Thalamic Astrocytomas: Surgical Anatomy and Results of a Pilot Series Using Maximum Microsurgical Removal

Abstract

Deep-seated astrocytomas within the basal ganglia and the thalamus are considered unfavourable for microsurgical removal since the circumferential neighbourhood of critical structures limits radical resection. On closer assessment, the thalamus has a unique configuration within the basal ganglia. Its tetrahedric shape has 3 free surfaces and only the ventrolateral border is in contact with vital and critical functional structures, e.g. the subthalamic nuclei and the internal capsule. The purpose of the present study was to investigate the feasibility of maximum microsurgical removal in a series of intrinsic thalamic astrocytomas. 14 patients with intrathalamic astrocytomas grades I to 4 as diagnosed by previous stereotactic biopsy or intra-operative frozen section were selected for maximum microsurgical removal. The infratentorial supracerebellar approach from the contralateral side was used for 4 limited neoplasms of the pulvinar. For the other 10 larger and more extensive processes a parieto-occipital 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 11 of 14 cases. Regional ancillary radiotherapy with 60 Gy was administered postoperatively for astrocytomas grades 3 and 4. Two patients operated on via the posterior transventricular approach had new postoperative partial hemianopia. Five of the 14 patients finally needed a ventriculo-peritoneal shunt. During the follow-up time of 6 to 52 months, tumor progression/recurrence was observed in 6 of the 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.

Gross Total Removal of Gliomas in the Pulvinar and Correlative Microsurgical Anatomy.

“…Tumors in the pulvinar may be approached 1) from above the tentorium using a parietal-transcorticaltransventricular approach, 38,39,42) 2) through the posterior part of the lateral ventricle using a posterior-interhemispheric-parasplenial-transventricular approach, 46) 3) through the corpus callosum using a posterior-interhemispheric-transcallosal approach, 1,10) 4) along the medial surface of the occipital lobe using a posterior-interhemispherictranstentorial approach, 23,34) or 5) from below the tentorium through the supracerebellar space using an infratentorial-supracerebellar approach. 38) Parietal -transcortical -transventricular approach: The cortical incision is made along the superior parietal lobule.…”

“…38) Parietal -transcortical -transventricular approach: The cortical incision is made along the superior parietal lobule. Once inside the trigone of the lateral ventricle, the choroid plexus and the crus of the fornix overlying the tumor are visualized and may have to be removed and/or incised to gain access to the lesion.…”

“…Radical or maximum removal of thalamic gliomas has been recently reported using an operating microscope with acceptable morbidity via several routes. 1,2,31,35,38,39,43) Circumscribed and histologically benign lesions may be considered favorable for microsurgical removal. Tumors of the pulvinar, in particular, tend to grow exophytically into the lateral and third ventricles, and sometimes extend posteriorly or inferiorly into the quadrigeminal and ambient cisterns (ipsilateral half of the posterior incisural space).…”

“…38) A paramedian approach from the contralateral side was developed to center the pulvinar within the limited field of access between the basal veins of Rosenthal of both sides. However, this route is restricted to partial removal and is not suitable for maximum surgical removal because sacrifice and manipulation of the deep venous system as well as dissection in the quadrigeminal cistern may result in critical neurological deficits.…”

“…4,8,28) These tumors have a bimodal age distribution, with the incidence being highest among children and adolescents, and in adults over 40 years old. 4,8,18,24,25,28,37,38,40) Unfortunately, little is known of the precise nature of these lesions due to a lack of histological verification in many published series. However, stereotactic biopsies of 44 cases showed that the majority of young patients harbored low-grade malignancy glial neoplasms (68.7%), whereas a large number of adult patients presented with high-grade malignancy glial tumors or metastases (78.6%).…”