Tumori della cresta neurale - Facoltà di Medicina e Chirurgia ...

ALLEGATO 1 Electron Microscopy of Tumors of the Peripheral Nerve Sheath
Tumors of the peripheral nerve are predominantly those of the nerve sheath but can also include
some peripheral primitive neuroectodermal tumors,
gastrointestinal autonomic nerve tumors, and peripheral neuroblastoma. neuroblastoma.
This presentation
will concern tumors of the peripheral nerve sheath - schwannoma,
schwannoma,
neurofibroma,
neurofibroma,
perineurioma, perineurioma,
and malignant peripheral nerve sheath tumor, tumor,
and their variants. variants.
THE CELLS OF THE NERVE SHEATH
The epineurium is a layer of connective tissue enclosing the other layers of the nerve.
The nerve sheath cells are principally the Schwann
cell and the perineurial cell, both characterized by cytoplasmic processes.
Schwann cells, the inside layer of the endoneurium, surround the axon and produce myelin,
external lamina and collagen. collagen.
They have interdigitating cytoplasmic processes and
continuous external lamina. In myelinated nerves there is one Schwann Schwann
cell per axon,
and in non-myelinated non myelinated nerves there are several axon segments within a single single
Schwann cell,
but with very few layers of schwannian plasma membrane.
The Schwann cell is neural-crest
neural crest derived and is positive for S100 protein, protein,
Leu7, laminin, laminin,
and myelin basic protein, and negative for cytokeratin, epithelial epithelial
membrane antigen (EMA), desmin and muscle actins. actins.
Perineurial cells form a few circumferential layers outside the endoneurium.
endoneurium.
They are bipolar (rarely rarely tripolar) tripolar)
cells with very long, thin processes. processes.
The perineurial cell differs from a fibroblast by the presence of external lamina (continuous
( continuous or interrupted),
interrupted),
pinocytosis, and intercellular junctions.
Perineurial cells derive from the arachnoid, and display positivity for EMA, but not for cytokeratin, cytokeratin,
S100 protein or (usually ( usually) ) Leu7,
although perineurial-like perineurial like cells occasionally show actin positivity. positivity
A third cell type has been identified within the endoneurium as a slender dendritic spindle cell which displays CD34 positivity, positivity,
and which appears to be distinct from Schwann, Schwann,
perineurial or endothelial cells. cells.
It may be analogous to the dermal dendritic fibroblast. fibroblast.
CD34 positive cells are found in increased numbers in neurofibromas and in Antoni B areas of schwannomas,
schwannomas,
but only in about 15% of MPNST.
(Cyril Cyril Fisher, Fisher,
London, London,
United Kingdom)
Kingdom