For children and young individuals with long-standing, medically refractory epilepsy, contrast-enhanced MRI is the preferred imaging modality. CT is typically not recommended in this population, since it has low sensitivity in diagnosing LEATs and other epilepsy-associated conditions, such as FCD and exposes patients to unnecessary radiation.

Tumors that make it into the group of LEATs are rare and not commonly observed in general populations without specific medical history. While there is no official list of LEATs, two that always make it into the group are DNET and GGG.

Dysembryoplastic neuroepithelial tumors (DNET), WHO Grade I.

DNETs are glioneuronal tumors, arising from grey matter, either cortical (most commonly) or deep grey matter (rare). Commonly associated with focal cortical dysplasia.

DNETs are responsible for up to 20% of refractory epilepsy cases in pediatric and young adult population. Most commonly are observed in temporal lobes; followed by frontal lobe.

CT appearance of hypodense mass can be mistaken for a cyst, or ischemic stroke.

DNETs are usually solid, but cystic and microcystic components can be present, giving its characteristic lobulated or multilobulated, „soap bubble “appearance.   

On MR T1-hypointense, T2-hyperintense, FLAIR hypointense; partial FLAIR suppression, with bright T2 rim – bright rim sign. No diffusion restriction. Calcification and contrast-enhancement are not typical but can be sometimes seen.

Gangliogliomas (GGG) and Gangliocytomas, WHO Grade I

Gangliogliomas (GGG) and gangliocytomas are rare tumors, unless in the case of epilepsy, GGGs are most common cause of temporal lobe epilepsy.  They are more commonly found in older children and young adults, thou cases of detecting them in adults have also been reported.

The differentiation of GGG and gangliocytomas are pathological.

Depending on the location, neocortical vs mesial temporal, gangliogliomas can look entirely different.

Neocortical GGG:

CT appearance:  a low-density, well-circumscribed, often solid/cystic cortical based lesion with little mass effect or edema. Solid portions of tumor can be isodense, mixed, or hypodense. Calcifications are common. Solid portion can enhance or enhancement can be totally absent.

MR : sharp margins, cortex and adjacent white matter is involved. Tumor can be solid, cystic, or cystic with mural node. T1 mixed signal intensity, T2 high signal intensity.  Diffusion normal or encreased. Enhancement is more common then in DNET, but not always present.

Mesial temporal GGG: poorly defined infiltrative mass, difficult to appreciate on CT.

On MR: a solid mass with faint low T1, high T2, no or faint enhancement.  Cysts are less common then in neocortical GGG. 

Most commonly Ganglioglyomas and ganglyocytomas present as an enhancing nodule with a cystic component, calcification is quit common.  

Pleomorphic Xanthoastrocytoma (PXA), WHO Grade II or III

Third most common LEAT is pleomorphic xanthoastrocytoma (PXA), which is circumscribed astrocytic tumor. Typically they are found in children and young adults. PXAs can be WHO grade II or III, their grading is completely histological.

PXAs are located supratentorially, about in the half of cases are observed in temporal lobes, followed by parietal lobe, frontal and occipital lobes.  Their location almost always is cortical and peripheral, abutting the leptomeninges, hence reative leptomeningeal involvement can be seen as a sign of dural tail, on contrast enhanced images.  

Its typical appearance is that of large, well-circumscribed cortical temporal mass, commonly with eccentric cystic component. Enhances more vividly than above-mentioned tumors. As for the all slow-growing peripheral tumors remodeling of inner table and calvarium may be seen.

CT: solid components can be isodense or hypodense to gray matter, maybe well or poorly demarcated, usually with little or no surrounding edema. Calcification is rare.

MR: On T1, the solid component appears iso- to hypointense to gray matter, while the cystic component is hypointense. T2, On T1, the solid component appears iso- to hypointense to gray matter, while the cystic component is hypointense

Enhancement: solid portions enhance vividly, homo or heterogeneously.

PLNTY, WHO Grade I

Polymorphous low-grade neuroepithelial tumours of the young (PLNTY) are recently described entity.

Low-grade diffuse glioma. Mainly arises in the cortex and temporal lobe. Imaging, solid or partially cystic appearance with unclear margins. It can feature punctate or coarse calcification, depending on the size of the tumor, these calcifications are located centrally within the lesions.

PLNTYs are usually located in the temporal lobe, though lesions in the parietal, frontal, and occipital lobes have also been reported.

Cystic components were seen in 89% of cases, typically peripheral. On CT, the mass appears hypo- or hyperdense, often with central coarse calcifications.

MRI shows iso- to hypointensity on T1, while T2/FLAIR reveals heterogeneous hyperintensity with a "salt and pepper" appearance due to calcifications. Cystic components vary in size and number. On T2*/SWI, smaller calcifications are common in younger patients, while larger central "blooming" calcifications are typical. DWI/ADC shows no restricted diffusion, and post-contrast T1 demonstrates slight or no enhancement.

Multinodular and vacuolating neuronal tumor, MVNT

MVNT is a rare glioneuronal tumour seen in young to middle-aged individuals, most commonly in the temporal lobes. It can be indolent and asymptomatic, incidentally detected and monitored only with imaging, while surgery is reserved for symptomatic cases.

Compared to DNT, MVNT appears "bubblier," forming clusters of small cyst-like lesions in the subcortical white matter.

CT shows non-enhancing low-attenuation lesions.

On MRI, it is hypointense on T1, hyperintense on T2—almost as bright as CSF—and remains hyperintense on FLAIR, and contrast-enhanced MRI typically reveals no enhancement, though faint focal enhancement may occur.

Isomorphic diffuse glioma

Isomorphic diffuse glioma is an indolent low-grade diffuse glioma, also referred to as isomorphic neuroepithelial tumour.  They tend to arise in children and young adults.

Imaging features are nonspecific.

Typically located in the supratentorial brain and appear as quite well circumscribed lesions a few centimetres in diameter.

On MR T1 hypointense, and T2 hyperintense with no enhancement, and no calcifications.

Papillary Glioneuronal Tumor – WHO grade 1.

Papillary Glioneuronal Tumor may be discovered due to seizures or incidentally and are most commonly diagnosed in younger patients, though they can occur at any age. Among LEATs, they most closely resemble GGG.

They are typically supratentorial, juxtaventricular, and most often found in the frontal lobe. Well-demarcated with solid and cystic components, they show intense but heterogeneous enhancement, with both solid and cystic portions enhancing. Coarse calcifications are frequently observed.

On MRI, they appear iso- to hypointense on T1 and inhomogeneously hyperintense on T2 and FLAIR, on FLAIR cystic components may suppress. Post-contrast T1 imaging shows avid but heterogeneous enhancement of the solid nodule.

Angiocentric glioma, WHO Grade I

Angiocentric glioma is a rare paediatric-type diffuse low-grade glioma, with only a few reported cases, primarily affecting children and young adults.

These tumors are typically cortical or subcortical, presenting as homogeneous, ill-defined masses due to gyral white matter infiltration and characteristic trans-cerebral extension toward the ventricular wall, often rendering the cortex unrecognizable.

They exhibit no significant mass effect, calcification, or enhancement.

On CT, they appear as expansile non-enhancing cortical tumors.

MRI shows hypointensity on T1, sometimes with a hyperintense rim, and hyperintensity on T2/FLAIR with ventricular extension along vessels and possible cystic-like areas. Post-contrast T1 imaging reveals no enhancement.