病例报道：寄生胎

Case Report: Fetus-in-Fetu

摘要: 背景：寄生胎(fetus-in-fetu, FIF)为极罕见的先天性异常，多位于腹膜后，临床表现缺乏特异性，易与肠梗阻或畸胎瘤等混淆。影像学检查对术前识别及手术决策具有重要价值。病例介绍：患儿男，2岁，以“腹部不适4天、哭闹、食欲差、2天未排便”入院。体检上腹部可触及约10 × 9 cm质韧肿块，活动度可，无明显压痛。腹部彩超提示小肠囊性扩张并左上腹混合回声包块，考虑肠梗阻。进一步盆腔CT示腹腔偏左巨大团块状混杂密度灶，内含脂肪、软组织及骨性密度影，周围伴囊性低密度，增强后见系膜血管与病灶内部结构相连，术前考虑腹腔内寄生胎；肿瘤标志物部分升高(如CEA、CA19-9等)。行开腹手术完整切除肿物，术中见肿物来源于腹膜后，囊实性，大小约15 × 9 × 8 cm，与胰腺及脾静脉关系密切；抽出囊液约400 ml白色浑浊黏稠液。病理示皮肤、胰腺、神经、骨/软骨/骨髓及完整肠壁、胃壁结构等分化良好组织，结合临床影像最终诊断为寄生胎。术后肿瘤标志物下降，随访15个月患儿生长发育正常。结论：儿童腹膜后巨大占位且影像显示脂肪/骨性成分并与宿主系膜血管相连时，应高度怀疑寄生胎。CT (必要时增强)对术前诊断与鉴别诊断至关重要；治疗以完整切除肿物及囊壁为主，术后建议结合肿瘤标志物与断层影像进行随访，以警惕少数复发或恶变相关风险。

Abstract: Background: Fetus-in-fetu (FIF) is an extremely rare congenital anomaly, mostly located in the retroperitoneum. Its clinical manifestations lack specificity and are easily confused with intestinal obstruction or teratoma. Imaging examinations are of great value for preoperative identification and surgical decision-making. Case Presentation: A 2-year-old male child was admitted to the hospital with the chief complaints of “abdominal discomfort for 4 days, crying, poor appetite, and no defecation for 2 days”. During physical examination, a firm mass approximately 10 × 9 cm in size was palpable in the upper abdomen, with good mobility and no obvious tenderness. Abdominal ultrasound indicated cystic dilation of the small intestine and a mixed echo mass in the left upper abdomen, suggesting intestinal obstruction. Further pelvic CT showed a large, heterogeneous density mass in the left side of the abdominal cavity, containing fat, soft tissue, and osseous density shadows, accompanied by cystic low density areas around it. After enhancement, the mesenteric blood vessels were found to be connected to the internal structure of the lesion. Preoperative diagnosis considered an intra-abdominal fetus-in-fetu; some tumor markers were elevated (such as CEA, CA19-9, etc.). An exploratory laparotomy was performed to completely remove the mass. During the operation, the mass was found to originate from the retroperitoneum, being cystic-solid, approximately 15 × 9 × 8 cm in size, and closely related to the pancreas and splenic vein. Approximately 400 ml of white, turbid, and viscous cystic fluid was aspirated. Pathology showed well-differentiated tissues such as skin, pancreas, nerves, bone/cartilage/bone marrow, and complete intestinal and gastric wall structures. Combined with clinical imaging, the final diagnosis was fetus-in-fetu. After the operation, the tumor markers decreased, and the child’s growth and development were normal during the 15-month follow-up. Conclusion: In children with a large retroperitoneal mass and imaging showing fat/osseous components connected to the host’s mesenteric blood vessels, fetus-in-fetu should be highly suspected. CT (enhanced CT if necessary) is crucial for preoperative diagnosis and differential diagnosis. The main treatment is complete resection of the mass and cyst wall. After the operation, it is recommended to conduct follow-up in combination with tumor markers and tomographic imaging to be vigilant against the risks of recurrence or malignancy in a small number of cases.