Oligodendroglioma Masquerading as a Cerebral Contusion

Clinical History

A 38-year-old male presented to the emergency department after a fall, with frontal cranial impact and loss of consciousness. At admittance he had a Glasgow Coma Scale Score of 14, without focal neurological deficits.

Imaging Findings

Admission CT showed a hyperdense frontal cortico-subcortical haemorrhagic lesion in the right frontal lobe, with peripheral hypodensity, concordant with vasogenic oedema.

Follow up CT at 3 months depicted reabsorption of the parenchymal haemorrhagic components without the expected cortico-subcortical atrophy. A space occupying lesion of the right frontal lobe was identified, mostly hypodense, with well defined margins and a small central calcification.

On MRI, performed one week after follow up CT, a heterogeneous lesion of the right frontal lobe involving the cortex and subcortical white matter, mostly hyperintense on T2WI, hypointense on T1WI, and with central blooming on SWI was identified. Contrast enhancement was minimal and heterogeneous. There was minimal peripheral vasogenic oedema. Altogether these alterations lead to local sulci effacement and obliteration of the frontal horn of the right lateral ventricle.
The patient underwent surgery and total mass resection was achieved. Histopathological analysis confirmed the diagnosis.

Discussion

Oligodendroglioma (OGs) is a glial neoplasm, arising from the oligodendogliocitic cells [1, 2]. Histopathologic classification recognizes two main types: well-differentiated (WHO grade II) and anaplastic (WHO grade III) [1-3]. It is the third most common glial neoplasm, comprising 5-18% of all gliomas and 5-10% of primary intracranial neoplasms in adults [1]. They occur more frequently in males, with a peak incidence in the 5^th-6^th decades [1, 3]. Children are rarely affected. OGs most commonly arise in the frontal lobes (50-65%), typically at the gray-white matter junction [3].
The most common form of presentation is seizures, reflecting the tumours' predilection for cortical gray matter [1, 3].

OGs are well-differentiated, commonly presenting as a mass involving the cortex and subcortical white matter [1].
They show low attenuation on CT [1], often with high-attenuation areas within the tumour: from calcifications (70-90%) or, less commonly, from haemorrhage [3]. The overlying skull may show pressure erosion.
On MRI, OGs are hypointense to gray matter on T1 and hyperintense on T2WI. There may be cystic degeneration and areas of "blooming" on susceptibility imaging (T2GE/SWI), due to the presence of calcifications and/or haemorrhage [1, 3]. Tumours with 1p/19q deletion show less homogeneous signal and have less sharp borders [3, 4].
Around 50% of ODs enhance, usually heterogeneously, with degree of enhancement varying widely [4]. Enhancement is not a reliable indicator of tumour grade, but relates to 1p/9q codeletion [3, 4]. Perfusion imaging may reveal regions of elevated rCBV mimicking a higher-grade neoplasm [3]. Haemorrhage is uncommon [3].
Because of ODs superficial location, adjacent to the skull vault, haemorrhagic tumours may be mistaken for traumatic contusions, specially if the clinical context is evocative. This may be specially true in a first seizure, if the patient falls and is admitted for head trauma.

Surgical resection is the mainstay of treatment, and most patients experience a long progression-free period [2]. For treatment, determination of molecular profiling (1p/19q deletion) is more important than the histological characteristics, as tumours with this deletion respond very favourably to chemotherapy. Radiation therapy is generally reserved for partially resected tumours [1-4].

Teaching points:
- Oligodendrogliomas typically affect the frontal lobes and are part of the differential diagnosis of tumours affecting the cortex and/or haemorrhagic tumours
- They represent one of the most frequently calcifying CNS tumours
- Although clinical history is helpful in guiding the imaging diagnosis, it can sometimes be misleading (as in the case presented, where the history of trauma led to an initial misdiagnosis)
- Follow up imaging, even of trivial lesions, should be evaluated carefully

Differential Diagnosis List

Final Diagnosis

Oligodendroglioma (WHO grade II)

URL:	https://www.eurorad.org/case/13265
DOI:	10.1594/EURORAD/CASE.13265
ISSN:	1563-4086