[Experimental study on destruction of the third ventricle floor in the midline:--examination for the trans-third ventricle approach].

Surgery of a basilar bifurcation aneurysm is a very difficult operation in neurosurgery. For the treatment of this lesion, two methods are widely used at present: one is the subtemporal approach developed by Drake and the other is the pterional approach by Yasargil. With either approach, however, the treatment of a basilar bifurcation aneurysm accompanied by megadolichobasilar anomaly is difficult and hazardous due to the necessity for excessive retraction of the brain, nerves and vessels. Recently we successfully treated two cases of ruptured basilar bifurcation aneurysm complicated with megadolichobasilar anomaly by the trans-third ventricle approach. The floor of the third ventricle was already partly destroyed by aneurysmal rupture in both cases. It was required to make a small split in the third ventricle floor in order to get a wider operative field. Postoperatively, however, no influence from the splitting of the floor was seen. An experimental study was carried out in dogs to determine the influence from the destruction of the floor of the third ventricle. Using microsurgical techniques, the third ventricle floor was opened along the midline. Dogs were sacrificed 30 days after surgery. The following items were evaluated before, during, and after surgery: clinical symptom, blood pressure, pulse, body temperature, serum electrolytes, serum osmotic pressure, pituitary hormones (anterior lobe), cortisol, ADH (2.5mol NaCl loading test), electroencephalogram, cerebral blood flow and pathological change. No significant abnormalities could be detected in endocrine and metabolic functions, and no histological changes were seen around the hypothalamus. In conclusion, it is justified to split the third ventricle floor along the midline if it is indicated.