**Core Concept**
Tigroid white matter signal on MRI refers to a characteristic hyperintense appearance of the white matter on T2-weighted images, due to abnormal myelin formation or degradation. This pattern is most classically associated with disorders of peroxisomal or myelin metabolism, particularly those involving defective oligodendrocyte function.

**Why the Correct Answer is Right**
Pelizaeus-Merzbacher disease (PMD) is a rare X-linked recessive disorder caused by mutations in the *PLP1* gene, leading to defective proteolipid protein (PLP) expression. This impairs oligodendrocyte maturation and myelin sheath formation. In PMD, the brain shows a "tigroid" pattern on T2 MRI — hyperintense white matter signals resembling a tiger’s stripe — due to disrupted myelin development, especially in the periventricular and subcortical white matter. This is a hallmark imaging feature.

**Why Each Wrong Option is Incorrect**
Option A: Pantothenate kinase deficiency primarily affects the brainstem and basal ganglia, with a "cerebellar atrophy" pattern and no tigroid white matter signal.
Option C: Neuroferritinopathy shows basal ganglia iron accumulation and T2 hypointensity, not tigroid white matter.
Option D: Aceruloplasminemia presents with iron overload, causing T2 hypointensity in basal ganglia and not tigroid white matter hyperintensity.

**Clinical Pearl / High-Yield Fact**
Tigroid white matter on MRI is pathognomonic for Pelizaeus-Merzbacher disease and should prompt genetic testing for *PLP1* mutations. Early diagnosis is critical due to progressive neurological decline.

✓ Correct Answer: B. Pelizaeus-merzbacher disease