PET-study of intracranial meningiomas: correlation with histopathology, cellularity and proliferation rate

Prediction of Meningioma WHO Grade Using PET Findings: A Systematic Review and Meta-Analysis

BACKGROUND AND PURPOSE

World Health Organization (WHO) grading of meningiomas reflects recurrence rate and prognosis. Positron emission tomography (PET) investigates metabolic activity, allowing for distinction between low- and high-grade tumors. As preoperative suspicion for malignant meningioma will influence surgical strategy in terms of timing, extent of resection, and risks taken to achieve a total resection, we systematically reviewed the literature on PET-imaging in meningiomas and relate these findings to histopathological analysis.

METHODS

Searches in PubMed, EMBASE, and The Cochrane Library, from inception to September 2019, included studies of patients who had undergone surgery for a histologically verified intracranial meningioma, with a PET-scan prior to surgery and description of (semi)quantitative PET values for meningiomas from two different WHO groups. Studies comparing more than 1 patient per WHO group were included in the meta-analysis.

RESULTS

Twenty-two studies (432 patients) were included. 18fluor-fluorodesoxyglucose (18F-FDG) PET was mostly described to differentiate benign from malignant meningiomas. Pooled data showed differences in mean (95% CI) Standardized Uptake Value (SUV) for WHO II/III compared to WHO I of 2.51 (1.36, 3.66), and in tumor-to-normal (T/N) ratio (T/N ratio) for WHO II/III versus WHO I of .42 (.12, .73).

CONCLUSIONS

We found that SUV and T/N ratio in 18F-FDG PET may be useful to noninvasively differentiate benign from malignant meningiomas. T/N ratio seems to have a high specificity for the detection of high-grade meningiomas. Other PET tracers were studied too infrequently to draw definitive conclusions. Before treatment strategies can be adapted based on 18F-FDG PET, prospective studies in larger cohorts are warranted to validate the optimal T/N ratio cutoff point.

Application of whole-body FDG-PET for cancer screening in a cohort of hospital employees

Whole-body positron emission tomography/computed tomography with the glucose analog 2-[F]fluoro-2-deoxy-D-glucose (FDG-PET/CT) has been extensively used to screen for underlying malignancies in asymptomatic individuals. We were able to survey a cohort of hospital employees using FDG-PET/CT and to report the results herein.A total of 116 hospital employees older than 55 years old were offered whole-body FDG-PET in our hospital. Ninety-seven employees (83.6%) completed the assessment from February 2014 to August 2014 in our PET center. The final confirmation of cancer was based on pathologic examination and follow-up after more than 1 year.Among the 97 participants, 92 were asymptomatic and 5 presented with previously diagnosed cancers. Six of the 92 asymptomatic participants (6.6%) with significant nodular lesions were referred for histological or cytological evaluation of the possibility of malignancy, and 1 case was considered clinically important and required surgical resection. The cancer discovery rate was 3.3% (3/92) with positive predictive value of 50% (3/6). In the 5 participants with previously identified cancers, no recurrence or metastasis was detected.The offer of whole-body FDG-PET for cancer screening was welcomed with enthusiasm by most of the hospital employees. PET/CT combines the merits of PET and CT and can be administered to and provide benefits to a select group of hospital employees.

Long-term evaluation of the effect of hypofractionated high-energy proton treatment of benign meningiomas by means of (11)C-L-methionine positron emission tomography

PURPOSE

To determine if (11)C-L-methionine PET is a useful tool in the evaluation of the long-term effect of proton beam treatment in patients with meningioma remnant.

METHODS

Included in the study were 19 patients (4 men, 15 women) with intracranial meningioma remnants who received hypofractionated high-energy proton beam treatment. Patients were examined with (11)C-L-methionine PET and MRI prior to treatment and after 6 months, and 1, 2, 3, 5, 7 and 10 years. Temporal changes in methionine uptake ratio, meningioma volume, meningioma regrowth and clinical symptoms throughout the follow-up period were evaluated.

RESULTS

In 17 patients the tumour volume was unchanged throughout the follow-up. The methionine uptake ratio on PET decreased over the years in most patients. In two patients the tumour remnant showed progression on MRI. In these patients, prior to the volume increase on MRI, the methionine uptake ratio increased. One patient experienced transient clinical symptoms and showed radiological evidence of a radiation-induced reaction close to the irradiated field.

