T2-FLAIR Mismatch Sign and Response to Radiotherapy in Diffuse Intrinsic Pontine Glioma

Pediatric diffuse intrinsic pontine glioma radiotherapy response prediction: MRI morphology and T2 intensity-based quantitative analyses

OBJECTIVES

An easy-to-implement MRI model for predicting partial response (PR) postradiotherapy for diffuse intrinsic pontine glioma (DIPG) is lacking. Utilizing quantitative T2 signal intensity and introducing a visual evaluation method based on T2 signal intensity heterogeneity, and compared MRI radiomic models for predicting radiotherapy response in pediatric patients with DIPG.

METHODS

We retrospectively included patients with brainstem gliomas aged ≤ 18 years admitted between July 2011 and March 2023. Applying Response Assessment in Pediatric Neuro-Oncology criteria, we categorized patients into PR and non-PR groups. For qualitative analysis, tumor heterogeneity vision was classified into four grades based on T2-weighted images. Quantitative analysis included the relative T2 signal intensity ratio (rT2SR), extra pons volume ratio, and tumor ring-enhancement volume. Radiomic features were extracted from T2-weighted and T1-enhanced images of volumes of interest. Univariate analysis was used to identify independent variables related to PR. Multivariate logistic regression was performed using significant variables (p < 0.05) from univariate analysis.

RESULTS

Of 140 patients (training n = 109, and test n = 31), 64 (45.7%) achieved PR. The AUC of the predictive model with extrapontine volume ratio, rT2SRmax-min (rT2SRdif), and grade was 0.89. The AUCs of the T2-weighted and T1WI-enhanced models with radiomic signatures were 0.84 and 0.81, respectively. For the 31 DIPG test sets, the AUCs were 0.91, 0.83, and 0.81, for the models incorporating the quantitative features, radiomic model (T2-weighted images, and T1W1-enhanced images), respectively.

CONCLUSION

Combining T2-weighted quantification with qualitative and extrapontine volume ratios reliably predicted pediatric DIPG radiotherapy response.

CLINICAL RELEVANCE STATEMENT

Combining T2-weighted quantification with qualitative and extrapontine volume ratios can accurately predict diffuse intrinsic pontine glioma (DIPG) radiotherapy response, which may facilitate personalized treatment and prognostic assessment for patients with DIPG.

KEY POINTS

Early identification is crucial for radiotherapy response and risk stratification in diffuse intrinsic pontine glioma. The model using tumor heterogeneity and quantitative T2 signal metrics achieved an AUC of 0.91. Using a combination of parameters can effectively predict radiotherapy response in this population.

T2-FLAIR mismatch sign, an imaging biomarker for CDKN2A-intact in non-enhancing astrocytoma, IDH-mutant

INTRODUCTION

The WHO classification of central nervous system tumors (5th edition) classified astrocytoma, IDH-mutant accompanied with CDKN2A/B homozygous deletion as WHO grade 4. Loss of immunohistochemical (IHC) staining for methylthioadenosine phosphorylase (MTAP) was developed as a surrogate marker for CDKN2A-HD. Identification of imaging biomarkers for CDKN2A status is of immense clinical relevance. In this study, we explored the association between radiological characteristics of non-enhancing astrocytoma, IDH-mutant to the CDKN2A/B status.

METHODS

Thirty-one cases of astrocytoma, IDH-mutant with MTAP results by IHC were included in this study. The status of CDKN2A was diagnosed by IHC staining for MTAP in all cases, which was further confirmed by comprehensive genomic analysis in 12 cases. The T2-FLAIR mismatch sign, cystic component, calcification, and intratumoral microbleeding were evaluated. The relationship between the radiological features and molecular pathological diagnosis was analyzed.

RESULTS

Twenty-six cases were identified as CDKN2A-intact while 5 cases were CDKN2A-HD. The presence of > 33% and > 50% T2-FLAIR mismatch was observed in 23 cases (74.2%) and 14 cases (45.2%), respectively, and was associated with CDKN2A-intact astrocytoma (p = 0.0001, 0.0482). None of the astrocytoma, IDH-mutant with CDKN2A-HD showed T2-FLAIR mismatch sign. Cystic component, calcification, and intratumoral microbleeding were not associated with CDKN2A status.

CONCLUSION

In patients with non-enhancing astrocytoma, IDH-mutant, the T2-FLAIR mismatch sign is a potential imaging biomarker for the CDKN2A-intact subtype. This imaging biomarker may enable preoperative prediction of CDKN2A status among astrocytoma, IDH-mutant.

