Medulloblastoma is a highly malignant primary brain tumor that originates in the cerebellum or posterior fossa.
| Medulloblastoma | |
|---|---|
| Specialty | Oncology  |
Originally considered to be a glioma, medulloblastoma is now known to be of the family of cranial primitive neuroectodermal tumors (PNET).[1]
Tumors that originate in the cerebellum are referred to as infratentorial because they occur below the tentorium, a thick membrane that separates the cerebral hemispheres of the brain from the cerebellum. Another term for medulloblastoma is infratentorial PNET. Medulloblastoma is the most common cranial PNET.[2]
Medulloblastoma is an invasive and rapidly growing tumor that, unlike most brain tumors, spreads through the cerebrospinal fluid (CSF) and frequently metastasizes to different locations in the brain and spine.
Incidence
Brain tumors are the second most common malignancy among children 0-19 years of age, and of those, medulloblastoma is the second most common CNS malignancy.[3] Medulloblastoma comprises less than 2% of CNS malignancies diagnosed in adults.[4]
Medulloblastoma has a bimodal incidence at the ages of 4-8 years, then in the early 20s and accounts for ~20% of childhood brain tumors. Males out of female 3:2 or 3:1 in many cases.
Pathogenesis
It is currently thought that medulloblastoma arises from cerebellar "stem cells" that have been prevented from dividing and differentiating into their normal cell types. This accounts from the varying histologic variants seen on biopsy. Rosette formation is highly characteristic of medulloblastoma and is seen in up to half of the cases.
Molecular genetics reveal a loss of genetic information on the distal part of chromosome 17, distal to the p53 gene, possibly accounting for the neoplastic transformation of the undifferentiated cerebellar cells. Medulloblastomas are also seen in Gorlin syndrome as well as Turcot syndrome. Another research has strongly implicated the JC virus, the virus that causes multifocal leukoencephalopathy.
Clinical manifestation
Symptoms are mainly due to secondary increased intracranial pressure due to blockage of the fourth ventricle and are usually present for 1 to 5 months before diagnosis is made. The child typically becomes listless, with repeated episodes of vomiting, and a morning headache, which may lead to a misdiagnosis of gastrointestinal disease or migraine. Soon, the child will develop a stumbling gait, frequent falls, diplopia, papilledema, and sixth cranial nerve palsy. Positional dizziness and nystagmus are also frequent and facial sensory loss or motor weakness may be present. Decerebrate attacks appear late in the disease.
Extraneural metastases to the rest of the body is rare, but usually only after craniotomy.
Diagnosis
The tumor is distinctive on T1 and T2-weighted MRI with heterogeneous enhancement and typical ___location adjacent to and extension into the fourth ventricle.
Histologically, the tumor is solid, pink-gray in color, and is well circumscribed. The tumor is very cellular, many mitoses, little cytoplasm, and has the tendency to form clusters and rosettes.
Treatment and Prognosis
Treatment begins with maximal resection of the tumor. The addition of radiation to the entire neuraxis and chemotherapy may increase the disease-free survival. This combination may permit a 5 year survival in more than 80% of cases. The presence of desmoplastic features such as connective tissue formation offers a better prognosis. Prognosis is worse if child is less than 3 years old, inadequate degree of resection, or if presence of any CSF, spinal, supratentorial or systemic spread.
Increase intracranial pressure may be controlled with corticosteroids or a ventriculoperitoneal shunt
Notes
- ^ George Jallo, MD, Medulloblastoma, eMedicine 2007.
- ^ Chris Hinz, Deneen Hesser, Focusing On Brain Tumors: Medulloblastoma, American Brain Tumor Association 2006, ISBN 0-944093-67-1.
- ^ James G. Gurney, Malcolm A. Smith, Greta R. Bunin, CNS and Miscellaneous Intracranial and Intraspinal Neoplasms, SEER Pediatric Monograph, National Cancer Institute
- ^ Selected Primary Brain and Central Nervous System Tumor Age-Specific Incidence Rates, Central Brain Tumor Registry of the United States, 1998-2002.
References
- Ropper, AH; Brown, RJ; Adams and Victor's Principles of Neurology, 2005, McGraw Hill
- Eibl RH, Kleihues P, Jat PS, Wiestler OD (1994) A model for primitive neuroectodermal tumors in transgenic neural transplants harboring the SV40 large T antigen. Am J Pathol. 1994 Mar;144(3):556-64
External links
- Roger Packer M.D, Medulloblastoma, Clinical Trials and Noteworthy Treatments for Brain Tumors 2002.
- Medulloblastoma support resources
- 00905 at CHORUS