Ganglioglioma

Ganglioglioma is a rare WHO grade 1 neoplasm typically affecting children and young adults, characterised by a mixture of ganglion and glial cells, and often demonstrating a cystic appearance with a mural nodule in the temporal lobe.

Description

Ganglioglioma is a benign, slow-growing glioneuronal tumour that typically affects children and young adults, comprising mixed neuronal and glial cell components. It represents the most common glioneuronal tumour (1-4% of all paediatric CNS neoplasms) and the most common neoplastic cause of temporal lobe epilepsy. Ganglioliomas are not always associated with epileptogenicity, even if a ganglioglioma is found in a patient with TLE. The seizure foci may be contralateral to the ganglioglioma, thus careful evaluation of the hippocampus, white matter abnormalities of the ipsilateral and contralateral anterior temporal lobe, and other focal lesions is needed.

Pathogenesis

The exact pathogenesis of gangliogliomas remains unclear. They are considered to arise from neural progenitor cells with the capacity for dual differentiation into neuronal and glial components. Genetic mutations, notably in the BRAF gene, have been identified in many cases.

Subtype

• Typical Ganglioglioma (WHO grade I): The most common subtype, primarily seen in children and young adults. Typically involves the temporal lobe.
• Anaplastic Ganglioglioma (WHO grade III): A rarer and more aggressive subtype, characterised by atypical histological features.

Epidemiology, Risk Factors & Associations

• Predominantly affects children and young adults (median age at diagnosis: 20-30 years).
• Slightly higher incidence in males.
• Frequently associated with chronic seizures, particularly temporal lobe epilepsy.

Clinical Features

The presentation is often related to the site of the tumour, with symptoms due to mass effect or seizure activity. A high proportion of patients present with longstanding, medically-refractory epilepsy.

Complications

• Intractable epilepsy.
• Rarely, malignant transformation to anaplastic ganglioglioma.

Pathological Features

Histopathology

• Macroscopic: Tumours are typically well-circumscribed and vary in size.
• Microscopic: Characterised by a mixture of mature ganglion cells (neuronal component) and glial cells (astrocytes or oligodendrocytes).

Serology

No specific serological markers.

Biochemistry

No specific biochemical markers.

Radiological Features

General Features

• Characteristically demonstrates a solid-cystic, enhancing, cortically-based mass in the temporal lobe.
• Calcification relatively common (35% of cases).
• Majority supratentorial (up to 90%). Infratentorial (10%).
• Remodelling of overlying calvarium may be seen.
• Ill-defined, adjacent cortical signal abnormality suggests associated focal cortical dysplasia (FCD)

CT

• Non-contrast: Iso- to hypodense solid-cystic mass. Calcifications may be seen.
• Contrast-enhanced: Variable enhancement of the solid component.

MRI

• T1WI: Iso- to hypointense solid component to grey matter with hypointense cystic component.
• T2WI/FLAIR: Hyperintense solid and cystic components. T2 hypointense foci of calcification.
• T1 C+: Variable enhancement of the solid component.
• SWI: Foci of blooming suggestive of calcification.
• DWI/ADC: No restricted diffusion.

Grading and Staging

Gangliogliomas are WHO Grade I tumours, with anaplastic gangliogliomas classified as Grade III. No specific staging system exists for these lesions as they are benign.

Diagnosis

Diagnosis is typically based on the characteristic imaging features and clinical history (e.g., refractory epilepsy), followed by histopathological confirmation after surgical resection.

Differential Diagnosis

• Dysembryoplastic Neuroepithelial Tumour (DNET): Often presents with a similar history of long-standing epilepsy. Wedge-shaped multicystic bubbly cortically based tumour. Less likely to enhance or contain calcifications.
• Pilocytic Astrocytoma: Commonly involves the cerebellum in children. May also demonstrate a cyst with an enhancing mural nodule but typically lacks calcifications.
• Pleomorphic Xanthoastrocytoma (PXA): Supratentorial cortical mass with enhancing nodule abutting pial surface. Leptomeningeal involvement and perilesional oedema more frequently than ganglioglioma.
• Focal Cortical Dysplasia: Ill-defined cortical thickening with indistinct grey-white matter junction. Tail of abnormal signal extends towards ventricle. No mass effect, enhancement or interval growth.
• Diffuse Low Grade Astrocytoma: Cortical mass-lesion with infiltrative margins. Enhancement less common.
• Oligodendroglioma: Uncommon in children. Typically calcified heterogenous mass, less defined than ganglioglioma. May remodel/erode calvarium.

Management

Management primarily involves surgical resection, aiming for seizure control and histological diagnosis. Postoperative radiotherapy may be considered for anaplastic gangliogliomas or cases with incomplete resection. Long-term follow-up with MRI is required to monitor for recurrence. There is excellent prognosis with complete resection.