[MRI in congenital nystagmus]

Congenital nystagmus (CN) that is present by the age of 3 months is the most common form of nystagmus in childhood. We present a prospective study (2001-2008) in which we report imaging findings in 48 children with CN.

Twenty-six boys and 22 girls with CN underwent a complete ophthalmologic assessment and a cerebral MRI (mean age of examination under general anesthesia: 11 months). Three CN groups were formed: neurologic (n=27), sensory visual disturbance (n=14), and isolated (n=7). Cerebral MRI was interpreted by the same pediatric neuroradiologist (NG). Of the children studied, 98 % were born at term. The MRI abnormalities were classified as morphologic abnormalities (malformative or nonmalformative) and as signal abnormalities. The location of brain abnormalities was within the posterior fossa, (brain stem, cerebellum, dental nuclei, cisterna magna) and the cerebral hemisphere (white matter, perivascular spaces, midline commissures, basal ganglia).

Pendular nystagmus was prevalent in sensory and neurologic nystagmus. On fundus examination, optic disc abnormalities were present in 70 % (19) of neurologic CN and associated with white matter abnormalities of the optic radiations in 40 % of cases. On MRI, malformative morphologic abnormalities were present in 27 cases, nonmalformative abnormalities were found in 67, and signal abnormalities in 68. Within the brain stem, signal abnormalities were found as a cockade appearance of the posterior pons in the reticular regions (neurologic n=14, sensory n=6, isolated n=3). Other bright (most frequent) signal abnormalities were found within the dentate nuclei of the posterior fossa (neurologic n=10, sensory n=3, isolated n=3) and the cerebral white matter (neurologic n=17, sensory n=7, isolated n=5) of which 24 (neurologic n=15, sensory n=5, isolated n=4) involved the optic radiations. Most of these abnormalities were related and were seen most frequently in neurologic nystagmus. The most frequent association was signal abnormalities of the white matter, ventricular dilatation, and dilatation of the perivascular spaces (60.4 %) (neurologic n=13, sensory n=6).

This study showed the fundamental contribution of the cerebral MRI in CN. Cerebral abnormalities were found at the pathways for ocular motility, particularly at the saccadic pathways.