Paediatric Radiology


 
Case 7 :  


A young male (11 years) presented with convulsions and headaches of 2 months duration. A MRI head was performed. 
What is the diagnosis?

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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