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a solitary fibrous tumor ( sft ) is a rare mesenchymal tumor previously called hemangiopericytoma ( fletcher , 2014 ) .
it has been commonly considered as intrathoracic tumor , although there have been many reported cases of extrathoracic sft , such as those in skin , muscles , thyroid , retroperitoneum , liver and so on ( van houdt et al . , 2013 ) .
sft originating from greater omentum is extremely rare and only few cases in this location have been described .
we report a case of sft of the greater omentum in a young woman , which mimicked a gynecologic neoplasm .
we have also summarized the clinical data of the reported cases of sft arising from greater omentum ( table 1 ) .
a 34-year - old woman with unremarkable medical history was diagnosed of pelvic mass in a routine gynecological exam . on physical examination ,
ultrasound revealed a pelvic mass of 6  cm with echogenicity similar to myometrium ( fig .
a solid ovarian lesion ( risk of malignancy of 34% with logistic regression model lr2 ) vs. subserous uterine myoma was suspected by sonographic findings .
tumor marker levels ( ca-125 , ca 19 - 9 , cea ) were within the normal range . with this differential diagnosis a laparoscopy was performed which showed a well - circumscribed , pedunculated , vascular tumor appended to the great omentum ( fig .
the feeding artery to the tumor was gastroepiploic artery and two lymph nodes with diameter greater than 1  cm were observed in the omentum .
laparoscopic resection of the tumor and great omentum was performed and then , both of them were removed by open mini - laparotomy ( fig .
histological examination showed characteristic features of benign solitary fibrous tumor in some areas of the tumor , such as a patternless architecture varying cellularity variably prominent hyaline stromal collagen and branched blood vessels .
however elsewhere , the tumor was much more hypercellular and consisted of rounded or ovoid cells with limited amounts of amphophilic cytoplasm showing frequent mitotic figures numbering up 13 per 10 high - power fields ( hpf ) .
immunohistochemical staining revealed diffuse positivity for cd34 , multifocal positivity for cd99 and nuclear positivity for beta catenin , while smooth muscle actin ( sma ) , desmin , kit and dog-1 were negative .
the case was reviewed by a multidisciplinary oncology team and she was advised not to undergo adjuvant treatment , but a careful follow up was initiated to rule out local recurrence or distant metastasis . at 32  months after surgery , the patient is disease - free .
the prevalence of sft is low and those originating from greater omentum are extremely rare . patients diagnosed of this type of tumor can experience abdominal pain or vomiting due to an abdominal mass , but they are mostly asymptomatic , as in the current case .
an acute abdomen because of the rupture of the tumor has been described in some patients ( bovino et al . , 2003 , kk et al . , 2009 ) .
according to the reported cases , sft of the greater omentum usually occurs in the fifth to seventh decade of life , with no gender predilection . nevertheless , our patient was younger than most of the other patients affected by this tumor .
diagnosing sft is difficult because of the resemblance to other lesions such as leiomyoma or mesothelioma ( van houdt et al . , 2013 ) .
moreover , if sft originates from greater omentum and is pedunculated as our case , it can mimic other more common pelvic tumors .
sfts are generally positive for cd34 , cd99 and bcl-2 and occasionally sma , but they are usually negative for s-100 , desmin and cytokeratins ( fletcher , 2014 , van houdt et al . , 2013 ) .
ultrasonographic appearance of sft has been described as a highly vascularized solid mass with well - defined margins ; computerized tomography usually shows similar findings ( bertolotto et al . , 1996 ) .
nevertheless , approximately 1520% of them are malignant ; especially tumors larger than 10  cm .
histological criteria of malignancy include high cellularity and mitotic activity ( more than 4 per 10 hpf ) , pleomorphism , cytonuclear atypia and tumor hemorrhage or necrosis ( demicco et al . , 2012 ) .
surgical resection is the treatment of choice , but malignant sft has a potential for local recurrence and metastases , even several years after surgery ( slupski et al . , 2007 ) . in some of the reported cases ,
an omentectomy was carried out in addition to tumor excision , even though there is no evidence that it decreases local recurrence .
we decided to resect the great omentum due to the finding of two suspicious lymph nodes . at present , based upon the low incidence of sft and poor existing data , the prognosis of these patients remains uncertain .
( 2012 ) carried out a retrospective study involving 110 patients and they found 5- and 10-year disease - specific survival rates of 89 and 73% , respectively .
moreover , they did a risk of metastasis stratification model based on age , size and mitotic index , which classified patients into low , moderate or high risk groups . according to this model
2013 ) analyzed the outcomes after diagnosis and treatment of sft in 81 patients , local recurrence rate at 5  years was 29% and metastasis rate was 34% .
factors related to worse prognosis were tumor size ( >  10  cm ) , positive resection margins and high mitosis rate ( more than 4 per 10hpf ) .
of the 21 cases of sft of the greater omentum reported , only 9 had a tumor size   10  cm , as our patient , and it is considered a good prognostic factor . on the other hand , high mitosis rate seems to be related to local recurrence and metastases , although data are not conclusive due to the limited number of cases .
the current case was considered as malignant because of the histological findings and complete excisional laparoscopic surgery was performed , with tumor - free surgical margins . because of its size of 6  cm , it could be expected as a good outcome , but the high mitosis rate increases the risk of recurrence and metastases . nowadays , there is no evidence for a beneficial role of adjuvant treatment , but some reports proposed adjuvant radiotherapy and show response to chemotherapy and other biological treatments , although its effectiveness has not been proven ( park et al . , 2011 , van houdt et al . , 2013 ) .
therefore , we decided not to provide adjuvant treatment to our patient . however , as the clinical behavior of solitary fibrous tumors is difficult to predict and she had a significant risk of recurrence or metastasis , a long - term follow up was initiated .
in summary , we have presented a rare case of sft arising from greater omentum in a young woman , which mimicked a gynecologic tumor .
this case is novel because the age of the patient is lower than the expected in this type of tumor ; besides , the combination of prognostic factors is not the most common : on the one hand , tumor size is a good prognostic factor , but otherwise the high mitotic index is associated with poor prognosis .
we want to emphasize that the diagnosis of a malignant tumor in a woman of reproductive age has some implications since tumor treatment and follow - up can affect her fertility .
the gynecologist should consider alternative diagnoses when faced with a pelvic tumor and have support of other specialists to ensure the best treatment for each patient . in cases of uncertain prognosis like this ,
written informed consent was obtained from the patient for publication of this case report and accompanying images .
a copy of the written consent is available for review by the editor - in - chief of this journal on request .
we report a case of solitary fibrous tumor ( sft ) of greater omentum in a young woman . 
 sft arising from the greater omentum can mimic a gynecologic neoplasm . 
 sfts are generally benign but some of them are malignant and have uncertain prognosis . 
 an adequate follow - up is essential in these patients .