A case of fetal decapitation with intrauterine survival: prenatal diagnosis by three-dimensional transvaginal ultrasound

Introduction

Decapitation in utero is an extremely rare and catastrophic event, most commonly caused by amniotic bands. Most cases result in first-trimester intrauterine fetal demise. We present a case of fetal decapitation in utero with intrauterine survival for weeks in a fetus that had previously been determined to be developing normally. To date, only a limited number of such cases have been reported in the medical literature (1-6).

Case presentation

All procedures in this study were performed in accordance with the ethical standards of the institutional and/or national research committee(s), and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for the publication of this article and the accompanying images. A copy of the written consent form is available for review by the editorial office of this journal.

A 32-year-old woman (gravida 2, para 1), with an unremarkable medical history, underwent her first ultrasound examination at 9 weeks’ gestation following spontaneous conception. The findings confirmed a single, viable pregnancy with a normal crown-rump length of 20 mm. The patient had no lower abdominal pain or vaginal bleeding, and there was no history of inciting trauma. She was referred to our department for further evaluation at 13 weeks’ gestation after anencephaly was suspected on routine first-trimester ultrasound examination at another hospital.

We systematically scanned the whole uterine cavity using two- and three-dimensional transvaginal ultrasound, as the transabdominal ultrasound provided poor-quality images. The ultrasound scans revealed a 13-week fetus, consistent with the femur length (12 mm) in utero. Fetal cardiac activity was positive (157/min), and fetal somatic movements were observed. However, the whole fetal head was absent on all views. Notably, this differed from typical anencephaly, which usually retains the residual part of the calvaria and brain (cerebral cortex).

The fetus also presented with bilateral nuchal cystic hygroma, hydrops, and bilateral talipes equinovarus (Figure 1A). An irregular solid mass containing bone and without flow signal was observed, measuring 20 mm × 21 mm × 25 mm. With the application of high-definition live (HDlive) flow ultrasound imaging, these structures were clearly visualized and appeared to represent the head (Figure 1B). The fetus and the mass moved independently with changes in maternal position within the amniotic cavity, without evidence of anatomical adherence. No amniotic bands were visible in the uterus after a thorough search of the amniotic cavity. Amniotic fluid was normal.

Figure 1 The ultrasonographic findings and postnatal appearance of the fetus (A) Complete absence of the whole fetal head with bilateral nuchal cystic hygroma, hydrops, and an irregular solid mass containing bone (arrow) beside the trunk; (B) the fetal appearance visualized using ultrasound high-definition live ultrasound mode, with the arrow indicating the irregular solid mass; (C) facial structures, including eyes, mouth, and ears, were identified in the mass.

An intrauterine fetal demise was identified one day later. The fetal physical examination revealed a male fetus with normal upper limbs and bilateral talipes equinovarus. The head and part of the neck were absent. A thin, translucent membrane covered the cephalic end of the neck, which was also surrounded by skin. Gross pathology confirmed the prenatal ultrasound findings and revealed no evidence of amniotic bands. Facial structures, including the eyes, mouth, and ears, were identified on the mass, confirming it as the separated head (Figure 1C). Whole-exome gene sequencing showed a normal result with a male karyotype. The findings indicated that fetal decapitation had occurred at approximately 10 weeks’ gestation based on the size of the head.

Discussion

Decapitation may occur secondary to acute disruptive events, such as strong uterine contractions (7), major trauma (8), or fetal adhesion. In two reported cases of fetal decapitation resulting from acute trauma, fetal demise occurred either immediately following or during the traumatic event, with evidence of skin tissue loss and hemorrhage at the neck transection site. Mazzitelli et al. hypothesized that fetal adhesion may result from elasticity of the amnion, leading to the entrapment of embryonic or fetal structures in the extraembryonic celomic space or from stickiness of the exposed exocelomic space following amnion disruption, resulting in adherence of anatomical parts of the embryo or fetus (6).

