Presentation
Headaches.
Patient Data
Acute non-communicating obstructive hydrocephalus with prominent transependymal edema secondary to a heterogeneous mass in the left cerebellum.
An ill-defined mixed solid and cystic tumor centered on the cerebellar vermis and extending predominately into the left cerebellum. A second enhancing solid nodule in the left lateral cerebellum. The solid components show heterogeneous enhancement and diffusion restriction (-600 x 10^-6 mm^2/s). A single tiny focus of susceptibility artefact in the central portion of the lesion. No T2 flow voids around the lesion.
Mass effect on the fourth ventricle, tonsillar descent, with marked dilatation of the lateral and third ventricles, with periventricular high T2 /FLAIR signal compatible with subependymal edema.
Conclusion:
Cerebellar tumor with mass effect causing obstructive hydrocephalus and tonsillar herniation. Medulloblastoma is the favored diagnosis (most likely SHH subtype).
Case Discussion
The patient went on to have a resection.
Histology
Sections show pieces of cerebellum infiltrated by tumor. The tumor is composed of sheets of cells. The malignant cells are relatively monomorphous with irregularly-shaped polygonal nuclei, granular chromatin and minimal cytoplasm. The cell density is somewhat variable, with highly cellular areas and less cellular areas where the tumor cells are set in a fibrillary background. Apoptoses are scattered throughout the tumor but mitotic figures are relatively infrequent. There are scattered true Homer Wright rosettes and perivascular psuedorosettes, as well as columns of cells. There is one small area there are some pale nodules of cells set within the tumor; these pale nodules are negative with reticulin stain, while the intermodular tumor is positive.
Immunohistochemistry:
- Synaptophysin shows patchy but strong positivity.
- Chromogranin shows weak focal positivity.
- CD45 is negative.
- GFAP shows patchy positivity.
- INI1 staining is retained.
- Beta-catenin shows strong cytoplasmic staining but no nuclear staining.
- p53 shows wild-type staining.
- ATRX staining is retained (not mutated)
- IDH1 R132H is negative (not mutated).
- GAB1 is diffusely and strongly positive.
FINAL DIAGNOSIS: Medulloblastoma, desmoplastic/nodular (histologically defined), and SHH-activated and TP53-wildtype (genetically defined).
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