CHAPTER 18

Orbital Disorders

Orbital anatomy is described in BCSC Section 2, Fundamentals and Principles of Ophthalmology, and Section 7, Orbit, Eyelids, and Lacrimal System. Many pediatric orbital disorders are also described in Section 7.

Abnormal Interocular Distance: Terminology and

Associations

Hypertelorism, orbital Excessive distance between the medial orbital walls as a result of lateralization of the orbits. This diagnosis is made radiographically, not clinically. Hypertelorism occurs in more than 550 disorders.

Hypertelorism, ocular Excessive interpupillary distance when compared to standard nomograms; it implies orbital hypertelorism.

Hypotelorism Smaller than normal distance between the medial orbital walls, with reduced inner and outer canthal distances. The finding is associated with more than 60 syndromes. Hypotelorism can be the result of skull malformation or a failure in brain development.

Telecanthus Greater than normal distance between the medial canthi. This can be secondary to hypertelorism, or it can be a primary soft-tissue abnormality (see also Chapter 17).

Exorbitism Variously defined as prominent eyes due to shallow orbits or as an increased angle of divergence of the orbital walls.

Congenital and Developmental Disorders: Craniofacial

Malformations

Craniosynostosis

Cranial sutures are present throughout the skull, which is divided into 2 parts, the calvarium and the skull base, via an imaginary line drawn from the supraorbital rims to the base of the occiput (Fig 18- 1). Craniosynostosis is the premature closure of 1 or more cranial sutures during the embryonic period or early childhood. Bony growth of the skull occurs in osteoblastic centers located at the suture sites. Bone is laid down parallel and perpendicular to the direction of the suture. Premature suture closure prevents perpendicular growth but allows parallel growth. This growth pattern, called Virchow’s law, results in clinically recognizable cranial bone deformations (Fig 18-2). The following

Figure 18-2 A, Normal sutures. Bone growth occurs at the suture, with bone laid down parallel and perpendicular to the direction of the suture. B, Virchow’s law. Prematurely fused sutures allow bone growth only in the parallel direction; perpendicular growth is inhibited. C, An example of Virchow’s law. Premature closure of the sagittal suture produces scaphocephaly (boatlike skull); the shaded area shows the normal skull shape. (Illustration by C. H. Wooley.)

Plagiocephaly The term plagiocephaly literally means “oblique head.” Most often plagiocephaly is deformational, the consequence of external compressive forces, occurring prenatally or during infancy. Deformational plagiocephaly resulting from intrauterine constraint (eg, oligohydramnios) is characterized by ipsilateral occipital flattening with contralateral forehead flattening. However, this condition may also result from unilateral coronal suture synostosis. On the synostotic side, the forehead and supraorbital rim are retruded (depressed), the interpalpebral fissure is wider, and the orbit is often higher than on the nonsynostotic side. The nonsynostotic side displays a protruding or bulging forehead, a lower supraorbital rim, a narrower interpalpebral fissure, and frequently a lower orbital position (Fig 18-3).

Figure 18-3 A, Fused coronal suture, with inhibition of perpendicular skull growth. B, Patient with left coronal synostosis. Note retruded left forehead, elevated brow, and wider interpalpebral fissure, with compensatory protrusion of the right

forehead, lower brow, and narrowed interpalpebral fissure. (Part A illustration by C. H. Wooley; part B courtesy of Jane Edmond, MD.)

Brachycephaly “Short head”; specifically refers to growth in the anterior-posterior axis. Brachycephaly is frequently the result of bilateral closure of the coronal sutures. The forehead is most often wide and flat.

Scaphocephaly “Boat head.” Scaphocephaly usually results from premature closure of the sagittal suture; the skull is thus long in the anterior-posterior axis and narrow bitemporally.

Dolichocephaly “Long head”; the skull shape is similar to that in scaphocephaly.

Kleeblattschädel “Cloverleaf skull”; the skull shape is trilobar. Kleeblattschädel is typically the result of synostosis of the coronal, lambdoidal, and sagittal sutures.

Fusion of calvarial sutures affects cranial shape and orbital development. Fusion of the skull base sutures affects orbital development and facial development. In contrast to calvarial suture fusion, which causes varied cranial deformations, skull base suture fusion causes only midface hypoplasia (Fig 18-4), a constellation of abnormalities consisting of maxillary hypoplasia, beak-shaped nose, hypertelorism, shallow orbits with proptosis and lagophthalmos, high-arched palate, and a prominent-appearing jaw due to retruded maxilla.

Figure 18-4 Crouzon syndrome. This patient evidences brachycephaly and “tower” skull with forehead retrusion, proptosis, inferior scleral show, and a small, beaklike nose. Also visible is the emerging midface hypoplasia. (Reproduced with permission

from Katowitz JA, ed. Pediatric Oculoplastic Surgery. New York: Springer; 2002:fig 31-23.)

