Horizontal gaze palsy with progressive scoliosis: CT and MR findings
- First Online:
- Cite this article as:
- Bomfim, R.C., Távora, D.G.F., Nakayama, M. et al. Pediatr Radiol (2009) 39: 184. doi:10.1007/s00247-008-1058-8
- 280 Downloads
Horizontal gaze palsy with progressive scoliosis (HGPPS) is a rare congenital disorder characterized by absence of conjugate horizontal eye movements and progressive scoliosis developing in childhood and adolescence. We present a child with clinical and neuroimaging findings typical of HGPPS. CT and MRI of the brain demonstrated pons hypoplasia, absence of the facial colliculi, butterfly configuration of the medulla and a deep midline pontine cleft. We briefly discuss the imaging aspects of this rare entity in light of the current literature.
KeywordsHorizontal gaze palsy Progressive scoliosis MRI
Horizontal gaze palsy with progressive scoliosis (HGPPS) is a rare, autosomal recessive disorder characterized by congenital absence of conjugate horizontal eye movements and preservation of vertical gaze and convergence, which is associated with progressive scoliosis developing in childhood and adolescence . MRI findings are midline pontine cleft, butterfly configuration of the medulla, brainstem hypoplasia, and absence of facial colliculi [1, 2, 3].
We report a child with HGPPS. The etiology, pathogenesis and clinical aspects are discussed with an emphasis on the imaging findings.
HGPPS is a rare autosomal recessive disorder that has been mapped to a 30-cM region on chromosome 11q23-25 . Lo et al.  proposed that the locus responsible for HGPPS is located in a 9-cM interval on chromosome 11q23. Bosley et al.  reported sporadic HGPPS in children of nonconsanguineous parents who harbored a compound heterozygous mutation of the ROBO3 gene.
A smooth horizontal gaze requires that the lateral rectus muscle of one eye, innervated by the abducens nerve, and the medial rectus muscle of the contralateral eye, innervated by the oculomotor nerve, work together. This coordinated activity is controlled by the abducens nucleus. This nucleus contains two populations of neurons—one that directly innervates the ipsilateral lateral rectus muscle and the other that consists of internuclear neurons that project through the medial longitudinal fasciculus to the contralateral oculomotor nucleus, whose motor neurons innervate the medial rectus muscle . The abducens nuclei are located in the lower part of the pontine tegmentum at the level of the floor of the fourth ventricle. They are surrounded by the axons of the motor nuclei of the facial nerve, curving around the abducens nuclei to form the internal genu of the facial nerve. This structure causes a prominence at the floor of the fourth ventricle and forms the facial colliculi [1, 2]. Lack of conjugate horizontal eye movement and absent facial colliculi on axial MR imaging with intact facial, vestibulocochlear, and oculomotor nerves suggest selective agenesis of the abducens nuclei .
The pathogenesis of progressive idiopathic scoliosis in HGPPS remains unclear. It has been suggested that it involves a primary neurological dysfunction involving the proprioceptive inputs mediated by the posterior column pathways of the spinal cord and medial lemniscus [1, 3]. The split pons sign is attributable to abnormal development of the abducens nuclei and medial longitudinal fasciculus occurring between gestational weeks 5 and 8 [1, 2]. Absence of the posterior prominence of the gracilis and cuneate nuclei is assumed to reflect hypoplasia of these posterior column nuclei. Hypoplasia of the medial lemniscus, which is located posterior to the pyramids, is thought to explain why the inferior olivary nuclei are unusually more prominent than the pyramids [1, 6]. The deep midline cleft along the ventral aspect of the medulla oblongata has been described as the result of uncrossed corticospinal tracts .
The differential diagnosis of HGPPS embraces several genetic disorders of eye movement, such as Duane retraction syndrome, Möbius syndrome and others. Clinical and neuroimaging findings can differentiate these entities from HGPPS. Duane retraction syndrome consists of a congenital abduction deficit of the eyeball accompanied by retraction of the globe on attempted adduction and by upshoots or downshoots of the affected eye on adduction. Pathological and imaging findings reveal aplasia or hypoplasia of the abducens nuclei and nerve . Möbius syndrome is a congenital disorder characterized by facial diplegia, paralysis of lateral gaze movements and other cranial nerve palsies. It is usually associated with cranial and musculoskeletal anomalies. MRI reveals brainstem hypoplasia with absence of the facial colliculi .
Clinical findings in our patient were characteristic of HGPPS and included absence of all horizontal gaze reflexes, conjugate pendular nystagmus and progressive scoliosis. Convergence and vertical gaze were preserved [1, 2, 3, 4, 5]. Eye movement symptoms were noticed earlier than scoliosis, which is in agreement with previously reported cases .
CT and MRI abnormalities observed in our patient were typical of HGPPS. CT examination showed brainstem hypoplasia and a flattened floor of the fourth ventricle, raising suspicion of HGPPS. MRI was performed soon after, and additionally demonstrated a deep midline cleft dorsally along the pontine tegmentum and ventral aspect of the medulla oblongata, as well as absence of the prominence of facial colliculi, and cuneate and gracilis nuclei. Moreover, the olives appeared prominent relative to the pyramids [1, 3, 5, 6].
In conclusion, we describe a case of HGPPS with typical clinical and imaging findings, and emphasize the value of MRI as a powerful imaging tool in the diagnosis of this rare entity.