fetus in fetu ( fif ) was first described by meckel in the early 19th century , and it was defined as a mass containing a vertebral axis often associated with other organs or limbs around this central axis in 19351 ) . since then , this disease entity has been rarely reported .
with advance in prenatal diagnosis techniques , more than half of the cases have been detected prenatally . in this report fif
differentiating a fif from other cause of meconium peritonitis is discussed with review of literature .
a 31-year - old primi pregnant woman with minimal prenatal care and no history of fertility medications or in vitro fertilization came to our institution at 33 weeks ' gestation .
obstetric sonography at 26 weeks ' gestation revealed a single fetus of appropriate size for gestational age , but bowel wall edema and small bowel obstruction were suspected .
sonography at 29 weeks ' gestation showed a large amount of amniotic fluid and the aforementioned findings were not changed .
sonography at 33 weeks ' gestation which was performed at our institution showed that a markedly dilated bowel and the bowel obstruction were still suspicious .
the amount of amniotic fluid was increased , and a 6.86.4 cm pseudocyst and a 4.393.22 cm calcified heteroechgenic mass were found ( fig .
our clinical diagnosis was a giant cystic type of meconium obstruction associated with peritonitis induced by perforation and atresia of the small bowel .
the weekly ultrasonographic follow - ups showed no significant interval changes . at 38-weeks ' gestation , a female newborn weighing 4,120 g was delivered by an elective cesarean section , with apgar scores of 2 , 4 and 9 at 1 , 5 and 10 minutes .
the baby had a grossly distended abdomen and did not present any evidence of dysmorphic features .
the patient had respiratory distress after birth which was probably induced by elevated abdominal pressure due to the abdominal mass and ascites and necessitated assisted ventilation .
laboratory tests showed no abnormalities except for a slightly decreased albumin level of 3.1 g / dl and an alpha - fetoprotein level of 5,845 ng / ml .
abdominal radiographs showed a large abdominal mass containing multiple calcifications in the lower abdomen ( fig .
abdominal ultrasonography showed a huge solitary and cystic mass which filled most of the abdomen .
abdominal computed tomography ( ct ) showed a well - demarcated intraabdominal mass measuring 15.610.2 cm , with a heterogeneous enhancing solid portion , fatty component and a cystic portion containing multiple calcification or ossification lesions .
a teratoma arising from both ovaries was the most likely diagnosis , and she underwent an elective laparotomy at 5 days of age . during surgery , we observed a small amount of ascites with a mass attached to the colon and mesocolon which was thought to be a splenic flexure ( fig .
3 ) . the mass did not have a cystic sac and had a buttock - like lesion with skin and hair follicles , fatty tissue , a finger and a coccyx .
a tubular structure was also identified along the mesenteric border of the sigmoid colon , which was suspected of an intestinal duplication cyst .
the mass measuring 1595 cm had a smooth surface partially covered with skin or thin membrane and 2 finger - like lesions ( fig .
4 ) . on section , most of the mass consisted of yellowish fat tissue , and the middle portion of the mass had a tubular structure which looked like an intestine .
microscopic examination showed a well developed gastrointestinal tract , liver , pancreas and finger as well as 3 germinative layers , but the vertebral axis was not identified .
meckel first coined the term " fetus in fetu " in the late 18th century to describe an encapsulated fetoid tumor within a fetus .
after then , willis1 ) stated in 1935 that the presence of an axial skeleton distinguishes between fif and a teratoma , which remains a clinical definition .
gonzalez - crussi4 ) defined fif in a narrower sense as " highly organotypic development and presence of a vertebral axis with arrangement of tissue around this axis " .
thirty - one cases of fif were reported before 1900 , and thereafter only 11 cases were reported between 1900 and 19563 ) .
its incidence is very low and is estimated to be 1 per 500,000 birth2 ) .
the incidence of fif has increased and the incidence seems to be higher than in previous reports . with advances in prenatal diagnosis techniques , more than half of the cases have been detected prenatally .
