**2.1. Diffuse astrocytoma IDH-mutant (DA IDH-mut)**

**Definition**. Tumoral proliferation which, from a histopathological point of view, shows an astrocytic phenotype with a diffuse growth pattern and IDH1 or IDH2 gene mutations.

As to *grading*, diffuse astrocytoma is deemed to be *grade II* (low-grade diffuse astrocytoma).

*Clinically*, the emergence of symptoms is usually insidious, as they precede the diagnosis by weeks months or sometimes years. Seizures are the symptom most likely to raise suspicions. There are studies underling the presence of the seizures at the debut in up to 80% of cases, approximately 50% presenting with uncontrollable seizures at the time of surgery. Factors predisposing to a poorer response to antiepileptic drugs are: partial seizure type, temporal location, and a longer seizure duration [18]. The most frequent location of those tumors is in the frontal lobe, followed by temporal and parietal lobe. Other associated symptoms could appear related to the location. Behavioral and personality changes, visual disturbances, aphasia, or agnosia are most frequently mentioned, meanwhile the increased intracranial pressure symptoms install later in the course of disease, related to the tumoral volumes and mass effect.

**Imaging**. *MRI* is the "golden standard" imagistic tool. For DA IDH-mut, the typical aspect is a homogeneous tumor with low signal intensity on T1-weighted images and a high intensity on T2-weighted sequences. This high T2 signal is rather related to edema, demyelination, or degenerative changes than to cellular atypia. Fluid-attenuated inversion recovery (FLAIR) sequences are the most appropriate for defining the infiltrating tumor margins. Usually, astrocytomas are confined in the white matter, meanwhile the oligodendrogliomas are cortical-based tumor, but this difference is attenuated in the later stages (**Figure 2**). Cystic components are not infrequent and low contrast enhancement could be observed in 20% of cases without malignant transformation [19].

**Figure 2.** Axial T2W (a), FLAIR (b), and T1W + C (c) MRI examination of a patient with right insular DA IDH-mut (personal archive).

*Advanced MRI techniques* such as diffusion-weighted imaging (DWI) and MRI spectroscopy will complete the anatomical information, while the functional MRI and diffusion tensor imaging (DTI) will offer important data for surgical planning. On *DWI*, DA IDH-mut presents a decrease cellularity and non-restricted diffusion. *MRI Spectroscopy* will reveal not only decreased N-acetylaspartate (NAA) peak, medium choline peaks, absence of lactate peak, and increased myo-inositol [20], but is also able to detect IDH mutation trough oncometabolite 2-hydroxyglutarate (2HG) present in tumor cells [21]. MRI could also serve as a *prognosis tool* if is combined with IDH status. Just recently it was suggested that minimum apparent diffusion coefficient (ADCMIN) threshold of 0.9 × 10−3 mm2 /s or less is associated with a worst prognosis especially when it is combined with IDH wild-type grade II diffuse astrocytomas [22]. *DTI with tractography* usually reveals a displacement rather than an infiltration or destruction of fiber tracts in DA IDH-mut tumors.

*Gliomatosis cerebri* no longer exists as an entity, being considered rather a specific growth pattern. More research is needed in order to identify the biological substrate of this unusual

**Definition**. Tumoral proliferation which, from a histopathological point of view, shows an astrocytic phenotype with a diffuse growth pattern and IDH1 or IDH2 gene mutations.

As to *grading*, diffuse astrocytoma is deemed to be *grade II* (low-grade diffuse astrocytoma).

*Clinically*, the emergence of symptoms is usually insidious, as they precede the diagnosis by weeks months or sometimes years. Seizures are the symptom most likely to raise suspicions. There are studies underling the presence of the seizures at the debut in up to 80% of cases, approximately 50% presenting with uncontrollable seizures at the time of surgery. Factors predisposing to a poorer response to antiepileptic drugs are: partial seizure type, temporal location, and a longer seizure duration [18]. The most frequent location of those tumors is in the frontal lobe, followed by temporal and parietal lobe. Other associated symptoms could appear related to the location. Behavioral and personality changes, visual disturbances, aphasia, or agnosia are most frequently mentioned, meanwhile the increased intracranial pressure symptoms install later in the course of disease, related to the tumoral volumes and mass effect. **Imaging**. *MRI* is the "golden standard" imagistic tool. For DA IDH-mut, the typical aspect is a homogeneous tumor with low signal intensity on T1-weighted images and a high intensity on T2-weighted sequences. This high T2 signal is rather related to edema, demyelination, or degenerative changes than to cellular atypia. Fluid-attenuated inversion recovery (FLAIR) sequences are the most appropriate for defining the infiltrating tumor margins. Usually, astrocytomas are confined in the white matter, meanwhile the oligodendrogliomas are cortical-based tumor, but this difference is attenuated in the later stages (**Figure 2**). Cystic components are not infrequent and low contrast enhancement could be observed in 20% of cases without malignant transformation [19].

