series). The hypertelorism and the anterior open bite add to the distinction from Crouzon’s disease. In fact, the maxillary alveolar arch is higher than the posterior part of the palate. Another main difference with Crouzon’s is the frequent sagittal dehiscence of the sutural system with the forehead frequently remaining wide open during the first year of life; this contributes to the abnormally wide forehead and face in this syndrome. Associated abnormalities of the central nervous system are more frequent than in other syndromic craniosynostoses. The exception is Chiari-like malformations, which are common in Crouzon’s, but, due to premature fusions of the lambdoid sutures, are uncommon in Apert’s.19 Because of these patients’ divergent frontal plane, bipartition procedures are more adapted to correct Apert’s-associated hypertelorism. Nevertheless, skull expansion (either anterior or posterior) is performed first, usually before 1 year of age to address the craniosynostotic skull.





Treatment/surgical technique



Surgical principles in facial clefts


Tessier’s breakthrough collaboration between plastic and neurological surgery allowed him to conceptually minimize the surgical border existing between the face and the skull and dramatically enhance the surgical treatment of upper facial clefts.20 Tessier demonstrated that the frontocranial route was a good approach to access the nose and orbits and that frontocranial problems can be treated simultaneously with facial problems. The fear of contamination from the facial cavities was so great among neurosurgeons in 1967 that, for their first case, Tessier and his neurosurgical colleague, Guyot, placed a dermal skin graft on the dura of the anterior cranial fossa after it had been elevated, voluntarily sacrificing both the olfactory nerves. A few months later, they performed the combined craniofacial approach. By 1970, a one-stage procedure to address the orbits from superior and inferior approaches was considered safe, and the olfactory nerves could be preserved (Converse).21 Preliminary disinfection of the nasal cavities, dissection of the mucosal domes and their immediate repair if opened, preservation or perfect repair of dura, changing of instruments if passing through the facial cavities, and perioperative antibiotic therapy were preventive measures that helped to avoid infection, osteitis, and meningitis.


There are two ways to mobilize the orbits when correcting orbital hypertelorism. The treatment planning varies according to the severity of the hypertelorism, the maxillary structure, and the age of the patient. An orbital shift can simply be performed in cases of normal or subnormal dental occlusion. In cases of restricted transverse maxillary structures, mobilization of both hemifaces (necessitating a facial bipartition) can be performed to correct the hypertelorism and the arched palate at the same time.


The classic approach described by Tessier et al. in 196720 consisted, after removal of the enlarged medial portion, of an en bloc mobilization of the orbits medially, the lower horizontal cuts being situated below the infraorbital rim, through the malar bone and the maxilla. In Tessier’s protocol, especially in adult patients, a supraorbital bar is kept in place in order to ensure stability of the mobilized orbits.22


Bipartition, proposed by van der Meulen23,24 and developed by Tessier,25,26 represents a mobilization of the two hemifaces (Fig. 32.3). Instead of cutting below the orbits, the surgeon makes the osteotomies through the zygomatic arch, the pterygomaxillary junction and medially through the palate. The medial resection must have a “V” shape because there will be an element of rotation, along with a narrowing on the midline. The rotation allows for widening of the maxillary arch and the nasal fossae and also for changing the axis of the orbits, which have a lateral slant.




Surgical techniques in facial clefts



Principles


The two main aims of surgery for this condition are to bring the orbits closer together and to create a nose of normal appearance. The basic anatomical anomaly is an increase in both the interorbital distance and the nasal bones whilst the glabellar region is much wider than normal. The enlarged portion of the midline structures is removed and, after mobilization of the orbits, the nasal skeleton is adjusted with the help of a bone graft if more dorsal projection is needed (Fig. 32.4).



This combined approach allows the surgeon to move the orbits and repair bony anomalies of the fronto-orbitonasal complex. Orbital displacement is key to the treatment of major craniofacial clefts. The orbit can be moved on a horizontal, vertical, anterior, or posterior axis to correct all anomalies. Reconstruction of a missing orbital roof or part of the forehead, canthopexies, and correction of soft-tissue problems can be performed simultaneously.


Not all hypertelorisms are symmetrical, and asymmetrical cases are more complex to correct. The cranial base is also asymmetrical and so the different distortions must be carefully evaluated by computed tomography three-dimensional reconstructions. Sometimes both orbits have to be moved in different directions.26,27

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Feb 21, 2016 | Posted by in General Surgery | Comments Off on Orbital hypertelorism
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