CONCLUSION

Proton beam treatment is a safe and effective treatment for achieving long-term growth arrest in meningioma remnants. Follow-up with (11)C-L-methionine PET may be a valuable adjunct to, but not a replacement for, standard radiological follow-up.

18-F fluorodeoxyglucose uptake in positron emission tomography as a pathological grade predictor for renal clear cell carcinomas

OBJECTIVES

To evaluate the usefulness of Fluorine-18 fluorodeoxyglucose positron emission tomography/computed tomography (18-F FDG-PET/CT) in the prediction of Fuhrman pathological grades of renal clear cell carcinoma (cRCC).

METHODS

This retrospective study was approved by our institutional review board, and written informed consent was waived. Thirty-one patients with pathologically proven cRCC underwent 18-F FDG-PET/CT for tumour staging. Maximum standardized uptake value of cRCC (tumour SUVmax) and mean SUV of the liver and spleen (liver and spleen SUVmean) were measured by two independent observers. Tumour SUVmax, tumour-to-liver SUV ratio, and tumour-to-spleen SUV ratio were correlated with the pathological grades.

RESULTS

Logistic analysis demonstrated that only the tumour-to-liver SUV ratio was a significant parameter for differentiating high-grade (Fuhrman grades 3 and 4) tumours from low-grade (Fuhrman grades 1 and 2) tumours (P = 0.007 and 0.010 for observers 1 and 2, respectively). Sensitivity, specificity, and positive and negative predictive values for detecting tumours of Fuhrman grades 3 and 4 were 64, 100, 100, and 77%, respectively, for observer 1, and 79, 88, 85, and 83%, respectively, for observer 2.

CONCLUSIONS

The tumour-to-liver SUV ratio with 18-F FDG-PET/CT appeared to be a valuable imaging biomarker in the prediction of high-grade cRCC.

KEY POINTS

• Tumour SUV max was correlated with the Fuhrman grades. • High-grade tumours have significantly higher SUV max than low-grade tumours. • Tumour-to-liver SUV ratio is useful in the prediction of high-grade cRCC.

Grading meningioma: a comparative study of thallium-SPECT and FDG-PET

The purpose was to compare capability of fluorine-18 fluorodeoxyglucose (FDG)-PET and thallium-201 (Tl)-SPECT for grading meningioma.This retrospective study was conducted as a case-control study under approval by the institutional review board. In the hospital information system, 67 patients (22 men and 45 women) who had both FDG-PET and Tl-SPECT preoperative examinations were found with histopathologic diagnosis of meningioma. The maximum FDG uptake values of the tumors were measured, and they were standardized to the whole body (SUVmax) and normalized as gray matter ratio (SUVRmax). Mean and maximum Tl uptake ratios (TURmean and TURmax, respectively) of the tumors were measured and normalized as ratios to those of the contralateral normal brain. Receiver-operating characteristic curve analyses of the 4 indexes were conducted for differentiation between low- and high-grade meningiomas, and areas under the curves (AUCs) were compared. Correlation coefficients were calculated between these indexes and Ki-67.Fifty-six meningiomas were classified as grade I (low grade), and 11 were grade II or III (high grade). In all 4 indexes, a significant difference was observed between low- and high-grade meningiomas (P < 0.05). AUCs were 0.817 (SUVmax), 0.781 (SUVRmax), 0.810 (TURmean), and 0.831 (TURmax), and no significant difference was observed among the indexes. Their sensitivity and specificity were 72.7% to 90.9% and 71.4% to 87.5%, respectively. Correlation of the 4 indexes to Ki-67 was statistically significant, but coefficients were relatively low (0.273-0.355).Tl-SPECT, which can be used at hospitals without a cyclotron or an FDG distribution network, has high diagnostic capability of meningioma grades comparable to FDG-PET.

