Two cases of recurrent pilocytic astrocytoma with leptomeningeal dissemination (LMD) are described. A 6-year-old boy presented with a cerebellar tumor, which was subtotally removed. Tumor recurrence with LMD occurred 4 years later. Reoperation for tumor removal followed by craniospinal irradiation stabilized the LMD over 5 years. A 4-year-old girl presented with a chiasmatic-hypothalamic tumor. Partial removal of the tumor was followed by radiation therapy. Tumor regrowth with LMD occurred 4 years later and was managed by reoperation, chemotherapy and radiotherapy. Tumor recurrence with LMD can be stabilized by multimodal treatment without tumor progression.

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The microvascular growth of ethylnitrosourea-induced rat glioma was observed using vascular casting and scanning electron microscopy (SEM). Light microscopy showed central necrosis and marginal invasive tumor cell growth with increased vascularity, and suggested that adopted pre-existing circulation was dominant in the inoculated brain tumors. In SEM, numerous buds or nodular protrusions and a few large and tortuous vessels along the tumor margin were seen at the early stage. In the intermediate stage, microaneurysms, buds with septum formation and anastomotic arches appeared, and these tumor vessels became more tortuous and larger, and extended as the tumor grew. Several "potato-shaped" huge vessels and linear nodular large vessels also appeared. In the late stage, glomeruli appeared and potato-shaped huge vessels increased in number. The neovascularization and microvascular growth of the tumors was characterized by three patterns: (a) growth of the parent vessels forming buds, (b) vascular growth in a meshwork formation producing glomeruli, and (c) vascular enlargement without a definite pattern creating potato-shaped huge vessels. The tumor vessels gradually lost their natural three-dimensional structure.

The effects of relatively low dose Gamma Knife irradiation on acoustic schwannoma were evaluated in 29 patients followed over 2 years after treatment. The mean dose delivered to the tumor periphery was 12.1 Gy. Lowering of the magnetic resonance signal intensity in the tumor center appeared in 69% and signs of tumor shrinkage appeared in 59% of cases. The cyst in the tumor enlarged in 3 cases, and 2 cases developed hydrocephalus. The percentage of pure-tone hearing preservation was 82% at 3 months, 73% at 6 months, 68% at 12 months, 64% at 18 months and 59% at 24 months in 22 out of 29 cases. Relatively low dose Gamma Knife radiosurgery was effective in suppressing tumor growth, with preservation of hearing.

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