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Findings: Axial CT image demonstrates a right cerebellar and fourth ventricle mass which is somewhat higher in attenuation than the remaining brain parenchyma. In addition, there is marked dilatation of the temporal horns indicating hydrocephalus. Axial T1 and T2 weighted images as well as a sagittal image following the intravenous administration of contrast demonstrates an approximately 4 cm fourth ventricular mass with probable extension toward the outlets of the fourth ventricle. There is very little enhancement following the intravenous administration of contrast.
Diagnosis: Ependymoma.
Discussion: Primary brain tumors are the second most common malignancies in the pediatric population behind lymphoid neoplasms. Posterior fossa tumors are more common in children above the age of two, while supratentorial tumors are more common in children less than age two.
Ependymomas are the third most common brain tumor in children and account for approximately 15% of posterior fossa malignancies. They classically arise from ependymal cells lining the fourth ventricle. Commonly, the tumor expands the fourth ventricle and extends through the foramen of Magendie and through the foramina of Luschka. The tumors are often calcified and may demonstrate a large cystic component. Inhomogeneous enhancement is usually seen. Because of their location, seeding throughout the subarachnoid space can be seen.
Patients typically present with nausea, vomiting, headache as well as ataxia. The over-all five year survival rate is approximately 50%. Supratentorial ependymomas, however, are usually more aggressive and have a poorer prognosis.
As stated above, ependyomomas are the third most common posterior fossa tumor in childhood behind juvenile pilocytic astrocytomas and medulloblastomas.
References:
Osborn Ann EG. Diagnostic Radiology. Mosby, St. Louis;
1994:401-407, 566-570.
Taveras JM. Neuroradiology, 3rd Edition. Williams & Wilkins,
Baltimore; 1996:576.
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