History:
A 50 year old woman with progressive dizziness was referred to Main
Street Radiology for a routine pre- and post-contrast brain.
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Findings:
A non-enhancing well circumscribed left cerebellar hemispheric lesion
was identified (Figures 1-3). The differential diagnosis included
neoplasm as well non-neoplastic entities such as demyelinating plaque,
unusual infarct, or cyst. As the findings were atypical, the patient
was recalled for further evaluation with advanced MR techniques,
specifically MR perfusion and MR spectroscopy.
MR perfusion (Figure 4) demonstrated
elevated perfusion of the lesion as controlled against normal
contralateral brain tissue, suggesting increased local
microvascularity such as seen in brain tumors.
MR spectroscopy (Figure 5) revealed
elevated choline (Cho) levels within the lesion and depressed N-acetylaspartate
(NAA) suggesting high cellularity and depressed neurotransmitter
production, also consistent with tumoral disease. Demyelinating
plaques have also been reported to have a similarly abnormal
spectroscopic signature, however are not known to have elevated
perfusion.
Discussion:
MR perfusion utilizes a dynamic injection of a standard dose of
gadolinium based contrast. Rapid "echo-planar" images are
then acquired during the first pass of the injection, allowing for
real time observation of tissue perfusion. This is in
contradistinction to standard contrast enhanced images which acquire
data minutes after a bolus injection of gadolinium. MR perfusion
techniques thus measure physiologic characteristics of tissue while
standard contrast MR is dependent on blood-brain barrier breakdown.
MR spectroscopy, similar to NMR
(nuclear magnetic resonance) technology used in chemistry labs,
enables separation of metabolite peaks within a tissue sample. In
brain, the important metabolites measured are choline, creatine, and
N-acetylaspartate. Measurement of these metabolites has been described
to have a wide variety of applications in brain imaging, and may be
helpful in evaluation of neoplasms, as well as epilepsy, demyelinating
disease, and infections, as well as a variety of other disorders.
MR perfusion and spectroscopy are
advanced techniques utilizing specialized MRI capabilities and
software, pioneered at research institutions across the United States
but available at Main Street Radiology. These advanced techniques can
be added to a routine brain MRI with contrast at no additional charge.
References:
Yang S, Wetzel S Cha S. Dynamic
Contrast-Enhanced T2*-Weighted MR Imaging of Gliomatosis Cerebri. AJNR.,
2002; 23: 350 - 355.
Yang S, Law M, Zagzag D, et al. Dynamic
contrast enhanced perfusion MRI measurements of endothelial
permeability: differentiation Between atypical and typical meningiomas.
AJNR 2003; 24:1554 -1559
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