探讨胎儿期腹膜后内寄生胎的超声与磁共振的影像特征，与出生后CT对比，提高内寄生胎的产前诊断水平。

回顾性分析2016年10月至2020年1月湖北省妇幼保健院6例腹膜后内寄生胎产前超声、磁共振影像及其临床资料，并与出生后CT、手术和病理结果进行对照分析。

产前超声首次发现肿块大小范围为11 mm×10 mm×11 mm至40 mm×37 mm×25 mm。超声发现肿块后完成磁共振检查。宿主出生1~12 d超声复查肿块大小范围为54 mm×45 mm×38 mm至125 mm×112 mm×83 mm。6例产前均正确诊断为腹膜后内寄生胎，最早于孕28⁺⁴周正确诊断。临床结局：6例宿主于出生5~16 d择期手术，其中3例行开放手术，3例行腹腔镜微创手术，随访至2021年9月均未复发。病理结果：6例腹膜后内寄生胎，单寄生胎4例，双胎内寄生胎2例；其中1例合并成熟性畸胎瘤。与病理结果对照，产前超声检出率由高到低依次为骨性组织、颅骨环、长骨、脊柱轴、肢芽、血管蒂等。磁共振检查能更准确地判断内寄生胎与腹内毗邻脏器结构之间的关系。

超声联合磁共振、CT成像有助于提高胎儿期腹膜后内寄生胎的诊断率。

To investigate the ultrasound and magnetic resonance imaging (MRI) characteristics of retroperitoneal fetus-in-fetu.

The prenatal ultrasound and MRI images of 6 cases of retroperitoneal fetus-in-fetu diagnosed at the Maternal and Child Health Hospital of Hubei Province from October 2016 to January 2020 were retrospectively analyzed, and the findings were compared with the postnatal computed tomography (CT), surgical, and pathological results.

The size of the masses at the first prenatal ultrasound diagnosis ranged from 11 mm×10 mm×11 mm to 40 mm×37 mm×25 mm, and the gestational age ranged from 22⁺² weeks to 34⁺¹ weeks. MRI was performed at 22⁺³ weeks to 40⁺⁵ weeks of gestational age. The mass size ranged from 54 mm×45 mm×38 mm to 125 mm×112 mm×83 mm on ultrasound during 1-12 days after birth. All the 6 cases were accurately diagnosed as retroperitoneal fetus-in-fetu before delivery, and the earliest diagnosis was made at 28⁺⁴ weeks of gestational age. Regarding clinical outcome, all the 6 cases underwent elective surgery during 5-16 days after birth, of which 3 underwent open surgery, and the other 3 underwent laparoscopic minimally invasive surgery, one of whom was converted to open surgery due to difficulties of laparoscopic mass separation. There was no recurrence during follow-up. With regard to pathological results, there were 6 cases of retroperitoneal parasitic fetuses, 4 cases of single parasites, and 2 cases of twin parasites; one case was associated with mature teratoma. Using the pathological results as the golden standard, the highest detection rate of prenatal ultrasound occurred in the bone tissue and skull ring, followed by long bones, spinal shafts, limb buds, vascular pedicles, and skin.

Ultrasound combined with MR and CT as multimodal imaging is helpful to improve the diagnosis of fetal retroperitoneal fetus-in-fetu.