Background Fetus in fetu (FIF) is a rare developmental abnormality in which a malformed fetus is found within the body of other twin. It was first described by Johann Friedrich Meckel in the late 18th century. Majority of cases have been described in neonates and children and only seven cases have been reported after the age of 15 years (table 1). The first reported case of FIF in an adult man, whose age was 47 years, is by Dagradi et al 1 All reported cases of adult FIF were in male gender. We aim to report this case since to the best of our knowledge this case is the first case of FIF in a female gender of 17 years age and reviewing the literature. Table 1 Fetus in fetu in adult cases published in between 1999 and 2016

Case presentation A 17-year-old woman presented with abdominal lump for 5 years, which was gradually increasing in size. It was associated with pain in abdomen which was on and off in nature. She was also complaining of early satiety but there was no history of significant weight loss. There was no history of altered bowel habits and urinary symptoms. Her menstrual history was within the normal limits. There was no history of twin birth or teratoma in the family. Her general, physical and systemic examinations were within the normal limits. On abdominal examination, there was a mass involving the whole of the abdomen (figure 1). This abdominal lump was firm to hard in consistency, its surface was irregular, margins were ill-defined and it was not moving with respiration. With these clinical information except to say abdominal tumour, it was not possible to conclude a final diagnosis. Figure 1 Showing abdominal lump with ill-defined margin.

Investigations On evaluation, beta-human chorionic gonadotropin (β-HCG), alpha feto protein and routine blood investigations were found within the normal limits. An abdominal contrast-enhanced computed tomography (CECT) scan showed a well-defined mass that measured approximately 25×23×15 cm, extending from epigastrium to upper pelvis (figure 2). It was showing fat density areas, soft tissue and multiple calcified density components of various sizes and shapes resembling the shape of vertebrae, ribs and long bones. This mass was causing displacement and compression of adjacent abdominal viscera. Figure 2 Abdominal contrast-enhanced computed tomography showing 25×23×15 cm mass with multiple calcified densities compressing the adjacent abdominal viscera.

Differential diagnosis On the basis of clinical findings (slow growing abdominal lump with firm to hard consistency, irregular surface and ill-defined margins) and CECT findings (well-defined mass with fat density areas and multiple calcified density resembling shape of vertebrae, ribs and long bones), a clinical diagnosis of FIF was made preoperatively.

Treatment On exploration, there was a large retroperitoneal encapsulated mass, extending from the under surface of the liver reaching up to the pelvic rim (figure 3). It was grossly displacing intra-abdominal viscera however no invasion was noted. The contents of the tumour consisted of hairs, mature bones and other body parts (figure 4). The contents were removed in toto and a part of cyst wall which was densely adherent to the mesenteric vessels was left behind in order to prevent devascularization of gastrointestinal tract. The remaining cyst wall was cauterised. On macroscopic examination, the mass measured 30×16×10 cm and was composed of hairy cheesy material, multiple teeth and structures resembling limb buds. On cutting section, it showed fatty, cartilaginous and bony areas along with another cystic area of size 8×7 cm. Microscopically, there was an admixture of different elements including neural, intestinal, cartilaginous and bone along with skin adnexal structures and adipose tissue. However, no immature elements were seen. A final diagnosis of FIF was given on the basis of histopathological findings. Figure 3 Showing encapsulated mass extending from the under surface of the liver reaching up to the pelvic rim. Figure 4 Specimen consists of hairs, mature bones and other body parts.

Outcome and follow-up Her postoperative period was uneventful. She has now been on our follow-up for the last 24 months with normal level of β-HCG and is doing well.