Typical & Atypical Neuroimaging of Pediatric Medulloblastoma Ayelet Eran, Arzu Ozturk, Nafi Aygun, Izlem Izbudak. Johns Hopkins Medical Institutions Rambam Health Care Campus

Medulloblastoma: atypical CT and MRI findings in children Medulloblastoma: atypical CT and MRI findings in children. Eran A, Ozturk A, Aygun N, Izbudak I. Pediatr Radiol. 2010 Apr 13.

Neuroradiologic considerations in Pediatric Medulloblastoma Posterior fossa mass lesions in children usually present a diagnostic challenge despite their frequent occurrence and the limited number of differential diagnostic possibilities. Consideration of medulloblastoma within the differential diagnosis mandates an aggressive surgical approach. Preoperative imaging of the entire neuro-axis is critical given the high propensity of drop metastases.

Medulloblastoma Highly malignant neuroepithelial tumor of the posterior fossa predominantly seen in children. Thought to arise from primitive, undifferentiated, small, round cells located in the superior medullary velum at the roof of the fourth ventricle. The revised 2000 WHO classification, reclassified the tumor as medulloblastoma.

Pathologic subtypes Regular medulloblastoma Large cell medulloblastoma Desmoplastic/nodular medulloblastoma Anaplastic medulloblastoma Medulloblastoma with extensive nodularity.

Medulloblastoma - epidemiology The most common malignant CNS tumor in children. Accounts for 38% of all pediatric posterior fossa tumors, representing the most common posterior fossa tumor in children. Most frequently occurs within the first decade of life, with a peak incidence in children at the age of 3 and 7.

Typical appearance Cerebellar mass, most commonly arising in midline. Imaging appearance reflects the tumor consistency, which is of well-packed small round cells with scarce cytoplasm and reduced free water.

CT appearance Hyperattenuating, midline vermian mass surrounded by vasogenic edema on non-contrast CT. Enhancement following IV contrast administration. Obstructive hydrocephalus is present in 95% of cases at presentation.

-IV +IV

MR appearance Iso- to hypointense relative to grey matter on T1 weighted images. Variable T2 signal Variable enhancement pattern. Reduced diffusivity. Look for leptomeningeal spread.

T2 DWI T1+GD ADC

Foraminal extension Extension into CSF foramina is considered a feature of ependymoma. Foraminal extension should be differentiated from the normal enhancement of the choroid plexus in the foramina of Luschka or primary CSF seeding of medulloblastoma.

Extension to foramen of Luschka Extension to foramen of Magendie Medullo +medullo

Leptomeningeal spread anaplastic

CPA involvement An extreme case of foraminal extension Usually an exophytic cerebellar lesion Other common entities in this region (vestibular schwannoma, meningioma) are rare in children.

CT - IV T1 T2 T1+GD anaplastic

Hemorrhage Hemorrhagic brain tumors in children are relatively rare. Differentiating hemorrhage from tumor on CT might sometimes be difficult, due to the inherent hyperattenuation of the tumor. Cases of massive hemorrhage into a tumor are especially challenging. Standard MR sequences usually suffice to differentiate a tumor from a hemorrhage.

desmoplastic

Eccentric/hemispheric location An eccentric or hemispheric location is considered typical for adult medulloblastoma. Desmoplastic medulloblastoma is frequently eccentric. Another distinct pattern in children is nodular, “grape-like” appearance that may predict a histological diagnosis of medulloblastoma with extreme nodularity (MBEN), that has a favorable prognosis.

CT-IV T2 T1 T1+GD desmoplastic

Medulloblastoma with extreme nodularity T1+GD T1+GD

Cyst May be found in as many as 80% of the cases. Numerous small cyst are more common

FLAIR T2

Enhancement pattern Enhancement pattern can be variable on MRI, ranging from diffuse and homogenous to focal and patchy. Non-enhancing tumor is atypical (7.5%) Enhancement pattern has no correlation with prognosis or pathologic subtype.

T1 T1+GD

Calcifications present in as many as 20% of the cases. Might lead the radiologist to favor the diagnosis of ependymoma. Maybe overlooked on MR

anaplastic CT-IV T2 T1+GD

Conclusion Medulloblastoma has a variable appearance and should in many cases be considered, even when atypical features are present. Some of the atypical radiological presentations are recognizable once seen.

Acknowledgment Drs Doris Lin, Thierry Huisman, Danny Reich for their assistance in collecting cases and manuscript preparation.

Thanks for your attention