Fig. 7.17  Congenital horizontal gaze palsy with scoliosis. T2-weighted fast spin echo axial MR imaging shows butterfly configuration of the medulla with flattening of the ventral surface, reduced anterior–posterior diameter and midline medullary cleft. Courtesy of Joseph Demer, M.D.

ments and had variable strabismus, horizontal nystagmus, and defective vertical smooth pursuit. Convergence can be preserved, and some people use convergence substitution as a substitute for horizontal gaze.241 All patients developed progressive scoliosis during early childhood. The disorder is found in both consanguineous and nonconsaguinous families.241 Heterozygotes were unaffected. This disorder produces a pathognomonic brainstem malformation. MR imaging shows a hypoplastic pons and medulla,622 with overall diminished anterior–posterior dimension (Fig. 7.17). The ventral surface of the pons is flat. The medulla fans out both dorsally and ventrally in a butterfly configuration. There is a prominent midline cleft in the medulla that extends down to the cervicomedullary junction. Affected patients had electrophysiologic evidence of ipsilateral corticospinal and dorsal column-medial lemniscus tract innervation. In contradistinction to most other congenital cranial dysinnervation disorders, the abducens nerves are normal in size and configuration.241 ROBO3 mutations may disturb brainstem morphogenesis by failing to promote decussation of long motor and sensory tracts in the pons and medulla. Impaired decussation of pontine ocular motor pathways may explain the absence of horizontal eye movements in this disorder.88

Möbius Sequence

Möbius sequence is a rare congenital disorder characterized by congenital facial weakness with horizontal gaze palsy296 or impairment of ocular abduction.781 Dysfunction of other cranial nerves, orofacial malformations, limb malformations, and musculoskeletal system defects are common associated features, but they are not obligatory for the diagnosis.

Möbius sequence is a sporadic multiple-malformation complex that affects the face and horizontal gaze mechanisms bilat-

Fig. 7.18  Möbius syndrome. Note characteristic flattening of lower facial features. Courtesy of Joseph Demer, M.D.

erally.566 Affected children have mask-like facies, with the mouth constantly held open (Fig. 7.18). The upper facial nerves are affected more than the lower facial nerves, and facial asymmetry is common due to asymmetric facial strength. The eyes may be straight, esotropic or, rarely, exotropic.191,200,518a,555 Those with straight eyes tend to have horizontal gaze palsy,200 and some use convergence substitution to look to the side.

Such children may be thought to have isolated bilateral sixth nerve paresis if the slow convergence movement and the associated pupillary constriction are not recognized. Another subset exhibits retraction of the globe on attempted adduction.518a As in Duane syndrome, congenital ocular motor synkinesis may contribute to the horizontal conjugate gaze paresis in some cases. Additional deficits affecting other cranial nerves, particularly V, IX, and XII, may produce feeding and sucking difficulties in the neonatal period and subsequent speech difficulties, with or without atrophy of the tongue.16 Rarely, the sixth cranial nerves may be spared.754

Möbius sequence may be associated with a wide variety of associated limb malformations (talipes equinovarus, brachydactyly, syndactyly, congenital amputations) as well as hypoplasia or absence of the branchial musculature, particularly the pectoralis muscle (Poland anomaly).16,454 Miller et al553 refer to the subgroup with associated limb anomalies as terminal transverse defects with orofacial malformations (TTV-OFM), a term originally used by Temtamy and McKusick.16 Endotracheal intubation may be especially