What are the key radiological and clinical features of metachromatic leukodystrophy, including head size, age of onset for different forms, and involvement of white and gray matter?

Metachromatic leukodystrophy typically presents with normal head size. The infantile form manifests between 1-2 years, while the juvenile form appears between 5-7 years. Radiologically, there is diffuse white matter involvement with sparing of the gray matter. It is the most common leukodystrophy, caused by a deficiency of the enzyme arylsulfatase A. Key diagnostic features include MRI showing symmetric periventricular and subcortical white matter changes. Clinically, look for progressive motor and cognitive decline. A common pitfall is confusing it with other leukodystrophies; however, the lack of gray matter involvement is a distinguishing feature.