Imaging features of rosette-forming glioneuronal tumours

To describe the imaging features of rosette-forming glioneuronal tumours (RGNTs) to enable accurate diagnosis.

Image data and clinical findings for seven patients with histopathologically confirmed RGNTs were studied comprehensively.

Six neoplasms were located near the midline and all were relatively well circumscribed. Most lesions were hypointense on T1-weighted images and hyperintense on T2-weighted images. Furthermore, five tumours were hypointense on diffusion-weighted imaging (DWI). On computed tomography (CT), the solid tumour portions showed hypo-attenuation compared with brain parenchyma. Obvious calcification was found in two cases, and hydrocephalus was seen in five. Cerebrospinal fluid (CSF) dissemination and multiple satellite lesions were not observed in these cases. Haemorrhage was found in one case. The "green bell pepper sign" was present in five cases on gadolinium-enhanced magnetic resonance imaging (MRI). Each of the patients accepted surgical treatment, and no recurrences occurred during follow-up.

RGNTs are very rare mixed glioneuronal tumours and mostly affect young people. They are usually hypointense on T1-weighted images and DWI, hyperintense on T2-weighted images, and hypo-attenuated on CT images. The "green bell pepper sign" after gadolinium enhancement, intratumoural haemorrhage, CSF dissemination, and multiple satellite lesions provide additional clues to the correct diagnosis. A relatively well-demarcated tumour with these features and a midline location should raise suspicion of an RGNT.