Evaluation of Medulloblastomas in Children

Examination

• Signs of hydrocephalus such as lethargy, upgaze paresis, or full fontanelle/splayed sutures in infants may be seen at presentation.
• Altered gait, either profound or subtle, may be demonstrated on examination at presentation.
• Cerebellar signs such as truncal or appendicular ataxia are less common.
• Cranial neuropathies are relatively uncommon at presentation.  The most common cranial neuropathy at presentation is sixth nerve palsy.

Laboratory Tests

• Routine preoperative testing: Routine screening lab tests are needed, and no abnormal results are expected.

Radiologic Tests

CT scan

• CT scans show hyperdense fourth ventricular mass: CT scan of the brain is often performed as a screening examination in patients who present with nausea, vomiting, or altered mental status. Medulloblastomas are typically hyperdense on CT scan and fill the fourth ventricle.

CT scan of medulloblastoma: The tumor fills the fourth ventricle causing obstructive hydrocephalus with prominent temporal horns. The tumor is hyperdense to normal brain, which is typical of medulloblastoma

MRI

• MRI of the brain: MRI of the brain with and without gadolinium is the imaging procedure of choice. Medulloblastomas typically (although not always) are intraventricular, may involve the vermis, and may invade the brainstem (20). The scan should be performed as soon as possible after admission unless the patient’s condition is deteriorating because of hydrocephalus. In that case, the hydrocephalus must be addressed first.
• Medulloblastoma typically hypointense on T1-weighted MRI and hyperintense on T2-weighted MRI: Most medulloblastomas enhance, at least partially, with gadolinium (14).

T1-weighted sagittal MRI of medulloblastoma: The lesion is hypointense on this T1-weighted sequence, which is typical of medulloblastomas, and fills the fourth ventricle. Supratentorial hydrocephalus and tonsillar herniation are noted.

T1-weighted sagittal MRI with gadolinium of medulloblastoma: Heterogeneous enhancement of the tumor is observed, which is typical of medulloblastomas.

T2-weighted sagittal MRI of medulloblastoma: The lesion is hyperintense on T2-weighted sequences, which is typical of medulloblastomas.

• MRI of the total spine: MRI of the total spine should also be obtained preoperatively to rule out the presence of leptomeningeal disease, which may affect surgical management.  It may be difficult to distinguish between leptomeningeal disease and surgical debris on postoperative spine MRI.

MRI of the spine of a child with medulloblastoma: The images show widespread leptomeningeal disease as a contrast-enhanced, hyperdense coating surrounding the spinal cord. 

Nuclear Medicine Tests

• None required

Electrodiagnostic Tests

• None required

Neuropsychological Tests

• Unusual preoperatively: No neuropsychological testing is typically performed at presentation, as children most often present with acute hydrocephalus.
• Useful to track treatment sequelae: Neuropsychological tests may provide useful information postoperatively or after adjuvant therapy depending on the patient’s status.

Correlation of Tests

• Age, clinical examination, and imaging: A young child presenting with signs of posterior fossa neurological dysfunction and imaging showing a tumor confined to the fourth ventricle has a medulloblastoma until histologically proved otherwise.
• Preoperative differential diagnosis: The differential diagnosis most often includes other neoplasms commonly found in the fourth ventricle in children, especially ependymoma and pilocytic astrocytoma. AT/RT while less common, is a consideration in younger children. Neoplasms of other pathological etiologies are possible but rare. Non-neoplastic lesions are easily excluded on imaging studies.
• Determination of operative plan: Patients with presenting signs and symptoms and imaging studies consistent with possible medulloblastoma or any other tumor in the differential diagnosis listed above require tumor resection to establish the pathological diagnosis, to alleviate hydrocephalus by removing the obstructing mass in the fourth ventricle, and to minimize tumor burden for oncological reasons.