MRI features as a helpful tool to predict the molecular subgroups of medulloblastoma: state of the art

Abstract

Medulloblastoma is the most common malignant pediatric brain tumor. Medulloblastoma should not be viewed as a single disease, but as a heterogeneous mixture of various subgroups with distinct characteristics. Based on genomic profiles, four distinct molecular subgroups are identified: Wingless (WNT), Sonic Hedgehog (SHH), Group 3 and Group 4. Each of these subgroups are associated with specific genetic aberrations, typical age of onset as well as survival prognosis. Magnetic resonance imaging (MRI) is performed for all patients with brain tumors, and has a key role in the diagnosis, surgical guidance and follow up of patients with medulloblastoma. Several studies indicate MRI as a promising tool for early detection of medulloblastoma subgroups. The early identification of the subgroup can influence the extent of surgical resection, radiotherapy and chemotherapy targeted treatments. In this article, we review the state of the art in MRI-facilitated medulloblastoma subgrouping, with a summary of the main MRI features in medulloblastoma and a brief discussion on molecular characterization of medulloblastoma subgroups. The main focus of the article is MRI features that correlate with medulloblastoma subtypes, as well as features suggestive of molecular subgroups. Finally, we briefly discuss the latest trends in MRI studies and latest developments in molecular characterization.

Keywords: MRI; childhood brain cancer; medulloblastoma; molecular characterization; molecular subgroups; pediatric brain tumors.

Figure 1.

Example of SHH desmoplastic medulloblastoma. Two-year-old boy. Axial T2w(a) magnetic resonance images show an intraventricular mass in the fourth ventricle extending into the right Lushka foramen. Axial T1w postcontrast (b) images show associated heterogeneous contrast enhancement.

Figure 2.

Example of Group 3 medulloblastoma. Five-year-old girl. Axial T2w(a) magnetic resonance images show an intraventricular mass in the fourth ventricle. Axial T1w postcontrast (b) image shows intense contrast enhancement and presence of cystic components.

Figure 3.

Example of desmoplastic Group 4 medulloblastoma. Four-year-old girl. Axial T2w(a) magnetic resonance images show an intraventricular mass in the fourth ventricle. Axial T1w postcontrast (b) images show associated homogeneous contrast enhancement.

Figure 4.

Medulloblastoma in a 16-year-old boy. Axial computed tomography shows a hyperdense intraventricular mass with signs of mineralization (arrow).

Figure 5.

Diffusion-weighted images with b=1000 (a) and apparent diffusion coefficient maps (b) in a fourteen-year-old boy with histologically proven medulloblastoma. A posterior fossa intraventricular mass is seen. The lesion presents with diffusion restriction. Medulloblastomas typically present with diffusion restriction.

Figure 6.

Apparent diffusion coefficient (ADC) maps in a six-year-old girl with pylocitic astrocytoma (a) and in a medulloblastoma (b, same patient as in Figure 4). In the patient with pylocitic astrocytoma the lesion does not show diffusion restriction. In the patient with medulloblastoma the lesion shows diffusion restriction.

Figure 7.

Magnetic resonance image of an eight-year-old girl (a,c) and of a three-year-old girl (b,d), both presenting with WNT medulloblastoma. Axial T2w (a,b) images of two patients show two masses localized respectively in the fourth ventricle (a) and in the right cerebellopontine angle (arrow) (b). Axial T1w postcontrast (c,d) images show heterogeneous enhancement of the two lesions.

Figure 8.

MRI of a six-year-old girl (a,c) and of a two-year-old girl (b,d) presenting with a classic and a desmoplastic SHH medulloblastoma. Axial T2w (a,c) images of two patients show two masses arising from the cerebellar hemispheres. Axial T1w postcontrast (c,d) images show almost no contrast enhancement of one lesion (c) and contrast enhancement in the other lesion (d).