Fetus-in-fetu in the cranium of a 4-month-old boy: histopathology and short tandem repeat polymorphism–based genotyping

Case report

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✓Fetus-in-fetu is a very rare condition in which one fetus is contained within another. About 100 cases have been reported, and in most of these the fetus was located in the retroperitoneum. The authors describe an extremely rare case of an intracranial fetus-in-fetu in an extraaxial location. This is the eighth intracranial fetus-in-fetu to be reported, the first intracranial extraaxial case, and involves the oldest documented patient with this condition.

Histopathological analysis of the mass revealed a degenerated amnionic membranelike tissue, well-differentiated extremities (including fingerlike structures), skin, matured lungs, well-formed intestines, cerebellar and cerebral tissue, and a notochord with ganglion cells. DNA analysis using short tandem repeat polymorphisms confirmed that the fetus-in-fetu mass and the host infant had heterozygous alleles and were of identical sex and genotype.

Abbreviations used in this paper: CT = computed tomography; MR = magnetic resonance; STR = short tandem repeat.

Article Information

Address correspondence to: Seung-Ki Kim, M.D., Ph.D., Division of Pediatric Neurosurgery, Seoul National University Children's Hospital, 103 Daehangno, Jongno-gu, Seoul 110-799, Republic of Korea. email: nsthomas@snu.ac.kr.

© AANS, except where prohibited by US copyright law.

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    Preoperative CT scans and MR images of the well-demarcated large cystic and solid mass mixed with internal fat and calcified components, occupying half of the total intracranial space and severely compressing the brain parenchyma. A: Unenhanced CT scan. B: Axial T1-weighted image. C: Axial T1-weighted image with Gd enhancement. D: Axial T2-weighted image. E: Sagittal T1-weighted image with Gd enhancement. F: Coronal T1-weighted image with Gd enhancement.

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    Intraoperative photographs obtained before debulking the mass (left), and during the process of debulking (right). The mass was covered with a whitish-yellow membrane pathologically confirmed to be amniotic and showed sharp extra-axial demarcation. The mass was easily detached from the surrounding brain parenchyma. A deformed, armlike structure with fingers was located extraaxially.

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    Photomicrographs of the various tissue types found in the fetus-in-fetu. H & E stain. A: Amnionic membrane-like tissue, covered by double layers of cuboidal epithelium and basal cells and supported by loose fibrous tissue is shown (original magnification × 40). B: Notochord (original magnification × 40). C: Cerebellum with Purkinje cells (original magnification × 200). D: Well-formed larynx (original magnification × 40). E: Lung tissue (original magnification × 100). F: Intestinal tissue (original magnification × 1.25).

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