The striate sign: peritumoural perfusion pattern of infiltrative primary and recurrent gliomas

Differentiating Glioblastomas from Solitary Brain Metastases: An Update on the Current Literature of Advanced Imaging Modalities

Differentiating between glioblastomas and solitary brain metastases proves to be a challenging diagnosis for neuroradiologists, as both present with imaging patterns consisting of peritumoral hyperintensities with similar intratumoral texture on traditional magnetic resonance imaging sequences. Early diagnosis is paramount, as each pathology has completely different methods of clinical assessment. In the past decade, recent developments in advanced imaging modalities enabled providers to acquire a more accurate diagnosis earlier in the patient's clinical assessment, thus optimizing clinical outcome. Dynamic susceptibility contrast has been optimized for detecting relative cerebral blood flow and relative cerebral blood volume. Diffusion tensor imaging can be used to detect changes in mean diffusivity. Neurite orientation dispersion and density imaging is an innovative modality detecting changes in intracellular volume fraction, isotropic volume fraction, and extracellular volume fraction. Magnetic resonance spectroscopy is able to assist by providing a metabolic descriptor while detecting variable ratios of choline/N-acetylaspartate, choline/creatine, and N-acetylaspartate/creatine. Finally, radiomics and machine learning algorithms have been devised to assist in improving diagnostic accuracy while often utilizing more than one advanced imaging protocol per patient. In this review, we provide an update on all the current evidence regarding the identification and differentiation of glioblastomas from solitary brain metastases.

Contrast enhancing spots as a new pattern of late onset pseudoprogression in glioma patients

INTRODUCTION

Magnet resonance imaging (MRI) of gliomas is assessed by Response Assessment in Neuro-Oncology Criteria (RANO), which define new contrast-enhancing lesions as a sign for tumor recurrence. Pseudoprogression after radiotherapy may mimic tumor progression in MRI but is usually limited to the first months after irradiation. We noted a late onset pattern of new contrast-enhancing spots (NCES) appearing years after radiotherapy.

METHODS

We prospectively collected 23 glioma patients with 26 NCES (three patients had two separate NCES events) between 2014 and 2016 in our weekly tumor board without further selection by diagnosis, molecular markers or pretreatment.

RESULTS

Retrospective analysis revealed a homogeneous collective of young patients (median age of 49 years at NCES) with mainly IDH-mutated glioma (61%). Initial histology showed 26% glioblastoma, 52% grade III and 22% grade II glioma. NCES occurred at late follow-up with a median of 52 months after tumor diagnosis and 30 months after the last radiotherapy. The majority of NCES regressed spontaneously within a median of 10 months (n = 11) or remained stable without further therapy with a median follow-up of 26 months (n = 7). Only 4 NCES developed MRI morphologically into tumor recurrence. Two NCES were resected without any histopathological proof of tumor recurrence, and in 2 other cases NCES were defined as ischemic stroke or radionecrosis.

CONCLUSION

We hypothesize that the late onset phenomenon of NCES predominantly represents a form of radiation-induced vasculopathy that is different from early pseudoprogression and should be considered especially in younger patients with IDH-mutated glioma before initiation of new therapy.

Quantitative T1-mapping detects cloudy-enhancing tumor compartments predicting outcome of patients with glioblastoma