Clinical characteristics of meningiomas assessed by ¹¹C-methionine and ¹⁸F-fluorodeoxyglucose positron-emission tomography

The clinical course of meningioma varies from case to case, despite similar characteristics on magnetic resonance (MR) imaging. Functional imaging including (11)C-methionine and (18)F-fluorodeoxyglucose (FDG) positron-emission tomography (PET) has been widely studied for noninvasive preoperative evaluation of brain tumors. However, few reports have examined correlations between meningiomas and findings on (11)C-methionine and FDG PET. The objective of this study was to clarify the relationship between tumor characteristics and (11)C-methionine and FDG uptake in meningiomas. For 68 meningiomas in 51 cases, (11)C-methionine uptake was evaluated by measuring both mean and maximum tumor/normal (T/N) ratio for the whole area of the tumors. FDG uptake in 44 of those meningiomas was also analyzed. Tumor size was measured volumetrically, and tumor-doubling time was estimated. Histopathological evaluation was performed in 19 surgical cases. Mean and maximum T/N ratios of (11)C-methionine PET were significantly higher in skull-base lesions than in non-skull-base lesions. Correlations of mean and maximum T/N ratio of (11)C-methionine PET with tumor-doubling time, MIB-1 labeling index, microvessel density and World Health Organization grading were not significant. Mean T/N ratio of (11)C-methionine PET correlated significantly with tumor volume according to logarithm regression modeling (P < 0.0001, R = 0.544). However, mean and maximum T/N ratio of FDG-PET correlated with none of the tumor characteristics described above. These results suggest that (11)C-methionine uptake correlates with tumor volume, but not with tumor aggressiveness.

Modern meningioma imaging techniques

Steady improvements in imaging modalities have enabled a new realm of capabilities in the identification and assessment of meningiomas. The cross-sectional imaging modalities, MRI and CT, have improved in resolution and fidelity. These modalites now provide not only improved structural information but also insights into functional behavior. MRI has, in particular, proven to have powerful capabilities in evaluating meningiomas because of the ability to assess soft tissue characteristics such as diffusion and vascular supply information, such as perfusion. Recent investigational advances have also been made using a combination of X-ray fluoroscopy for selective catheterization followed by MR perfusion measurement performed with intra-arterial injection of contrast. Together all these modalities provide the radiographer with powerful capabilities for evaluating meningiomas.

Intracranial meningiomas of atypical (WHO grade II) histology

Atypical (WHO grade II) meningiomas occupy an intermediate risk group between benign (WHO grade I) and anaplastic (WHO grade III) meningiomas. Although grade II meningiomas have traditionally been recognized in only about 5% of cases, after changes in diagnostic criteria with the current 2007 WHO standards, they now comprise approximately 20-35% of all meningiomas. Given the magnitude of this change, much work is now needed to solidify the adoption of these standards, to render inter-observer and inter-institutional comparisons more uniform, and to more carefully define the incidence of grade II histology. However, it is clear that they carry a several-fold increased risk of recurrence, as well as an increased rate of mortality. We will discuss the definition, diagnosis, and treatment of patients with atypical meningioma; review the current phase II cooperative trials; and draw attention to some questions timely for pre-clinical and clinical research.

18F-FDG PET in the assessment of tumor grade and prediction of tumor recurrence in intracranial meningioma

PURPOSE

The purpose of this study was to investigate the role of (18)F-fluorodeoxyglucose (FDG) PET in detecting high-grade meningioma and predicting the recurrence in patients with meningioma after surgical resection.

METHODS

Fifty-nine patients (27 men and 32 women) with intracranial meningioma who underwent preoperative FDG PET and subsequent surgical resection were enrolled. All patients underwent clinical follow-up for tumor recurrence with a mean duration of 34+/-20 months. The tumor to gray matter ratio (TGR) of FDG uptake was calculated and a receiver-operating characteristic (ROC) curve of the TGR was drawn to determine the cutoff value of the TGR for detection of high-grade meningioma. Further, univariate analysis with the log-rank test was performed to assess the predictive factors of meningioma recurrence.

RESULTS

The TGR in high-grade meningioma (WHO grade II and III) was significantly higher than that in low-grade ones (WHO grade I) (p=0.002) and significantly correlated with the MIB-1 labeling index (r=0.338, p=0.009) and mitotic count of the tumor (r=0.284, p=0.03). The ROC analysis revealed that the TGR of 1.0 was the best cutoff value for detecting high-grade meningioma with a sensitivity of 43%, specificity of 95%, and accuracy of 81%. Of 59 patients, 5 (9%) had a recurrent event. In the log-rank test, the TGR, MIB-1 labeling index, presence of brain invasion, and WHO grade were significantly associated with tumor recurrence. The cumulative recurrence-free survival rate of patients with a TGR of 1.0 or less was significantly higher than that of patients with a TGR of more than 1.0 (p=0.0003)

CONCLUSION

FDG uptake in meningioma was the significant predictive factor of tumor recurrence and significantly correlated with the proliferative potential of the tumor.

