Gangliocytoma

Gangliocytomas are rare indolentCNS tumours (WHO(WHO grade 1), primarily encountered in children, and frequently discovered as the cause of epilepsy. They are considered one of the long-term epilepsy-associated tumours (LEATs).

They differ from gangliogliomas by the absence of neoplastic glial cells, although both tumours are defined by the presence of displaced ganglion cells (large mature neurones that show cytological or architectural abnormalities).

On imaging, these tumours are usually characterised by cortical solid lesions with little associated mass effect and minimal or no surrounding vasogenic oedema. Calcification and cyst formation can occur, and contrast enhancement is generally present.

Terminology

Gangliocytomas should not be confused with dysplastic cerebellar gangliocytoma of the cerebellum, better known as Lhermitte-Duclos disease.

Epidemiology

Gangliocytomas account for 0.1-0.5% of all brain tumours but 1-3% of tumours in epilepsy series ⁵. They tend to be diagnosed in children and young adults, with a peak age between 10 and 30 years of age ²⁶.

Clinical presentation

No clinical differences between gangliogliomas and gangliocytomas are recognised. Tumours in the cerebral cortex, particularly the temporal lobe, present most commonly with epilepsy which is often lonstanding at the time of diagnosis ^4,6.

Pathology

Gangliocytomas may arise anywhere within the neuroaxis, however, over 80% are found in the temporal lobes ^4-6.

Microscopic appearance

The tumour is composed of abnormal large mature neurones, usually with a multipolar morphology ⁵. Some neurones are binucleated and cytoplasmic vacuolization or ballooning is seen ⁵. The Microcalcification can also be seen ⁵.

The key feature in distinguishing gangliocytomas from gangliogliomas is identifying a lack of neoplastic glial cells. Similarly, ensuring no small round blue cell component or neuroblasts are seen is important to exclude more aggressive tumours (such as medulloblastoma and neuroblastoma) which can have similar appearing ganglion cells ⁵.

Immunophenotype

• synaptophysin: positive

• neurofilament: positive

• chromogranin-A: positive

• MAP2: positive

• NFP: variable

• GFAP: negative

Radiographic features

Appearances of gangliocytomas are indistinguishable from gangliogliomas ^5,6. They tend to occur in the cortex, most often in the temporal lobes. Because of cortical location and slow growth, calvarial remodelling may be seen in some cases ⁶.

CT

Gangliocytomas typically appears hyperattenuating on non-contrast imaging. They usually only have little associated mass effect and minimal or no surrounding vasogenic oedema. Calcification and cyst formation can occur¹.

MRI

• T1: solid components typically hypointense

• T2: solid components are typically mildly hypointense ²; cystic areas are hyperintense; calcification if present can be hypointense

• T1 C+ (Gd): solid components enhance

• T2*/SWI: signal loss due to calcification

Treatment and prognosis

These tumours tend to grow slowly and do not undergo anaplastic change, unlike gangliogliomas that can (rarely) have higher grade glial components. Resection is curative with a 7.5 year progression-free survival rate of 94% ⁶.

Differential diagnosis

• ganglioglioma: difficult if not impossible to distinguish from each other

• cortical dysplasia

• dysembryoplastic neuroepithelial tumour (DNET)

• polymorphous low-grade neuroepithelial tumour of the young (PLNTY)

• papillary glioneuronal tumour