Contrast enhancement of glioblastomas (GBM) is caused by the decrease in relaxation time, T1. Here, we demonstrate that the quantitative measurement of T1 (qT1) discovers a subtle enhancement in GBM patients that is invisible in standard MRI. We assessed the volume change of this “cloudy” enhancement during radio‐chemotherapy and its impact on patients’ progression‐free survival (PFS). We enrolled 18 GBM patients in this observational, prospective cohort study and measured 3T‐MRI pre‐ and post contrast agent with standard T1‐weighted (T1w) and with sequences to quantify T1 before radiation, and at 6‐week intervals during radio‐chemotherapy. We measured contrast enhancement by subtracting pre from post contrast contrast images, yielding relative signal increase ∆T1w and relative T1 shortening ∆qT1. On ∆qT1, we identified a solid and a cloudy‐enhancing compartment and evaluated the impact of their therapy‐related volume change upon PFS. In ∆qT1 maps cloudy‐enhancing compartments were found in all but two patients at baseline and in all patients during therapy. The qT1 decrease in the cloudy‐enhancing compartment post contrast was 21.64% versus 1.96% in the contralateral control tissue (P < 0.001). It was located at the margin of solid enhancement which was also seen on T1w. In contrast, the cloudy‐enhancing compartment was visually undetectable on ∆T1w. A volume decrease of more than 21.4% of the cloudy‐enhancing compartment at first follow‐up predicted longer PFS (P = 0.038). Cloudy‐enhancing compartment outside the solid contrast‐enhancing area of GBM is a new observation which is only visually detectable with qT1‐mapping and may represent tumor infiltration. Its early volume decrease predicts a longer PFS in GBM patients during standard radio‐chemotherapy.

Facing contrast-enhancing gliomas: perfusion MRI in grade III and grade IV gliomas according to tumor area

Tumoral neoangiogenesis characterizes high grade gliomas. Relative Cerebral Blood Volume (rCBV), calculated with Dynamic Susceptibility Contrast (DSC) Perfusion-Weighted Imaging (PWI), allows for the estimation of vascular density over the tumor bed. The aim of the study was to characterize putative tumoral neoangiogenesis via the study of maximal rCBV with a Region of Interest (ROI) approach in three tumor areas—the contrast-enhancing area, the nonenhancing tumor, and the high perfusion area on CBV map—in patients affected by contrast-enhancing glioma (grades III and IV). Twenty-one patients were included: 15 were affected by grade IV and 6 by grade III glioma. Maximal rCBV values for each patient were averaged according to glioma grade. Although rCBV from contrast-enhancement and from nonenhancing tumor areas was higher in grade IV glioma than in grade III (5.58 and 2.68; 3.01 and 2.2, resp.), the differences were not significant. Instead, rCBV recorded in the high perfusion area on CBV map, independently of tumor compartment, was significantly higher in grade IV glioma than in grade III (7.51 versus 3.78, P = 0.036). In conclusion, neoangiogenesis encompasses different tumor compartments and CBV maps appear capable of best characterizing the degree of neovascularization. Facing contrast-enhancing brain tumors, areas of high perfusion on CBV maps should be considered as the reference areas to be targeted for glioma grading.

Elevated peritumoural rCBV values as a mean to differentiate metastases from high-grade gliomas

PURPOSE

Increased relative cerebral blood volume (rCBV) was previously found in peritumoural oedema of glioblastomas (GBM). Supposing that peritumoural rCBV is not increased in metastases, we aimed to evaluate whether rCBV values of the whole peritumoural area are accurate to differentiate solitary metastasis from GBM irrespective of the peritumoural oedema.

METHODS

Contrast-enhanced T1-weighted (T1-w) and T2*-weighted dynamic susceptibility contrast MRI was performed in 52 patients with contrast-enhancing solitary brain tumours before surgery. In each T1-w slice depicting the contrast-enhancing tumour, a rim within approximately 15 mm was defined in the peritumoural area. The rCBV values were normalised to rCBV values of the contralateral normal white matter. Differences between metastases and GBM for normalised rCBV values for each slice were determined with the Mann-Whitney U test (p < 0.05).

RESULTS

Histopathological examination revealed 29 GBM and 23 metastases. Peritumoural rCBV was significantly lower in metastases than in GBM (p < 0.01). Using the cutoff value 1.0 for discriminating metastases from GBM yielded a sensitivity of 96%, specificity of 64%, a positive predictive value of 68% and a negative predictive value of 95%.

CONCLUSIONS

The rCBV in the peritumoural area of contrast-enhancing brain tumours has a high diagnostic accuracy to discriminate metastases from GBM irrespective of surrounding oedema and without the bias of slice selection and ROI positioning. Metastases should be excluded, if at least one tumour-depicting slice reveals an increase of peritumoural rCBV compared to the normal contralateral brain (normalised rCBV value >1). Conversely, the decrease of peritumoural rCBV may not reliably exclude GBM.