Congenital Orbital Malformations

Malformations of the eyes, the orbits, and their surrounding tissues can be congenital or acquired. Congenital deformities occur in isolation, in combination, or as a component of broader, sometimes systemic, malformation syndromes. They can lead to a massive restriction in sight, or they may only pose a cosmetic problem, or may even cause no symptoms and either remain undetected or be diagnosed as incidental findings during routine examinations. ^{1,​ 2} Congenital orbital anomalies have diverse causes such as genetic defects, numerical chromosomal aberrations, in utero exposure to exogenic teratogenic noxae (e.g., medicaments, infectious microorganisms), or peripartal complications (e.g., oligohydramnion). ^{2,​ 3,​ 4,​ 5} The cause of many deformities lies in individual genetic defects leading to a series of anomalies, which in turn defines a sequence or a syndrome. ^{2,​ 3}

10.1.1 Hypertelorism

In hypertelorism there is an enlarged interorbital and inner and outer canthal distance as well as an expanded interpupillary distance. ^{1,​ 2,​ 3} There can also be a defect in the Lamina cribrosa where applicable in connection with an anterior encephalocele. Hypertelorism has been documented in the context of over 550 cases. It is often misdiagnosed when the bridge of the nose is flat and there are epicanthal folds, exotropia, eyebrows wide apart, narrow palpebral fissures, and isolated canthal dystopias. ^{2,​ 3}

Three basic mechanisms have been described for the formation of hypertelorism, each of which provides a plausible explanation for the occurrence of the orbital malformation in the context of syndromes. The first entails a premature ossification of the minor sphenoidal wing, which leads to the fixing of the orbits in the fetal position. The second involves a developmental disorder of the nasal capsule with consecutive protrusion of the primitive brain vesicle into the space thus created, with the result that further development of the eye position is blocked, as can be observed in a frontal encephalocele. ^{2,​ 6} The third potential mechanism is represented by developmental disorders in the area of the base of the skull, which occur, for example, in craniosynostosis syndromes such as Apert’s syndrome and Crouzon’s syndrome or in midfacial malformations such as frontonasal dysplasia or craniofacial dysmorphia. ^{2,​ 3,​ 7,​ 8}

As with hypotelorism, prenatal diagnosis can be made sonographically by measuring the interorbital distance when the 95th percentile curve is exceeded. ^{9,​ 10} The operative correction is aimed at removing skeletal deformities and soft tissue changes simultaneously and is based on the concept of Tessier’s combined intra- and extracranial method, which still today represents the basis of surgical treatment. ^{11,​ 12} In this the interorbital distance is narrowed by means of a paramedian bone resection. After a frontal segment is removed, a circular osteotomy is performed at depth in the interior of the orbit socket and the paranasally expanded ethmoidal cells and other bony parts are resected up to the lamina cribrosa so that the eyeball can follow the correction made to the bone ^{13,​ 14}

10.1.2 Hypotelorism

Hypotelorism is a reduced distance between the medial orbit walls (interorbital distance) with likewise reduced inner and outer canthal distance. ^{1,​ 2,​ 3} It occurs most commonly in connection with a holoprosencephaly, a malformation of the cerebrum, in which an incomplete splitting of the forebrain occurs in the third to sixth embryonal week as the result of a defect in the area of the midline developmental field of the head. ^{2,​ 15} Hypotelorism also occurs with other craniofacial malformations, which range from cyclopia—a rare malformation of the facial part of the skull in which the two eye primordia merge into one bony eye socket and which is often associated with holoprosencephaly—to a mild anomaly from a single central upper incisor in connection with unostentatious hypotelorism. ^{2,​ 3}

Diagnosis can be made prenatally by means of sonography; ^{9,​ 10} surgical treatment is based on the technique of the “functional orbit” of Tessier and Guiot as well as its diverse modifications. ^{12,​ 16,​ 17} The principle of transversal displacement, which was first described for hypertelorism, is accordingly reversed with hypotelorism. An osteotomy is performed on the medial orbit wall paranasally and the resection needed takes place in the area of the lateral orbital roofs. Removal of the lateral parts of the cheekbones can also be considered. The bony orbits are rotated laterally and the diastases at the side of the laminae cribriformes as well as in the area of the nose and the orbit sockets are bridged using osteoplastic techniques. ¹¹

