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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).
January 2022

A 24-year-old woman with no relevant medical history presents to the emergency department for an episode of nausea, right-sided altered sensation, and aphasia, followed by a generalized tonic-clonic seizure. On arrival to the ED, the patient has no acute complaints and a normal neurologic exam.

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