**Figure 2.** Axial T2W (a), FLAIR (b), and T1W + C (c) MRI examination of a patient with right insular DA IDH-mut

invasive capacity [17].

(personal archive).

**2. Low-grade gliomas**

**2.1. Diffuse astrocytoma IDH-mutant (DA IDH-mut)**

98 Glioma - Contemporary Diagnostic and Therapeutic Approaches

*CT scan* reveals a homogeneous lesion, poorly defined, with no contrast enhancement. This can be associated with cystic changes and calcifications that are more specific for oligodendrogliomas.

**Macroscopy**. In section, the tumor does not display clearly delineated limits, on account of its infiltrative growth pattern. We can see areas of soft consistency or firmer ones, granular areas, and cystic ones. Cystic changes can include sponge-like areas, consisting of cysts of various sizes that may have a gelatinous aspect. There can be only one large cysts, filled with liquid, and this is associated with the identification of gemistocytes during microscopy. The calcifications can be focal or diffuse, and in this case, the appearance is one of grittiness.

**Histological diagnosis**. Under the microscope, we see a diffuse tumoral proliferation consisting of atypical fibrillary astrocytes. Hypercellularity is moderately increased, the tumor imperceptibly blending with the surrounding normal structures. Cellular proliferation (star-shaped cells, with extensions) is situated on a fibrillary loose matrix which often forms microcystic structures. The main characteristic is the nuclear atypia, neoplastic astrocytes being based on the aspect of the nucleus. This is enlarged, hyperchromatic, and irregular in shape [23].

The *differential diagnosis* is performed with the help of reactive astrocytosis. The diagnosis can be done only on the basis of morphological criteria, but more often than not, this requires an extremely nuanced approach. The morphological criteria include a numerical increase, but especially the homogeneous aspect of the nuclei, as we are dealing with a clonal neoplastic proliferation. As opposed to neoplastic astrocytes, the reactive ones have a heterogeneous nuclear aspect, with nuclei of various sizes and with cytoplasm in variable quantities. The background of these nuclei is of normal or increased density in the case of tumoral proliferation, and of decreased density in the case of reactive astrocytosis. Immunohistochemistry is extremely useful in distinguishing between reactive and tumoral astrocytes. As the IDH1 mutation falls under the definition of this type of tumor, the antibody identifying the protein altered by the presence of the R132H mutation can be used. Also, the tumoral cells displaying the TP53 mutation can be identified through a recourse to the antibody [24].

Mitotic activity is low to absent, the presence of a mitosis in a large biopsy being compatible with the diagnosis. If a mitosis is present in the context of an important nuclear anaplasia within a small biopsy, then the diagnosis of anaplastic astrocytoma cannot be ruled out. The proliferation index determined by way of Ki-67 is under 4%. If there is a gemistocytic component, the proliferation rate is significantly reduced [25].

As we are dealing with low proliferation rate tumor, the changes induced by hypoxia, such as microvascular proliferation and necrosis, are absent.

Secondary structures (Sherer) such as perineuronal satellitosis, subpial infiltration, and perivascular aggregation can also be present.

Other entities that need to be factored in for the differential diagnosis are: the normal brain, the demyelinating disease, anaplastic astrocytoma, oligodendroglioma, and pilocytic astrocytoma. In what concerns the diffuse pattern, the differential diagnosis must be done with lymphomas and small-cell carcinomas [26].

Gemistocytic astrocytoma is a variant of the grade II diffuse astrocytoma, characterized by the presence of more than 20% angular neoplastic astrocytes, with abundant eosinophilic cytoplasm. The nucleus is pushed toward the periphery, showing nucleoli and a dense chromatin. Electronic microscopy reveals the presence of numerous mitochondria and glial filaments, as also confirmed by the positive GFAP. A characteristic feature is the presence of the perivascular cuffing lymphocyte [27].

The classical morphopathological aspect is astrocytic, but an "oligodendroglioma-like" component can be accepted in the absence of 1p/19q codeletion.