10.1.3 Cyclopia and Synophthalmia

With these very rare facial malformations, which occur mainly in connection with holoprosencephaly, there is a joint orbit with two eyeballs lying next to each other (synophthalmia) or just one eye (cyclopia). Characteristic are a poor formation of the prechordal segment of the skull and an underdevelopment of the mouth–nose–throat area. ⁹ A severely abnormal development of the prosencephalon results in a partial or complete fusion of the optic vesicles. ^{18,​ 19} As these malformations are usually associated with holoprosencephaly, their prognoses are mostly poor. ⁹

10.1.4 Anophthalmia and Microphthalmia

Anophthalmia and microphthalmia are among the most common congenital ocular malformations and represent a significant factor in congenital blindness. ^{20,​ 21} Reduced orbital growth is found not only with microphthalmia but also with anophthalmia. ⁹ They occur in isolation or in association with a syndrome. Microphthalmia designates a miniaturized eyeball, anophthalmia indicates a complete absence of the eye structure. ²⁰

Primary anophthalmia (absence of the eye structure) is characterized by a sporadic, non–syndrome-associated occurrence; it affects both eyes in approximately 75% of cases. Secondary anophthalmia results from a developmental defect of the entire neural tube. When there is a malformation or poor development of the optic vesicle after evagination from the diencephalon, one speaks of a degenerative anophthalmos, with which there is the possibility of evidence of neuroectodermal elements in the orbit. ^{18,​ 20,​ 21}

Microphthalmos can occur unilaterally or bilaterally and may be the expression of a primary ocular developmental disorder or may occur within the context of a craniofacial dysplasia and more extensive syndromes such as trisomy 13 and 18. ^{1,​ 20,​ 21} It also occurs in connection with ocular malformations such as persistent primary hyperplastic vitreous body, nuclear cataract, or coloboma. ¹ Diverse genetic mutations associated with anophthalmia or microphthalmia have now been identified. ^{20,​ 21,​ 22}

Prenatal diagnosis is based on the evidence of an orbit that is too small with values under the 5th percentile curve along with evidence of a missing or too small eyeball; particular attention is given to comparison with the contralateral side in order to be better able to differentiate abnormalities in the area of the eyeball. ⁹ Satisfactory treatment for microphthalmos is usually possible with conformers or overlying prostheses. Expansion of the conjunctival sac with self-inflating hydrogel expanders leads to an earlier and better capability for accommodating prostheses and improving facial symmetry. With congenital clinical anophthalmos, first of all a stretching of the conjunctival sac is required with highly hydrophilic hydrogel expanders. Subsequently the use of self-inflating orbit expanders or a dermis fat transplant is recommended. In older children (>5 years) with a contracted conjunctival sac incapable of taking a prosthesis and marked facial asymmetry, as well as patients who have previously undergone several operations, extensive orbital osteotomies and flap techniques have to be considered. ²³

10.1.5 Facial Clefts

In contrast to lip–jaw–palate clefts, the formation of clefts affecting the other parts of the face is very rare. There are diverse classifications for describing these rare facial clefts; for example, those according to Harkins, van der Meulen, or Tessier. ^{24,​ 25,​ 26}

Prediction can be made about the cleft formation to be anticipated based on the fusion lines of the embryo’s facial bulges. ²⁷ For example, an incomplete fusion in the pair of lower maxillary bulges leads to a median lower jaw cleft formation. ²⁷

The failure of an upper maxillary bulge to fuse with a lateral nasal bulge causes a diagonal facial cleft, which runs from the edge of the lower eyelid to the lower edge of the nasal opening wherein the nasolacrimal duct remains as an open groove. It can occur on one or on both sides and be combined with lip–jaw–palate clefts. ^{27,​ 28}

Transverse facial clefts arise where the fusion of the upper and lower maxillary bulges is disrupted while the cheeks are being formed and the early primitive mouth cleft, which extends to the area of the ear structure, remains in various versions (macrostomy). ²⁸

The midfacial cleft can be construed as having been caused by a defective frontalization of nose and eyes during the fusion of the central nasal bulges. Here the medial facial furrows (e.g., between both processus globulares) fail to disappear. ²⁸

