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，又称腹腔内韧带样纤维瘤（intra-abdominal desmoid tumor））较为罕见，目前文献中仅报道过少量病例。其临床谱涵盖无症状、恶心、早饱感、腹痛及消化道出血。尽管该肿瘤在组织学上呈良性特征，但可发生局部侵袭，侵袭性亚型可导致显著的发病率与死亡率升高。

病例报告
本文报道1例52岁西非男性患者，病程1年，表现为间歇性便血与间歇性腹胀。结肠镜检查发现1枚直径4mm的直肠息肉及内痔。食管胃十二指肠镜检查（EGD）显示，距十二指肠壶腹远端4~5cm处存在严重十二指肠狭窄。进一步行腹盆部增强计算机断层扫描（CT）检查，可见肠系膜内一枚5.0×3.7×4.3cm的肿块，包绕十二指肠远端节段。遂行剖腹探查术，从空肠处完整切除该肿块。组织病理学检查与免疫组化分析结果证实，该病变为肠系膜纤维瘤病（韧带样纤维瘤），细胞核β-连环蛋白（β-catenin）和平滑肌肌动蛋白（SMA）呈阳性表达，STAT6、结蛋白（desmin）、钙调肌球蛋白（caldesmon）、广谱细胞角蛋白（pan-cytokeratin）及c-KIT均呈阴性表达，Ki67指数小于1%。

结论
本病例报告凸显了肠系膜纤维瘤病的诊断难点，因其临床表现缺乏特异性。识别肠系膜纤维瘤病的不典型表现及相关危险因素，有助于早期诊断、病情管理与治疗。尤为重要的是，这也有助于预防肠梗阻、肠缺血及瘘管形成等并发症。