Longstanding medically refractory epileptic seizures

Clinical History

A 19-year-old woman known for sleep-related generalised epileptic seizures for 10 years presented with a first paroxystic episode of distorted visual perception of objects and scintillating scotomas followed by loss of consciousness and convulsions. EEG showed a right hemispheric epileptogenic focus.

Imaging Findings

MR imaging shows a well demarcated multicystic-like cortico-subcortical lesion in the posterior aspect of the inferior gyrus of the right temporal lobe with pressure effect on the bone leading to thinning of the adjacent skull. The signal intensity of the lesion follows that of cerebrospinal fluid (CSF) on all sequences confirming its cystic-like nature. No spontaneous hyperintensity is demonstrated on T1W images. T2W images further demonstrate the pseudocystic nature of the lesion with “soap bubble” appearance, without surrounding oedema. The FLAIR sequence confirms the presence of a pseudocystic lesion with a hyperintense rim. No enhancement is observed on T1W images after administration of gadolinium contrast media.

Discussion

Dysembryoplastic neuroepithelial tumour (DNET) is a World Health Organisation (WHO) grade I benign glioneuronal tumour[1] and is the most common brain neoplasia associated with intractable seizures[2]. Macroscopically, DNETs are mucinous or gelatinous lesions of friable consistency[3]. Histologically, cortical dysplasia and an oligodendroglial pattern (“specific neuronal unit”) are identified[4].
Young patients are most commonly affected and usually present with medically refractory seizures[2]. Additional focal neurologic deficits may coexist but are uncommon[4]. This case illustrates the need for MR imaging in patients with partial-onset seizures, but more generally, in all patients with epilepsy, even without a clinically or EEG suspected focus. However, if location-related seizures are suspected, imaging plays a key role in identifying and locating the lesion, and in evaluating its resectability.
The modality of choice for the diagnosis of DNET is MRI. DNETs are commonly located peripherally[4] in the temporal or frontal lobes and less often in the parietal lobe[5]. The tumour may produce a typical “soap bubble” appearance with extension beyond the cortical gray matter boundary and bone scalloping[4]. Oedema is practically never observed and enhancement after intravenous contrast is variable[4] and not associated with malignancy. Advanced MRI techniques (proton MR spectroscopy and diffusion weighted and perfusion imaging) have shown to be of value in differentiating DNET from other cortical lesions[6]. The differential diagnosis of DNET includes Taylor dysplasia[7], dilated perivascular spaces, pleomorphic xanthoastrocytoma[7] and ganglioglioma[7]. In this case, the cortico-subcortical location in the temporal lobe, the multicystic-like appearance, the absence of enhancement and scalloping of the skull are in keeping with the literature and consistent with the diagnosis, especially in light of the clinical history. Final diagnosis is however usually achieved by histology of the resected specimen[1].
Treatment consists of surgical resection and neither chemotherapy nor radiotherapy are indicated for DNET[2,3]. Prognosis regarding seizure control is usually excellent when total resection is achieved. In this case, the patient is currently reticent to have surgery despite the persistence of seizures. Given the absence of a histological diagnosis, the presumed diagnosis of DNET was made based on imaging findings, in view of the pathognomonic MRI appearance, and the clinical history.
This case illustrates the crucial role of imaging in the diagnosis of DNET and shows that sometimes the imaging findings are very specific for this diagnosis. More importantly, MR imaging can exclude a malignant tumour thus sparing young patients from the negative effects of chemotherapy and radiotherapy.

Differential Diagnosis List

Final Diagnosis

Dysembryoplastic Neuroepihelial Tumour (DNET)

URL:	https://www.eurorad.org/case/9982
DOI:	10.1594/EURORAD/CASE.9982
ISSN:	1563-4086