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A non-enhancing, well-defined mass within the left lateral ventricle is in contact with the septum pellucidum (which is bowed to the right) and possibly extending down into the ipsilateral foramen of Monro. The left lateral ventricle is dilated. This lesion is T1 hypointense, T2 hyperintense and demonstrates higher signal than CSF on FLAIR study.
ADC demonstrates facilitated diffusion compared to brain (>1400 x 10-6 mm2/s). The remainder of the brain is normal. No features to suggest tuberous sclerosis.
The intraventricular mass within the left lateral ventricle is favored to represent a subependymoma. Central neurocytoma is a less likely differential given lack of enhancement.
The patient went on to have a resection.
Sections show a paucicellular glial tumor with extensive microcystic change. Glial cells form small clusters and aggregates set within a fibrillary background. No necrosis or mitoses are seen.
FINAL DIAGNOSIS: subependymoma, WHO grade I.