Supplementary Material for: Distal duodenal stricture secondary to mesenteric fibromatosis (intra-abdominal desmoid tumor) of the jejunum

Introduction
Mesenteric fibromatosis (intra-abdominal desmoid tumor) is rare, with only a few cases reported in the literature. Clinical symptoms range from asymptomatic, nausea, early satiety, abdominal pain, and gastrointestinal bleeding. Although histologically benign, such a tumor may become locally invasive, and aggressive forms contribute to significant morbidity and mortality.

Case Presentation
We report the case of a 52-year-old West African male with a 1-year history of intermittent hematochezia and intermittent bloating. Colonoscopy revealed a 4mm rectal polyp and internal hemorrhoids. Esophagogastroduodenoscopy (EGD) revealed a severe duodenal stricture 4-5 cm distal to the ampulla. Further work-up with contrast-enhanced computed tomography (CT) of the abdomen and pelvis revealed a 5.0 x 3.7 x 4.3 centimeter mass within the mesentery, encasing the distal portion of the duodenum. Exploratory laparotomy was performed, and the mass was excised from the jejunum. Histopathology findings and immunohistochemical analysis revealed the diagnosis to be mesenteric fibromatosis (desmoid tumor), positive for nuclear β-catenin and SMA, and negative expression of STAT6, desmin, caldesmon, pan-cytokeratin, or c-KIT. The Ki67 index is <1%.

Conclusion
This case report highlights the diagnostic challenges of mesenteric fibromatosis due to its nonspecific clinical presentation. Recognizing uncommon presentations of mesenteric fibromatosis and risk factors aids in early diagnosis, management, and treatment. Importantly, this also aids in the prevention of complications such as intestinal obstruction, bowel ischemia, and fistula formation.

引言
肠系膜纤维瘤病（mesenteric fibromatosis，腹腔内韧带样纤维瘤）较为罕见，目前文献报道的病例寥寥无几。其临床表现多样，可无明显症状，亦可表现为恶心、早饱、腹痛及消化道出血。尽管该肿瘤在组织学上呈良性表现，但可发生局部浸润，侵袭性病例可导致显著的发病率与死亡率升高。

病例报告
本次病例报告介绍1例52岁西非男性患者，该患者有1年间歇性便血及间歇性腹胀病史。结肠镜检查可见1枚4mm直肠息肉及内痔。食管胃十二指肠镜（Esophagogastroduodenoscopy，EGD）检查提示，壶腹远端4~5cm处存在重度十二指肠狭窄。随后行腹部及盆腔增强计算机断层扫描（contrast-enhanced computed tomography，CT）检查，结果显示肠系膜内存在一枚5.0×3.7×4.3cm的肿块，包绕十二指肠远端段。遂行剖腹探查术，从空肠处切除该肿块。组织病理学检查及免疫组化分析确诊为肠系膜纤维瘤病（desmoid tumor，韧带样纤维瘤），肿瘤细胞核β-连环蛋白（β-catenin）及平滑肌肌动蛋白（smooth muscle actin，SMA）呈阳性表达，信号转导与转录激活因子6（STAT6）、结蛋白（desmin）、钙调结蛋白（caldesmon）、广谱细胞角蛋白（pan-cytokeratin）及c-KIT均呈阴性表达，Ki67增殖指数<1%。

结论
本次病例报告凸显了肠系膜纤维瘤病的诊断难点——其临床表现缺乏特异性。识别肠系膜纤维瘤病的罕见临床表现及相关危险因素，有助于实现早期诊断、干预与治疗。尤为重要的是，此举还有助于预防肠梗阻、肠缺血及瘘管形成等并发症。