Rising Signal Intensity Observed in Extra-Axial Brain Tumours - A Potential Pitfall in Perfusion MR Imaging

CCT Lim, TPL Roberts, YY Sitoh, F Hui
Correspondence: C C T Lim, tchoyoson_lim@ttsh.com.sg

ABSTRACT
Objective Dynamic perfusion magnetic resonance (MR) techniques may be used to track the susceptibility effects of gadolinium contrast material as it passes through the brain. We describe three intracranial tumours that showed progressively rising signal intensity above the baseline during first-pass contrast-enhanced echo-planar imaging (EPI) MR imaging.
Methods Multiphase acquisition using single-shot EPI was performed during rapid bolus contrast injection. Ten studies, using either spin-echo or gradient-echo EPI sequences, were carried out in eight patients with intracranial tumours. Time-signal intensity graphs and regional cerebral blood volume (rCBV) were reviewed.
Results In seven studies, the signal intensity within the tumour showed initial signal drop and quick recovery to baseline and increased rCBV. Three studies revealed progressively rising signal intensity. These patients were all imaged using a spin-echo EPI method and subsequent histology revealed meningioma, hemangiopericytoma and pinealblastoma.
Conclusion Dynamic perfusion MR methods may be used to study intracranial tumours. However, in short relaxation time spin-echo EPI, the T1- effect of gadolinium becomes noticeable during the first-pass acquisition in extra-axial tumours that lack a well-developed blood-brain barrier. Careful selection of patients and pulse sequence is essential to avoid this potential pitfall.

Keywords: magnetic resonance imaging, echo-planar imaging, brain neoplasms, perfusion, hemangiopericytoma
Singapore Med J 2003; 44(10): 526-530