Thalamic astrocytomas: Surgical anatomy and results of a pilot series using maximum microsurgical removal

Deep-seated astrocytomas within the basal ganglia and the thalamus are cons idered unfavourable For microsurgical removal since the circumferential nei ghbourhood of critical structures limits radical resection. On closer asses sment, the thalamus has a unique configuration within the basal ganglia, It s tetrahedric shape has 3 free surfaces and only the ventrolateral border i s in contact with vital and critical functional structures, e.g. the subtha lamic nuclei and the internal capsule. The purpose of the present study was to investigate the feasibility of maximum microsurgical removal in a serie s of intrinsic thalamic astrocytomas. 14 patients with intrathalamic astrocytomas grades I to 4 as diagnosed by p revious stereotactic biopsy or intra-operative frozen section were selected for maximum microsurgical removal. The infratentorial supracerebellar appr oach from the contralateral side was used for 4 limited neoplasms of the pu lvinar. For the other 10 larger and more extensive processes a parieto-occi pital transventricular approach was chosen. Final histology gave the result of astrocytoma grade 1 or 2 in 4 patients, and of astrocytoma grade 3 or 4 in 10 patients. Postoperative MRI confirmed reduction of the tumor mass by 80 to 100% in 1 1 of 14 cases. Regional anc illary radiotherapy with 60 Gy was administered postoperatively for astrocy tomas grades 3 and 4. Two patients operated on via the posterior transventr icular approach had new postoperative partial hemianopia. Five of the 14 pa tients finally needed a ventriculo-peritoneal shunt. During the follow-up t ime of 6 to 52 months, tumor progression/recurrence was observed in 6 of th e 10 high grade and none of the low grade neoplasms. The present pilot series demonstrates the feasibility of the microsurgical concept. Comparison with other treatment modalities, such as brachytherapy, requires future consideration.