AB027. Distinguishing oligodendroglioma from astrocytoma: a radiological case report

Background: Oligodendroglioma, the third most common glioma, accounts for 5% of primary brain tumors and around 20% of all glial neoplasms. It is a rare brain tumor that develops from glial cells called oligodendrocytes, which cover nerve cells. Oligodendroglioma is classified as an adult diffuse glioma in the fifth edition of the World Health Organization (WHO) Classification of Tumors of the Central Nervous System (CNS). Patients may present with cognitive impairment, aphasia, behavioral changes, and seizures. The symptoms at presentation are often related to the anatomic location of the tumor.

Case Description: A 55-year-old female presented with episodes of facial seizure with drooping on the right side of her face 4 months before coming to our hospital. Her seizures lasted around one minute, causing her to be unable to speak during the seizure. She also complained of chronic headaches in the last 1 year. She initially underwent a non-contrast computed tomography (CT) scan of the brain. The scans showed an isodense calcified mass on the perifalcine anterior left lobe with surrounding peritumoral edema. Magnetic resonance imaging (MRI) brain confirmed the presence of an intraaxial white matter mass involving the left frontal lobe. This tumor did not demonstrate any contrast enhancement. MRI findings were suggestive of a low-grade astrocytoma. Histopathological examination following craniotomy and tumor removal surgery confirmed the diagnosis of oligodendroglioma not otherwise specified (NOS) CNS WHO grade II. Molecular analysis revealed to be isocitrate dehydrogenase (IDH) wildtype, inconsistent with the classic molecular profile of oligodendroglioma. The patient underwent adjuvant radiotherapy following surgery. Subsequent follow-up assessments demonstrated stable disease with improvement in symptoms.

Conclusions: Differentiating between oligodendroglioma and astrocytoma poses a significant challenge due to their overlapping clinical and radiological features, yet understanding their key differences is crucial for accurate diagnosis. On MRI, calcification strongly favors oligodendrogliomas, while T2/fluid-attenuated inversion recovery (FLAIR) mismatch sign favors astrocytoma. Only 50% of oligodendrogliomas appear to be contrast-enhanced. While oligodendrogliomas and astrocytomas share some similarities, careful consideration is essential for accurate differentiation, even though histopathological and molecular findings are the final determinants of diagnosis.

Keywords: Oligodendroglioma; astrocytoma; grade II glioma; grade III glioma; case report