Page 74 - Read Online

Page 6 of 11 Elefante et al. Mini-invasive Surg 2021;5:7 I http://dx.doi.org/10.20517/2574-1225.2020.102

challenging. Tissue characterization, identification of important features for surgical planning, and
prognostic biomarkers individuation can be enhanced by the use of advanced imaging techniques.

Spectroscopy
Spectroscopy is an MRI technique used to assess metabolite concentration in a region of interest. Therefore,
it can be used for differential diagnosis both to differentiate between intra- and extra-axial masses and to
exclude the hypothesis of dural metastases in the case of extra-axial dural-based mass in oncologic patients.
Meningiomas show elevated choline and decreased N-acetylaspartate as well as decreased creatinine,
a metabolic profile common to other neoplastic processes and therefore quite unspecific; conversely,
increased alanine has demonstrated to be specific for meningioma but can be difficult to identify [32,33] .
An elevated metabolite peak at 3.8 parts per million has been described in meningiomas, allowing to
differentiate them from high-grade gliomas and intracranial metastasis. MR spectroscopy has been
demonstrated to not be able to differentiate atypical meningiomas from typical ones [34,35] . Lactate peak is
considered suggestive of aggressiveness, but it can also be found in benign meningiomas. Nevertheless,
lactate and macromolecular peaks have demonstrated significant differences in meningothelial, fibrous, and
[36]
oncocytic subtypes, showing the potential to characterize various lesion components .
Perfusion imaging
MR perfusion is a technique used to assess blood flow in tissues and includes the dynamic susceptibility
contrast (DSC) technique and the dynamic contrast enhancement (DCE) technique, both requiring the
administration of intravenous gadolinium, and arterial spin labeling. Meningiomas are highly vascular
lesions, deriving their blood supply from meningeal arteries and consequently demonstrating very high
perfusion. The complete lack of the blood-brain barrier determines increased contrast leakage and
permeability, represented by a typical time-intensity curve: rapid drop during the first pass of contrast
[37]
and slow return to a level lower than brain parenchyma . MR perfusion can be useful in differential
diagnosis, in particular to differentiate meningiomas from dural-based metastases and from high-grade
gliomas invading the dura mater. Indeed, MR perfusion may differentiate between meningioma and dural
metastases from various origins (breast, colon, and prostate) but not from hypervascular metastases, such
[38]
as those from melanoma, renal carcinoma, or Merkel cell carcinoma (increased cerebral blood volume) .
The assessment of the time-intensity curve can distinguish a primary glial neoplastic process from
intracranial metastases/meningiomas: in the former, the curve shows more than 50% return to baseline,
while, in the latter, the curve shows less than 50% return to baseline due to breakdown in blood-brain
barrier and dural-based blood supply. Meningioma vascularity appears to be significantly related to cerebral
blood flow (CBF) values [39-41] and lately a significant correlation between CBV and expression of vascular
endothelial growth factor has also been demonstrated, suggesting the possibility to use perfusion MR to
predict refractoriness to conventional treatment and possible responsiveness to anti-angiogenic therapies.
Correlation between relative CBV (rCBV) and Ki67 proliferative index has also been demonstrated in
meningiomas but several studies have shown contrasting results about a possible correlation between
tumoral perfusion parameters and meningioma grade, probably because of increased vascular permeability
of meningiomas, due to lack of blood-brain barrier [22,42,43] . On the contrary, peritumoral rCBV has shown
a potential diagnostic role: although peritumoral rCBV usually shows decreased values in meningiomas,
[44]
possibly due to peritumoral vasogenic edema , its values are higher in the case of anaplastic meningiomas
[45]
(WHO Grade III) compared with the other types . Similarly, decreased peritumoral CBF can be measured
[46]
with CT perfusion, potentially representing ischemic tissue salvageable after meningioma resection .
Arterial spine labeling has the advantage of assessing perfusion without the confounding permeability
influence, potentially allowing to differentiate WHO Grade I from WHO Grades II and III intracranial
[47]
meningiomas . Vascular permeability represents another measurable parameter, assessed directly via
DCE technique and contributing to meningioma grading: atypical meningiomas have shown higher values
[48]
of Ktrans compared with benign meningiomas . MR perfusion can be helpful also in distinguishing some