CNS & pituitary tumors

Contributed by Jared T. Ahrendsen, M.D., Ph.D.

Contributed by Jared T. Ahrendsen, M.D., Ph.D., Nitin R. Wadhwani, M.D. and Rachel A. Multz, M.D.


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Contributed by Jared T. Ahrendsen, M.D., Ph.D.

Images hosted on other servers:

A 5 year old boy presents with an intracranial mass that appears to arise adjacent to the splenium of the corpus callosum. A resection is performed and shows the tumor morphology above. The tumor cells are positive for synaptophysin, NSE and INI1 and negative for GFAP and Olig2. What is the most likely molecular alteration in this tumor?

1. Biallelic loss of SMARCB1
2. DICER1 mutation
3. H3 K27M mutation
4. IDH1 R132H mutation
5. SHH pathway activation

B. DICER1 mutation. The microscopic image shows a tumor of the pineal region with high N:C ratio, nuclear molding and numerous apoptotic bodies. The morphologic and anatomic features of the tumor, combined with the patient’s young age, indicate that this tumor is most likely a pineoblastoma. DICER1 mutations can be seen in both the miRNA processing altered 1 and miRNA processing altered 2 subgroups of pineoblastoma. Answer D is incorrect because IDH1 R132H mutations are typically seen in adult type diffuse gliomas, which are uncommon in children and are positive for GFAP and OLIG2. Answer A is incorrect because biallelic loss of SMARCB1 is seen in atypical teratoid / rhabdoid tumors, which can be seen in young children and can show some morphologic overlap with pineoblastoma; however, these tumors show loss of INI1 by immunohistochemistry and are variably positive for GFAP. Answer E is incorrect because SHH pathway activation is seen in a subset of medulloblastoma. They typically arise in the posterior fossa of younger children but can show significant morphologic overlap with pineoblastoma. Answer C is incorrect because H3 K27M alterations are seen in diffuse midline gliomas, which are positive for Olig2 and can show variable positivity for GFAP.

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Reference: Pineoblastoma

A 5 year old boy presents with symptoms of increased intracranial pressure. Brain imaging reveals a mass centered in the pineal region and biopsy reveals a diagnosis of pineoblastoma. Which of the following immunostains is most specific for this diagnosis?

1. Beta catenin
2. CRX
3. H3 K27M
4. INI1
5. LIN28A

B. CRX. CRX is a transcription factor involved in retinal and pineal lineage differentiation. It is often diffusely positive in pineoblastoma and other pineal parenchymal tumors. Answer A is incorrect because aberrant nuclear beta catenin expression is generally observed in adamantinomatous craniopharyngioma and WNT activated medulloblastoma. Answer D is incorrect because loss of nuclear INI1 expression is commonly seen in atypical teratoid / rhabdoid tumors. Answer E is incorrect because LIN28A expression is commonly observed in embryonal tumors with multilayered rosettes and a subset of other tumors but is negative in pineoblastoma. Answer C is incorrect because H3 K27M is generally encountered in diffuse midline glioma, not pineoblastoma.

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Reference: Pineoblastoma