Case 1 and case 2: Central neurocytoma, WHO II, complicated by hemorrhage.
Neurocytoma is an uncommon low grade tumour5 with neuronal differentiation representing 0.25-0.5% of all intracranial tumors1. It occurs in young adults with a mean age of 29 years1. It was first described by Hassoun et al4 in an effort to describe a neuronal tumour which is distinct from a supratentorial primitive neuroectodermal tumour. It is classically intraventricular (central neurocytoma), located close to the foramen of Monro, although parenchymal (extraventricular) neurocytomas have been described5. The anterior portion of the lateral ventricle is the most common site6. Because of its location it usually presents with symptoms and signs of obstructive hydrocephalus. MR imaging usually shows a solid well demarcated intraventricular mass which can have cystic components or features of calcification2. The tumor is isointense or slightly hyperintense2 and shows moderate contrast enhancement1. It is associated with a good prognosis with gross total resection3. GRADE?
Neurocytoma is composed of small round bland neurons with little cytoplasm, growing as sheets or clusters in a delicate neuropil background, sometimes with rosette formation. Synaptophysin is typically strongly positive1. Cells show variable positivity for NSE and Neu N1. The differential diagnosis includes clear cell ependymoma and neuroblastoma/ supratentorial PNET and if the cytoplasm is clear the tumour appears identical to oligodendroglioma. The former can be excluded with absence of GFAP and EMA staining, whereas the nuclear atypia and proliferation of PNET far exceeds that of neurocytoma. Distinction from oligodendroglioma is most difficult as oligodendroglioma can express neuronal markers like neurocytoma. Useful features of neurocytoma are "pushing", rather than infiltrative, border, neuropil background, strong diffuse positivity with synaptophysin, absence of deletion at 1p/19q1.
IVH usually results from intraventricular extension of a primary parenchymal or subarachnoid hemorrhage (ie. secondary intraventricular hemorrhage) . Primary IVH is uncommon but can occur due to vascular malformation, intraventricular tumor (choroid plexus papilloma, central neurocytoma) or aneurysm of a distal striate artery. Hemorrhage in neurocytoma is regarded as rare (19 cases in the literature: 16 central neurocytoma; 3 extraventricular neurocytoma).7 Terakawa et al estimated the rate of hemorrhage in neurocytoma as 3%. Peri-operative hemorrhage was described in 1/19 cases in a retrospective review3, and was associated with death. Rapid deterioration after hemorrhage, as seen in our case 1, is reported in central neurocytoma3.
These two cases highlight that IVH can occur with central neurocytoma and illustrate that such hemorrhage can have devastating consequences despite being a low grade tumor.
Contributed by Jane Cryan, Sarah Power, Francesca Brett