Rosette-forming glioneuronal tumours (RGNTs) are a rare form of glioneuronal tumour typically arising in the midline, involving the 4th ventricle, with an average diameter of 3-3.5cm. They comprise two histological components: one containing uniform populations of neurocytes forming rosettes/perivascular pseudorosettes and one resembling pilocytic astrocytoma. Symptoms include headache, obstructive hydrocephalus and location-dependent focal neurology. Fewer than 100 RGNT’s have been previously reported, and the full range of their clinical manifestations has yet to be established. Rarely they are discovered incidentally, with eight cases of incidental RGNT identified on imaging reported in the literature. Incidental discovery of an RGNT post-mortem has not been previously reported. 

We present the case of a 27 year old gentleman, without significant medical comorbidities who presented with severe headache, vomiting and left sided weakness. His blood pressure was 310/190 mmHg and shortly after admission he suffered a cardiac arrest and died. Neuropathological examination demonstrated a large right hemispheric acute hematoma in the basal ganglia with intraventricular extension. A 4cm x 4cm partly cystic mass was incidentally identified posteriorly and to the right of the optic chiasm, infiltrating the basal forebrain, optic chiasm and pituitary gland. Histologically, the mass was consistent with an RGNT, WHO Grade I.

This represents the first reported case of an incidental RGNT identified post-mortem. It highlights that RGNTs can remain asymptomatic even when large and present in an eloquent area of the brain, including the optochiasmatic region. Two prior reports of RGNTs in this region presented with visual field deficits. Conversely our patient reported no symptoms prior to his demise from a hypertensive intraparenchymal hemorrhage, despite his RGNT’s larger than average size. Hypothalamic involvement and recurrent nocturnal pyrexia have previously been reported with an optochiasmatic RGNT, raising the possibility of hypothalamic homeostatic failure resulting in hypertensive crisis in our case.