PLEXIFORM NEUROFIBROMA
Plexiform neurofibromas are characterized by the
presence of multiple fascicles and nodules composed of Schwann
cells and collagen surrounded by perineurial cells. Put another
way, multiple foci, probably interconnected, of
intraneural hyperplasia of Schwann cells and other elements of
peripheral nerve are present. Focal aggregates of Schwann cells
( microscopic schwannomatosis) are seen in a few examples, but Verocay bodies or
foci of prominent nuclear palidasing (cf. schwannomas) are not a
feature of prototypic neurofibromas. The relative proportion of Schwann
cells to perineurial cells is variable from area to area.
Neural filaments or axons are scattered between the Schwann cells, but
the ratio of neural filaments or axons to Schwann cells is less than
one to one (cf. neuromas). Round cells and/or
lymphocytes are sometimes seen within the endoneurium which may
be focally or diffusely expanded by accumulations of tissue mucin.
Exclusive intraneural
localization is often seen in examples not involving the skin.
However, intraneural patterns are usually associated with an extraneural
or diffuse component when they are found in the dermis.
A plexiform neurofibroma of skin was once thought to be a specific indicator for neurofibromatosis (von Recklinghausen's disease or NF1), but there have been cases where this did not seem to be the case. Malignant transformation occasionally occurs, but prophylactic excision would not be an attractive option given the multiple nature, including involvement of deep or visceral sites, of such lesions in neurofibromatosis.
For a more complete and much better discussion of this subject, see chapter 36 by Reed and Argenyi in the eighth edition of Lever's Histopathology of the Skin.
A plexiform neurofibroma of skin was once thought to be a specific indicator for neurofibromatosis (von Recklinghausen's disease or NF1), but there have been cases where this did not seem to be the case. Malignant transformation occasionally occurs, but prophylactic excision would not be an attractive option given the multiple nature, including involvement of deep or visceral sites, of such lesions in neurofibromatosis.
For a more complete and much better discussion of this subject, see chapter 36 by Reed and Argenyi in the eighth edition of Lever's Histopathology of the Skin.
From a young adult who has had similar
lesions removed or biopsied:
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| Fig. 1 Very low power (direct scan)
showing multiple fascicles of varying appearance composed of spindle
cells involving the dermis and subcutis. Most of the intervening
reticular dermis has been replaced by spindle cells associated with
delicate, collagenous stroma. Mitoses were not found in the lesion. |
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| Fig. 2. Cross section of a very
cellular fascicle of spindle cells that are almost randomly oriented. |
Fig. 3. Cross
section of a very
cellular fascicle showing peripheral spindle cells oriented
perpendicular to the central spindle cells. The location and
orientation of these cells would suggest they are perineurial cells. |
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| Fig. 4. The
central core of this
structure has the features of a normal small nerve cut in
cross-section. This is surrounded by several layers of spindle
cells oriented perpendicular to the long axis of the nerve. This focus
may represent hyperplasia of perineurial cells without significant
hyperplasia of Schwann cells. |
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| Fig. 5. Spindle cells, round cells,
and collagen fibers are widely separated by stroma containing tissue
mucin in this fascicle. |
Fig. 6. High power view showing
some of the round cells, collagen fibers, and tissue mucin (pale blue
material). |
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