Gemistocytic astrocytoma

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Sujit Routray, M.D. [2]

Synonyms and keywords: Gemistocytic astrocytomas; Diffuse astrocytoma; Low grade astrocytoma

Overview

Gemistocytic astrocytoma is a histologic subtype of low grade astrocytoma, with a poorer prognosis than other matched WHO grade II astrocytic tumors, and with no specific imaging features.

Pathophysiology

Pathogenesis

• Gemistocytic astrocytoma is characterized by a significant gemistocyte population, which are large cells with their cytoplasm filled with eosinophilic material displacing the nucleus eccentrically.
• It is important to note that other gliomas (e.g. fibrillary astrocytoma and oligodendroglioma) can have occasional gemistocytes, without being designated a gemistocytic astrocytoma. A cut off of 20% of the tumor cells being gemistocytes may be used before designating it as a gemistocytic astrocytoma.

Gross Pathology

• Gemistocytic astrocytoma is almost always supratentorial and usually located in the frontal lobes.

Microscopic Pathology

• On microscopic histopathological analysis, gemistocytic astrocytoma is characterized by:

• Neoplastic fibrillary astrocytes embedded in the tumor matrix
• Gemistocytes > 20% of the tumor cells
• Low cellular density
• Mild nuclear atypia (enlarged, irregular contour, hyperchromasia, and coarsened nuclear chromatin pattern)
• Mucinous fluid containing microcystic spaces
• No mitoses, microvascular proliferation, and necrosis

Differentiating Fibrillary Astrocytoma from other Diseases

• Gemistocytic astrocytoma must be differentiated from:

• Fibrillary astrocytoma
• Protoplasmic astrocytoma
• Oligoastrocytoma
• Stroke
• Cerebritis
• Encephalitis (herpes simplex encephalitis)
• Anaplastic astrocytoma
• Oligodendroglioma
• Angiocentric glioma

Epidemiology and Demographics

Age

• Gemistocytic astrocytoma is a rare disease that tends to affect the children and young adult population.
• The peak age at which gemistocytic astrocytoma is diagnosed ranges between 20-40 years.
• The mean age at diagnosis is 35 years.

Gender

• Males are more commonly affected with gemistocytic astrocytoma than females. The male to female ratio is approximately 1.5 to 1.

Natural History, Complications and Prognosis

Natural History

• If left untreated, patients with gemistocytic astrocytoma may progress to develop seizures, focal neurological deficits, hydrocephalus, or malignant transformation to anaplastic astrocytoma or glioblastoma multiforme.

Complications

• Common complications of gemistocytic astrocytoma include:

• Hydrocephalus
• Malignant transformation to anaplastic astrocytoma or glioblastoma multiforme.

Prognosis

• Gemistocytic astrocytoma has a poorer prognosis than the other matched WHO grade II (low-grade) astrocytic tumors ([[fibrillary astrocytoma, protoplasmic astrocytoma, and oligoastrocytoma).
• The 5-year survival rate of patients with gemistocytic astrocytoma is approximately 30%.
• The median survival time with treatment is only 2.5 years.

History and Symptoms

History

• When evaluating a patient for gemistocytic astrocytoma, you should take a detailed history of the presenting symptom (onset, duration, and progression), other associated symptoms, and a thorough family and past medical history review.

Symptoms

• Symptoms of gemistocytic astrocytoma include:

• Headaches
• Seizures
• Changes in mood
• Hemiparesis
• Changes in personality
• Changes in vision
• Speech difficulties

CT

• Head CT scan is helpful in the diagnosis of gemistocytic astrocytoma. On CT scan, gemistocytic astrocytoma is characterized by:

• Isodense or hypodense mass
• Positive mass effect
• Wispy enhancement ( most low-grade astrocytomas are without any enhancement. In fact, presence of enhancement would suggest more aggressive tumors)
• Calcification in 10-20% (more common in mixed tumors relating to an oligodendroglial components, i.e. oligoastrocytoma)
• Cystic or fluid attenuation components

MRI

• Brain MRI is helpful in the diagnosis of gemistocytic astrocytoma. On MRI, gemistocytic astrocytoma is characterized by:

MRI component	Findings
T1	Isointense to hypointense compared to white matter Usually confined to the white matter and causes expansion of the adjacent cortex
T2	Hyperintense compared to white matter Always follow the white matter distribution and cause expansion of the surrounding cortex Cortex can also, be involved in late cases in comparison to the oligodendroglioma, which is a cortical based tumor from the start "Microcystic changes" along the lines of spread of the infiltrative astrocytoma is a very unique behavior for the infiltrative astrocytoma, however, it is only appreciated in a few number of cases Hyperintense T2 signal is not related to cellularity or cellular atypia, but rather edema, demyelination, and other degenerative changes
T1 with contrast	No enhancement Small ill-defined areas of enhancement are not rare; however, when enhancement is seen, it should be considered as a warning sign for progression to a higher grade
Diffusion weighted imaging (DWI)	No restricted diffusion Increased diffusibility is the key to differentiate the gemistocytic astrocytoma from the acute ischemia

Other Imaging Findings

Magnetic Resonance Spectroscopy

• MR spectroscopy may be helpful in the diagnosis of gemistocytic astrocytoma.
• Findings on MR spectroscopy include:

• Elevated choline peak, low N-Acetylaspartate peak, elevated choline:creatine ratio
• Elevated myo-inositol (mI) and mI/creatine ratio
• Lack of the lactate peak seen at 1:33

• Lactate peak represents the necrosis seen in aggressive tumors (WHO grade IV)

Magnetic Resonance Perfusion

• MR perfusion may be helpful in the diagnosis of gemistocytic astrocytoma, which demonstrates no elevation of relative cerebral blood volume (rCBV).

Biopsy

• Biopsy of gemistocytic astrocytoma tumor, taken through a needle during a simple surgical procedure, helps to confirm the diagnosis.