our case was also detected prenatally , but it was misdiagnosed as cystic meconium peritonitis .
meconium peritonitis represents aseptic peritonitis caused by the spreading of meconium into the fetal peritoneal cavity .
cyst occurs when the site of perforation is not sealed and a thick - wall cyst is formed within the intestinal loops .
the cystic type of meconium peritonitis is thought to be a life - threatening condition .
therefore , rapid deterioration of fetal status can be possible in this type . in this regard meconium pseudocyst
must be antenatally differentiated from other intra - abdominal cystic images such as urinary bladder distention , ovarian cyst , intestinal duplication , hematoma , teratoma and fetal infection5 ) .
fif can be presented prenatally as an abdominal cystic mass with diffuse calcification or ossification by ultrasonography .
ct or mri has sometimes been used as a confirmatory diagnostic tool to differentiate between these diseases .
however , if the vertebral axis - like structure is seen within a mass on prenatal imaging , it is also helpful in differential diagnosis .
it is still controversial whether the presence of the vertebral axis should be included in the diagnostic criteria for fif .
some previously reported cases without the vertebral axis were diagnosed as fif as in our case .
it is thought to occur at the very early stage of embryo development before the ventral fusion of the lateral body walls .
the spectrum is diverse from conjoined symmetric twins to a form of organized teratoma , but fif is thought to be a different category from teratoma based on its organo - level development , rarity of malignant potential and the possession of the same karyotype with the host .
chromosome analysis was performed on 29 cases , which showed the same chromosomes as the host 's .
miura et al.6 ) reported that in 2 cases undergoing dna methylation assay , 46.7% and 66.7% of clones from the mass had an unmethylated paternal allele .
they suggested that 2 isolated blastocysts originated from one zygote , and one of the two was implanted into the other blastocyst during the process of methylation . in this
regard , presence of vertebral axis to diagnosis of fif may not be a prerequisite factor .
pathological confirmation is essential for a final diagnosis , and genetic testing can provide unambiguous evidence for a fetus in fetu .
several cases have been reported in older children with a delay in diagnosis and 1 case in a 39-year - old man , was and they showed no malignant potential7 ) .
the prognosis of intracranial fif is not good . only 1 case survived , and 2 cases were stillborn ,
2 cases were terminated fatally due to intracranial hypertension , and 2 cases were terminated with their parents order .
hopkins et al.8 ) reported a retroperitoneal fif presenting as a right abdominal mass which proved to be a teratoma with malignant components requiring chemotherapy8 ) .
there are 2 other cases with local recurrence as a teratoma without malignant potential in the literature ; they were located in the retropenitoneum and recurred at 1 and 2 years of age , respectively9 , 10 ) .
for this reason , it is necessary to regularly follow up patients with fif for the surveillance of recurrence .
we report a case of fif which was misdiagnosed as cystic meconium peritonitis prenatally . abdominal cystic mass should be differentiated from various conditions .
although fif is considered as a rare disease , it has been increasingly reported in the literature .
thus , fif should also be included in the differential diagnosis of cystic masses in fetus .
 fetus - in - fetu ( fif ) is a rare congenital condition in which a fetiform mass is detected in the host abdomen and also in other sites such as the intracranium , thorax , head , and neck . 
 this condition has been rarely reported in the literature . herein , we report the case of a fetus presenting with abdominal cystic mass and ascites and prenatally diagnosed as meconium pseudocyst . 
 explorative laparotomy revealed an irregular fetiform mass in the retroperitoneum within a fluid - filled cyst . 
 the mass contained intestinal tract , liver , pancreas , and finger . 
 fetal abdominal cystic mass has been identified in a broad spectrum of diseases . however , as in our case , fif is often overlooked during differential diagnosis . 
 fif should also be differentiated from other conditions associated with fetal abdominal masses . 
Introduction
Case report
Discussion
Conclusion