Presentation
Increasing headache over a number of weeks. This patient initially had a CT scan (not shown) which demonstrated a left sided lesion. MRI was performed to further characterize it.
Patient Data
MRI with contrast demonstrates a large heterogeneous mass arising from the left thalamus and growing exophytically into the lateral ventricle. It is associated with dilatation of both lateral ventricles, in keeping with obstruction of their outflow at the foramen of Munro. Areas of the mass are intrinsically high signal on T1 weighted imaging and show signal drop-out on T2 weighted sequences, suggestive of hemorrhage, and on DWI the mass is quite high signal (low on ADC map - not shown), consistent with a degree of restricted diffusion, suggesting high cellularity. Following contrast administration, the mass heterogeneously enhances.
In the posterior fossa, particularly on the ventral surface of the brainstem, there is leptomeningeal enhancement, likely representing CSF seeding.
The large mass is comprised of a hemorrhagic component (yellow dotted line) and a solid enhancing cellular component (blue dotted line).
Extensive leptomeningeal disease is also present (green arrows).
This patient went on to have a craniotomy and debulking of the tumor.
Histology
MICROSCOPIC DESCRIPTION: Paraffin sections confirm the frozen section diagnosis. This is a cellular astrocytic tumor showing moderate to marked nuclear pleomorphism, confluent tumor necrosis, and vascular thrombosis. Microvascular proliferation is not a well-developed feature. There are occasional mitotic figures, and apoptoses are relatively frequent. An oligodendroglial component is not identified. A low-grade component is not identified.
FINAL DIAGNOSIS: Left thalamic astrocytoma WHO grade 4 (glioblastoma).
Case Discussion
This case elegantly demonstrates how intraparenchymal lesions can grow exophytically into the ventricles, mimicking intraventricular masses. The key observation is the degree of involvement of the thalamus and adjacent white matter. Compare this case with a similar-appearing case of central neurocytoma.
Note: IDH mutation status is not provided in this case and according to the current (2016) WHO classification of CNS tumors, this tumor would, therefore, be designated as a glioblastoma NOS.
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