they are found most commonly in the cranial and peripheral nerves , and occurrence in the omentum is very rare .
however , there have been some cases reported to develop serious complications and , if there was malignancy , to cause metastasis or recurrence .
we presented a case of schwannoma originating from the great omentum , including histological and immunohistological studies .
a 55-year - old man was referred to our department for the treatment of a tumor detected close to the stomach by ultrasound . medical examination including
ultrasound had been regularly performed to follow up his gallbladder stone for the past 6 years .
although he had no complaints and symptoms , the tumor had been increasing in size over one year .
abdominal and endoscopic ultrasound showed a 2.0  1.3 cm cystic mass lateral to the wall of the stomach .
its component included an 11.8  5.7 mm elevated lesion ( fig . 1 , fig
computed tomography scan of the abdomen and pelvis showed a 2.6  1.9 cm cystic mass , which was slightly enhanced , and a gallbladder stone ( fig .
3 ) . magnetic resonance imaging demonstrated a hyperintense mass on t2-weighted image . a distance from the stomach wall
laboratory tests , including tumor makers , were normal . under a perioperative diagnosis of cystic tumor in the abdomen and cholelithiasis
, we performed laparoscopic resection with vessel sealing system , which revealed a 2.0 cm mass arising from the great omentum , not adherent to other organs .
grossly , the tumor was configured by a well - encapsulated round mass measuring 30  18  15 mm in diameter ( fig .
histologically , the spindle - shaped cells were arranged in interlacing bundles and fascicles , together with varying numbers of tumor cells containing various amounts of light brown or grayish pigment ( fig .
these alternate with looser antoni b tissue , which is comprised of cells showing clear , vacuolated cytoplasm due to lipid accumulation .
immunohistochemically , most of the neoplastic cells reacted moderately to nse , ncam and s-100 protein ( fig .
schwannomas are classified as one kind of the peripheral nerve sheath tumors , of which schwannnoma and neurofibroma are the most frequent . currently , the most precise determination of the tumor 's cell type is established by its immunohistochemical profile , ultrastructural features , or both . a tumor composed of cells with distinctly schwannian characteristics
schwannomas are known to mainly arise from the peripheral and caranial nerves , the extremities and the retroperitoneum .
they are seldom found in the abdomen , especially the extragastrointestinal tract , of which solitaly schwannoma of the great omentum is an extremely rare tumor . in 303 schwannomas reported by das gupta
, one case originated from the retroperitoneum , others from the central nervous system and peripheral nerve . in another review of the literature , stout and
of these , 37 were in the stomach , 3 in the small bowel , and none in the omentum and the abdominal cavity . previously published cases of schwannoma in the omentum were collected from a computerized medical literature search ( pubmed ) . only 6 cases of schwannoma from the great omentum have been observed   ( table 1 ) .
we can see that more cases of schwannoma from the lesser omentum have been recorded than from the great omentum .
it is mentioned that the lesser omentum contains a small amount of nerves in almost equal distribution , the great omentum has a paucity of nervous tissue and anatomically consists of fat and lymphatic tissue .
we found a case of malignant schwannoma arising from the omentum which demonstrated peritoneal metastasis , and another reported case of the small intestine emphasized poor prognosis since only 2 of 24 patients survived for more than 5 years .
benign schwannomas are also reported to increase in size and to eventually cause complications by compressing other organs or by causing bleeding in or outside the gastrointestinal tract .
pigmented schwannoma is another type of schwannoma , usually arising from the sympathetic nervous system .
additionally abdominal schwannomas cause diagnostic problems because clinical symptoms are uncharacteristic or misleading even if the tumor is large .
ct imaging typically showed a low attenuation mass , peripheral enhancement and cystic degeneration pattern .
mri disclosed schwannoma of low signal intensity on t1-weighted image and high signal intensity on t2-weighted image . in spite of these characteristic , it is difficult to exclude other abdominal tumors , leiomyomas , lymphomas and unspecified sarcomas etc . while previous cases confirm that the tumor may attain a considerable size , bigger than 5 cm or producing symptoms , our case of a schwannoma which was small and asymptomatic is hardly diagnosed .
however this tumor showing progression in size is thought to have potential to behave very aggressively despite benign histological features , which stresses the need of more information on this type of tumor and diagnosis .
consequently , histological analysis of the surgical specimen is necessary for a correct diagnosis , and common treatment for schwannoma is surgery .
therefore laparoscopic resection seemed to be the most adequate method to diagnose and rule out malignant tumor as a minimally invasive surgery .
the majority of tumors can be safely resected , the surgeon being careful of the dividing feeder vessels because schwannomas are well known as hypervascular tumors . to our knowledge
there are no case reports documenting other treatments , including chemotherapy for schwannomas in the abdominal cavity .
 schwannoma in the abdomen is an uncommon neoplasm that occurs most frequently in the cranial and peripheral nerves ; it is extremely rare in the great omentum and only 6 cases of schwannoma of the great omentum have been observed previously . 
 we report the case of a schwannoma found in the great omentum of a 55-year - old man who was treated with laparoscopic surgery . 
 though it was difficult to diagnose preoperatively , the tumor showed malignant potential by rapidly increasing in size . 
 histologically it was configured by a well - encapsulated round mass measuring 30  18  15 mm in diameter . 
 immunohistochemically most of the neoplastic cells reacted moderately to nse , ncam and s-100 protein . 
 we document the clinicopathological study of a schwannoma of the great omentum , followed by a review of the literature . 
Introduction
Case Report
Discussion