Immunohistochemically, the battery of antibodies that can be used includes: GFAP, vimentin, IDH R132H, p53, ATRX, Olig2, and Ki67. GFAP and vimentin are positive, but of variable expression. The existence of an antibody that makes it possible to indirectly identify the R132H mutation, present in approximately 90% of tumors, is one way of identifying the tumor cells featuring this mutation. Another important antibody is ATRX, and the presence of the mutation leads to the loss of nuclear expression in the tumor cells. P53 can be used, as an intense nuclear expression is consistent with the presence of the TP53 mutation. Olig2 is nearly always present. As already indicated, Ki-67 can be used in assessing the proliferation index [28–31].

> in the pathogenesis of diffuse gliomas [41]. Furthermore, ATRX deficiency can create a context of generalized genetic instability which, when P53 is intact, can induce apoptosis. The occurrence of a P53 mutation alongside the ATRX one can allow tumor cells to survive [42]. This instability is reflected in the occurrence of low-level amplifications for other oncogenes, such as MYC and CCND2 [43]. The TP53 mutation is also present in nearly all IDH-mutant gemistocytic astrocytomas, in both gemistocytes and non-gemistocytes, indicating that gemistocytes are oncogenically non-reactive cells [44]. Quite interestingly, the presence of the ATRX mutation is mutually exclusive with the mutation of the gene that encodes the catalytic component of TERT telomerase. The mutations of the TERT gene are characteristic for oligo-

Diffuse Astrocytoma and Oligodendroglioma: An Integrated Diagnosis and Management

http://dx.doi.org/10.5772/intechopen.76205

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**Figure 3.** Integrated histological and molecular diagnosis of diffuse astrocytoma IDH-mutant grade II.

The methylation of the MGMT gene promoter is present in more than 50% of IDH-mutant astrocytomas, but the presence of this methylation is not correlated with the status of G-CIMP

The genetic profile of diffuse astrocytomas is different in children and in adults; so, we can talk of adult-type and pediatric-type diffuse astrocytomas. The genetic profile of pediatric tumors involves amplifications and rearrangements of the MYB gene, alterations of FGFR1,

dendrogliomas and wild-type glioblastomas [45].

and mutations of BRAF (V600) and KRAS [47].

[46]. By definition, 1p/19q codeletion is absent (**Figure 3**).

**Genetic diagnosis**. Integrated genomic analysis has made it possible to identify the IDH gene mutation in glioblastomas, leading to the "IDH era" in diffuse gliomas [32]. The sequencing of a large number of brain tumors has revealed the high incidence of the IDH gene mutation in lowgrade astrocytomas and oligodendrogliomas, suggesting that it might play a role in the early onset of such tumors [33]. The presence of this mutation is relevant for both diagnosis and prognosis, its absence meaning a less favorable prognosis [34]. A study conducted on a large cohort has indicated a survival rate of 10.9 years for the diffuse astrocytomas with the IDH mutation [35]. The consequence-inducing mechanism involves the excessive production and the accumulation of an oncometabolite—2 hydroxyglutarate [36]. This mutation leads to significant epigenetic changes and to changes in the regulation of the expression of differentiating factors [37]. More particularly, we witness a hypermethylation of the genome, generating tumors with the CpG island methylator phenotype (CIMP) [38]. This group of tumors shows a distinct biological behavior, with epigenetic changes in the whole genome, by remodeling the methylome and reorganizing the transcriptome. This leads to the activation of key genetic programs and to the emergence of a cellular phenotype allowing for better survival rates. Also, the IDH allows for chromosomal aberrant interactions, with the activation of the oncogene expression [39].

ATRX encodes a chromatin-binding protein. The mutations of this gene are associated with epigenetic changes [40]. It also activates the alternative telomere lengthening mechanism, necessary

As we are dealing with low proliferation rate tumor, the changes induced by hypoxia, such as

Secondary structures (Sherer) such as perineuronal satellitosis, subpial infiltration, and peri-

Other entities that need to be factored in for the differential diagnosis are: the normal brain, the demyelinating disease, anaplastic astrocytoma, oligodendroglioma, and pilocytic astrocytoma. In what concerns the diffuse pattern, the differential diagnosis must be done with

Gemistocytic astrocytoma is a variant of the grade II diffuse astrocytoma, characterized by the presence of more than 20% angular neoplastic astrocytes, with abundant eosinophilic cytoplasm. The nucleus is pushed toward the periphery, showing nucleoli and a dense chromatin. Electronic microscopy reveals the presence of numerous mitochondria and glial filaments, as also confirmed by the positive GFAP. A characteristic feature is the presence of the perivascu-

