Protoplasmic astrocytoma

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Sujit Routray, M.D. [2]Roukoz A. Karam, M.D.[3]

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

Overview

Protoplasmic astrocytoma is a rare variant of diffuse low grade astrocytoma with characteristic histological and imaging features. It has been suggested that protoplasmic astrocytoma represents a variant of dysembryoplastic neuroepithelial tumors (DNET), as they share histologic and imaging features. Currently, protoplasmic astrocytoma is classified as a subtype of diffuse low-grade astrocytoma. The possibility that a primary cerebral neoplasm represents a protoplasmic astrocytoma should be considered in a patient with a large frontal or temporal tumor that has a very high signal on T2 with a large proportion of the tumor showing substantial T2 FLAIR suppression.

Classification

Protoplasmic astrocytoma is a subtype of astrocytoma and is included in the classification of astrocytoma. For more information about the classification of astrocytoma, click here.

Pathophysiology

Gross Pathology

• Protoplasmic astrocytoma appear to have a predilection for the frontal and temporal lobes.

Microscopic Pathology

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

• Scant cytoplasm
• Rounded prominent nuclear contour
• Flaccid processes

• Low cellular density
• Mild nuclear atypia (enlarged, irregular contour, hyperchromasia, and coarsened nuclear chromatin pattern)
• Mucinous fluid containing microcystic spaces (prominent feature)
• Abscence of mitoses, microvascular proliferation, and necrosis
• temporal and frontal lobes were the most likely site of origin.

Immunohistochemistry

• Protoplasmic astrocytoma is demonstrated by positivity to tumor marker such as GFAP.

Causes

There are no causes for protoplasmic astrocytoma.

Differentiating Protoplasmic Astrocytoma from other Diseases

• Protoplasmic astrocytoma must be differentiated from:

• Gemistocytic astrocytoma
• Oligoastrocytoma
• Stroke
• Cerebritis
• Herpes simplex encephalitis
• Anaplastic astrocytoma
• Oligodendroglioma
• Angiocentric glioma

Epidemiology and Demographics

Age

• Protoplasmic astrocytoma is a rare disease that tends to affect young adults.
• The mean age at diagnosis is 32 years.

Gender

• Males are more commonly affected with protoplasmic astrocytoma than females. The male to female ratio is approximately 1.67 to 1.

Risk Factors

There are no established risk factors for protoplasmic astrocytoma.

Screening

There is insufficient evidence to recommend routine screening for protoplasmic astrocytoma.

Natural History, Complications and Prognosis

Natural History

• If left untreated, patients with protoplasmic astrocytoma may progress to develop seizures, focal neurological deficits, and hydrocephalus.
• Protoplasmic astrocytoma is a slow growing tumor with an indolent course.

Complications

• Common complication of protoplasmic astrocytoma include:

• Hydrocephalus

Diagnosis

Diagnostic Study of Choice

The diagnosis of protoplasmic astrocytoma is based on a tissue biopsy.

History and Symptoms

• When evaluating a patient for protoplasmic 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 of protoplasmic astrocytoma include:

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

Physical Examination

Patients with protoplasmic astrocytoma usually appear

Laboratory Findings

There are no diagnostic laboratory findings associated with protoplasmic astrocytoma.

Electrocardiogram

There are no ECG findings associated with protoplasmic astrocytoma.

X-ray

There are no x-ray findings associated with protoplasmic astrocytoma.

Echocardiography or Ultrasound

There are no echocardiography/ultrasound findings associated with protoplasmic astrocytoma.

CT scan

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

• Hypodense mass
• Positive mass effect
• No enhancement
• Cystic or fluid attenuation, due to the aforementioned prominent mucinous microcystic component

MRI

• The possibility that a primary cerebral neoplasm represents a protoplasmic astrocytoma should be considered in a patient with a large frontal or temporal tumor that has a very high signal on T2 with a large proportion of the tumor showing substantial T2 FLAIR suppression.
• Brain MRI is helpful in the diagnosis of protoplasmic astrocytoma. On MRI, protoplasmic astrocytoma is characterized by:

MRI component	Findings
T1	Hypointense compared to white matter
T2	Hyperintense compared to white matter
Fluid-attenuated inversion recovery (FLAIR)	Large areas of T2 hyperintensity suppress on FLAIR These are not macrocystic, but rather represent the areas with abundant microcystic change
T1 with contrast	Little or no enhancement
Diffusion weighted imaging (DWI)	No restricted diffusion

Other Imaging Findings

Magnetic Resonance Spectroscopy

• MR spectroscopy may be helpful in the diagnosis of protoplasmic astrocytoma, which demonstrates elevated choline/creatine ratio.

Magnetic Resonance Perfusion

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

Other Diagnostic Studies

Electroencephalogram

• Electroencephalogram (EEG) is performed in cases of protoplasmic astrocytoma to record the continuous electrical activity of the brain and locate the seizure activity.

Treatment

Medical Therapy

There is no specific chemotherapy regimen for protoplasmic astrocytoma. It is managed as an astrocytoma.