Cerebellar astrocytomas: Therapeutic management

Summary

The therapeutic management of cerebellar astrocytomas is almost exclusively surgical. Although a few patients survive for long periods without treatment, the majority die without surgery. Total excision is advised to prevent recurrence which almost always follows non-total removal of tumour. Moreover, radical excision is feasible since the cerebellum has a remarkable capacity to compensate after large amounts of tissue have been removed. Morbidity is related to damage to the deep cerebellar nuclei, infiltration of the brain stem, secondary adhesions, and infection. Tumours may not be macroscopically visible at the time of first operation which in turn emphasizes the need for a detailed radiological work-up using, in particular, the CT scan. Biopsy alone, decompression alone, and/or aspiration are usually followed by rapid recurrence and no more than 30% of patients thus treated are recurrence-free five years after surgery. Approximately 40% of patients have subtotal resections and, of these, only 35% are recurrence-free five years post-operatively. Despite the high risk of recurrence following subtotal removal, subtotal excision may still be followed by prolonged survival since two thirds of the patients in the present study were still alive ten years or more after surgery. This is due in part to the unpredictable behaviour of cerebellar astrocytomas, a fact clearly demonstrated by serial CT studies of patients with partially excised tumours which demonstrate that residual tumour may occasionally regress or even remain static for many years. Total removal, when possible, is the treatment of choice and was carried out in 41% of patients in the present study. Ninety-five per cent of patients were free of recurrence for 25 years or more following total removal. In fact, recurrence following total removal has only rarely been recorded and is more often found when the initially excised tumour contains atypical and/or malignant features. Still, a benign histology does not preclude recurrence even when a total macroscopic excision has been achieved. This again emphasises the unpredictable nature of these tumours and the need for long-term radiological follow-up. Overall, operative mortality should be around 5% and even less for unilateral, hemispheric, circumscribed, nodular cerebellar astrocytomas. Conversely, the operative mortality for tumours of the vermis may approach 30% and generally increase with each subsequent operation, being maximal in the first post-operative month.

Radiotherapy does not reduce the rate of recurrence nor prolong the overall survival period to death in patients with subtotal removal of tumour. There may also be an attendant risk of radio-necrosis and radiation-induced malignancy. Nevertheless, radiotherapy may still have a place in the treatment of these tumours since there is still some evidence to suggest that craniospinal irradiation may reduce the risk of tumour dissemination from malignant cerebellar astrocytomas. Recurrence in cerebellar astrocytomas has been defined in different ways. Thus, some consider it to be the appearance of tumour following cyst aspiration, whilst others regard it to be the reappearance of tumour following either subtotal or total removal. Thirty-five recurrences were noted in the present study after all modes of surgery and the tumours recurred from 2 to 21 years postoperatively. From previous studies, it is clear that most tumours recur within three to five years and that late recurrences may be of two types. The first is an “unpredictable form” which behaves in a manner unrelated either to the extent of surgery or the type of histology. The second arises from a malignant change in an initially benign tumour.

Long-term clinical and radiological follow-up at six month intervals is essential since the CT scan is able to detect tumours before they become symptomatic and because detection will, at the earliest stages, possibly allow the removal of recurrent tumour before brain stem infiltration has occurred. When the first operation is a simple aspiration, decompression, or subtotal removal and recurrence takes place, it may still be possible to remove tumour totally and prolong survival greatly through reoperation.