The classical morphopathological aspect is astrocytic, but an "oligodendroglioma-like" com-

Immunohistochemically, the battery of antibodies that can be used includes: GFAP, vimentin, IDH R132H, p53, ATRX, Olig2, and Ki67. GFAP and vimentin are positive, but of variable expression. The existence of an antibody that makes it possible to indirectly identify the R132H mutation, present in approximately 90% of tumors, is one way of identifying the tumor cells featuring this mutation. Another important antibody is ATRX, and the presence of the mutation leads to the loss of nuclear expression in the tumor cells. P53 can be used, as an intense nuclear expression is consistent with the presence of the TP53 mutation. Olig2 is nearly always present.

**Genetic diagnosis**. Integrated genomic analysis has made it possible to identify the IDH gene mutation in glioblastomas, leading to the "IDH era" in diffuse gliomas [32]. The sequencing of a large number of brain tumors has revealed the high incidence of the IDH gene mutation in lowgrade astrocytomas and oligodendrogliomas, suggesting that it might play a role in the early onset of such tumors [33]. The presence of this mutation is relevant for both diagnosis and prognosis, its absence meaning a less favorable prognosis [34]. A study conducted on a large cohort has indicated a survival rate of 10.9 years for the diffuse astrocytomas with the IDH mutation [35]. The consequence-inducing mechanism involves the excessive production and the accumulation of an oncometabolite—2 hydroxyglutarate [36]. This mutation leads to significant epigenetic changes and to changes in the regulation of the expression of differentiating factors [37]. More particularly, we witness a hypermethylation of the genome, generating tumors with the CpG island methylator phenotype (CIMP) [38]. This group of tumors shows a distinct biological behavior, with epigenetic changes in the whole genome, by remodeling the methylome and reorganizing the transcriptome. This leads to the activation of key genetic programs and to the emergence of a cellular phenotype allowing for better survival rates. Also, the IDH allows for

As already indicated, Ki-67 can be used in assessing the proliferation index [28–31].

chromosomal aberrant interactions, with the activation of the oncogene expression [39].

ATRX encodes a chromatin-binding protein. The mutations of this gene are associated with epigenetic changes [40]. It also activates the alternative telomere lengthening mechanism, necessary

microvascular proliferation and necrosis, are absent.

100 Glioma - Contemporary Diagnostic and Therapeutic Approaches

ponent can be accepted in the absence of 1p/19q codeletion.

vascular aggregation can also be present.

lymphomas and small-cell carcinomas [26].

lar cuffing lymphocyte [27].

**Figure 3.** Integrated histological and molecular diagnosis of diffuse astrocytoma IDH-mutant grade II.

in the pathogenesis of diffuse gliomas [41]. Furthermore, ATRX deficiency can create a context of generalized genetic instability which, when P53 is intact, can induce apoptosis. The occurrence of a P53 mutation alongside the ATRX one can allow tumor cells to survive [42]. This instability is reflected in the occurrence of low-level amplifications for other oncogenes, such as MYC and CCND2 [43]. The TP53 mutation is also present in nearly all IDH-mutant gemistocytic astrocytomas, in both gemistocytes and non-gemistocytes, indicating that gemistocytes are oncogenically non-reactive cells [44]. Quite interestingly, the presence of the ATRX mutation is mutually exclusive with the mutation of the gene that encodes the catalytic component of TERT telomerase. The mutations of the TERT gene are characteristic for oligodendrogliomas and wild-type glioblastomas [45].

The methylation of the MGMT gene promoter is present in more than 50% of IDH-mutant astrocytomas, but the presence of this methylation is not correlated with the status of G-CIMP [46]. By definition, 1p/19q codeletion is absent (**Figure 3**).

The genetic profile of diffuse astrocytomas is different in children and in adults; so, we can talk of adult-type and pediatric-type diffuse astrocytomas. The genetic profile of pediatric tumors involves amplifications and rearrangements of the MYB gene, alterations of FGFR1, and mutations of BRAF (V600) and KRAS [47].

There are two entities that increase the susceptibility to diffuse astrocytomas. Low-grade astrocytomas are usually diagnosed in patients with Ollier-type multiple enchondromatosis [48]. Also, those having the Li-Fraumeni syndrome are more likely to develop diffuse gliomas, but these are high-grade anaplastic astrocytomas and high-grade glioblastomas [49].
