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PEDIATRIC TUMORS
John Hicks
Texas Children's Hospital, Houston, TX

INDEX OF TABLES

Part A: ELECTRON MICROSCOPY

Ultrastructural Features of Small Round Cell Tumor of Childhood

Neuroblastoma (Fig. 1)
Neurosecretory Granules
Neurites, Neurofilaments and Intertwining Cell Processes
Schwann Cells
Satellite Cells
Differentiation Toward Ganglion Cells
Neuroblasts
Intermediate Cells
Ganglion Cells, Immature
Ganglion Cells, Mature

Rhabdomyosarcoma (Figs. 4A & B)
Myosin (Thick) and Actin (Thin) Filaments
Z-disc Material
Myosin/Ribosome Complex
Leptomeric Fibrils
Randomly Oriented Intermediate Filaments

Ewings Sarcoma Figs. 3)
Glycogen Deposits

Lack of Intervening Stroma
Rare Cell Processes and Neurosecretory Granules
Rudimentary Cell Junctions/Small Desmosomes
Few Cytoplasmic Organelles Except Polysomes
Intermediate Filaments, small foci

Peripheral Primitive Neuroectodermal Tumor (PPNET)
Neurites with Microtubules
Pleomorphic Neurosecretory Granules
Intervening Supporting Stroma
Tangles of Neurites
Glycogen Particles, numerous and dispersed
Prominent Polysomes

Leukemia/Lymphoma (Fig. 2)
Round Cells Lacking Cell Junctions
No Matrix
+/- Granules and Lysosomes

 

Selected Electron Micrographs of Small Round Cell Tumor of Childhood
Figure 1 - Neuroblastoma Figure 2 - Lymphoma
Figure 1: Neuroblastoma in Pediatrics: Intertwining cell processes with occasional dense core granules. Figure 2: Lymphoblastic Lymphoma in Pediatrics: Dyscohesive neoplastic cells with close apposition of cell membranes, but with no intercellular junctions. Nuclei with prominent nucleoli and cytoplasm with lack of tumor-defining ultrastructural features.
Figure 3 - Ewing's sarcoma Figure 4A - Rhabdomyosarcoma
Figure 3: Ewing’s Sarcoma in Pediatrics: Relatively bland appearing tumor cells with dispersed chromatin and single nucleoli. Cytoplasm contains abundant "lakes" of glycogen. Figure 4A: Rhabdomyosarcoma in Pediatrics: Frequent disorganized, haphazardly arranged z-band material and thick and thin myofilaments in cytoplasm.
Figure 4B - Rhabdomyoblast Figure 4B. Well organized myofilament differentiation in well differentiated rhabdomyoblast.

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