Presentation
Seizure.
Patient Data
A sizable mass appears to be intra-axial, within the right frontal lobe. It does not have contrast enhancement or calcification but is profoundly hypoattenuating without definite cystic components. It exerts little positive mass effect despite its size and there is, perhaps, thinning of the overlying bone, both features suggesting the lesion is longstanding and indolent.
It most likely represents a low-grade adult-type glioma. Although unlikely, this lesion could represent an extra-axial cystic lesion (e.g. cystic meningioma). MRI is required for further characterization.
An intra-axial mass arises from the middle and inferior frontal gyri on the right with only minimal positive mass effect, despite its relatively large size.
The lesion is of very high T2 signal, and much of it at least partially suppresses on FLAIR.
There is no associated contrast enhancement, no raised cerebral blood volume and ADC values are markedly facilitated. MR spectroscopy at the periphery of the lesion demonstrates decreases in all metabolites (not shown).
Conclusion:
This lesion most likely represents a diffuse adult-type glioma. In a 30-year-old, and the absence of calcification and in the presence of T2-FLAIR mismatch, this most likely represents an astrocytoma IDH-mutant. There are no high-grade features.
Case Discussion
This case was first understood as an extra-axial lesion, however reviewing the images in the multidisciplinary meeting a new conclusion was reached: the tumor involves the cortex in the right frontal lobe and its features are those that suggest a low-grade glioma, such as a protoplasmic type (partial suppression on FLAIR). The adjacent bone remodeling suggests a long-term growth.
The patient underwent surgical resection and the tumor was confirmed histologically.
Histology
MICROSCOPIC DESCRIPTION: Paraffin sections show a moderately hypercellular astrocytic glioma. Tumor cells are predominantly of protoplasmic morphology with uniform small round hyperchromatic nuclei and a paucity of processes. Prominent microcyst formation is noted in several areas of the tumor. No mitotic figures are identified and there is no vascular endothelial cell proliferation and no necrosis. The features are of diffuse astrocytoma of protoplasmic type (WHO Grade II).
DIAGNOSIS: Diffuse astrocytoma of protoplasmic type (WHO Grade II).
Note: Previously, protoplasmic astrocytomas were classified as a subtype low-grade astrocytoma, however, as of the 4th revised edition (2016) of the WHO classification of CNS tumors, protoplasmic astrocytomas no longer exist as distinct entities, but rather are considered as a pattern of certain gliomas, requiring IDH +/- 1p19q status for full classification.
IDH mutation status is not provided in this case and thus according to the 4th revised edition and 5th edition of the WHO classification of CNS tumors, this tumor would, therefore, be designated as a diffuse astrocytoma NOS.
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