Discussion
Schwannomas are benign peripheral nerve sheath tumors derived from
Schwann cells which rarely arise in the soft tissues of the
gastrointestinal tract. Schwann cells, discovered by Theodore Ambrose
Hubert Schwann almost two centuries ago, are specialized cells dedicated
to axon myelinization and nerve trauma repair (7). Schwannomas can arise
sporadically or in the context of a few congenital conditions associated
with multiple schwannomas, such as familial schwannomatosis, Carney
complex syndrome and neurofibromatosis type 2 (8). The tumorigenesis of
these soft tissue tumors in type 2 neurofibromatosis, is associated with
the loss of the suppressor gene NF2 function, located on chromosome
22q12, which encodes Merlin (moezin-ezrin- radixin like protein, also
known as schwannomina) (9). Merlin acts as a scaffold protein indirectly
linking F-actin, modulating cell signals that promote cell survival and
proliferation through, among others, tyrosine kinase receptors, cell
adhesion, small GTPases, mammalian target of rapamycin (mTOR) and
PI3K/Akt (10).
Within the gastrointestinal tract, schwannomas are usually found in the
gastric corpus and in the right colon. There is a wide age range with
peak incidence in the seventh decade and a female predominance for
gastric schwannomas (11). Colonic schwannomas have no gender
predominance, they are usually located on the cecum, and the macroscopic
features vary from polypoid masses to bulging over the serosal surface.
Schwann cells are associated with the Auerbach´s and Meissner´s plexus
(12). We therefore, hypothesized that if the tumorigenic Schwann cell is
in the submucosal plexus the tumor configuration could be polypoid or
intraluminal. Additionally, if the tumorigenic Schwann cell is in the
myenteric plexus the tumor configuration could be non-luminal.
The presentation of symptoms depends on the location and macroscopic
configuration of the tumor. Clinical presentation of schwannoma as a
polypoid intraluminal mass is rare, and this macroscopic configuration
tends to produce lower gastrointestinal bleeding, or obstruction
symptoms (13). Other symptoms such as vague abdominal pain or even the
clinical presentation of an incidentally gastrointestinal mass detected
by radiological imaging, have also been reported in gastrointestinal
schwannoma cases (14,15). Presurgical diagnosis is the exception and not
the rule, and just a few cases have been diagnosed in pre-surgical
specimens. The rarity of the tumor in the gastrointestinal tract, the
depth of the tissue obtained through the endoscopic procedure,
submucosal location and confounding biopsy factors such as ulceration
and severe inflammatory infiltrate hinder a precise diagnosis in biopsy
specimens. In the diagnostic work-up of a mesenchymal mucosal-submucosal
gastrointestinal lesion, there is a wide differential diagnosis (16).
There were not histopathological criteria for malignancy,
gastrointestinal stromal tumor (GIST), was ruled out with the negativity
of KIT, DOG1 and CD34, as well as muscular tumors due to negativity of
Desmin and SMA. The strong nuclear and cytoplasmic positivity for S100
protein, narrowed the differential diagnosis in this case. The
morphology was not typical for Clear Cell Sarcoma Like Gastrointestinal
Tumor, usually these kinds of tumors are negative for GFAP (17), and
positive for neuroendocrine markers (18). The benign morphology, the
combined positivity for S100, SOX10 and GFAP after ruling out other
mesenchymal tumors, favored the diagnosis of schwannoma.
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