October 27, 2016
A 4-year-old boy admitted in the emergency room with headache, diplopia, and papilledema
Supratentorial CNS Embryonal Tumor (formerly PNET)
- Background:
- Primitive neuroectodermal tumors (PNETs) represent a group of highly aggressive, undifferentiated malignant tumors of the central nervous system. They are WHO grade IV tumors with a tendency to subarachnoid dissemination.
- Cerebral supratentorial PNETs are rare tumors and account for 5% of all intracranial tumors in children. Typically they occur during the first 10 years of life and have a male predilection.
- The term PNET has been removed from the diagnostic lexicon in the new WHO 2016 classification. They should be referred to as embryonal tumors with multilayered rosettes (ETMR) if the C19MC amplification is present, atypical teratoid/rhabdoid tumors if there is INI1 loss, or simply CNS embryonal tumors NOS if there is no inmunohytochemical information available.
- Clinical Presentation:
- Symptoms and signs are non-specific and include seizures, nausea, vomiting, headache, irritability and lethargy.
- Key Diagnostic Features:
- MR reveals well marginated lesion, isointense on T1WI, T2WI, and FLAIR, with necrotic-cystic changes, blood products, and calcifications.
- Typically there is avid heterogeneous enhancement and restricted diffusion due to the high cellularity of the tumor.
- There is CSF tumor dissemination in a large proportion of patients, and spinal imaging is important for disease staging.
- It is important to consider the diagnosis of supratentorial PNET in a child with a large supratentorial mass and signs of high cellularity (iso/hyperdensity on CT, isointensity on T2W and restricted diffusion).
- Differential Diagnoses:
- CNS embryonal tumors and ATRT typically occur in children; however, ATRT occurs more frequently under the age of 2. Both tumors present as large heterogeneous masses, with signs of restricted diffusion due to their high cellularity; however, ATRT tends to be less homogenous, with intratumoral hemorrhage occurring more frequently, as well as peripheral cysts.
- DWI can help differentiate PNET from other glial tumors and from parenchymal ependymomas that usually show no restricted diffusion and are typically hyperintense on T2W (while PNET tends to be isointense). Both these tumors are also heterogenous due to cystic and hemorrhagic foci; however, focal astrocytomas typically show no calcifications, while in intra-axial ependymomas calcifications are frequent.
- Treatment:
- Treatment usually includes surgical resection and craniospinal radiation with or without chemotherapy.
