Ganglioglioma

Gangliogliomas are uncommon and accounting for around 2% (from 0.4% to 3.8%) of all primary intracranial tumours, although they make up a greater proportion of primary cerebral tumours in children (up 10%). They are of low grade (WHO Grade I or II) and typically occur in the temporal lobes although they have been described in all parts of the central nervous system.

Children and young patients are usually afflicted, and no gender predominance is noted. The most common presentation is with temporal lobe epilepsy, presumably due to the temporal lobe being a favoured location.

Histology

Gangliogliomas are composed of two cell populations:

1. ganglion cells (large mature neuronal elements): ganglio-
2. neoplastic glial elements (primarily astrocytic): -glioma

It is the grade of the glial component that determins biological behaviour. Dedifferentiation into high grade tumours does occasionally occur, and it is usually the glial component (into a GBM). Only rarely is it the neuronal component (into a neuroblastoma) 

They are closely related to gangliocytomas, which contains essentially only mature neural ganglion cells, and ganglioneurocytoma which in addition have small mature neoplastic  neurons.

Imaging findings

Imaging findings mirror the various patterns of growth which these tumours may demonstrate, and unfortunately their appearance is very variable. Patially cystic mass with an enhanging mural nodule is seen in 35-55% of cases. They may also simply present as a solid mass expanding the overlying gyrus. An infiltrating mass is uncommon and may reflect higher grade. 

CT

Non specific findings of a mass which is:

• iso or hypodense
• frequently calcified ~35%
• bony remodeling or thinning can indicate the slow growing nature of the tumour
• enhancement is seen in approximately 50% of cases (involving the solid non-calcified component)

MRI

• T1: iso to hypointense, with variable contrast enhancement
• T2: hyperintense solid component, with variable signal in the cystic component depending of amount of proteinacaous material or presence of blood products.
• Calcified areas will bloom on GE / SWI sequences
• Peritumoural FLAIR / T2 oedema is distinctly uncommon

Treatment

Local resection is the treatment of choice and determines prognosis. In the brain where a reasonable resection margin can be achieved, prognosis is good. In the spinal cord where this is not possible without devastating deficits local recurrence is very common. 

 If only incomplete resection is achievable, or tumour recurrence occus then radiotherapy may be of some benefit.

Differential diagnosis

The differential diagnosis is very broad and should be restricted by location.

Temporal lobe

• pleomorphic xanthoastrocytoma
• ganglioneuroma
• pilocytic astrocytoma
• DNET

See Temporal lobe tumour DDx

Spinal cord

• astrocytoma
• ependymoma 

Cortical tumour

• oligodenroglioma
• pleomorphic xanthoastrocytoma
• ganglioneuroma