Solving the hypomyelination conundrum - Imaging perspectives.

Hypomyelinating Leukodystrophies (HLDs) are a genetically heterogeneous, clinically overlapping group of disorders with the unifying MR imaging appearance of myelin deficit in the brain. In fact, it is the MRI phenotype that typically raises the diagnostic suspicion in this single largest group of undiagnosed leukodystrophies and guides gene testing for confirmation. This article reviews the neurobiology of myelination, focussing on the complex interplay of molecular genetic pathways and presents a practical clinico-radiological diagnostic algorithm based on the neuroimaging patterns of the common hypomyelinating disorders. The authors also address the current controversies about the definition and use of the term 'hypomyelination'.