Case of the Month
Section Editor: Nicholas Stence, MD
Children's Hospital Colorado, Aurora, CO
January 2022
Next Case of the Month Coming February 1...
Supratentorial CNS Embryonal Tumor, Not Otherwise Specified (Formerly PNET) with Recurrent Lesions and Leptomeningeal/Subarachnoid Seeding
- Background:
- Supratentorial CNS embryonal tumors, not otherwise specified (NOS) are rare but highly aggressive, malignant, undifferentiated/poorly differentiated tumors of neuroepithelial origin (WHO grade IV) with affinity for leptomeningeal/subarachnoid dissemination.
- The 2016 WHO classification divided the formerly known CNS PNET into 1 of 2 groups: the genetically defined entity ETMR (C19MC-altered) and everything else with no available immunohistochemical information, defined as CNS embryonal tumor, NOS.
- Clinical Presentation:
- Typically presents in the pediatric population (commonly in the first 10 years) and with a male predilection
- Clinical manifestations are unspecific; if the location is supratentorial, it may present with raised intracranial pressure, seizures, headache, and focal neurologic deficits.
- Key Diagnostic Features:
- At neuroimaging, the diagnosis CNS embryonal tumor, NOS should be considered for any hypercellular and heterogeneous tumor of the CNS in the pediatric population.
- Spinal imaging is important for disease staging due to the relatively common subarachnoid seeding.
- Peritumoral vasogenic edema extension is surprisingly slight compared with the size of the tumor and its aggressive characteristics.
- CT: Iso- to hyperattenuating; heterogeneous (due to cysts, calcifications, hemorrhage)
- MRI: Highly variable T1 signal (hypo- to isointense); iso- to hyperintense T2 signal (solid components with high-signal, necrotic-cystic constituents but low signal due to calcified components/blood products); heterogeneous enhancement and leptomeningeal seeding may be seen; restricted diffusion at DWI/ADC mapping; increased CBV may result from vascular endothelial hyperplasia; spectroscopy tends to show higher choline than in malignant gliomas (higher cellularity and mitotic activity) and a relatively specific taurine elevated peak (3.4 ppm).
- Differential Diagnoses:
- In the pediatric population, the main differential includes other CNS embryonal tumors, such as medulloblastoma, atypical teratoid/rhabdoid tumor, and embryonal tumors with multilayered rosettes.
- When referring to adults, we may include other entities such as astrocytoma, ependymoma, oligodendroglioma, or metastatic tumor (still rare in the third decade of life).
- In this case, the initial MRI resembled a high-grade glioma due to lesion heterogeneity, high vasogenic edema, restricted diffusion of the solid components, and elevated rCBV, despite the well-defined margins.
- In this case, the later MRI showed recurrent lesions in the supra- and infratentorial compartments, and also dissemination for the leptomeninges and by the subarachnoid space, compatible with the already available pathologic diagnostic of an embryonal CNS tumor, NOS.
- Treatment:
- Poor prognosis, with a low 5-year survival rate
- Treatment of the whole neuraxis may be necessary (surgical excision and/or radiotherapy and/or chemotherapy).
- Prophylactic craniospinal irradiation is essential for initial treatment (once leptomeningeal dissemination is commonly observed, as it occurred in our case).
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