Peritrigonal T2 White Matter Hyperintensity

Myelination is a dynamic process that occurs during fetal life and goes on after birth in a well-defined, predetermined manner. On T1-weighted images, the pattern of myelination reaches the adult aspect at 1 year of age; on T2-weighted images, at about 2 years of age.  On MR images, the last associative area to mature is considered to be the peritrigonal zone—a triangular region posterior and superior to the trigones of the lateral ventricles characterized by a persistent high signal intensity on T2-weighted images . Our MRI image of 5 year old child shows peritrigonal linear areas of hyperintensity that can be referred to perivascular spaces. According to Paper entitled "Terminal Zones of Myelination: MR Evaluation of Children Aged 20–40 Months" -- American Journal of Neuroradiology 23:1669-1673, November-December 2002, the so-called terminal zones are most likely subcortical areas rather than the peritrigonal area.

ADRENOLEUKODYSTROPHY-MRI

X-linked recessive disorder which occurs due to deficiency of peroxisomal enzyme Acyl Coa Synthetase. It is a white matter demyelination involving occipital lobes and splenium in bilateral and symmetric pattern (demyelination moves from centre to periphery). Males between 3-10 yrs of age are affected. Auditory pathways are involved commonly with sparing of subcortical white matter. On NECT, large symmetric low density lesion are seen in peritrigonal parieti-occipital white matter. Enhancement is noted in advancing rim surrounded with peripheral nonenhancing edematous zone. Calcifications may be seen. On MRI, central necrotic zone appears low on T1, high on T2. Intermediate zone enhances following contrast administration. Peripheral zone appears hypointense on T1 and high on T2. In one study, published in AJNR Vol 18, Issue 1, medullary and pontine corticospinal tract involvement was present in eight out of ten patients with ALD. So, pontomedullary corticospinal tract involvement is a common finding in ALD and is unusual in other leukodystrophy. On diffusion weighted images, advancing rim of demyelination shows restricted diffusion and appears as bright signal which is very well documented in our case.

Radiology Grand Rounds XXIII

Here is a case of Cannavan's Disease for the Radiology Grand Rounds submitted by Dr Sumer Sethi of Teleradiology Providers. Concept and Archive of the Radiology Grand Rounds is available at- Radiology Grand Rounds.

Canavan’s disease
Deficiency of N- acetylaspartate cyclase enzyme – Increase in NAA.

"Canavan disease demonstrates bilateral symmetric T2 white matter hyperintensity, including involvement of the subcortical arcuate fibers. This disease appears diffusely throughout the cerebral white matter, does not enhance at computed tomography (CT) or MR imaging, and demonstrates variable involvement of the basal ganglia and cerebellar white matter. For example, both Canavan disease and Alexander disease demonstrate macrocephaly with bilaterally symmetric increased T2 signal intensity of cerebral white matter and involvement of subcortical arcuate fibers. MR spectroscopy, however, has been shown to be a useful diagnostic tool in making this distinction. There is an accumulation of NAA in patients with Canavan disease because of a deficiency in the myelin synthesis pathway; thus, MR spectroscopy reveals a markedly elevated NAA peak. "

In other white matter diseases there is Axonolysis hence NAA decreases, Defective myelination leads to increased Choline and lactate is seen in the activer disease.

Further reading (Radiology 2006;241:310-324.)

Hope you enjoyed this edition of Radiology Grand Rounds submissions are requested for the next Radiology Grand Rounds posted every month last sunday. If you interested in hosting any of the future issues contact me at sumerdoc-AT-yahoo-DOT-com.

Case by-Dr.Sumer K Sethi, MD
Consultant Radiologist ,VIMHANS and CEO-Teleradiology Providers
Editor-in-chief, The Internet Journal of Radiology
Director, DAMS (Delhi Academy of Medical Sciences)