Etiology of craniosynostosis

Early suture fusion can occur sporadically as an isolated abnormality (eg, sagittal suture synostosis and most cases of unilateral coronal suture synostosis), or it can be part of a genetic syndrome and thus associated with other abnormalities. Craniosynostosis syndromes are usually autosomal dominant conditions, often with associated limb abnormalities. Many of these syndromes have overlapping features, which makes accurate diagnosis based on clinical findings difficult. Identification of specific mutations may be diagnostic, as approximately 50% of patients with syndromic craniosynostosis are found to have mutations that result in increased calvarial cell differentiation and bone matrix formation.

Craniosynostosis syndromes

Common systemic features of the craniosynostosis syndromes include fusion of multiple calvarial sutures and skull base sutures. Syndactyly (partial fusion of the digits) and brachydactyly (short digits), ranging in severity, are hallmarks of these syndromes, with the exception of Crouzon syndrome.

Crouzon syndrome Crouzon syndrome is the most common autosomal dominant craniosynostosis syndrome. Over 30 mutations, all occurring in the FGFR2 gene on chromosome 10, cause the Crouzon phenotype.

Calvarial bone synostosis often includes both coronal sutures, resulting in a broad, retruded forehead; brachycephaly; and tower-shaped skull. The skull base sutures are also involved, leading to varying degrees of midfacial retrusion. There is marked variability of the skull and facial features,

with milder cases escaping diagnosis through multiple generations. Hypertelorism and proptosis, with inferior scleral show (lower eyelid below limbus), are the most frequent features of Crouzon syndrome (see Fig 18-4). Hydrocephalus is common, but intelligence is usually normal. Findings are usually limited to the head. The absence of hand and foot anomalies can aid the clinician in the diagnosis.

Apert syndrome Patients with Apert syndrome usually have multiple fused calvarial sutures, most often both coronal sutures, and skull base suture fusion. The skull shape and facial features of these patients resemble those of Crouzon patients, but Apert syndrome is associated with an often extreme amount of syndactyly (Fig 18-5), in which most or all digits of the hands and feet are completely fused (mitten deformity). Apert syndrome is likely to be associated with internal organ malformations (cardiovascular and genitourinary) and mental deficiency. Hydrocephalus is less common in this syndrome than in Crouzon syndrome. The condition is autosomal dominant. Two mutations, both in the FGFR2 gene on chromosome 10, account for most cases.

Figure 18-5 Patient with Apert syndrome. A, Note “tower” skull, brachycephaly, forehead and superior orbital rim retrusion, maxillary hypoplasia, beaklike nose with depression of nasal bridge, and trapezoid-shaped mouth (common in infancy in Apert syndrome). B, Extreme syndactyly of the digits; the thumb is spared but is broad and deviated. C, Syndactyly of the

toes analogous to that of the hands. (Part A reproduced with permission from Cohen MM Jr, Kreiborg S. A clinical study of the craniofacial features in Apert syndrome. Int J Oral Maxillofac Surg. 1996;25(1):45–53. Parts B and C reproduced with permission from Cohen MM Jr, Kreiborg S. Hands and feet in the Apert syndrome. Am J Med Genet. 1995;57(1):82–96.)

Pfeiffer syndrome Patients with Pfeiffer syndrome have craniofacial abnormalities resembling those of Apert patients but often have more severe craniosynostosis, resulting in a cloverleaf skull. There is a high risk of hydrocephalus. The syndactyly is much less severe, and patients have characteristic short, broad thumbs and toes. This syndrome is autosomal dominant and caused by mutations in the

FGFR1 or FGFR2 gene.

Saethre-Chotzen syndrome The features of Saethre-Chotzen syndrome are much milder than those of other craniosynostosis syndromes; this syndrome is therefore underdiagnosed. Early suture fusion is not a constant feature but, when present, typically involves 1 coronal suture (plagiocephaly), resulting in an asymmetric face. Other common features are ptosis, low hairline, and ear abnormalities. Abnormalities of the hands and feet include brachydactyly and mild syndactyly (Fig 18-6). Intelligence is usually normal. The condition is autosomal dominant and caused by mutations in the TWIST gene on chromosome 7.

Figure 18-6 Patient with Saethre-Chotzen syndrome. Note the facial asymmetry, flat forehead, low-set hairline, mild left ptosis, lateral deviation of the great toes, shortened toes, and partial syndactyly of fingers 2 and 3. (Courtesy of the March of

Dimes.)

Ocular complications of craniosynostosis

Proptosis Proptosis (or exorbitism) results from the reduced volume of the bony orbit. The severity of the proptosis in patients with craniosynostosis is not uniform and frequently increases with age