ABSTRACT
AIM:To observe the structural basis of ocular motility abnormalities in patients with congenital fibrosis of the extraocular muscles type Ⅰ ( CFEOM Ⅰ) due to missense mutations in the developmental kinesin KIF21A using high - resolution magnetic resonance imaging ( MRI) . METHODS: Totally 11 affected individuals reported KIF21A mutations were correlated with MRI studies demonstrating extraocular muscles ( EOMs ) size, location, contractility, and innervation. EOMs and the motor nerve in the orbits were imaged with T1 weighted in a triplanar scan using a dual-phased coils with 2. 0mm thick. Motor nerves were imaged at the brainstem using head coils and 3D-FIESTA with 0. 6-mm thick. RESULTS: Patients with CFEOM Ⅰ exhibited different degrees of hypoplasia of oculomotor nerve, the abducens nerve and the trochlear nerve were also affected, of which 8 cases of orbital section could see the signal of abnormal nerve dominated by oculomotor nerve to lateral rectus. The both sides of six EOMS in all patients exhibited variable atrophy and abnormal bright internal signal on T1 imaging, particularly severe for the superior rectus and levator muscles. CONCLUSION: High - resolution MRI can directly demonstrate pathology of motor nerves,affected EOMs, and ‘Pulley' hypoplasia caused by CFEOM Ⅰ due to mutations in KIF21A,and these findings suggest that the neuronal hypoplasia is the etiological factor of CFEOM.
ABSTRACT
<p><b>BACKGROUND</b>Although neuroradiological findings of Möbius syndrome have been reported as a result of brain and brainstem abnormalities, magnetic resonance imaging (MRI) now permits the direct imaging of the cranial nerve (CN) and branches in the orbits. This study presents the MRI findings in patients with sporadic Möbius syndrome.</p><p><b>METHODS</b>Prospectively, CNs were imaged in the cistern using head coils and three dimensional fast imaging employing steady-state acquisition (3D-FIESTA), yielding a 0.5 mm(2) resolution in planes of 0.8 mm thickness in seven patients with sporadic Möbius syndrome. The cavernous and intraorbital segment of the CN and the extraocular muscles (EOMs) were imaged with T1 weighting in all patients. The cavernous segment was imaged in coronal planes, while the intraorbit in quasicoronal planes were imaged using surface coils. Intraorbital resolution was 0.16 mm(2) within 2.0 mm thick planes.</p><p><b>RESULTS</b>In the seven patients, the CN were absent or showed hypoplasia in the cistern, cavernous sinus, and orbit. Abducens (CN VI) and facial (CN VII) nerves were absent on the affected sides. Unilateral CN IX (glossopharyngeal nerve) in two cases displayed dysplasia. Branches from the inferior division of CN III were observed to innervate the lateral rectus (LR) bilaterally in three cases and unilaterally in one case, and had intimate continuity with the LR muscle in two cases bilaterally and two cases unilaterally. Hypoplasia of EOMs was shown in five cases. Dysplasia of the medulla on the left side was found in one patient.</p><p><b>CONCLUSIONS</b>Direct imaging of CNs and EOMs by MRI is useful in diagnosis of Möbius syndrome. It can directly demonstrate the abnormalities of the CN and orbital structures. The absence or hypoplasia of CN VI and CN VII may be the most common radiologic features in sporadic Möbius syndrome, and hypoplasia of CN IX may be an associated feature. The abnormality of EOMs and aberrant innervations in the orbit should be observed, and may be important for the study of the etiology.</p>