Dysembryoplastic Neuroepithelial Tumor (DNET)

Findings

Axial T1-WI (Figure 1) demonstrates a well-defined, cortical based intraxial mass in the right temporal lobe which is hypointense to brain parenchyma. The mass is hyperintense on T2-WI (Figure 2). No surrounding edema is seen. The right temporal horn is seen normally. No enhancement is detected on post-gadolinium T1-WI (Figure 3). Scalloping of the adjacent skull is noted with the lesion “pointing” towards the ventricle (Figure 3).


Diagnosis: Dysembryoplastic Neuroepithelial Tumor (DNET)


DNET is an uncommon benign intracortical lesion that is classified by WHO as a “neuronal and mixed neuronoglial tumor”. These are commonly associated with cortical dysplasia. DNETs show no or very slow growth over time and are WHO Grade I.

These tumors virtually always manifest in patients with medically refractory partial seizures. The vast majority of patients are younger than 20 years, and males are more commonly affected. The temporal lobe is the most common site (62%), followed by the frontal lobe (31%).

The imaging appearance of dysembryoplastic neuroepithelial tumor is similar to those of other low-grade glial tumors. On CT, a wedge shaped low-density area is seen in a cortical/ subcortical location “pointing” towards the ventricle. Calcification may be seen in 25% of cases. Scalloping of the adjacent inner table of the skull suggests long standing nature of the lesion.

At MR imaging, DNET tumors most commonly manifest as cortical masses that are hypointense on T1-weighted images and hyperintense on T2-weighted images without surrounding vasogenic edema. Pseudocystic, multinodular “bubbly” mass may be seen. DNETs usually do not enhance- faint focal punctuate or nodular enhancement may be seen in 20% cases.

The prognosis is excellent with long survival even with incomplete tumor resection. Most patients have a significant reduction in seizure frequency. Tumor recurrence is very rare.