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    Amar Gajjar, MD

    Amar Gajjar, MD

    Medulloblastoma: MRI scans may be misleading

    Irradiation and high-dose chemotherapy used to treat two types of brain tumors—medulloblastoma and supratentorial PNET—can cause changes in the brain’s white matter that look like tumors when seen on MRI scans, according to a team of St. Jude investigators. White matter is the part of the brain composed of nerves that are covered in a pearly white sheath. Much of the cerebral cortex, where high-level thinking occurs, is made of white matter.

    The study demonstrates that this damage, called white matter lesions (WMLs), can be mistaken for returning cancer, prompting physicians to treat the patient aggressively—and needlessly—with more radiation and chemotherapy. 

    “Irradiation and high-dose chemotherapy are treatments we want to use as sparingly as possible,” says Amar Gajjar, MD, member of Hematology-Oncology and director of  Neuro-Oncology. “This new information represents an important caution sign for physicians who otherwise might assume that WMLs are actually tumors that need further treatment.”

    Gajjar is senior author of the report, which appears in the November 15 issue of Journal of Clinical Oncology. The report is the first to describe both the finding and the actual incidence of early-onset WMLs—that is, how frequently these lesions occur in patients with medulloblastoma or PNET who have been treated with radiation and high-dose chemotherapy following surgery. The study is also the first to note that the presence of WMLs is associated with a decline in intellectual function. 

     “Even though these changes tend to be only temporary, some children with these changes tend to develop permanent neurologic problems, such as difficulty swallowing,” said Maryam Fouladi, MD, an assistant member of Hematology-Oncology and lead author of the report.

    Other St. Jude authors of this report include Fred Laningham, MD; James Langston, MD; and Larry Kun, MD, all of Radiological Sciences; and Raymond Mulhern, PhD, Behavioral Medicine. The study was done in collaboration with researchers at Baylor College of Medicine in Houston, Texas; Australia’s Royal Children’s Hospital in Melbourne; the Children’s Hospital at Westmead; and the University of Sydney.


    Last update: December 2004