The rare facial clefts often influence orbital growth and are also often associated with malformations of the brain. ²⁷

10.1.6 Craniosynostoses

Craniosynostoses are caused by a premature closure of one or several cranial sutures and often exhibit a characteristic abnormal head shape. ^{27,​ 29} Primary craniosynostoses have their origin in a disrupted ossification; the pathogenesis of secondary suture synostoses is very varied and includes, inter alia, metabolic and endocrinal disorders as well as poor brain growth. ^{27,​ 30}

Primary craniosynostoses can be broken down further into nonsyndromal (85%) and syndromal forms (15%). ²⁷ Nonsyndromal craniosynostoses usually manifest in a premature closure of a single cranial suture, whereas syndromal craniosynostoses are often characterized by multiple fused sutures and facial, brain, and other malformations. Apert’s syndrome is usually associated with extensive syndactyly, Crouzon’s syndrome with a market midface hypoplasia, exophthalmos and hypertelorism. Evidence of mutations in fibroblast growth factor receptor genes have been found with various syndromal craniofacial synostoses. ²⁷

Trigonocephaly

Trigonocephaly is caused by a premature ossification of the metopic suture. The craniosynostosis causes bulging in the area of the central forehead, which in many cases is identifiable as a distinct bony ridge. Due to the additional flattening of the frontolateral region, the frontal bone takes on the shape of a triangle in horizontal section. The forehead appears flat, narrow, and high with a clear broadening of the back of the head. There is hypotelorism with, for the most part, unaffected midfacial growth. ^{25,​ 31,​ 32}

Plagiocephalus

This malformation, which is often misinterpreted as birth-related or positional damage, is caused by a unilateral coronal or lambdoid synostosis. The forehead on the side affected is flat, the sagittal shortening of the skull goes right to the back of the head. The sphenoidal wing on the ipsilateral side is thickened, the anterior skull base is shortened. Characteristically, on the inside of the cranial vault there are impressiones digitatae (impressions of cerebral gyri) as an indication of a local constriction of the brain. The orbit socket is mainly flattened supraorbitally. Due to the growth in the direction of the suture affected, the facial axis deviates toward the healthy side, whereby the eye axis likewise tends toward the healthy side with a simultaneous contralateral descent of the occlusal plane. ^{31,​ 32}

Oxycephaly

In oxycephaly there is a bilateral coronal suture synostosis, whereby a flat, high forehead develops as well as a skull that is shortened in the sagittal direction and broadened in the transversal direction. The anterior cranial fossa is distinctly shortened, the sphenoidal wing is markedly thickened, and intracranial pressure is often massively raised with consequent generalized impressiones digitatae. Due to a shortened orbit socket solely in the supraorbital area, it is only at this location that an exophthalmos occurs; the poorly marked nasofrontal angle is typical. ^{31,​ 32}

Brachycephaly

Brachycephaly with its extreme form of cloverleaf skull is characterized by a premature coronal suture synostosis with a simultaneous fusion of the skull base sutures and possible involvement of viscerocranial sutures. As the growth of the sphenoid bone mass as a whole is constricted, the malformation does not remain restricted to the neurocranium but has massive effects on the viscerocranium right into the stomatognathic system. Clinically striking are a shortening of the skull and the base of the skull sagittally with bulges in the area of the forehead and temples, which results overall in a short, broad, and round skull. There is hypertelorism and the markedly flattened orbit sockets cause exophthalmos. The middle part of the face is markedly hypoplastic and, as a result of the inhibited rotation of the upper jaw, there is a circular open bite. ^{31,​ 32}

Scaphocephaly

Premature ossification of the sagittal suture causes a transversal narrowing of the skull with compensatory increased growth sagittally giving the appearance of a long, narrow skull with a high forehead. ^{31,​ 32}

The causes of rare secondary craniosynostoses are typically found in endocrinal and metabolic disorders such as renal osteodystrophy, hyperthyrosis, and hypophosphatasia, in which the physiological bone metabolism is disrupted. When hydrocephaly has been operated for, one may also observe secondary synostoses on occasion due to a premature easing of the natural growth pressure of the brain. ^{27,​ 32}

