Fetal intestinal volvulus, an uncommon yet potentially devastating anomaly characterized by the aberrant rotation of the intestinal tract around the mesenteric axis, poses a formidable challenge in prenatal diagnostics due to the rarity and propensity of the condition for severe complications. With an estimated incidence of symptomatic neonatal malrotation of approximately 1 in 6000 live births [1, 2, 3], volvulus without malrotation constitutes an even rarer subset, rendering the prenatal identification of the condition both critical and elusive. The pathophysiology of the condition, driven by mechanical torsion of the mesentery, precipitates a cascade of adverse sequelae, including intestinal necrosis, atresia, perforation, meconium peritonitis, and ascites, each of which significantly elevates the risk of fetal and neonatal morbidity or mortality [4, 5]. The absence of specific antenatal clinical manifestations further complicates timely diagnosis, often delaying intervention until irreversible damage has occurred, underscoring the imperative for advanced imaging modalities to facilitate early detection and inform clinical management.

Prenatal ultrasound has emerged as a crucial tool in elucidating the characteristic features of fetal intestinal volvulus, notably the whirlpool sign—a spiral configuration of dilated bowel loops—and the vascular spiral sign, wherein the mesenteric vein encircles the mesenteric artery on Doppler imaging [6, 7]. These ultrasonographic hallmarks enable early diagnosis, thereby informing intervention strategies and enhancing neonatal prognosis. These ultrasonographic hallmarks, complemented by nonspecific findings such as bowel dilation and ascites, can allow clinicians to differentiate volvulus from other causes of fetal abdominal pathology, thereby guiding critical decisions regarding prenatal counseling and postnatal surgical planning. Recent studies have further refined the diagnostic utility of these signs, highlighting the specificity of these signs in identifying volvulus and their prognostic implications in complications such as atresia and necrosis [8, 9]. Larger case series, such as those reported by Taşdemir et al. [10] and Montironi et al. [1], have further underscored the heterogeneity of volvulus presentations and the pivotal role of ultrasound in optimizing outcomes; however, the literature remains sparse in cases without malrotation, a distinct entity that may arise from alternative etiological mechanisms, such as localized ischemia or transient intrauterine obstructions [11].

The rarity of fetal intestinal volvulus without malrotation, coupled with its diagnostic complexity, necessitates detailed characterization of the ultrasonographic and clinical profiles involved to enhance prenatal management strategies. The absence of malrotation, typically associated with aberrant mesenteric vessel positioning, suggests that mechanical or vascular insults may independently precipitate volvulus, a hypothesis warranting further investigation. Moreover, the frequent association with intestinal atresia, as reported in prior studies, underscores the need to elucidate the interplay between volvulus-induced ischemia and developmental anomalies, which may inform risk stratification and therapeutic approaches [4, 12]. Despite the challenges posed by the low incidence of the condition, which limits large-scale studies, case series, such as the present investigation, offer valuable insights into its diagnostic and prognostic nuances, contributing to the evolving landscape of fetal medicine.

This study aimed to delineate the prenatal ultrasonographic characteristics and clinical outcomes of seven cases of fetal intestinal volvulus without malrotation diagnosed at a tertiary care center between July 2021 and December 2024. By correlating ultrasonographic findings, including whirlpool and vascular spiral signs, with postnatal surgical or autopsy results, this study sought to elucidate the diagnostic reliability of ultrasound and its impact on clinical decision-making. Through a detailed analysis of these rare cases, we aimed to provide a robust evidence base for prenatal counseling, enhance early detection, and inform strategies to mitigate the severe complications associated with this condition, thereby addressing a critical gap in the literature and advancing the field of prenatal diagnostics.

Seven fetuses were diagnosed with intestinal volvulus without malrotation via prenatal ultrasound at the Women and Children’s Hospital, School of Medicine, Xiamen University, between July 2021 and December 2024. All diagnoses were confirmed based on postnatal surgical or autopsy findings, ensuring diagnostic accuracy and reliability. Maternal age ranged from 24 to 34 years, with initial ultrasound diagnoses made between 23 and 33 weeks of gestation (Table 1). A total of 27 ultrasound examinations were performed, with follow-up assessments conducted every 1–2 weeks to monitor disease progression, as justified by the potential for rapid deterioration [7]. All examinations utilized the GE Voluson E8 or E10 systems, with a standardized protocol and validation by a chief physician to minimize operator-dependent variability and information bias.

