Evidence suggests that medulloblastomas originate from two different germinal zones within the cerebellum. The ventricular zone gives rise to the more common classic midline medulloblastomas, whereas granule neuron precursor cells of the external granule layer are believed to give rise to the lateral cerebellar hemispheric desmoplastic medulloblastomas. The tumors may spread contiguously to the cerebellar peduncle, along the floor of the fourth ventricle, into the cervical spine, or above the tentorium. At the time of diagnosis there is spread via the cerebrospinal fluid (CSF) to other intracranial sites, the spinal cord, or both in 10% to 30% of patients.[1,2,3]
Once childhood acute myeloid leukemia (AML) has been diagnosed, tests are done to find out if the cancer has spread to other parts of the body.
The extent or spread of cancer is usually described as stages. In childhood acute myeloid leukemia (AML), the subtype of AML and whether the leukemia has spread outside the blood and bone marrow are used, instead of the stage, to plan treatment. The following tests and procedures may be used to determine if the leukemia has spread:
Magnetic resonance imaging (MRI) is the method of choice to evaluate for intracranial or spinal cord subarachnoid metastases. To avoid postoperative artifacts, such imaging is best performed preoperatively, but postoperative evaluation is also useful when obtained at least 10 days following the operative procedure. The entire spine must be imaged in at least two planes, with contiguous magnetic resonance slices performed before and after gadolinium enhancement. The significance of positive CSF cytology in samples obtained within the first 7 to 10 days of diagnosis is unclear, as is the significance of tumor cells in cisternal fluid obtained at the time of surgery. However, CSF tumor cells found 2 to 3 weeks after diagnosis portends a poorer prognosis.[1,2,3] Extracranial spread of medulloblastoma at the time of diagnosis is less than 1%. Although bone scans and bone marrows have been routinely obtained in some older prospective studies, their yield was low and they are primarily recommended for infants or those with widespread intracranial disease, intraspinal disease, or those with symptoms and signs consistent with possible dissemination.[2,3] CSF shunts placed at the time of surgery have not been shown to increase the risk of leptomeningeal relapse.
Historically, staging has been primarily based on an intraoperative evaluation of both the size and extent of the tumor, coupled with postoperative neuroimaging of the brain and spine and cytological evaluation of CSF. MRI of the brain and spine (often done preoperatively), postoperative MRI of the brain to determine the amount of residual disease, and lumbar CSF analysis are now used to determine staging.[1,2,3] Surgical impressions, including direct observation of dissemination at the time of diagnosis, extent of residual disease following surgery, and involvement of the brain stem, are still incorporated into staging systems.
Staging of Pineoblastoma
Staging for children with pineoblastomas is the same as that performed for children with medulloblastoma. Dissemination at the time of diagnosis occurs in 10% to 30% of patients. Because of the location of the tumor, total resections are uncommon, and most patients have only a biopsy or a subtotal resection before postsurgical treatment.[4,5] Similar to other central nervous system (CNS) primitive neuroectodermal tumors (PNETs), all pineoblastomas are treated as high-risk embryonal tumors. Prognosis is worse for patients with disseminated disease at the time of diagnosis.[4,5]