His mother provides a history of increasing headaches over past month, gait disturbances, and possible seizure activity.
No metabolic abnormality.
Large, solid mass in the left cerebellar hemisphere with ill-defined margins and significant surrounding T2 signal abnormality representing vasogenic edema. This exerts mass effect upon and displaces the 4th ventricle. Mild hydrocephalus. Diffuse, heterogeneous enhancement following IV gadolinium infusion. CT scan demonstrates a notably low attenuation mass, and inferior displacement of the cerebellar tonsils to the level of the foramen magnum.
Resection, if complete, is usually sufficient. It has not yet been decided if this patient will undergo additional Tx.
The mass arises from the left cerebellar hemisphere and not the 4th ventricle, and is hypodense on CT. These findings make medulloblastoma far less likely. A mass entirely outside the ventricle makes ependyoma less likely. While pilocytic astrocytomas (PA) are usually cystic with an enhancing mural nodule, this case represents the less common solid variant. Approximately 85% of posterior fossa astrocytomas in childhood are pilocytic - the remainder are fibrillary-diffuse. Pilocytic astrocytomas are WHO Grade 1; whereas fibrillary may be Grade 2-4. Enhancement in PA is almost universal. Enhancement in diffuse astrocytoma is associated with vascular changes and a higher tumor grade - either Grade 3 or Grade 4.
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Cerebellar astrocytoma accounts for about 11 - 30% of primary CNS tumors in children, and has a post-resection survival of up to 94% at 10 years. This tumor makes up about one-third of childhood posterior fossa tumors, typically presenting late in the first decade or in the early second decade. These well-circumscribed masses are often completely resected surgically, with no other therapy required.
Cerebellar astrocytoma tends to involve the hemispheres, although extension into or origin within the vermis or even the fourth ventricle have been described infrequently. It may be predominantly cystic with a mural nodule (as shown in a different patient, Film .4), multicystic, or predominantly solid (diffuse) on CT or MR. Recognizable cysts occur in up to 80%. Histologically, most are juvenile pilocytic astrocytomas similar to those of the third ventricle region. Diffuse infiltrating fibrillary types occur in up to 15% of cerebellar astrocytomas and have a less favorable prognosis. Frank malignancy, leptomeningeal seeding, and spontaneous hemorrhage are distinctly unusual.
Radiographically, cerebellar astrocytoma arises within the cerebellar hemisphere and less often in the vermis, and displaces the fourth ventricle without invading it. On CT, 10-25% contain foci of calcification. The mass is hypointense on T1-weighted and hyperintense on T2-weighted MR, with one or more cystic components. After contrast administration, the mural nodule and/or solid components enhance, rendering nonenhancing cysts more conspicuous.
In children, vermian or diffuse astrocytoma or those involving the fourth ventricle may mimic medulloblastoma or ependymoma. In older adolescents or adults, hemangioblastoma may present as a cystic mass indistinguishable from cerebellar astrocytoma. Metastasis is the most common posterior fossa neoplasm in adulthood. Rarely vascular malformation, abscess, or lymphoma might have a similar radiographic appearance.
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