3.1 Ultrasonographic Findings

The ultrasonographic findings for all seven cases are summarized in Table 1, which details the gestational age at diagnosis and the presence of key signs. Table 2 quantifies the frequency of findings across all 27 examinations. Characteristic signs included the whirlpool sign (Fig. 1), annotated with arrows to highlight the spiral-shaped mass of dilated bowel loops), a spiral-shaped mass of dilated bowel loops, and the vascular spiral sign (Fig. 2A: 2D ultrasound; Fig. 2B: 3D ultrasound, with arrows indicating the mesenteric vein swirling around the mesenteric artery), observed in all cases (7/7). Nonspecific findings included bowel dilation (7/7), ascites (6/7), abdominal pseudocysts (2/7), coffee bean sign (2/7), hydramnios (1/7), and increased middle cerebral artery flow velocity (1/7). Among the 27 examinations, the detection rates were as follows: whirlpool sign, 20/27 (74.1%); vascular spiral sign, 20/27 (74.1%); bowel dilation, 23/27 (85.2%); ascites, 18/27 (66.7%); cystic abdominal masses, 5/27 (18.5%); coffee bean sign, 2/27 (7.4%); hydramnios, 3/27 (11.1%). Detailed case descriptions are provided below:

$\bullet$ Case 1 (diagnosed at 32 weeks, 1 day): Initial ultrasound revealed the whirlpool sign (Fig. 1) and vascular spiral sign (Fig. 2A,B), with dilated bowel loops (inner diameter $>$7 mm) and ascites (Table 1). Four follow-up examinations confirmed persistent whirlpool and vascular spiral signs with increasing ascites, suggesting progressive complications. Postnatal surgery at 34 weeks confirmed volvulus with type III intestinal atresia, necrosis and meconium peritonitis.

Fig. 1.

Two-dimensional ultrasound image of the whirlpool sign. (A, B) Images characterized by a spiral-shaped mass of dilated bowel loops, observed in all seven cases of fetal intestinal volvulus, confirming the diagnostic reliability of this technique. Arrows indicate the spiral configuration of the dilated bowel loops, and a scale bar is included for spatial reference. The little finger indicates the center of the whirlpool sign.

Fig. 2.

Ultrasound images of the vascular spiral sign. (A) Two-dimensional color Doppler ultrasound of the vascular spiral sign, with the mesenteric vein swirling around the mesenteric artery, a direct indicator of volvulus; arrows highlight the swirling mesenteric vein, and a scale bar is included. (B) Three-dimensional power Doppler ultrasound enhances the visualization of the vascular spiral sign, observed in all cases. Arrows indicate the vascular spiral pattern, with a scale bar provided for reference. The little finger indicates the center of the whirlpool sign.

Table 2. Summary of ultrasonographic findings across all examinations.

Case no.	No. of examinations	Whirlpool sign	Vascular spiral sign	Bowel dilation	Coffee bean sign	Ascites	Abdominal pseudocysts	Hydramnios
1	4	4/4	4/4	4/4	0/4	3/4	0/4	0/4
2	5	4/5	4/5	5/5	2/5	4/5	0/5	3/5
3	4	3/4	3/4	4/4	0/4	3/4	0/4	0/4
4	3	3/3	3/3	3/3	0/3	0/3	0/3	0/3
5	5	3/5	3/5	4/5	0/5	4/5	2/5	0/5
6	3	3/3	3/3	3/3	0/3	2/3	0/3	0/3
7	3	3/3	3/3	3/3	2/3	3/3	3/3	0/3
Total	27	23/27 (85.2%)	23/27 (85.2%)	26/27 (96.2%)	4/27 (14.8%)	18/27 (66.7%)	5/27 (18.5%)	3/27 (11.1%)

$\bullet$ Case 2 (diagnosed at 25 weeks, 4 days): Ultrasound identified the whirlpool and vascular spiral signs, bowel dilation, ascites, hydramnios, and the coffee bean sign, indicative of strangulated obstruction (Table 1). Five follow-up examinations showed worsening ascites and persistent coffee bean signs consistent with severe obstruction. Surgery at 34 weeks and 4 days confirmed volvulus with type III atresia, necrosis, and meconium peritonitis.

