Imaging features of a pediatric cerebellar ganglioglioma

A 14-year-old boy presented dizziness and subsequently head trauma.

The neurological exam was normal.

There was a history of cervical pain and occasionally decreased coordination in both hands for several months.

He underwent an emergency CT, showing a solid-cystic cerebellar tumour with a small focus of calcification.

In our institution, the MRI confirmed a solid-cystic tumour centred in the vermis and the right cerebellar hemisphere. The margin was partially well-defined and no significant perilesional oedema was depicted. The maximum diameter was 6 cm. The solid portion was isointense to grey matter on T1WI and heterogeneous on T2WI (figure 1). There was high signal intensity on DWI sequence with a low value in the ADC map, suggesting high cellularity. In its anterolateral aspect, some foci of low signal on T2WI and susceptibility sequence (SWI) confirmed the small calcification previously described on CT (figure 2). The solid portion showed moderate multinodular enhancement (figure 3). In addition, most caudal folia were visible without anomalous enhancement, suggesting cerebellar atrophy (figure 1c).

There was no evidence of intracranial or leptomeningeal spread and the ventricular system size was normal.

In children, one-half of central nervous system (CNS) tumours arise from posterior fossa. In the cerebellum, the most common tumour is medulloblastoma followed closely by pilocytic astrocytoma. Ependymomas and atypical teratoid rhabdoid tumours are less frequent [1].

We present a cerebellar tumour with both high-grade and low-grade features:

On one hand, it has high-grade semiology suggesting medulloblastoma because it is isointense to grey matter on T1WI and heterogeneous on T2WI and the solid portion shows restricted diffusion [2].  In 2016, the World Health Organization (WHO) divided medulloblastoma into four genetically defined subgroups [3]. Our case could be a type 2 medulloblastoma also known as SHH (sonic hedgehog) protein activation subgroup, because it is centred in vermis and right cerebellar hemisphere, it shows enhancement without evidence of dissemination and it occurs in a preadolescent child [4].

However, there is no evidence of significant perilesional oedema or hydrocephalus, and enhancement pattern is multinodular not diffused. There are low-grade pilocytic astrocytomas with unusual imaging features, mostly solid or solid-cystic, as in our case. In those cases, the solid portion may show restricted diffusion and enhancement is usually intense but irregular due to its characteristic fenestrations within the endothelial cells [5].

Despite this, calcification and intratumoral haemorrhage can be present but are unusual, both in medulloblastoma and pilocytic astrocytoma.

The pathological analysis confirmed that our case was a cerebellar ganglioglioma. Cerebellar gangliogliomas (CGGs) are rare tumours consisting of neoplastic ganglion and glial cells, and are, generally, WHO grade I [6]. CGGs most commonly appear in older children and young adults with a slightly more predilection in males.  CGG should be considered in the differential diagnosis of cerebellar tumours when a solid-cystic mass with calcification is encountered (figure 2c). Also, it is very characteristic of CGG to have the caudal folia patent due to local flow trapping of cerebrospinal fluid, mimicking cerebellar atrophy (figure 1c).  In summary, CGGs are tumours usually hypodense on CT and heterogeneous on T2WI. Enhancement is often moderate and irregular (figure 3), its solid part can show restricted diffusion but they don’t show up with hydrocephalus or significant perilesional oedema because they are usually low-grade tumours (figure 2) [7].