HIER - Congress Company

Advanced MR neuroimaging of brain tumours
Mw. Dr. M. Smits
Afdeling radiology, Erasmus MC, Rotterdam
Prof. dr. A. van der Lugt
Afdeling radiology, Erasmus MC, Rotterdam
Learning objectives
1. To know the added value of Magnetic Resonance
(MR) perfusion, diffusion weighted imaging and MR
spectroscopy in the diagnostic work-up, neurosurgical
intervention and follow-up of primary brain tumours.
2. To know the added value of functional MR imaging
and diffusion tensor imaging in guiding neurosurgical
intervention of primary brain tumours.
3. To know the pitfalls of post-therapeutic imaging,
including pseudoprogression and pseudoresponse.
Introduction
Brain neoplasms are divided into primary brain tumours and
metastatic tumours. The most common primary intra-axial
brain tumours are those derived from the neuroepithelial
tissue, the majority of which are gliomas. Indications for
imaging of brain tumour patients can be divided into three
categories: 1) diagnostic work-up; 2) guiding neurosurgical
intervention; and 3) follow-up.
Diagnostic work-up
For the diagnostic work-up of a brain lesion contrastenhanced
MR imaging is the modality of choice,
complemented with computed tomography (CT) for the
assessment of the presence of calcifications.
Differential diagnosis
Localisation, extent, signal intensity characteristics and
contrast enhancement patterns generally make a first
distinction between tumoural and non-tumoural lesions
possible. One of the most commonly encountered diagnostic
dilemmas in this respect is the differentiation between
necrotic tumour and abscess. Both lesions present as a fluidfilled
ring-enhancing lesion and are often indistinguishable
on conventional MR imaging. Diffusion weighted imaging
(DWI) has shown to be an invaluable imaging technique to
make such a distinction possible, demonstrating diffusion
restriction in abscess and elevated diffusion in necrotic
tumours such as metastases and glioblastoma multiforme.
Exceptions, with diffusion restriction in necrotic tumours,
do occur, for instance in the presence of haemorrhagic
components.
Tumour grading
Brain tumours are both classified and graded to predict
biological behaviour. Therapeutic management algorithms
neuroradiologie
are based on tumour grade, indicating the need for accurate
tumour grading. The grading system as proposed by the
World Health Organisation (WHO) is the most widely
used and consists of grades I to IV, with grade I tumours
being the most benign, showing no tendency to malignant
progression, and grade IV tumours being the most malignant.
The histological grading of gliomas is based on the tumour’s
cellularity, mitosis, necrosis, pleomorphism and vascular
proliferation. Radiological tumour grading is commonly
based on the demonstration of enhancement after contrast
administration. Typically, high grade glioma show contrast
enhancement, which is due to the destruction of the bloodbrain
barrier by malignant tumour cells as well as to the
leakage of contrast media from the immature angiogenic
tumour vessels. Conversely, no contrast enhancement is
observed in non-vascular, low grade gliomas.
Despite such typical findings, most anaplastic astrocytomas
(WHO grade III) do not enhance while up to 50% of
oligodendrogliomas (WHO grade II) do show enhancement.
Perfusion imaging
Higher sensitivity and predictive value for tumour grading
and prognosis may be obtained with T2* weighted first-pass
dynamic susceptibility weighted contrast enhanced (DSC)
perfusion imaging (1). The relative cerebral blood volume
(rCBV) is the most widely used parameter obtained with
DSC for brain tumour grading. The rCBV increase shows a
reliable correlation with tumour grade and increased tumour
vascularity (1). The angiogenic activity of high grade tumours
results in the presence of increased microvascular density
and many slow-flowing collateral vessels, resulting in
increase of rCBV in high grade tumours (1).
Maximum rCBV ratios of low grade glioma are reported to
be between 1.1 and 2.1, while those in high grade glioma
are in the range of 3.5 to 7.3 (1). Using an rCBV ratio cut-off
value of 1.75, high grade glioma can be differentiated from
low grade glioma with 95% sensitivity (2). Specificity
is relatively low at 70%, due to the misclassification of
low grade gliomas with elevated rCBV, most notably
oligodendroglioma.
Relative CBV measurement may also be used to obtain
prognostic information. Law et al. showed that patients with
high grade glioma and an rCBV ratio of less than 1.75 had
a stable disease course, while those with an rCBV ratio of
greater than 1.75 showed rapid deterioration (2).
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