Duane Retraksiyonu Olan Mobius Sendromu: Abdusens Sinir Yokluğu ve Fasyal Sinir Hipoplazisi

1. 1Gulhane Military Medical Academy, Department Of Ophthalmology, Ankara, Turkey
2. 2Gulhane Military Medical Academy, Department Of Radiology, Ankara, Turkey

Sorumlu Yazar: The etiology of Mobius syndrome is multifactorial, and several theories have been proposed, with the most supported theory being that of ischemic or hypoxic insult to the fetus.9 Other infectious and genetic etiologies have also been proposed. In addition, the use of misoprostol, a prostaglandin-E1 analog, has been implicated.10 Cronemberger et al10 reported 18.8% use of misoprostol and Ghabrial et al11 reported 43% significant event during intrauterine life among Mobius patients. However, no pharmacotherapies had been taken by the mother during uneventful pregnancy, and delivery was uncomplicated in the present case. Neuroimaging (CT and MRI) findings of Mobius syndrome include hypoplasia of the pons or medulla with correspondent CN6 and CN7 hypoplasia, absence of the medial colliculus at the level of the pons, absence of the hypoglossal prominence suggestive of CN12 nuclei hypoplasia, cerebellar hypoplasia, depression of the 4th ventricle, and calcification in the pons in the region of the CN6 nuclei.2-8 Combined with the knowledge obtained from neuropathologic studies, ischemic/hypoxic theory came forward as the possible mechanism.12 We observed a typical presentation of Mobius syndrome as both CN6 and CN7 were involved clinically and radiologically. Sano et al4 found absence of the facial nerve canal in the middle ear on CT, a narrow nerve in the middle ear on MRI but no associated CN6 finding. Verzijl and coworkers13 reported bilateral absence of cisternal and canalicular portions of both facial nerves in six Mobius syndrome patients. Of these six, four had bilateral Type 3 Duane syndrome. Another study by the same group reported up to a 34% incidence of bilateral Duane syndrome in a series of 37 Mobius syndrome patients. Yong-Hong et al5 found absence of CN6 or hypoplasia in the brainstem and an extra branch of the inferior division of CN3 to the lateral rectus as the most common type of presentation of Duane retraction. There seems to be an alternative pathway, mostly from CN3, of innervation by other cranial nerves. However, we did not trace the CN3 up to the endpoint of innervation on MRI. A large Italian case series demonstrated that nearly half of the patients had strabismus, most of whom were esotropic.14 However, they reported no Duane retraction component. As in our case, visual acuity was better than 20/50 in tested eyes as a result of alternating fixation. Their findings agreed with Verzijl et al’s that Mobius syndrome is a complex syndrome of rhombencephalic maldevelopment involving predominantly motor nuclei and axons.15 However, Dumars et al16 reported extraneuronal findings which included hypoplasia of the posterior bony orbit, displaced rectus muscle paths, and abnormal insertions of the superior and inferior oblique muscles, which show that it is not only a brain stem dysplasia. Thereby, it remains unknown whether the primary defect is actually maldevelopment of brainstem nuclei, nerves, or their associated muscles, and whether the process is dysplastic or degenerative. Genetic testing or orbital imaging was not obtained in our patient and the patient was no longer available for follow-up. Direct imaging of extraocular muscles and innervating cranial nerves by MRI and further genetic analyses would provide relevant information regarding the diagnosis, etiology and treatment of this complex strabismus entity. Though there are some reports especially regarding Poland-Mobius variant in the local literature, this is the first report that gives clinically relevant MRI findings in a Mobius syndrome case.17-19 Address for Correspondence/Yazisma Adresi: Murat Küçükevcilioglu MD, Gülhane Military Medical Academy, Department of Ophthalmology, Ankara, Turkey Phone: +90 312 304 58 72 E-mail: mkucukevcilioglu@gata.edu.tr Received/Gelis Tarihi: 12.07.2012 Accepted/Kabul Tarihi: 09.10.2012