Staging of CNS Embryonal Tumors

Staging of Medulloblastoma
Staging of Pineoblastoma
Staging of CNS PNETs
Staging of Other CNS Embryonal Tumors

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.[1-3]

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.[1-3] 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.[2]

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.[1-3] 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 for children with pineoblastomas is the same as that performed for children with medulloblastoma.[4] Dissemination at the time of diagnosis occurs in 10% to 30% of patients.[4] 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]

Patients with CNS PNETs are staged in a fashion similar to that used for children with medulloblastoma. CNS PNETs may be disseminated at the time of diagnosis, although the incidence of dissemination may be somewhat less than that of medulloblastomas or pineoblastomas, with dissemination at diagnosis being documented in approximately 10% to 20% of patients.[6,7] CNS PNETs are often amenable to resection; in series, 50% to 60% of patients were totally or near-totally resected.[6,7]

Dissemination of both medulloepitheliomas and ependymoblastomas may occur, and the tumors are staged in the same way as medulloblastoma.

1. Fouladi M, Gajjar A, Boyett JM, et al.: Comparison of CSF cytology and spinal magnetic resonance imaging in the detection of leptomeningeal disease in pediatric medulloblastoma or primitive neuroectodermal tumor. J Clin Oncol 17 (10): 3234-7, 1999.  [PUBMED Abstract]
   
   
2. Zeltzer PM, Boyett JM, Finlay JL, et al.: Metastasis stage, adjuvant treatment, and residual tumor are prognostic factors for medulloblastoma in children: conclusions from the Children's Cancer Group 921 randomized phase III study. J Clin Oncol 17 (3): 832-45, 1999.  [PUBMED Abstract]
   
   
3. Yao MS, Mehta MP, Boyett JM, et al.: The effect of M-stage on patterns of failure in posterior fossa primitive neuroectodermal tumors treated on CCG-921: a phase III study in a high-risk patient population. Int J Radiat Oncol Biol Phys 38 (3): 469-76, 1997.  [PUBMED Abstract]
   
   
4. Jakacki RI, Zeltzer PM, Boyett JM, et al.: Survival and prognostic factors following radiation and/or chemotherapy for primitive neuroectodermal tumors of the pineal region in infants and children: a report of the Childrens Cancer Group. J Clin Oncol 13 (6): 1377-83, 1995.  [PUBMED Abstract]
   
   
5. Timmermann B, Kortmann RD, Kühl J, et al.: Role of radiotherapy in the treatment of supratentorial primitive neuroectodermal tumors in childhood: results of the prospective German brain tumor trials HIT 88/89 and 91. J Clin Oncol 20 (3): 842-9, 2002.  [PUBMED Abstract]
   
   
6. Cohen BH, Zeltzer PM, Boyett JM, et al.: Prognostic factors and treatment results for supratentorial primitive neuroectodermal tumors in children using radiation and chemotherapy: a Childrens Cancer Group randomized trial. J Clin Oncol 13 (7): 1687-96, 1995.  [PUBMED Abstract]
   
   
7. Reddy AT, Janss AJ, Phillips PC, et al.: Outcome for children with supratentorial primitive neuroectodermal tumors treated with surgery, radiation, and chemotherapy. Cancer 88 (9): 2189-93, 2000.  [PUBMED Abstract]