What causes the tigroid pattern on T2-weighted MRI of the brain?
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Answer:
The tigroid or leopard-skin pattern is confluent T2 hyperintensity of the cerebral white matter containing multiple small punctate and linear areas of preserved lower signal, so that the abnormal white matter looks striped or spotted. The spared foci correspond to perivascular myelin that is relatively preserved around the medullary veins and arterioles within the demyelinated white matter. The classic cause is metachromatic leukodystrophy, in which the pattern appears within symmetric, confluent, periventricular and centrum semiovale demyelination that begins frontally and around the atria, spares the subcortical U-fibres until late, and progresses caudally with corpus callosum and corticospinal tract involvement. The same appearance is described in Krabbe disease, Pelizaeus-Merzbacher disease and other lysosomal and peroxisomal leukodystrophies, so it narrows rather than settles the diagnosis. Recognising the pattern early matters because enzyme replacement, haematopoietic stem cell transplantation and gene therapy are effective only before substantial neurological decline, and recent work stresses that early MRI signs, or their absence, are critical to diagnosis. Confirmation is by arylsulfatase A activity in leucocytes, urinary sulfatides and ARSA genotyping, with the caveat that pseudodeficiency alleles produce low enzyme activity without disease.
Why is it called so?
The stripes of spared white matter within diffusely abnormal signal resemble the markings of a tiger or leopard.
Pathophysiology
Metachromatic leukodystrophy is an autosomal recessive deficiency of arylsulfatase A, which prevents degradation of sulfatides. Sulfatide accumulates within oligodendrocytes, Schwann cells and macrophages and is toxic to myelin-maintaining cells, producing progressive demyelination of central and peripheral nervous system white matter. Myelin immediately surrounding the small penetrating vessels is relatively spared, possibly because of better metabolic support or differences in oligodendrocyte turnover in that zone, so islands of normal-signal myelin persist within the demyelinated field and generate the striped appearance. Peripheral nerve involvement produces a demyelinating neuropathy and cauda equina enhancement, which is a useful supporting finding on spinal imaging.
Alternative names: Leopard-skin pattern; stripe pattern
Other associated named signs: Butterfly pattern of confluent periventricular demyelination and the subcortical U-fibre sparing that characterises the leukodystrophies
References
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