Oligoastrocytoma

Mischgliome or Oligoastrozytome are diffuse gliomas in middle adulthood, which have units of an oligodendroglioma and astrocytoma. They are grade II and anaplastic WHO Oligoastrozytome classified grade III according to the WHO classification of tumors of the central nervous system in Oligoastrozytome WHO. Oligoastrozytome be attributed to the oligodendroglial tumors.

Causes

The cause of Oligoastrozytomen is unknown. There are Einzellfallberichte oligodendroglial tumors, which occurred after CNS irradiation or brain injury in the context of scars. Even individual oligodendroglial tumors in patients with multiple sclerosis were observed. In singular families oligodendroglial tumors occurred more frequently.

Clinical symptoms

As with all glioma patients suffer from general intracranial pressure such as headache, persistent nausea and vomiting. Many patients are initially conspicuous by an epileptic seizure. In addition, focal symptoms will be added, depending on the location of the tumor in the brain.

Imaging

Preoperative magnetic resonance imaging ( MRI ) with and without contraindications agent administration, meanwhile, is the primary imaging has become. Part of a magnetic resonance imaging is also postoperatively. Contrast enhancement in the tumor is interpreted as a sign of anaplasia. Computed tomography (CT ) is likewise used.

Histology

Histologic characteristics and grading of oligodendroglial component, see → oligodendroglioma and astrocytic component, see → astrocytoma.

Oligoastrozytome are neuropathologically thankless tumors because there is no sharply defined boundaries between the proportion of the oligodendroglial and astrocytic component of the. Although a plurality of borders have been proposed, such a definition is not feasible: a histological section is only a two-dimensional section of a three-dimensional process. The pathologist evaluated this section under the assumption that it is representative of the remaining tissue. But a quantitative assessment fails inevitably with such a concept.

Another aggravating problem of histopathological diagnosis, the reactive astrocytes in a glial tumor. In these cells, there is a reaction of the non-tumorous glia of the CNS to injury by the tumor. Reactive astrocytes are some cases, however, difficult to differentiate from astrocytic tumor cells.

A distinction is made for T. Oligoastrozytomen between biphasic with a unique oligodendroglial and astrocytic component and a diffuse between Oligoastrozytomen. These tumors are found individual astrocytic tumor cells between oligodendroglial tumor cells. It has not been shown previously that these individual astrocytic tumor cells tumor cells and reactive astrocytes are not really (see above). Because there is no sharp demarcation between oligodendrogliomas and Oligoastrozytomen the incidence of Oligoastrozytoms varies considerably, some neuropathologies try the diagnosis largely to avoid, while others make frequent than that of oligodendroglioma.

Another problem is the graduation of Oligoastrozytomen: according to the WHO definition of astrocytic tumors is the detection of more than one mitosis already an important reason to graduate the tumor as anaplastic astrocytoma WHO grade III. In oligodendrogliomas, however, several mitoses are allowed for a WHO grade II. Thus, it may happen that the same tumor is assessed by neuropathology as oligodendroglioma WHO grade II, of the other as anaplastic oligoastrocytoma WHO grade III. However, this requires different therapeutic approaches (see below).

Immunohistochemistry

The most important immunohistochemical markers GFAP - specific antibodies, which astrocytic, but not highlight the oligodendroglial tumor cells. Furthermore, the proliferation rate was to be determined by MIB1 -specific antibodies.

Molecular Pathology

Oligoastrozytome usually have either an oligodendroglial ( LOH 1p/19q ) or astrocytic genotype ( TP53 mutations). These two pathogenetic changes are exclusive. Furthermore, it was shown that both components of the histological Oligoastrozytoms have an identical genotype, ie the Oligoastrocytoma is of monoclonal origin. In the course of the transition to anaplasia among other homozygous deletions on chromosome arm 9p be seen with the tumor suppressor genes CDKN2A and CDKN2B. Also suitable allelic losses on chromosome 10 in front.

Cell of origin

The cell of origin of Oligoastrozytoms is not known. Whether they are tumors that arise from glial, as the name suggests the glial tumors is questionable. Rather, it concerns with glial tumors to malignant transformed glial progenitor cells or even stem cells to degenerate. For this purpose, the current scientific literature provides some indication. An interesting observation is the detection of monoclonality of Oligoastrozytomen. From the observation that both histological components have the same genetic changes, one can conclude that the postulated degenerate progenitor cell has the potential either to adopt an astrocytic or oligodendroglial phenotype. Thus, the hypothesis can be formulated that the glial phenotype is a result of a less pathogenic genotype specific, but rather is determined by unknown geweblichen environmental factors. In the exaggerated form may be considered as a model approach Oligoastrozytome to show that the morphological classification of glial tumors is further away from the actual tumor as the genetic classification.

Therapy

The therapy of Oligoastrozytomen is equal to that of oligodendrogliomas and astrocytomas. The focus is on the surgical resection of the tumor. Because of the infiltrative nature of glioma growth a cure by surgery is hardly possible. However, the tumor volume is reduced by resection, so that inter alia the intracranial pressure problem is mitigated and less cell mass present, which can further dedifferentiate. In WHO grade III anaplastic Oligoastrozytomen also radiotherapy of 50 to 60 Gy is recommended. Alternatively, a BCNU chemotherapy comes into question. Apparently, the Oligoastrozytome with an oligodendroglial genotype ( LOH 1p/19q ) clearly vulnerable with respect to radiation and chemotherapy than those tumors without loss. A determination of 1p and 19q on Allelverlusten should be sought.

Forecast

Because of the diagnostic blurring oligoastrozytären tumors, it is difficult to compare different studies with each other. May be the detection of Allelverlusten on 19q 1p and is important for the prediction as histology. Overall, the prognosis of Oligoastrozytomen is similar to that of oligodendrogliomas and astrocytomas.