Protoplasmic 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: Protoplasmic astrocytomas; Diffuse astrocytoma; Low grade astrocytoma

Overview

Protoplasmic astrocytoma is a rare variant of diffuse low grade astrocytoma with histological and imaging features which are fairly characteristic. It has been suggested that protoplasmic astrocytoma represents a variant of dysembryoplastic neuroepithelial tumors (DNET), as they share histological as well as imaging features. Currently, they are classified as a subtype of diffuse low-grade astrocytoma.

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:

• Neoplastic protoplasmic astrocytes

• 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)
• No mitoses, microvascular proliferation, and necrosis

Immunohistochemistry

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

Differentiating Protoplasmic Astrocytoma from other Diseases

• Protoplasmic astrocytoma must be differentiated from:

• Fibrillary astrocytoma
• 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.

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

History and Symptoms

History

• 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

• Symptoms of protoplasmic 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 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

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

MRI component	Findings
T1	Iso- to hypointense compared to adjacent brain
T2	Iso- to hyperintense Small flow-voids may be observed within the tumor
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	Marked homogenous enhancement

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).

Electroencephalogram

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

Biopsy

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

Treatment

• The treatment of protoplasmic astrocytoma depends on the clinical presentation, tumor size, and location.

• Surgery: The predominant therapy for protoplasmic astrocytoma is surgical resection.
• Radiotherapy: Radiotherapy may be used in protoplasmic astrocytoma post-operatively or at the time of recurrence or progression.
• Chemotherapy: Chemotherapy may have a role in recurrent and de-differentiated tumors.

Treatment of protoplasmic astrocytoma

Surgery

Radiotherapy

Chemotherapy