Certain types of brain tumors can be diagnosed antenatally. Where the prognosis is hopeless, medical termination of pregnancy can be carried out. Utero Diagnosis of brain tumors is usually done with an ultrasound, a CT or MRI. Sampling of fetal blood, amniotic fluid and the chronic villus is today a practical proposition. Biochemical and karyotyping studies of these, will eventually enable one to even predict if the fetus will ultimately develop a brain tumor. It is only a question of time before many brain tumors can be diagnosed antenatally. Progress is being made in identifying biochemical and genetic markers which could one day predict even the occurrence of a neurological illness late in life. Neurological diseases of genetic origin in which diagnosis may eventually be possible in the unborn include:
- Myotonic dystrophy.
- Huntingtons disease.
- Spinocerebellar ataxia.
- Alzheimer’s disease.
- Tay sachs disease.
- Amyotropic lateral sclerosis.
- Down’s syndrome.
- Neurofibromatosis type 2.
- Muscular dystrophy.
“Fetal Neurosurgery” is technically not impossible. Utero shunts and ultrasound guided fetal brain biopsies are possible. Complex craniotomies on the exteriorized primate fetus, with little risk either to the fetus or the mother, have been successfully carried out. The fetal brain cell can regenerate, reorganize and heal better than the adult neuron. It is indeed an attractive proposition to remove a brain tumor in utero.
Oncofenes, brain tumors and neurogenetics
Ten years ago, this subject was non existent. Ten years from now genetic mapping may be part of the clinical work–up of a patient with a suspected brain tumor. Applied genetics is making inroads into neuro oncology at a rapid pace. Strong evidence now exists, that genetic factors play a role in the causation of certain types of brain tumors. The exact identification of the concerned onocogenes and later on replacing the defective gene in time, is fraught with almost insurmountable difficulties. A start is being made. Abnormal genes in several types of brain tumors have been identified. Meningiomas and Schwanomas are now known to be associated with loss of chromosome 22. In fact the telomeric end of 17 in medulloblastomas and loss of chromosome 10 in glioblastomas have also been documented. The specific genes manufacturing, the protein neurofibromin in NF–1, merlin in NF–2 and EGFR in glioblastomas have recently been isolated. In the future, gene therapy for some of these tumors may even be possible. Gene therapy may involve replacement of a defective gene or inactivation of an abnormal gene. Modified viruses may be used as vectors to carry the normal gene. This is injected into the host cell. The neuro–oncologist of the next century will be a molecular biologist. By the year 2025, the genetic basis of several facets of human behavior would have been unraveled. This may result in brain mind manipulation including the manipulation of learning, memory and several types of emotions. 25% of all genetic diseases are diseases of the brain. The genetic basis of at least 40 distinct neurological diseases have already been identified. New ideas will result in new tools and new therapies.
Brain tumor markers
Identifying a brain tumor by analyzing a blood sample may one day be possible. Traditionally only alfafeto protein and human chorionic gonadotrophin were recognized by the neurosurgeon as tumor markers. Putrescine, desmosterol glucoronidase, spermidine and spermine are some of the biochemical markers indicating the presence of brain tumors.
Investigating brain tumors
Several tools, currently of an esoteric nature, are likely to be available in a clinical setting. These include:
Magnetic resonance spectroscopy
MRI at present is used to identify the structural pathology of a tumor in the brain. Using sophisticated software, the MRI can be used to study metabolites within a selected region of interest (the tumor). Spectral peaks will indicate the metabolite produced by the tumor. Millimolecular concentrations of brain tumor, metabolites can be detected non invasively. Metabolic finger printing of brain tumors will eventually be available in a clinical setting, as one more tool, to precisely identify the nature of a tumor preoperatively. Functional MRI, Magnetic Source Imaging and Optical Imaging will also be used.
Refinements in the technology of Single Photon Emission Computed Tomography will result in increasing clinical application. Known as the poor Man’s PET (Post Emission Tomography) this will be able to distinguish between true tumor recurrence and radiation necrosis. It will also indicate the exact site from which a stereostactic biopsy is to be taken in tumors with necrotic components. Functional imaging is enabling us to take a re–look at how the brain itself works. Epilepsy surgery, understanding higher cognitive functions, and how information in the motor cortex, visual and auditory cortex is processed will eventually be understood.