Lysosomal storage disorders that result from mutations of genes that encode lysosomal hydrolases, compounds that are involved in the degradation of mucopolysaccharides (glycosaminoglycans). A deficiency of the enzyme results in the accumulation of various glycosaminoglycans within lysosomes.
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The different types include
Patients develop hydrocephalus for many reasons
1. Compression of the upper cervical cord in the craniocervical junction
2. Impaired CSF resorption due to meningeal mucopolysaccharide deposits
3. Bony overgrowth of the skull base narrowing venous outflow pathways leading to increased venous pressure
MRI demonstrates
1. Delayed myelination
2. Atrophy
3. Hydrocephalus which may also manifest enlargement of the subarachnoid spaces and optic nerve sheaths. This may result in optic nerve atrophy.
4. Enlarged perivascular spaces
5. White matter changes of T2 abnormalities. Enlarged perivascular spaces in the corpus callosum and basal ganglia are seen in types IH, II, IIA, VI. Diffuse white matter T2 haziness is seen in types IH, II, and III resulting in decreased grey-white matter differentiation.
MRS may have multiple glycosaminoglycans present resonating between 3.3 to 4.4 ppm.
References: Pediatric neuroimaging, 6th edition, AJ Barkovich