Final Diagnosis
Papillary glioneuronal tumor, CNS WHO grade 1
Methylation profiling (Heidelberg classifier, v12.5) placed the tumor in the papillary glioneuronal tumor, PRKCA-fused class with a calibrated score of 0.85.
Discussion
Papillary glioneuronal tumors (PGNTs) are rare supratentorial tumors primarily affecting young adults (median age at onset: 16 years), with no sex predilection [WHO]. They most frequently arise within the temporal lobe, having the appearance of a solid and cystic mass on MRI. The solid portions of the tumor are T1 isointense to hypointense and T2 hyperintense, with areas of contrast enhancement. PGNTs are characterized histologically by a biphasic pattern consisting of flat-to-cuboidal glial cells forming pseudopapillary structures and a neuronal interpapillary component in a background of neuropil. The neuronal component generally consists of medium-sized, monomorphic neurons, with ganglion cells observed in a minority of cases. Vascular hyalinization may be prominent in some cases. The glial pseudopapillary structures show immunoreactivity for glial markers such as GFAP and Olig2, while the neuronal component shows positive staining for neuronal markers, including synaptophysin and NeuN. PGNTs exhibit a characteristic SLC44A1::PRKCA fusion, which is virtually unique to these tumors. Both the biphasic morphologic pattern and fusion of PRKCA are required for diagnosis. The prognosis for treated PGNT is favorable, with 5-year progression-free survival reported as greater than 80%. Recurrence of PGNT is exceptional and has been reported in only one molecularly confirmed case.
Conclusion
PGNT is a rare, benign tumor of young adults with characteristic biphasic morphology and PRKCA gene fusion.
References
- Hou Y, Pinheiro J, Sahm F, et al. Papillary glioneuronal tumor (PGNT) exhibits a characteristic methylation profile and fusions involving PRKCA. Acta Neuropathol 137, 837–846 (2019). https://doi.org/10.1007/s00401-019-01969-2
- Ahmed A, Dawood H, Gerard J, et al. Surgical Resection and Cellular Proliferation Index Predict Prognosis for Patients with Papillary Glioneuronal Tumor: Systematic Review and Pooled Analysis. World Neurosurg. 107, 534-541 (2017). ISSN 1878-8750. https://doi.org/10.1016/j.wneu.2017.08.041.
- Varlet P, Komori T, Rosenblum MK, et al. Papillary glioneuronal tumor. In: WHO Classification of Tumours Editorial Board. Central nervous system tumours [Internet]. Lyon (France): International Agency for Research on Cancer; 2021. (WHO classification of tumours series, 5th ed.; vol. 6). Available from: https://tumourclassification.iarc.who.int/chapters/45.