Cerebral oligodendroglioma

A 31-year-old woman presents with a new-onset seizure.

Non-enhanced CT (Fig. 1) shows a low density in the left frontal lobe with cortical sulcal effacement. There are intralesional hyperdense foci, compatible with calcifications, and a central area with fluid attenuation, corresponding with cyst formation. There is midline shift and subfalcine herniation to the right side. There is no contrast enhancement (Fig. 1).

MRI shows increased signal of the left frontal lobe on T2-WI and FLAIR sequences (Fig. 2). On T1 MPRAGE sequences, the lesion is hypointense, with effacement of cortical sulci. There are no susceptibility artefacts on T2* sequences. The lesion shows no contrast enhancement after IV administration of gadolinium nor diffusion restriction. The cystic changes in the centre of the lesion are confirmed. Histopathologic examination of the biopsy specimen confirms an oligodendroglioma. Genetic analysis demonstrates a 1p/19q co-deletion.

Oligodendroglioma is a glial tumour and is characterised by a 1p/19q co-deletion, which differentiates the lesion from other glial tumors [1]. It usually affects adults between 40 and 60 years old [2]. Epileptic seizures are the most common initial presentation, with or without generalisation [3].

On CT, oligodendroglioma usually presents as a hypodense mass, predominantly with a cortical-subcortical location, but it can be of heterogeneous density. It typically has a supratentorial location, most commonly in the frontal lobe [2,4]. Intratumoral calcification is present in about 90% of cases [2]. Cystic formation and haemorrhage are not frequent [2,5]. The lesion is hypointense on T1-WI and heterogeneous hyperintense on T2-WI. Subtle, multifocal enhancement is present in about 50%.

Oligodendrogloma shows no diffusion restriction. On perfusion imaging, it may show elevated relative cerebral blood volume (rCBV). Moderately elevated choline (Cho) and decreased N-acetylaspartate (NAA) without a lactate peak is seen on MR spectroscopy [2,6].

The differential diagnosis of epilepsy-associated tumors with calcifications include gangliogliomas, dysembryoplastic neuroepithelial tumours (DNET), pleomorphic xanthoastrocytomas (PXA) and low-grade diffuse astrocystomas. Ganglioglioma can be either predominantly solid or predominantly cystic, and is usually located in the mesial temporal lobe [7,8]. DNETs are typically multicystic cortical-based lesions, commonly located in the mesial temporal or frontal lobe [5,9]. PXAs are cortical-based cystic tumours with a solid, mural component and leptomeningeal enhancement [8]. The most common location is the temporal lobe (49%) [7]. In low-grade diffuse astrocytoma, cortical involvement is typically absent [2].

Ganglioglioma, DNET and PXA typically occur in younger patients than an oligodendroglioma. Intralesional calcification are rarely present in low-grade diffuse astrocytoma, PXA and DNET and in about 40% of gangliogliomas. Compared to oligodendroglioma, cystic formation is more prominent and frequent in DNET and PXA. However, these imaging features are insufficient to reliably distinguish oligodendroglioma from other epilepsy-associated tumors [5,7,8].

Therefore, biopsy is mandatory to confirm the diagnosis. Treatment requires a multi-disciplinary approach. Surgical resection reduces mass effect and symptoms, delays progression and improves survival. Both chemotherapy and radiotherapy may be considered [6]. Oligodendroglioma has a better prognosis than glial tumours without 1p/19q co-deletion, with a median survival of 14 years after chemoradiotherapy. However, in most patients, the final outcome is infaust [10].

In conclusion, a cortical-subcortical-based mass in the frontal lobe with intralesional calcification in patients between the age of 40- 60 years presenting with epilepsy is suggestive of an oligodendroglioma. Histological confirmation is required for final diagnosis.

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