check these papers 

Neurology. 2003 Aug 12;61(3):369-74.

Analysis of MRI patterns aids prediction of progression in X-linked adrenoleukodystrophy.

Loes DJ1, Fatemi A, Melhem ER, Gupte N, Bezman L, Moser HW, Raymond GV.

review

http://www.ojrd.com/content/pdf/1750-1172-7-51.pdf

According to the best my knowledge  the most frequently abnormalities of white matter  in childhood X-ALD are firstly observed in posterior part of brain - splenium of corpus callosum, and then parieto-occipital white matter.

Frontal white matter is rarely affected.

Also in my opinion  parieto-occipital and splenium of corpus callosum are the most frequent sites of abnormalities

The most usual type of ALD starts in the splenium and central parietooccipital white matter. There is a form, found even in children, in which the anterior part of the corpus callosum and white matter around the frontal horns are first affected. The type in which the brain stem tracts and capsulae internae are first involved is mainly seen in adult persons. The most infrequent pattern is involvement of the cerebellar white matter, cerebellar peduncles and brain stem tracts. Cerebellar start of ADL has been described at least in one child.

There is form of adult onset X-linked adrenoleukodystrophy (X-ALD) known as Adreno-myeloneuropathy (AMN) seen within the third or fourth decade, however age ranges from 14 to 60 years. In these patients the frontopontine or corticospinal projection fibers in the brainstem are involved without involvement of the periventricular or deep white matter. Lesions are initially seen in the internal capsule and brain stem tracts and later develop in cerebellar peduncles, splenium of the corpus callosum, and optic radiation. This pattern is seen in 10–15 % of all cerebral XALD patients and mainly in adult XALD patients with clinical signs of AMN, but has also been reported in children with mainly pyramidal signs. Since your patient is a child the possibility is less but cannot be excluded in appropriate clinical history/biochemical abnormalities.

Reference - Magnetic Resonance of Myelination and Myelin Disorders, M.S. van der Knaap, J. Valk

Thank you all for the inputs. The child suspected to have ALD with atypical white matter lesions has VLCFA levels consistent with ALD and a novel mutation of the ABCD1 gene. 

can white matter abnormalities be observed exclusively in the brainstem corticospinal tracts and internal capsule on MRI in absence of occipital or frontal white matter involvement?

Initially, involves predominantly the parietal-occipital lobes and posterior visual pathways, but it extends forward into the frontal and temporal lobes as the disease progresses.

Unlike the focal plaque-like character of multiple sclerosis, adrenoleukodystrophy tends to be contiguous within fiber tracts and often is confluent within the larger white matter bundles of the centrum semiovale.

According to image finding,  Both periventricular and subcortical white matter are affected, and in advanced disease the internal capsule, corpus callosum, corticospinal tracts and other white matter fiber tracts in the brain stem can be involved.

I hope it is helpful  Thanks