supratentorieller primitiver neuroectodermaler Tumor (PNET)

Supratentorial

primitive neuroectodermal tumor in an adult: a case report and review of the literature. Magnetic resonance image of mass. A: Flair showing mild peritumoral edema, B: T1-weighted image without contrast, C: T1-weighted image with contrast showing homogenous enhancement, D: Gradient echo.

jmedicalcasereports.biomedcentral.com • CC-by-2.0

Primitive

neuroectodermal tumor of the central nervous system in a 5-year-old.

Wikipedia • CC BY-SA 3.0

Magnetic

resonance imaging of pineal region tumours. Primitive neuroectodermal tumour (PNET) involving the pineal gland in a 3-year-old boy. Well-circumscribed, tumour arising from the pineal gland (arrow), which has mostly intermediate signal as well as high signal foci on sagittal T1-weighted image (a) and intermediate, low and high signal on axial T2-weighted image (b). The pineal tumour demonstrates heterogeneous contrast enhancement on sagittal T1-weighted image (c). The tumour causes obstructive hydrocephalus by exerting localised mass effect and compression of the quadrigeminal plate, cerebral aqueduct and third ventricle

insightsimaging.springeropen.com • Open Access

Toddler with

left arm weakness. Axial CT without contrast of the brain (above left) shows an ill-defined large heterogenous right periventricular mass causing midline shift to the left. Axial T2 (above right) and T1 MRI without contrast (below left) of the brain show the mass to be fairly well circumscribed, primarily solid with some cystic components, and to show heterogenous enhancement on axial T1 MRI with contrast (below right). The diagnosis was primitive neuroectodermal tumor.

pediatricimaging.org • CC-by-nc-sa 4.0

Lizenz: CC BY-SA 4.0

supratentorieller primitiver neuroectodermaler Tumor (PNET)

Primitiver neuroektodermaler Tumor des ZNS Radiopaedia • CC-by-nc-sa 3.0 • de

Primitive neuroectodermal tumors (or CNS PNET) were considered aggressive neoplasms of the brain, most frequently encountered in the pediatric population. Importantly, the term no longer appears in the current WHO classification of CNS tumors .

Please refer to embryonal tumors with multilayered rosettes (ETMR) for a current discussion.

Terminology

The term has fallen out of favor and has been removed from the 2016 update to the WHO classification of CNS tumors, now incorporated into the term embryonal tumors with multilayered rosettes (ETMR) .

Traditionally a number of tumors variably fell under the umbrella term CNS PNET :

medulloblastoma: by far the most common (discussed separately)
supratentorial PNET: 15% of all CNS PNET
- pineoblastoma: most common supratentorial PNET (discussed separately)
- ependymoblastoma: also removed from the WHO in 2016 and incorporated into ETMR
- medulloepithelioma (discussed separately)
spinal PNET: rare

Additionally, a primitive neuronal component can also be identified in glioblastomas, previously referred to as glioblastoma with PNET-like component but now simply recognized as a histological pattern .

The remainder of this article focuses on what has historically been denoted as supratentorial primitive neuroectodermal tumor (sPNET).

Note: CNS PNETs should not be confused with peripheral primitive neuroectodermal tumor (pPNET) which are musculoskeletal tumors.

Epidemiology

They typically occur in the pediatric population, usually during the first 10 years of life, with a mean age of 5 years . There is a recognized male predilection.

Clinical presentation

Clinical presentation is non-specific and cannot be distinguished from other aggressive intracranial masses. Symptoms of raised intracranial pressure, seizures and focal neurology may be present.

Pathology

Supratentorial PNETs are composed of primitive undifferentiated neuroepithelial cells and are WHO grade IV tumors. They are small round blue cells, malignant embryonal tumors which can show divergent differentiation of variable degree along neuronal, glial, or rarely mesenchymal lines. They are extremely variegated in histology and this reflects in their imaging characteristics. Homer Wright rosettes are seen.

Associations

Radiographic features

Supratentorial PNETs, by definition, occur above the tentorium and can either arise in the cerebral hemispheres or within the lateral ventricles.

CT

often seen as a large irregular mass
typically iso to hyper-attenuating on non-contrast imaging
cystic components are common (≈65% )
calcification can be common (≈70% )
shows heterogeneous contrast enhancement

Angiography

Non-specific and range from avascular to hypervascular .

MRI

The extent of peritumoral vasogenic edema is surprisingly low given the size of the mass and the aggressive tumor characteristics .

T1: highly variable and can be hypointense to isointense
T2
- generally high signal solid components
- cystic components are common
- low signal portions due to calcific components
T1 C+ (Gd)
- shows markedly heterogeneous enhancement
- leptomeningeal seeding is common
DWI: often shows restricted diffusion
MR spectroscopy
- elevated choline
- decreased NAA
- elevated taurine (Tau) peak (relatively specific for PNET)

Treatment and prognosis

Supratentorial PNET's generally have a poorer prognosis than medulloblastomas, with a low 5-year survival rate. Leptomeningeal and/or subarachnoid seeding are common, necessitating imaging and treatment of the whole neuraxis.