In the present case: (I) the pregnant woman had no clinical history related to uterine contractions or trauma; and (II) the fetus and the mass moved independently with changes in maternal position within the amniotic cavity, without evidence of anatomical adherence. We hypothesized that this was a case of spontaneous fetal decapitation caused by amniotic bands; however, this remains speculative due to the lack of definitive evidence.

Fetal decapitation is not typically considered a distinct pathological entity but rather a severe manifestation of a broader disruptive anomaly, such as amniotic band sequence or early embryologic disruption. This type of acrania is most likely attributable to amniotic bands, which can produce disruptive events. Through end-artery injury, such bands can obstruct normal embryonic or fetal development, resulting in a spectrum of severe congenital disorders involving the craniofacial area, abdominal wall, or other more complex anomalies.

Mazzitelli et al. noted that among seven reported cases of acephaly, only one showed evidence of amniotic bands. Similarly, among five reported cases of spontaneous intrauterine decapitation, only one had identifiable amniotic bands (1-6). Thus, although amniotic bands are often suspected as the underlying cause, direct evidence is often lacking upon examination.

In the present case, no amniotic bands were detected on either ultrasound examination or gross pathological assessment. Regarding the absence of amniotic bands in cases of decapitation, two explanations have been proposed. First, amniotic bands may regress or dissolve following the decapitation event. Second, mechanisms such as extraembryonic coelomic entrapment and exocoelomic stickiness may lead to fetal decapitation.

It is generally assumed that fetal demise occurs shortly after decapitation. However, in two previously documented cases, fetal cardiac activity persisted until gestational weeks 14 and 15, even though decapitation had occurred at week 10 (2,4). In the present case, the fetal head size suggested that decapitation was not a recent event, indicating that the fetus continued to grow after early separation of the cranium from the body. This finding suggests that the embryo/fetus has the potential for growth after decapitation. It is unusual that this fetus had the potential for subsequent growth after decapitation. One possible explanation for this finding is that prompt clotting of the severed neck vessels caused by substantial and sustained applied pressure may have contributed to temporary survival. However, this remains speculative without supporting histological or vascular evaluation, and further studies are needed to explore the underlying mechanism.

Fetal lymphedema and hydrops have also been reported in cases of fetal decapitation. Lymphedema distal to the level of band constriction may contribute to fetal hydrops, which is commonly observed in the trunks of decapitated fetuses. Bilateral clubfeet have also been reported in such cases. According to Tonni et al., this deformity is likely related to the fetus’s severely abnormal neurological condition (5).

The detached fetal head, as a separate entity, may be overlooked in ultrasound examinations due to a primary focus on the diagnosis of common anencephaly. In the present case, the fetus was initially misdiagnosed with anencephaly at the other hospital. This case highlights the unpredictable nature of amniotic band-related fetal defects, which may be subtle or atypical. Advanced three- and four-dimensional ultrasonography now enables improved evaluation of these bands and their associated anomalies. In our case, the floating head and the fetal amoralities were clearly visualized using HDlive low ultrasound imaging.

Conclusions

We present a rare case of a fetal decapitation occurring in early pregnancy without visible amniotic bands in which the fetus survived in utero for several weeks, with fetal demise occurring at 13–14 weeks. This is a rare case in which both the severed head and trunk were clearly identified on serial prenatal ultrasound examinations using three-dimensional image-enhancing technology. This case highlights the ability of transvaginal ultrasonography to visualize both rare and common intrauterine pathologic presentations.

Acknowledgments

None.

Footnote

Funding: None.

Conflicts of Interest: Both authors have completed the ICMJE uniform disclosure form (available at https://qims.amegroups.com/article/view/10.21037/qims-2026-1-0284/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All procedures performed in this study were in accordance with the ethical standards of the institutional and/or national research committee(s) and with the Helsinki Declaration and its subsequent amendments. Written informed consent was obtained from the patient for publication of this article and accompanying images. A copy of the written consent is available for review by the editorial office of this journal.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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