The Fetus acardius amorphus was delivered by a 32 year-old woman, gravida 2, para 4. She presented at 29 gestational weeks for an emergency caesarian section for a twin pregnancy, because of premature rupture of membranes at the Department of Gynecology and Obstetrics, University Hospital Heidelberg, Germany. The woman gave birth to a healthy girl, as well as a boy. The boy died a few days after delivery because of a brain haemorrhage as a complication of continuous positive airway pressure (CPAP) ventilation for treatment of premature lungs. Interestingly, the mother originally presented as a triplet pregnancy early in gestation. Ultrasound examination within the first trimester of pregnancy showed the presence of three heartbeats. However, later in the pregnancy, fetal ultrasound of the second trimester only confirmed presence of two viable fetuses. At delivery, besides a placenta, an ovoid mass completely covered by skin was delivered. Both, placenta as well as the additional mass was sent for pathology evaluation to the Institute of Pathology, University Hospital Heidelberg, Germany. Informed written consent was obtained from the parents to perform autopsy and to use the fetus acardius for research purposes and publication.
Gross examination of the placenta demonstrated a normotrophic, monochorionic-biamnionic placenta in 22 x 10 x 3 cm of diameter and a weight of 630 g. The placenta correlated with a triplet gestation, attached with a trivascular umbilical cord. Furthermore, the placenta showed features of a physiologically circulated and appropriate-for-gestational-age developed placenta, with focal areas of dystrophic calcifications as well as focal spots of increased fibrin aggregates within the intervillous space. There was no evidence of acute or chronic inflammation or ischemia. In addition, an ovoid mass was attached to the placenta via a small pedicle, identified as Fetus acardius amorphus.
Autopsy was performed on the fetus acardius amorphus. Macroscopic examination of the fetus acardius amorphus demonstrated a mass, 10.5 x 6.5 x 7.5 cm in diameter, and covered by mature skin with sparse, superficial hair on the surface (Figure 1(a)). This mass was attached to the placenta via a 12 cm long pedicle, consisting of two major blood vessels, an artery and a vein. Furthermore a small cyst-like structure with opaque fluid inside was observed at one end of the mass, covered by intact skin and a pedicle of hair (Figure 1(a)). The center of the mass demonstrated an organized bone column with cartilage surrounded by colloidal tissue and focal red masses (Figures 1(b), 1(c1) and 1(c2)). X-ray analysis of the skeletal system with Facitron showed the presence of a complete vertebral column with the presence of a rudimentary rib cage (Figures 1(c1) and 1(c2)). At one end of the vertebral column, an ovoid bone structure was noted which could represent a rudimentary pelvis (Figures 1(c1) and 1(c2)). However, there was no axial organization of a head, limbs or cranial-caudal poles present (Figures 1(c1) and 1(c2)). After general gross examination of the anomalous embryo, representative tissue sections were fixed in 10% formalin, embedded in paraffin and stained with hematoxylin and eosin (H&E) or immunohistochemistry for histological examination. In addition, sex determination of the fetus acardius amorphus was performed on paraffin sections of gonadal tissue using the ZytoDot 2C CEN X/Y Probe from ZytoVision. Sex identification analysis showed in CISH analysis a male gender with XY karyotype in interphase cells (Figures 1(d1) and 1(d2)). Detailed karyotype analysis was not performed because of insufficient tissue material.
As macroscopically organ structures could not be identified, with the exception of the vertebral column and the skin, random sections of the core of the mass were taken for detailed histology analysis. Histology analysis of the core mass showed differentiated skin tissue with all layers including epidermis, dermis and subcutis (Figure 2(a1)) as well as bronchus-like structures with respiratory epithelium with apical cilia and mucous-producing cells on top (Figures 2(a2) and 2(a3)). Furthermore, the core mass also demonstrated bone and cartilage tissue, as well as bone marrow with megakaryocytes, erythrocyte precursor cells as well as myelocytes in between (Figures 2(b1) and 2(b2)). Differentiated muscle cells with shapoid myocytes harboring an ovoid nucleus in the center were present as well (Figures 2(b3) and 2(b4)). The cyst-like structure showed brain tissue with hippocampal neurons (Figures 2(c1) and 2(c2)). Additionally parts of the urogenital tract were detected with male gonadal structures with testicles consisting of seminiferous tubules surrounded by a thin smooth muscle layer (Figures 2(c3) and 2(c4)). Inside the seminiferous tubules, spermatogonia as well as Sertoli cells were present, Leydig cells were embedded between the semiferous tubules, respectively (Figures 2(c3) and 2(c4)).
Moreover, within the focal red masses parts of the gastrointestinal tract with small as well as large intestine were identified (Figures 3(a) and 3(b)). The intestine was organized in a crypt villous axis, and enterocytes showed an apical brush border strongly positive for the brush border protein villin in both, crypts and villi (Figure 3). In addition, Goblet cells were identified with positive mucin 2 stains (Figure 3). Ganglion cells positive for Calretinin were detected within the Meissner and Auerbach Plexus (Figure 3).
Intriguingly, the most curious finding of this case of Fetus acardius amorphus was the abnormalities within the renal tissue (Figure 4). Indeed, the kidney of the Fetus acardius amorphus demonstrated differentiated glomeruli, but a complete lack of proximal tubules, confirmed by PAS staining as well as villin immunohistochemistry (Figure 4(a)). Findings of the fetus acardius amorphus were compared to a fetus without any evidence of abnormalities (control) and a fetus with bilateral renal hypoplasia (disease control). Both control cases were aborts from women between 20 and 25 weeks of gestational age. The control case was an intrauterine fetal death without finding an underlying maternal or fetal cause of death; the disease control was a fetus with intrauterine death because of bilateral renal hypoplasia. In both control cases, proximal tubules were present (Figure 4(a)).
In addition, within the medulla, clusters of erythrocyte precursor cells were detected, usually just found in the spleen and liver as a sign for extramedullary hematopoiesis (Figure 4(b)). Immunofluorescence of those clusters of cells showed positivity for the myeloid marker MAC 387, identifying these cells as erythrocyte precursor cells (Figure 4(b)). This was interesting because, in general, extramedullary hematopoiesis in the kidney occurs if oxygenation is impaired. Therefore, immunohistochemistry for investigating angiogenesis within the kidney was performed. Stainings of vessels with CD31 showed particularly in the renal cortex of the Fetus acardius amorphus increased presence of CD31 positive vessels, mainly within the interlobular area (Figure4(c)). Interestingly, those vessels were strongly positive in immunofluorescence stains for smooth muscle actin (Figure 4(d)). Those SMA positive vessels also seemed to have a higher degree of dilation, when compared to both controls (Figure 4(d)). However, the vessel wall did not seem to appear thicker in the case of Fetus acardius amorphus when compared to both controls. Those findings, the lack of proximal tubules, extramedullary hematopoiesis, and increased number of smooth muscle actin positive vessels are also commonly found in cases of tubular dysgenesis, although in tubular dysgenesis, arterial wall thickening and disorganization of interlobular and afferent arteries has been additionally described, which was not identified in our case of Fetus acardius amorphus. Taken together, our case of fetus acardius amorphus showed histomorphological features of tubular dysgenesis, which could occur secondary to major cardiac malformations, or the lack of a functional heart, as is the case in this presentation of Fetus acardius amorphus.