Anaesthetic Management of Retroperitoneal Fetus-in-Fetu - A Rare Case Report and Literature Review
Authors: Lokeshwaran Sivachandran  , Pratibha Mudgal  , Sapna Bathla  , Shipra Aggarwal  
Published: December 2023

Fetus-in-fetu (FIF) is a rare congenital anomaly caused by the abnormal development of monochorionic diamniotic twins. It usually presents as an abdominal mass in infancy or early childhood. It has to be differentiated from teratoma which has the potential to be malignant. Here, we report a case of a 13-month-old girl child with fetus-in-fetu in the retroperitoneum. In spite of its rare incidence, preoperative diagnosis is possible through various imaging techniques. The child underwent exploratory laparotomy and complete excision of FIF under general anaesthesia. Even though complete resection is curative, long-term follow-up with alpha fetoprotein and beta-human chorionic gonadotropin is essential for monitoring malignant transformation.
Fetus-in-fetu (FIF), otherwise called as cryptodidymus, is an extremely rare congenital disease caused by the abnormal development of monochorionic diamniotic twins. Its incidence is about 1 in 5,00,000 births and so far, only 200 cases are reported worldwide.[1] FIF occurs when a complete foetus is parasitized by one or multiple incomplete foetuses. It can be divided into two types namely internal and external. If a foetus is inside the body of a host, it is known as internal fetus-in-fetu, it is referred to as an external fetus-in-fetu if it is attached to any surface of the host.
There is no gender predisposition noted in the incidence of FIF but few articles found a male predominance in the ratio of 2:1.[2] Even though FIF occurs mostly in infants and children < 3 years of age, there are cases reported in adults and pregnant women as well. The oldest patient with FIF recorded in the literature was 47 years old during the time of diagnosis.[3] The most common presentation of FIF is gradually enlarging abdominal mass almost 80% in the retroperitoneum.
Differentiation from other abdominal tumours including teratomas, is necessary because the latter has potential for malignancy. FIF is usually malformed because of the pressure exerted by the host organs. It can affect their host, hence, early diagnosis and management is crucial. Various imaging modalities like radiography, Color-Doppler ultrasound, Computed Tomography (CT), Magnetic Resonance Imaging (MRI) have increased the pre-operative diagnosis rate.[4] Treatment of FIF is essentially surgical and prognosis after en bloc resection is favourable. In this article, we present the anaesthetic management of a rare case of retroperitoneal fetus-in-fetu in a girl child.
The perioperative management of fetus-in-fetu cases is not yet reported anywhere in the literature. The preoperative evaluation and optimisation is very crucial since it reflects on the anaesthetic management and post-operative recovery. Explorative laparotomy in the paediatric age group is quite challenging because of the associated major fluid shifts, blood loss as the mass is located adjacent to the large vessels. Smooth induction and extubation are essential to minimise hemodynamic fluctuations. Meticulous fluid management and adequate analgesia are critical for enhanced recovery. This case report will aid anaesthesiologists in the deeper understanding regarding management of fetus-in-fetu cases.