= PNET = PRIMARY CEREBRAL NEUROBLASTOMA

= group of very undifferentiated tumors arising from germinal matrix cells of primitive neural tube = rare presentation of neuroblastoma

Incidence:<5% of supratentorial neoplasms in children, 30% of posterior fossa tumors

Age: mainly in children <5 years of age/ early adolescence; M÷F = 1÷1

Path: most undifferentiated form of malignant small cell neoplasms grouped with Ewing sarcoma, Askin tumor

Histo: highly cellular tumor composed of >90–95% undifferentiated cells (histologically similar to medulloblastoma, pineoblastoma, peripheral neuroblastoma)

• signs of increased intracranial pressure / seizures

Location:

1. supratentorial: deep cerebral white matter (most commonly in frontal lobe), pineal gland, in thalamic + suprasellar territories (least frequently)
2. posterior fossa (= medulloblastoma)
3. outside CNS: chest wall, paraspinal region, kidney

• large (hemispheric) heterogeneous mass with tendency for central necrosis (65%), cyst formation, hemorrhage (10%)
• intratumoral coarse dense calcifications (71%)
• thin rim of edema
• mild / moderate enhancement of solid tumor portion

CT:

• large hypodense / mixed-density mass with well-defined margins
• solid tumor portions hyperdense ← high nuclear to cytoplasmic ratio

MR:

• mildly hypointense on T1WI + hyperintense on T2WI
• remarkably inhomogeneous due to cyst formation + necrosis
• areas of signal dropout due to calcifications
• hyperintense areas on T1WI + variable intensity (usually intermediate) on T2WI due to hemorrhage
• inhomogeneously moderately enhancing mass with tumor nodules + ringlike areas surrounding central necrosis after Gd-DTPA

Cx: meningeal + subarachnoid seeding (15–40%)

DDx: Neuroblastoma usually NOT metastatic to brain!