Imaging in neurooncology

Imaging in patients with brain tumors aims toward the determination of the localization, extend, type, and malignancy of the tumor. Imaging is being used for primary diagnosis, planning of treatment including placement of stereotaxic biopsy, resection, radiation, guided application of experimental therapeutics, and delineation of tumor from functionally important neuronal tissue. After treatment, imaging is being used to quantify the treatment response and the extent of residual tumor. At follow-up, imaging helps to determine tumor progression and to differentiate recurrent tumor growth from treatment-induced tissue changes, such as radiation necrosis. A variety of complementary imaging methods are currently being used to obtain all the information necessary to achieve the above mentioned goals. Computed tomography and magnetic resonance imaging (MRI) reveal mostly anatomical information on the tumor, whereas magnetic resonance spectroscopy and positron emission tomography (PET) give important information on the metabolic state and molecular events within the tumor. Functional MRI and functional PET, in combination with electrophysiological methods like transcranial magnetic stimulation, are being used to delineate functionally important neuronal tissue, which has to be preserved from treatment-induced damage, as well as to gather information on tumor-induced brain plasticity. In addition, optical imaging devices have been implemented in the past few years for the development of new therapeutics, especially in experimental glioma models. In summary, imaging in patients with brain tumors plays a central role in the management of the disease and in the development of improved imaging-guided therapies.

Using positron emission tomography with [(18)F]FDG to predict tumor behavior in experimental colorectal cancer

This study investigates the relationship between FDG uptake as determined by positron emission tomography (PET) imaging and rates of tumor growth, cellular GLUT1 transporter density, and the activities of hexokinase and glucose-6-phosphatase in a solid tumor implant model. Five different human colorectal xenografts of different growth properties were implanted in athymic rats and evaluated by dynamic (18)F-FDG-PET. The phosphorylating and dephosphorylating activities of the key glycolytic enzymes, hexokinase and glucose-6-phosphatase, were measured in these tumor types by spectrophotometric assays and the expression of GLUT1 glucose transporter protein was determined by immunohistochemistry. Correlations among FDG accumulation, hexokinase activity, and tumor doubling time are reported in these colon xenografts. The results indicate that the activity of tumor hexokinase may be a marker of tumor growth rate that can be determined by (18)F-FDG-PET imaging. PET scanning may not only be a useful tool for staging patients for extent of disease, but may provide important prognostic information concerning the proliferative rates of malignancies.

Analysis of 76Br-BrdU in DNA of brain tumors after a PET study does not support its use as a proliferation marker

76Br-bromodeoxyuridine has previously been suggested as a PET tracer to characterize proliferation potential. However, in animal studies a large fraction of the tissue radioactivity is due to 76Br-bromide, which remains extracellular for extensive periods and contributes significantly to the level of radioactivity. The present project aimed at investigating whether in human brain tumors, sufficient amounts of 76Br-bromodeoxyuridine would be incorporated into DNA, to motivate further attempts with this tracer. Eight patients with brain tumors: 3 meningiomas, 2 astrocytoma grade IV, 1 astrocytoma oligodendroglioma grade II-IV and 2 metastases, were examined with PET and 76Br-BrdU on three occasions: immediately after injection of the tracer, at 4-6, and at 18-20 hours after administration. After the first PET study, diuresis was introduced and maintained for about 12 hours. About 20 hours after tracer administration, 200 mg/m(2) bromodeoxyuridine was administered to 7 patients median 5.8 (range 1-22) hours prior to operation allowing the immunohistochemical analysis of the proliferation potential. During the operation, tumor samples were taken and radioactivity in DNA extracted and measured. The uptake of radioactivity was higher in the tumors than in brain parenchyma. However, in the operative samples only 1-27% (average: 9%) of the radioactivity was found in the DNA fraction. The plasma radioactivity remained high throughout the study with only minimal signs of elimination by the diuresis. 76Br-BrdU is extensively metabolized to 76Br-bromide, and only a minor fraction of the radioactivity is found in the DNA fraction, making it unlikely that this tracer can be used for assessment of proliferation potential.