The T2-FLAIR mismatch sign in oncologic neuroradiology: History, current use, emerging data, and future directions

The T2-Fluid-Attenuated Inversion Recovery (T2-FLAIR) mismatch sign is a radiogenomic marker that is easily discernible on preoperative conventional MR imaging. Application of strict criteria (adult population, cerebral hemisphere location, and classic imaging morphology) permits the noninvasive preoperative diagnosis of isocitrate dehydrogenase (IDH)-mutant 1p/19q-non-codeleted diffuse astrocytoma with near-perfect specificity, albeit with variably low sensitivity. This leads to improved preoperative planning and patient counseling. More recent research has shown that the application of less strict criteria compromises the near-perfect specificity of the sign but remains adequate for ruling out IDH-wildtype (glioblastoma) phenotype, which bears a far grimmer prognosis compared to IDH-mutant diffuse astrocytic disease. In this review, we elaborate on the various definitions of the T2-FLAIR mismatch sign present in the literature, illustrate these with images obtained at a comprehensive cancer center, discuss the potential of the mismatch sign for application to certain pediatric-type brain tumors, namely dysembryoplastic neuroepithelial tumor and diffuse midline glioma, and elaborate upon the clinical, histologic, and molecular associations of the T2-FLAIR mismatch sign as recognized to date. Finally, the sign's correlates in diffusion- and perfusion-weighted imaging are presented, and opportunities to further maximize the diagnostic and prognostic applications of the sign in the context of the 2021 revision of the WHO Classification of Central Nervous System Tumors are discussed.

Diffuse Midline Gliomas: Challenges and New Strategies in a Changing Clinical Landscape

Diffuse intrinsic pontine glioma (DIPG) was first described by Harvey Cushing, the father of modern neurosurgery, a century ago. Since then, the classification of this tumor changed significantly, as it is now part of the broader family of diffuse midline gliomas (DMGs), a heterogeneous group of tumors of midline structures encompassing the entire rostro-caudal space, from the thalamus to the spinal cord. DMGs are characterized by various epigenetic events that lead to chromatin remodeling similarities, as two decades of studies made possible by increased tissue availability showed. This new understanding of tumor (epi)biology is now driving novel clinical trials that rely on targeted agents, with finally real hopes for a change in an otherwise unforgiving prognosis. This biological discovery is being paralleled with equally exciting work in therapeutic drug delivery. Invasive and noninvasive platforms have been central to early phase clinical trials with a promising safety track record and anecdotal benefits in outcome.

T1-T2 Mismatch Sign as a Predictor of Ipsilateral Ischemic Change After Carotid Artery Stenting

BACKGROUND

Magnetic resonance (MR)-plaque imaging reflects the characteristics of carotid plaque. We evaluated the relationship between MR-plaque images and ischemic change after carotid artery stenting (CAS).

METHODS

MR-plaque images were acquired from patients with carotid artery stenosis before CAS treatment. We calculated the relative signal intensity of plaque components compared with that of the sternocleidomastoid muscle and evaluated the presence/absence of T1-T2 mismatch and match sign. We then assessed the appearance of new ischemic lesions after CAS on diffusion-weighted imaging (DWI). Factors associated with the appearance of a high-intensity lesion on DWI were retrospectively analyzed.

RESULTS

A total of 64 patients with carotid artery stenoses treated with CAS were included in this study. In univariate analysis, T1-T2 mismatch sign was associated with the appearance of high-intensity lesions on DWI after CAS (odds ratio [OR], 12.00; 95% confidence interval [CI], 3.593-40.072; P < 0.0001), whereas T1-T2 match sign and high intensity on T2-weighted imaging were negatively associated (OR, 0.061, 95% CI, 0.007-0.502, P = 0.009 and OR, 0.085; 95% CI, 0.022-0.334, P = 0.0004, respectively). In multivariate logistic regression analysis, T1-T2 mismatch sign was independently associated with the appearance of a high-intensity lesion on DWI after CAS (OR, 16.695; 95% CI, 1.324-210.52; P = 0.0295).

CONCLUSIONS

T1-T2 mismatch sign on MR-plaque imaging is significantly associated with the appearance of new ischemic lesions after CAS. T1-T2 mismatch sign may be useful in considering treatment strategies for carotid artery stenosis.

IDH-mutant Astrocytoma Arising in the Brainstem with Symptom Improvement by Foramen Magnum Decompression: A Case Report

Diffusely infiltrative midline gliomas are known to have a poor prognosis. The standard treatment for typical diffuse midline glioma in the pons is local radiotherapy as surgical resection is inappropriate. This case reports a brainstem glioma in which stereotactic biopsy and foramen magnum decompression were concomitantly performed to confirm the diagnosis and improve symptoms. A 23-year-old woman was referred to our department with a chief complaint of headache for six months. Magnetic resonance imaging (MRI) showed diffuse T2 hyperintense swelling of the brainstem with the pons as the main locus. Enlargement of the lateral ventricles was observed because of cerebrospinal fluid obstruction out of the posterior fossa. This was atypical for a diffuse midline glioma in terms of the longstanding slow progression of symptoms and patient age. Stereotactic biopsy was performed for diagnosis, and foramen magnum decompression (FMD) was concomitantly performed to treat the obstructive hydrocephalus. The histological diagnosis was astrocytoma, IDH-mutant. Post-surgery, the patient's symptoms were relieved, and she was discharged on the fifth day after surgery. The hydrocephalus was resolved, and the patient returned to normal life without any symptoms. The tumor size follow-up with MRI demonstrated no marked change for 12 months. Even though diffuse midline glioma is considered to have a poor prognosis, clinicians should contemplate if it is atypical. In atypical cases like the one described herein, surgical treatment may contribute to pathological diagnosis and symptom improvement.