IS Case 257: Medulloblastoma
Imaging Sciences URMC 2009
Publication Date: 2009-06-26
Patient is a 4-year-old child presenting with seizures and five days of truncal ataxia
There is a lobulated mass arising from the cerebellar vermis with surrounding areas of perilesional edema as demonstrated by low CT attenuation (Fig. 1) and T2 hyperintensity on MRI (Fig. 3). Sagittal T1 post-contrast MRI of the brain confirms the infratentorial location of the enhancing mass (Fig. 4).
Medulloblastoma, a primitive neuroectodermal tumor (PNET), is the most frequent posterior fossa tumor in children (40-55% of cases). It is most frequently diagnosed between the ages of 1 and 10 years and represents less than 1% of all adult central nervous system tumors. The majority of cases are sporadic, however familial cases have been reported.
Some propose that the undifferentiated cells originate in the posterior medullary velum and then migrate superolaterally later in life. This may explain why medulloblastoma most commonly appears midline arising from the cerebellar vermis in children and may manifest as truncal ataxia. In adults, lesions are typically found in the lateral cerebellar hemispheres which may result in dysmetria of the ipsilateral arm or leg.
At CT, these tumors appear hyperattenuating compared to normal brain reflecting their hypercellularity (Fig. 1) and they show marked enhancement (Fig. 4). Surrounding vasogenic edema and resultant hydrocephalus from compression of the fourth ventricle may also been seen. The diagnostic test of choice is contrast enhanced MRI which demonstrates T1 hypointense (Fig. 2) and T2 hyperintense (Fig. 3) signal as well as enhancement. Metastatic lesions in the spine (drop metastasis) may be identified with MRI prior to surgery.
Medulloblastoma is primarily treated with surgical excision and chemoradiation therapy. Corticosteroids are useful for decreasing vasogenic edema and certain cases may require placement of a ventriculostomy catheter. Post-operative contrast enhanced MRI is essential within 48 hours of surgery and prior to the onset of enhancing reactive gliosis for staging and to evaluate for residual tumor which may be amendable to re-exploration and resection. Current 5 year survival rates are at least 50%. Other considerations for a posterior fossa tumor in a child are ependymoma and pilocytic astrocytoma.
- Koeller KK, Rushing EJ. From the archives of the AFIP: medulloblastoma: a comprehensive review with radiologic-pathologic correlation. Radiographics. 2003 Nov-Dec;23(6):1613-37. PMID: 14615567 [PMID: 14615567]
- Maher CO, Raffel C. Neurosurgical treatment of brain tumors in children. Pediatr Clin North Am. 2004 Apr;51(2):327-57. PMID: 15062674 [PMID: 15062674]