Pediatric Medulloblastoma Workup
- Author: Tobey J MacDonald, MD; Chief Editor: Max J Coppes, MD, PhD, MBA more...
The routine pretreatment laboratory evaluation for medulloblastoma includes CBC count, electrolytes, liver, and renal function tests.
Baseline thyroid function studies and viral titers are also recommended.
A CT scan of the head with and without contrast has more than 95% sensitivity for the detection of brain tumors.
On CT scans, prominent hydrocephalus and a solid, homogeneous, isodense to hyperdense, contrast-enhancing, midline cerebellar mass are characteristic of (although not diagnostic of) medulloblastoma.
Head and spinal MRI with and without gadolinium should be performed in all patients with CT or clinical findings consistent with medulloblastoma.
MRI can be useful in such instances by better demonstrating the anatomic origin and extent of tumor (see the image below).
Preoperative and postoperative MRI is required for detection and measurement of residual disease following surgical resection. Postoperative MRI evaluation should be performed within 72 hours of surgery to delineate residual tumor from the postsurgical inflammatory changes that are visualized on MRI at this time.
Spinal MRI is the most sensitive method available for detection of spinal cord metastasis.
Because medulloblastoma can metastasize outside the CNS, especially to bone, a bone scan with plain film correlation may be useful in symptomatic patients.
A baseline hearing test (audiography or brainstem auditory-evoked response [BAER]) is recommended because of the potential toxicity from radiation and chemotherapy.
Some investigational treatment protocols may require additional tests, such as echocardiography, pulmonary function tests, or other more specific tests, for the purposes of monitoring treatment-related toxicity.
CSF cytologic examination is useful for the detection of microscopic leptomeningeal tumor dissemination. However, neither clinical symptoms nor negative CSF cytologic findings can be relied on to indicate the presence of nodular spinal cord disease. As many as 50% of patients with positive spine MRI studies are asymptomatic and have negative cytologic results.
Funduscopic examination (or CT or MRI) must be performed before lumbar puncture (LP) to rule out the presence of hydrocephaly.
In known cases of medulloblastoma, LP generally is deferred until 2 weeks postoperation to avoid the presence of tumor cells that have disseminated as a result of surgery.
Bone marrow aspirate and biopsy
Medulloblastoma rarely metastasizes to bone marrow.
These tests should be reserved for patients who demonstrate abnormal peripheral blood findings that have no clear etiology.
Medulloblastomas are undifferentiated embryonal neuroepithelial tumors of the cerebellum. They are highly cellular, soft, and friable tumors composed of cells with deeply basophilic nuclei of variable size and shape, little discernible cytoplasm, and often abundant mitoses (see the image below).
These characteristics give the microscopic appearance of a small, round, blue cell tumor. Morphologically identical tumors arising in the pineal region are termed pineoblastomas, and those arising in other CNS locations are called primitive neuroectodermal tumors (PNETs).
Homer-Wright rosettes (ringlike accumulations of tumor cell nuclei around a neuropil-containing or fibrillary core) and pseudorosettes are variably present (see the image below).
These tumors express neuronal and neuroendocrine markers, including synaptophysin and neurofilament proteins.
Various degrees of glial or neuroblastic differentiation are noted, suggesting that the primitive cell of origin possesses the capacity for bipotential differentiation. A histologic variant with abundant stromal component, desmoplastic medulloblastoma, occurs dominantly in the lateral cerebellar areas of adolescents and adults. Another more recently described variant is characterized by marked features of anaplasia that is associated with MYCC oncogene amplification.
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