Papel de la difusión en la evaluación de los meningiomas: correlación radiopatológica

Clinical applications of diffusion weighted imaging in neuroradiology

Abstract

Diffusion-weighted imaging (DWI) has revolutionised stroke imaging since its introduction in the mid-1980s, and it has also become a pillar of current neuroimaging. Diffusion abnormalities represent alterations in the random movement of water molecules in tissues, revealing their microarchitecture, and occur in many neurological conditions. DWI provides useful information, increasing the sensitivity of MRI as a diagnostic tool, narrowing the differential diagnosis, providing prognostic information, aiding in treatment planning and evaluating response to treatment. Recently, there have been several technical improvements in DWI, leading to reduced acquisition time and artefacts and enabling the development of diffusion tensor imaging (DTI) as a tool for assessing white matter. We aim to review the main clinical uses of DWI, focusing on the physiological mechanisms that lead to diffusion abnormalities. Common pitfalls will also be addressed.

Teaching Points

• DWI includes EPI, TSE, RESOLVE or EPI combined with reduced volume excitation.

• DWI is the most sensitive sequence in stroke diagnosis and provides information about prognosis.

• DWI helps in the detection of intramural haematomas (arterial dissection).

• In diffusion imaging, ADC is inversely proportional to tumour cellularity.

• DWI and DTI derived parameters can be used as biomarkers in different pathologies.

Use of Diffusion Weighted Imaging in Differentiating Between Maligant and Benign Meningiomas. A Multicenter Analysis

BACKGROUND

Meningioma is the most frequent intracranial tumor and is often an incidental finding on imaging. Some imaging-based scores were suggested for differentiating low- and high-grade meningiomas. The purpose of this work was to compare diffusion-weighted imaging findings of different meningiomas in a large multicenter study by using apparent diffusion coefficient (ADC) values for predicting tumor grade and proliferation potential.

METHODS

Data from 7 radiologic departments were acquired retrospectively. Overall, 389 patients were collected. All meningiomas were investigated by magnetic resonance imaging (1.5-T scanner) by using diffusion-weighted imaging (b values of 0 and 1000 s/mm(2)). The comparison of ADC values was performed by Mann-Whitney U test.

RESULTS

World Health Organization grade I was diagnosed in 271 cases (69.7%), grade II in 103 (26.5%), and grade III in 15 patients (3.9%). Grade I meningiomas showed statistically significant higher ADC values (1.05 ± 0.39 × 10(-3) mm(2)s(-1)) in comparison with grade II (0.77 ± 0.15 × 10(-3) mm(2)s(-1); P = 0.001) and grade III tumors (0.79 ± 0.21 × 10(-3) mm(2)s(-1); P = 0.01). An ADC value of <0.85 × 10(-3) mm(2)s(-1) was determined as the threshold in differentiating between grade I and grade II/III meningiomas (sensitivity, 72.9%; specificity, 73.1%; accuracy, 73.0%). Ki67 was associated with ADC (r = -0.63, P < 0.001). The optimal threshold for the ADC was (less than) 0.85 × 10(-3) mm(2)s(-1) for detecting tumors with high proliferation potential (Ki67 ≥5%).

CONCLUSIONS

The estimated threshold ADC value of 0.85 can differentiate grade I meningioma from grade II and III tumors. The same ADC value is helpful for detecting tumors with high proliferation potential.

Correlation between magnetic resonance imaging grading and pathological grading in meningioma

OBJECT

This study investigated the specific preoperative MRI features of patients with intracranial meningiomas that correlate with pathological grade and provide appropriate preoperative planning.

METHODS

From 2006 to 2012, 120 patients (36 men and 84 women, age range 20-89 years) with newly diagnosed symptomatic intracranial meningiomas undergoing resection were retrospectively analyzed in terms of radiological features of preoperative MRI. There were 90 WHO Grade I and 30 WHO Grade II or III meningiomas. The relationships between MRI features and WHO histopathological grade were analyzed and scored quantitatively.

RESULTS

According to the results of multivariate logistic regression analysis, age ≥ 75 years, indistinct tumorbrain interface, positive capsular enhancement, and heterogeneous tumor enhancement were identified factors in the prediction of advanced histopathological grade. The prediction model was quantified as a scoring scale: 2 × (age) + 5 × (tumor-brain interface) + 3 × (capsular enhancement) + 2 × (tumor enhancement). The calculated score correlated positively with the probability of high-grade meningioma.

CONCLUSIONS

This scoring approach may be useful for clinicians in determining therapeutic strategy and in surgical planning for patients with intracranial meningiomas.