An interdisciplinary process is obligatory in making a diagnosis, involving neuropediatrics, ophthalmology, and ENT. In the context of imaging diagnostics, transcranial sonography with the imaging of the brain sutures is indispensable. Conventional radiology can give indications of increased cerebral pressure through expanded emissary foramina. ³² However, CT with 3D reconstructions is the procedure of choice to ensure adequate preoperative planning and the capture of complex craniosynostoses. It allows a precise analysis of the skull malformation as well as possible intracranial changes, for example, of the ventricle system and other cerebral structures. ^{27,​ 32,​ 33} MRI is additionally indicated as an imaging investigation for syndromal craniosynostoses with associated cerebral anomalies. ²⁷

The surgical correction of cranial synostoses is often undertaken several times. If the orbits are involved, fronto-orbital advancement with its various modifications serves to correct the upper half of the orbit. ^{34,​ 35,​ 36} This is mostly conducted between the 6th and 12th months of life and is based on the repositioning of the fronto-orbital area by osteoplasty as well as ensuing osteosynthesis. It can be adjusted individually according to the positioning of the bone segments removed. ^{37,​ 38} In the combined neurosurgical–facial surgical intervention, operative access is achieved via a coronal incision. Following the craniotomy, in standardized fronto-orbital advancement the osteotomy of the nasofrontal suture is conducted in the orbit sockets and from there via the orbit vault to the zygomaticofrontal suture after ventrally releasing the temple muscles from the temporal fossa while preserving the supra-orbital nerves. From here an osteotomy is performed in a bow shape to the coronal suture whilst forming a retention shape (tongue-in-groove technique) in the parietal area. Once the opposite side is reached along the coronal suture, the osteotomy is continued analogously. The resulting fronto-orbital section of bone is divided into a frontal and an orbital segment via a horizontal incision. First of all, the frontal bone flap is removed and then the orbital segment. The parts are extricated osteoplastically in accordance with their deformity and relocated forward using resorbable osteosynthesis material to fix them in a new position. ³⁹ In this way space is created for the brain and the conditions are fulfilled for skull growth to be normalized by exploiting autoregulative forces, whereby not only functional but also aesthetic improvement is the aim. ³⁸ For a comprehensive harmonization of the orbit shape as well as of the midface, an additional Le Fort II or Le Fort III distraction is indicated further down the line in many cases in order to give a final shape to the often hypoplastic midface underneath the zygomaticofrontal suture.

Apert’s Syndrome

Apert’s syndrome, also called acrocephalosyndactyly, is the most common syndromal craniosynostosis and is mainly characterized by brachyturricephaly, caused by a premature fusion of the coronal suture and possibly of the sagittal suture, as well as sometimes multiple symmetric syndactyly. ^{27,​ 38,​ 40} In its extreme form a cloverleaf skull can occur, which is characterized by a premature synostosis of all skull sutures with the exception of the metopic suture and the squamous suture. As regards the facial morphology, there is often marked hypoplasia of the midface, hypertelorism with an antimongoloid eyelid axis position, and strabismus. ³⁸ Although most cases occur sporadically, an autosomal-dominant inheritance with complete penetrance and higher variance is documented. Specific mutations have been found in the fibroblast growth factor receptor gene (FGFR2), which plays a central role in the complex regulation of the morphogenesis of the skull and of the limbs. ^{27,​ 41} Although 70% of the patients are of normal intelligence, associated cerebral anomalies such as agenesis of the corpus callosum or encephaloceles have been documented. ²⁷

Crouzon’s Syndrome

Crouzon’s syndrome, also known as dysostosis craniofacialis, is the second most common syndromal craniosynostosis ^{27,​ 42} ( ▶ Fig. 10.1, ▶ Fig. 10.2). It displays autosomal-dominant inheritance with mutations in the FGFR2 gene. The premature suture synostosis mainly affects the coronal suture, leading to a brachycephalic or an oxycephalic skull configuration. However, the lambdoid as well as the sagittal suture can just be equally affected. ³⁸ The facial abnormalities are in particular maxillary retrognathia, strabismus divergens, exophthalmos, hypertelorism, and lateral slanting of the eyelid axes. Progressive hydrocephaly and malformations in the venous outflow belong, inter alia, to the associated intracranial anomalies. ²⁷

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