Lowgrade Gliomas In Adults

Tumors where it is uncertain whether complete or radical resection can be achieved Tumors that recur after treatment Tumors that cause intractable epilepsy

1. Tumors that are Too Large for Complete Resection to be Possible Without Unacceptable Risk

Complete resection is clearly impossible in patients where the tumor is bilateral, having crossed the corpus callosum, or involves the basal ganglia and insular cortex. Early involvement of the corpus callosum is not, in itself, a complete contraindication to surgery, since it is possible to resect areas of the corpus callosum without major risk. However, the significance of corpus callosum involvement is that in most cases it is associated with bilateral hemispheric infiltration, and one of the fundamental rules of neurosurgery remains that bilateral hemispheric damage is associated with a high risk of major neurological deficit. In a very small proportion of these cases, at the time of presentation, there will be symptoms of raised intracra-nial pressure. In these cases standard debulking surgery is indicated. Since there is no evidence that debulking surgery prolongs survival in patients without raised intracranial pressure, some authors [7] have argued that there is little justification in carrying out such surgery in the absence of raised pressure. Others have argued, for instance Berger et al. [8], that aggressive debulking surgery delays recurrence when compared with more conservative resection, but no studies have shown any certain benefit in terms of long-term survival. It is an article of faith for some neurosurgeons that debulking surgery, sometimes described more impressively as "cytoreduction", is beneficial, but the fact remains that this is entirely unproven, and any theoretical benefits must also be balanced against the greater morbidity of aggressive surgery. Even with very large tumors several years can pass before raised pressure develops and palliative surgery becomes indicated. Since there is also no evidence [9] that radiotherapy prolongs life in this group of patients, there is little purpose in carrying out a biopsy (stereo-tactically or otherwise) unless there is doubt about the interpretation of the scan or unless the neurosurgeon's neuro-oncological colleagues strongly favor adjuvant treatment in such cases.

If it has been decided not to treat a patient in this group, and instead to follow up the patient with repeat scans, the tumor will, sooner or later, be shown to be growing larger, probably before the onset of the symptoms of raised intracranial pressure. A more rational approach might be to postpone repeating the scan until such symptoms have developed. However, most patients will wish to be followed up with scans, in the hope that they will not show any progression, and it is very difficult for the surgeon to refuse to organize follow-up scanning. However, once the scan shows progression - albeit asymptomatic - it is very difficult to continue to withhold treatment even though treatment is, by definition, palliative and there are no new symptoms to palliate.

There are two possible options. Firstly, further conservative treatment may be given with the blunt admission to the patient that there is no convincing evidence that treatment will make a significant difference. Secondly, treatment can be recommended in the hope that it will slow down the rate of progression, even though the evidence is lacking that such treatment works. In the author's experience, most patients will favor the latter policy.

Treatment can take the form of surgery and radiotherapy, or debulking surgery alone.

Biopsy will be required with either policy. Biopsy can be either closed or open, depending on the location of the tumor and the surgeon's preference. Different parts of the tumor can show different histological features and there is an argument either for multiple targets, if biop-sied stereotactically, or for removing a reasonable volume of tumor if open biopsy is carried out. With large tumors it must be remembered that biopsy without debulking can precipitate post-operative cerebral herniation. Pre-operative steroids are essential and, on occasion, debulking surgery, even in the absence of symptoms of raised intracranial pressure, may need to be carried out as part of the biopsy. Treatment can also be confined to debulking surgery, and radiotherapy postponed until there is further evidence of progression, provided that histology shows that the tumor has not undergone malignant change. Once such malignant change has occurred, the tumor should be treated as a high-grade tumor, and palliative adjuvant treatment is then indicated in the great majority of cases.

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