Enlargement of the Optic Chiasm: A Novel Imaging Finding in Glutaric Aciduria Type 1

Abstract

Patients with glutaric aciduria type 1, without early diagnosis and initiation of preventive treatment, often develop movement disorders and various degrees of motor disability due to striatal area-specific damage induced by an acute episode of metabolic decompensation. The neuroimaging phenotype of patients with glutaric aciduria type 1 includes characteristic cyst-like bilateral enlargement of the Sylvian fissures and anterior subarachnoid spaces and signal abnormalities including supratentorial white matter and deep gray matter structure T2 hyperintensities, frequently associated with restricted diffusion. In this retrospective study, we add to the neuroimaging spectrum of glutaric aciduria type 1, a novel imaging finding present regardless of a previous metabolic crisis: the enlargement of the optic chiasm associated with signal abnormalities in the anterior intracranial visual structures observed in 6 of 10 patients. These optic pathway abnormalities are suggested as useful diagnostic clues for glutaric aciduria type 1, and possible pathophysiologic mechanisms are discussed.

FIG 1.

A 16 -month-old patient with GA-1, having experienced a metabolic crisis. A and D, Axial FLAIR and coronal T2-weighted images. B and E, Axial diffusion sequences. C and F, Axial ADC maps. Characteristic bat wing widening of the Sylvian fissures and enlargement of subarachnoid temporal spaces are shown. Lateral ventricular moderate dilation is also shown. Bilateral symmetric atrophy and abnormal T2-FLAIR hyperintense signal in striatal area show increased diffusion on ADC maps, suggesting striatal necrosis related to the history of metabolic decompensation. The globus pallidi and thalami also demonstrate bilateral abnormal hyperintensity associated with restricted diffusion away from the acute metabolic crisis. Patchy areas of hyperintense T2-FLAIR signal abnormalities without restricted diffusion are found in the superficial bilateral white matter, persisting on the follow-up for up to 6 years. The optic chiasm is thickened, displaying abnormal hyperintense T2 signal and restricted diffusion also involving the intracranial optic nerves.

FIG 2.

A 7-year 10-month-old patient with GA-1, free from a history of previous metabolic crisis. A and D, Coronal T2-weighted images. B and E, Axial diffusion sequences. C and F, Axial ADC maps. Characteristic Sylvian fissure enlargement and anterior arachnoid temporal cysts are shown. Note the absence of signal abnormalities in the deep gray matter structures, especially in the striatum; however, abnormal hyperintense T2 signal is observed bilaterally in the periventricular white matter displaying restricted diffusion. Abnormal areas of T2 signal with restricted diffusion are also demonstrated in the bilateral medial wall of the hypothalamus and in the markedly enlarged optic chiasm.

FIG 3.

Coronal T2-weighted images showing enlargement of the optic chiasm and displaying an abnormal T2 hyperintensity in 3 different patients. A, A 7-year 10-month-old patient without a history of a previous metabolic crisis. B, An 8-year-old patient not having experienced a metabolic decompensation. C, A 10-month-old patient with a history of encephalopathic crisis at 8 months of age.

FIG 4.

Midline sagittal T1-weighted images showing enlargement of the optic chiasm. A, A 10-month-old patient with GA-1 and a history of encephalopathic crisis, compared with B, a healthy child of a similar age.