Anaplastic Ganglioglioma

A previously healthy 55-year-old man was admitted in the hospital because of a focal-onset seizure that evolved into a generalized tonic-clonic seizure. Prodromal or premonitory symptoms were absent. He had no history of epilepsy. On examination, he was conscious and oriented, without any focal neurologic deficit.

Brain MRI was performed on the second hospital day and included the following sequences: T1-weighted (before and after administration of gadolinium-based contrast agent), T2-weighted, diffusion-weighted imaging (DWI), and dynamic-susceptibility contrast (DSC) perfusion imaging from which relative cerebral blood volume (rCBV) maps were obtained. This MRI showed a poorly marginated, rounded intra-axial mass (tumour size, 36 x 40 x 39 mm) located in the right frontal lobe with a heterogeneous signal intensity and a centre that was hyperintense on T2-weighted images but hypointense on T2-FLAIR images, suggestive of an area of necrosis, and with minimal surrounding vasogenic oedema (Figure 1A and 1B). On contrast-enhanced T1-weighted image, the lesion showed a focal nodular enhancement in its lateral margin that also exhibited restricted diffusion on DWI and markedly elevated rCBV (Figure 1C – 1F).

The patient finally underwent craniotomy for gross total resection. Histopathologic examination confirmed the diagnosis of anaplastic ganglioglioma, WHO grade III.

Gangliogliomas are rare tumours that arise from ganglion cells and are considered WHO grade I, accounting for 1.3% of all brain tumours. Most of these occur in children and young adults, generally between 10 and 30 years of age, with a slight male predominance. Involvement of the temporal lobes is the most common gangliogliomas location (80% of cases), followed by frontal, occipital, and parietal lobes. Anaplastic ganglioglioma (AGG) is a rare variant of gangliogliomas and represents <8% of them. This type of tumour can develop either de novo or arise from malignant degeneration of a pre-existing WHO grade I ganglioglioma [1,2].

AGG occurs most frequently in patients with ages relatively older than grade I gangliogliomas [1]. Clinical presentation is characterized by seizures, focal neurological deficits, and increased intracranial pressure. The major pathologic findings of AGG include mitotic activity, increased cellularity, nuclear pleomorphism, microvascular proliferation, and necrosis (3). Compared with their grade I counterparts, AGG is an aggressive tumour and has a dismal prognosis. Furthermore, they do not show a predilection for the temporal lobes [2].

On MR imaging, AGG may present as a heterogeneous mass with an enhancing solid component surrounding a central necrotic area. This solid component is usually iso-hypointense on T1WI and hyperintense on T2/FLAIR. MR perfusion and diffusion-weighted imaging can help to demonstrate the aggressive behaviour of the lesion [2]. Unlike grade I gangliogliomas, the lesions generally tend to be larger and poorly delineated. Mass effect and perilesional oedema might be present [1].

The treatment of choice for AGG consists of complete surgical resection with adjuvant radiation and chemotherapy; however, their natural course is characterized by local recurrence or leptomeningeal spread. Anti-BRAF inhibitors can also be used as adjuvant therapy due to the presence of BRAF V600E mutation in 39% of AGG [4,5].

Teaching point

Imaging features of anaplastic ganglioglioma on MRI are nonspecific and indistinguishable from high-grade infiltrating gliomas.