Inflammatory changes have been postulated to contribute to secondary brain injury after aneurysmal subarachnoid hemorrhage (SAH). In human specimens after SAH as well as in experimental SAH using mice, we show an intracerebral accumulation of inflammatory cells between days 4 and 28 after the bleeding. Using bone marrow chimeric mice allowing tracing of all peripherally derived immune cells, we confirm a truly CNS-intrinsic, microglial origin of these immune cells, exhibiting an inflammatory state, and rule out invasion of myeloid cells from the periphery into the brain. Furthermore, we detect secondary neuro-axonal injury throughout the time course of SAH. Since neuronal cell death and microglia accumulation follow a similar time course, we addressed whether the occurrence of activated microglia and neuro-axonal injury upon SAH are causally linked by depleting microglia in vivo. Given that the amount of neuronal cell death was significantly reduced after microglia depletion, we conclude that microglia accumulation inflicts secondary brain injury after SAH.

Glioblastoma multiforme WHO grade IV is the most common and malignant variant of astrocytic tumors. Loss of heterozygosity of chromosome 10 and mutations in the tumor suppressor gene PTEN on 10q are molecular hallmarks of glioblastomas. Recently, mutations were identified in PIK3CA, encoding a protein that antagonizes the function of PTEN protein in the PI3K/Akt pathway. To address the question whether an exclusive mutation pattern can be observed in PIK3CA and PTEN, we determined the frequency of mutations in both genes. All coding exons were examined by single strand confirmation polymorphism and direct sequencing. Additionally, we analyzed chromosome 10 for loss of heterozygosity and evaluated the mutational status of TP53. In 70 glioblastomas, 5 (7%) PIK3CA mutations and 10 (14%) PTEN mutations were found. All mutations in PIK3CA located to exons 1, 9 and 20, thereby supporting the concept of mutational hot spot regions. In all but one glioblastoma, mutations were seen either in PIK3CA or in PTEN. In conclusion, the frequency of PIK3CA mutations in glioblastomas appears to be much lower than initially reported.

The WHO classification defines different histological variants of meningiomas. Mutations of the tumor suppressor gene NF2 on 22q have been described in 30% to 60 % of sporadic meningiomas. However, the vast majority of the meningiomas that have been subject to NF2 analysis belong to the most frequent variants like transitional, fibroblastic and meningothelial meningiomas. Within these subtypes, transitional and fibroblastic meningiomas harbor significantly more NF2 mutations than meningothelial meningiomas, indicating molecular subsets of these tumors. To determine whether rare meningioma variants carry NF2 mutations we analyzed 80 tumors. NF2 mutations were detected in 5 (36%) of 14 psammomatous, 1 (11%) of 9 angiomatous, 2 (22%) of 9 clear cell, 1 (33%) of 3 chordoid and 1 (100%) of 1 papillary meningioma. In the single papillary meningioma, 2 different NF2 mutations were observed. No NF2 mutations were found in 33 secretory, 7 microcystic, 2 lymphoplasmacyte-rich, one rhabdoid and one metaplastic meningioma. In the control group of 25 fibroblastic meningiomas, 11 cases were identified to carry an NF2 mutation. These results support the concept of different molecular subgroups of meningiomas which overlap with histological variants.

Cerebellar liponeurocytoma, first recognized as a distinct entity in the revised WHO classification of Tumors of the Central Nervous System in 2000, is a rare tumor with characteristic histological features and predominant location in the cerebellum. The proliferative index is usually low, and previous reports supported a favorable prognosis. We report a case of a second recurrence of a cerebellar liponeurocytoma with increased proliferative and mitotic activity in which extensive immunohistochemical characterization and genetic profiling were performed. The tumor specimen was characterized in terms of genetic changes frequently associated with gliomas and medulloblastomas. Considering the low number of reported cases, the prognosis of cerebellar liponeurocytoma seems difficult to assess. Our case suggests the existence of different histological grades of cerebellar liponeurocytoma and its possible progression towards a dedifferentiated, malignant phenotype, which has not yet been adequately taken into consideration in the current WHO classification.

Giant Cell Glioblastoma (gcGBM) and Pleomorphic Xanthoastrocytoma (PXA) are rare astroglial tumors of the central nervous system. Although they share certain histomorphological and immunohistochemical features, they are characterized by different clinical behavior and prognosis. Nevertheless, few cases remain uncertain, as their histomorphological hallmarks and immunophenotypes do correspond to the typical pattern neither of gcGBM nor PXA. Therefore, in addition to the routinely used diagnostic histochemical and immunohistochemical markers like Gömöri, p53 and CD34, we analyzed if genetic variations like MGMT promoter methylation, mutations in the IDH1/2 genes, or BRAF mutations, which are actually used as diagnostic, prognostic and predictive molecular markers in anaplastic glial tumors, could be helpful in the differential diagnostic of both tumor entities. We analyzed 34 gcGBM and 20 PXA for genetic variations in the above-named genes and found distinct distributions between both groups. MGMT promoter hypermethylation was observed in 3 out of 20 PXA compared to 14 out of 34 gcGBM (15% vs. 41.2%, p-value 0.09). BRAF V600E mutations were detected in 50% of the PXA but not in any of the gcGBM (50% vs. 0%, p-value < 0.001). IDH1 R132 and IDH R172 mutations were not present in any of the PXA and gcGBM cases. Our data indicate, that in addition to the histological and immunohistochemical evaluation, investigation of MGMT promoter methylation and in particular BRAF V600E mutations represent reliable additional tools to sustain differentiation of gcGBM from PXA on a molecular basis. Based on these data specific BRAF kinase inhibitors could represent a promising agent in the therapy of PXA and their use should be emphasized.