Other Gliomas



Other Gliomas





Astroblastoma


Clinical Context

The sum of knowledge of this rare glial neoplasm encompasses fewer than 300 cases, many of those known only through large tumor registry databases such as surveillance, epidemiology, end results (SEER) taken over the course of more than 35 years (1). A literature review in 2011 revealed only 116 cases, the many of which were individual case reports (2). In one large review, most of the patients were younger than 18 years, and the distribution was bimodal with a second peak in the third decade and a female predominance of around 2.5:1 (2). The population characteristics of other cases reported in the literature, however, differ from those in the large SEER database, which show a broad age distribution and an even sex distribution (1). These differences could possibly reflect changes in diagnostic practices during the long period covered by SEER and the absence of peer review for SEER diagnoses. In contrast, most other reported astroblastomas are from 1989 or later, when more restrictive histopathologic criteria were suggested (3). No familial predisposition or other disease associations have been described.

Magnetic resonance imaging (MRI) and computed tomography (CT) studies most often reveal a circumscribed supratentorial mass that is calcified, well circumscribed, and heterogeneously enhancing (4,5). The vast majority of cases have been in the cerebral hemispheres, with rare examples arising elsewhere (2). An identifying feature of astroblastoma on postcontrast, T1-weighted images is a “bubbly” appearance created by multiple intratumoral cysts (4). The extent of surrounding edema is highly variable.

Although two general categories of histologic aggressiveness are recognized, well-differentiated and malignant, definitive WHO grading remains to be established. Treatment for these lesions usually consists of surgical excision that is followed by radiation therapy in malignant cases. In the former, recurrence-free survival in reported cases with gross total resection has been favorable, around 85% at 5 years (2). One recent series showed statistically significant decreases in survival associated with mitotic index of ≥5/10 hpf, but not with overall grade (high vs. low), patient age, or sex (6).



Histopathology






FIGURE 6-1 Astroblastomas invariably contain pseudorosettes of glial cells with broad columnar foot processes planted on vascular cores.

Although several series describe its characteristics, the exact criteria defining this entity are not universally agreed upon. The unifying histologic feature of astroblastoma is perivascular pseudorosettes similar to those of ependymoma, but with broad column-like foot processes that extend from the vessel surface (Figure 6-1). The perivascular cells in astroblastoma are relatively distinct with well-defined cell borders, whereas the fibrillar processes in ependymoma blend together and obscure the borders of perivascular tumor cells. The stout bands of cytoplasm terminate in an uneven layer of nuclei that have little or no cytoplasm on their outer aspect.

The other cardinal features of astroblastoma are circumscription and vascular hyalinization. The vast majority of astroblastomas show thickening and sclerosis of blood vessels, with a minority also containing regional hyalinization. They are, as a rule, circumscribed histologically, with pushing borders and little intermingling with surrounding brain parenchyma. Although focal infiltration can be seen, the significance of this is unknown.

The remaining features of astroblastoma are variable. The cells are usually elongated with small, oval to round nuclei but can be polygonal with other nuclear patterns. Focal rhabdoid change with peripheral cytoplasmic clearing is common (Figure 6-2). Necrosis is seen more often in cases with multiple malignant features but can be present in otherwise low-grade examples (5). Pseudopalisading of tumor cells around necrosis can be seen and is similar to that seen in glioblastoma.

Histologically malignant features in astroblastoma include elevated mitotic rates (>5/10 hpf), vascular proliferation, nuclear atypia, loss of
architecture, and palisading necrosis; however, the boundary between malignant and low-grade astroblastoma is not a universally accepted one.






FIGURE 6-2 Solid sheets of cells between pseudorosettes and rhabdoid change are common in astroblastoma.


Immunohistochemistry and Genetics

Immunoreactivity for vimentin, S100, and GFAP, all in a cytoplasmic pattern, is typical of astroblastoma, albeit focal in some cases. Cytoplasmic EMA reactivity is present in some cases, and it is usually focal and lacks the ring-like positivity seen in ependymomas. The glial marker Olig2 is expressed in the vast majority of astroblastomas, and expression of ATRX and SMARCB1/INI1 are retained (6).

Comparative genomic hybridization in a set of seven astroblastomas showed an absence of chromosomal abnormalities that are common in astrocytomas and ependymomas and no consistent specific copy number changes (5). BRAF V600E mutations were detected in DNA from 38% of another set of astroblastomas, opening the possibility for targeted therapy in some cases, should they recur (6).


Differential Diagnosis

Ependymomas are histologically similar to astroblastomas; however, most astroblastomas occur in adulthood and are almost exclusively found in the cerebral hemispheres. Nevertheless, ependymomas can occur in the cerebral hemispheres of adults perhaps as frequently as the rare astroblastoma. The hallmark of astroblastoma that is not seen in ependymoma is the broad, column-like cytoplasm in perivascular tumor cells. Perivascular hyaline is also more suggestive of astroblastoma.


Papillary glioneuronal tumor has some histologic overlap with astroblastoma at low magnification but lacks broad cytoplasmic processes and has a biphasic pattern of GFAP and synaptophysin staining.


Chordoid Glioma (WHO Grade II)


Clinical Context

This rare entity was first described by Brat et al. in 1998 and added to the WHO classification in 2000. Only a few dozen cases have been described, and understanding of its biology is still evolving as cases accumulate. Most cases arise in adults at a mean age of around 46 years, but the range is broad and extends from 5 to 71 years (7,8). Almost twice as many females have been reported with chordoid glioma than males (7). No associations with other diseases have been observed. Suggested to derive from the organum vasculosum of the lamina terminalis (OVLT) (9,10), the vast majority of chordoid gliomas originate in the anterior third ventricle, with the exception of a single substantiated case from near the occipital horn of the lateral ventricle (11). Presenting symptoms and signs are variable, but similar to other third-ventricular/hypothalamic tumors, with headache, visual problems, and hydrocephalus being common (8,12,13).

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Oct 22, 2018 | Posted by in NEUROLOGY | Comments Off on Other Gliomas

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