The correlation between apparent diffusion coefficient and tumor cellularity in patients: a meta-analysis

Objective

To perform a meta-analysis exploring the correlation between the apparent diffusion coefficient (ADC) and tumor cellularity in patients.

Materials and Methods

We searched medical and scientific literature databases for studies discussing the correlation between the ADC and tumor cellularity in patients. Only studies that were published in English or Chinese prior to November 2012 were considered for inclusion. Summary correlation coefficient (r) values were extracted from each study, and 95% confidence intervals (CIs) were calculated. Sensitivity and subgroup analyses were performed to investigate potential heterogeneity.

Results

Of 189 studies, 28 were included in the meta-analysis, comprising 729 patients. The pooled r for all studies was −0.57 (95% CI: −0.62, −0.52), indicating notable heterogeneity (P<0.001). After the sensitivity analysis, two studies were excluded, and the pooled r was −0.61 (95% CI: −0.66, −0.56) and was not significantly heterogeneous (P = 0.127). Regarding tumor type subgroup analysis, there were sufficient data to support a strong negative correlation between the ADC and cellularity for brain tumors. There was no notable evidence of publication bias.

Conclusions

There is a strong negative correlation between the ADC and tumor cellularity in patients, particularly in the brain. However, larger, prospective studies are warranted to validate these findings in other cancer types.

Intracranial hemangiopericytoma: MR imaging findings and diagnostic usefulness of minimum ADC values

PURPOSE

To describe the clinical and magnetic resonance (MR) imaging features of primary intracranial hemangiopericytoma (HPC), and to assess the usefulness of minimum apparent diffusion coefficient (MinADC) value of HPC in the differential diagnosis from meningioma.

MATERIALS AND METHODS

From 2004 to 2010, fifteen patients with primary intracranial HPC were included. The clinical data, conventional MR findings (n = 15), and diffusion weighted image (DWI) features (n = 10) were retrospectively analyzed. MinADC value of the HPCs (n = 10) was measured on ADC map and was compared with that of meningiomas (n = 37).

RESULTS

In 15 cases of HPC, isointense signal was detected on both T1-weighted images (T1WI) and T2-weighted images (T2WI) in 11 cases, and heterogeneous signal was demonstrated in 4 cases. Isointensity (n = 9) and iso- and slight hyperintensity (n = 1) were shown on DWI. The mean MinADC value of HPC [(1.116 ± 0.127) × 10(-3) mm(2) /s] was significantly higher than that of meningioma [(0.875 ± 0.104) × 10(-3) mm(2) /s] (P < 0.01). For the differentiation between HPC and meningioma, the critical cutoff MinADC value was 0.991 × 10(-3) mm(2) /s, which provided the best combination of sensitivity (88.9%) and specificity (82.4%).

CONCLUSION

MinADC value may be an useful tool for the differentiation between HPC and meningioma.

New pathology classification, imagery techniques and prospective trials for meningiomas: the future looks bright

PURPOSE OF REVIEW

Advances in functional and metabolic imaging have been added to the diagnostic armamentarium for meningioma. New prospective trials have been initiated, and it is foreseen that American Society of Clinical Oncology evidence-level II will be soon available for this brain tumor. This review will focus on recent advances in radiology and their significance for clinical care. The new WHO classification will be detailed.

RECENT FINDINGS

Brain invasion is an important criterion in the 2007 WHO classification for atypical meningioma. Apparent diffusion coefficient values on MRI observed with grade II and grade III meningiomas are significantly decreased when compared to benign tumors. [F]fluorodeoxyglucose PET may also predict tumor grade and tumor recurrence. Radio-labeled amino acid PET may be used to delineate target volume for radiotherapy planning. Stereotactic biopsy guidance and functional therapy monitoring could be foreseen using PET-MRI. One phase II study is assessing the benefit of dose escalation for nonbenign meningioma and another evaluates the therapeutic strategy of observation, standard- and high-dose radiotherapy for low-risk, intermediate-risk and high-risk patients.

SUMMARY

The use of functional MRI, with or without PET imaging, may be useful in assessing the potential clinical outcome of meningioma. Various therapeutic strategies, including observation and high-dose radiotherapy, are evaluated in two ongoing phase II studies.

Metastatic meningioma: The role of whole‑body diffusion-weighted imaging

We report the case of a 74-year-old male patient with a completely resected anaplastic meningioma who developed multiple metastases two years later (subcutaneous tissue near the surgical area, cervical lymph nodes, lung, pleura and bones). The primary tumor and all of the metastases showed a significant restricted diffusion. Whole‑body diffusion-weighted imaging (DWI) was performed for assessment of the metastases. This case demonstrated the usefulness of this technique in screening extracranial metastases in patients with malignant 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.