Detection of a prenatal mature tumor arising from the external genitalia in a female fetus: fetus‐in‐fetu or teratoma?

Abstract

We describe an unusual fetal perineal tumor detected by ultrasonography (US) at 20 weeks of gestation. The sonographic features and location were very uncommon. Magnetic resonance imaging (MRI) was contributory. Histological examination of the surgical specimen showed either a mature teratoma or a fetus-in-fetu (FIF).A 30-year-old woman, gravida 1, was referred for prenatal US at 20 weeks of pregnancy. A perineal mass measuring 31 × 21 mm and apparently arising from the fetal external genital organs was identified. The mass was bilobar, had a solid structure and did not show obvious vascularization. The sex of the fetus was difficult to determine, and amniocentesis was performed, along with biochemical, hormonal and genetic studies, including testosterone and 17-OH progesterone assay, and SRY by molecular biology. The fetus had a normal female karyotype (46, XX) and a normal hormone profile in the amniotic fluid [testosterone: 7, 8 nmol/L (max: 9 nmol/L) 17-OH progesterone: 123 ng/dL (max: 300 ng/dL)]. The SRY gene was absent.

Fetus in fetu from newborn’s mediastinum: case report and a review of literature

“…The most common site of localization of FIF is in the retroperitoneum (80%), but it can be also found in the skull, oropharynx, left ventricle, sacrum, ovary, testis, or external genitalia of the host twin [9,14]. To our knowledge, this is the fourth case of FIF localized in the thorax.…”

Dorsolumbar Parasitic Rachipagus Twin, Case Report

“…If the fetus is located inside the body of its twin, this process occurs in the other twin's body cavities; this condition is termed fetus in fetu. 8,13,19 Sometimes, a malformed, abnormal fetus enveloped inside its twin may remain totally silent until later ages, or it can cause an intra-abdominal or sometimes an intrathoracic mass. However there have been a few reports of parasitic twin location in the head, sacrum, scrotum, and even in the oral cavity.…”

“…7,21 This attached part composed of primitive embryonic tissue prevents closure of the neural tube during later development, resulting in spina bifida, or other neural tube defects. 8,14 Thus, the most A C B anticipated anomaly of the living fetus is the closure defect of the dorsal vertebral column. Location of the spinal lipoma at the same level and the origin of the parasite support this explanation.…”

“…Unlike teratoma, 6%-10% of which are malignant, rachipagus is regarded as a benign condition. 2,8 Treatment is surgical. Parasitic twin excision is sufficient for treatment, and it does not require complicated separation procedures.…”

“…8,18 Teratoma is defined as a true tumor arising from the uncontrolled growth of pluripotent stem cells. 13,18 Sometimes, teratoma may contain mature tissues such as respiratory epithelium, fat tissue, hair follicles, fingers, teeth, and jawbones.…”