Table 3.

Differential diagnosis table for brain magnetic resonance imaging findings in Homocystinuria.

	CT	MRI
CBS deficiency (white matter disease only)	Brain swelling Symmetrical/diffuse cerebral white matter hypoattenuation, possibly involving cerebellum	Brain swelling Symmetrical/diffuse cerebral white matter T1 and T2 prolongation with diffusion restriction May involve cerebellum and basal ganglia May see papilledema and optic nerve sheath dilation No contrast enhancement
CBS deficiency (acute neurovascular disease)	Potentially bilateral and symmetrical white matter hypoattenuation and brain swelling in setting of dural venous sinus thrombosis Territorial infarcts in arterial thrombosis Arterial/venous filling defect on CT angiography/venography May see intraparenchymal hematomas with dural venous sinus thrombosis	Potentially symmetrical white matter T1 and T2 prolongation, potentially with diffusion restriction and/or intraparenchymal hematoma, in the setting of dural venous sinus thrombosis Territorial diffusion restriction in arterial thrombosis Arterial/venous filling defect on MR angiography/venography No contrast enhancement (acutely)
Hypoxic-ischemic injury	Brain swelling Loss or reversal of grey-white attenuation differences Decreased basal ganglia attenuation Sometimes increased attenuation of the cerebellum relative to cerebrum	Brain swelling Possible basal ganglia T1 shortening and T2 prolongation Diffusion restriction in basal ganglia, cerebral cortex, vascular watershed territories Elevated lactate peak on MRS No contrast enhancement (acutely)
Metachromatic leukodystrophy [23]	Symmetrical central cerebral white matter hypoattenuation Progressive brain volume loss	Symmetrical central cerebral white matter T1 and T2 prolongation, as well as diffusion restriction, initially sparing the subcortical white matter, sometimes with concentric stripes of normal and abnormal signal Progressive brain volume loss Decreased choline peak on MRS No contrast enhancement
Canavan disease [23]	Diffuse symmetrical cerebral and cerebellar white matter hypoattenuation, involving subcortical white matter and globi pallidi	Diffuse symmetrical cerebral and cerebellar white matter T1 and T2 prolongation, as well as diffusion restriction, involving subcortical white matter and globi pallidi [24] Elevated NAA peak on MRS No contrast enhancement
Urea cycle defects [23]	Brain swelling Diffuse cerebral edema	Brain swelling Localized T1 and T2 prolongation in the insular cortex, perirolandic cortex, and basal ganglia, with greater involvement of the frontal lobe cortex in older patients
Maple syrup urine disease [23]	Possible brain swelling Hypoattenuation of the deep cerebellar white matter, dorsal brainstem, cerebral peduncles, posterior limb of the internal capsule and perirolandic white matter Possible generalized white matter hypoattenuation	Possible brain swelling T1 and T2 prolongation, as well as diffusion restriction, of the deep cerebellar white matter, dorsal brainstem, cerebral peduncles, posterior limb of the internal capsule and perirolandic white matter Presence of a branched chain ketoacid peak on MRS