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Paediatric Radiology |
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Imaging
Findings T2W images show a mixed intensity mass, predominantly cystic while sagittal T1W images reveal cyst showing hemorrhage. Diagnosis: PRIMITIVE
NEUROECTODERMAL TUMOR (PNET) PNET
was first conceptualized by Hart and Earle (1) who defined them as highly
cellular tumors composed of more than 90 to 95% undifferentiated cells.
PNET's are histologically similar to medulloblastomas.
PNET's are uncommon tumors, comprising less than 5% of
supratentorial neoplasms in children, commonly seen in children under age
of 5 years and presenting as raised intracranial pressure or seizures. PATHOLOGY: PNET's
most frequently occur in the deep cerebral white matter and are usually
quite large at the time of presentation.
Grossly, they have sharp margins, even though histological
examination shows spread of the tumor cells peripherally beyond the
apparent tumor edge. Necrotic areas and foci of calcification are seen in
almost one half of tumors. IMAGING
FINDINGS: NON CONTRAST CT: The solid portions of the tumor tend to be hyperdense when compared to
normal brain, cystic areas and foci of punctuate calcification are common;
hemorrhage is seen in approximately 10%. AFTER IV CONTRAST: There is always enhancement, which may be solid and homogenous,
heterogeneous or ring like depending upon the size and number of
associated cysts and necrotic foci. MR APPEARANCE OF
PNET's: Is
that of a large, apparently well-marginated mass that can be located
either in the cerebral hemisphere or in the lateral ventricle. Appearance ranges from homogenous to markedly heterogenous to
a rim of solid tumor surrounding central necrosis, punctate calcifications
may be not be apparent or appear as foci of low signal intensity. The
cystic areas are of low intensity on T1 weighted sequences and of very
high intensely on T2 weighted sequences when hemorrhage is present, it is
of high signal intensity on T1 weighted sequences and mixed intensity on
the T2 weighted sequences, depending upon the chemical state of the Iron.
Infusion of paramagnetic contrast results in enhancement similar to
that seen on CT when a large, sharply marginated mass is seen in a young
child, the diagnosis of PNET should be suggested particularly when the
mass is markedly heterogenous. REFERENCES: Hart
MD, Earle K.M. Primitive neuroectodermal tumor of the brain in children. Cancer
– 1973; 32: 890 - 897. Kingly
DPE, Horwood - Nash DC. Radiological
features of the neuroectodermal tumors of children. Neuroradiology, 1984;
26: 463 - 467. Atlmon.N.
Fitz CR. Chiang.S.H, Hoewood
- Nash Radiologic characteristics of primitive neuroectodermal tumors in
childern. An J Neuroradiology 1985; 6: 15 - 18. Chambers
EF, Turski PA, Sobel .D. Radiologic characteristics of primitive cerebral
neuroblastomas Radiology 1981; 139: 101 - 104. CONTRIBUTION Dr.
Ashok Raghavan, Manipal Hospital, Bangalore
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