$\bullet$ Case 3 (diagnosed at 28 weeks, 0 day): The whirlpool and vascular spiral signs were accompanied by bowel dilation and ascites (Table 1). Four follow-up examinations showed stable findings, with no additional complications. Surgery at 31 weeks and 2 days confirmed volvulus with necrosis and meconium peritonitis, without atresia.

$\bullet$ Case 4 (diagnosed at 23 weeks, 3 days): Initial ultrasound detected the whirlpool and vascular spiral signs with bowel dilation (Table 1). Three follow-up examinations revealed no ascites or additional complications. After extensive counseling regarding the risk of severe postnatal complications (e.g., short bowel syndrome due to extensive necrosis), the parents opted for pregnancy termination at 26 weeks. An autopsy confirmed volvulus with necrosis.

$\bullet$ Case 5 (diagnosed at 23 weeks, 4 days): Initial ultrasound showed extensive bowel dilation, with whirlpool and vascular spiral signs detected at the second follow-up (25 weeks; Table 1). Ascites and abdominal pseudocysts were noted in the subsequent examinations (n = 5). Surgery at 36 weeks 6 days confirmed volvulus with type III atresia, necrosis, and meconium peritonitis.

$\bullet$ Case 6 (diagnosed at 33 weeks, 6 days): The whirlpool and vascular spiral signs were observed with bowel dilation and ascites (Table 1). Three follow-up examinations revealed stable findings. Surgery at 37 weeks and 2 days confirmed a volvulus with type III atresia and necrosis.

$\bullet$ Case 7 (diagnosed at 25 weeks, 3 days): Ultrasound revealed the whirlpool and vascular spiral signs, bowel dilation, ascites, abdominal pseudocysts, and the coffee bean sign (Table 1). An increased middle cerebral artery flow velocity suggests fetal distress. Five follow-up examinations revealed worsening ascites and loss of peristalsis, indicating perforation. Surgery at 33 weeks and 4 days confirmed volvulus with type III atresia, necrosis, meconium peritonitis, and perforation, which led to neonatal death.

This case series presents the prenatal ultrasonographic characteristics and clinical outcomes of seven fetuses diagnosed with intestinal volvulus in the absence of malrotation, a rare and potentially catastrophic condition that poses significant diagnostic and therapeutic challenges. Consistent detection of the whirlpool sign, characterized by a spiral configuration of dilated bowel loops, and the vascular spiral sign, defined by the mesenteric vein encircling the mesenteric artery on Doppler imaging, across all cases underscores the pivotal role of these characteristics as diagnostic hallmarks, corroborating prior observations in the literature [4, 5, 7]. These findings, detailed in the Results section (Tables 1,3; Figs. 1,2), were observed in 74.1% of the 27 ultrasound examinations, affirming the reliability of these diagnostic hallmarks in identifying volvulus without malrotation, a subset of cases less frequently reported than those associated with rotational anomalies [4]. Unlike traditional presentations of volvulus, which often manifest with aberrant positioning of the superior mesenteric vessels due to malrotation, the absence of malrotation in our cohort, confirmed by surgical or autopsy findings, suggests alternative etiological pathways, potentially driven by mechanical torsion of the mesentery, independent of developmental rotation defects.

The absence of malrotation in our cohort suggests that alternative mechanisms, such as localized ischemia or abnormal mesenteric fixation, may contribute to the development of volvulus. Localized ischemia, potentially resulting from transient vascular insults in utero, could induce mesenteric torsion, leading to volvulus independent of rotational anomalies. Similarly, inadequate mesenteric fixation may allow excessive mobility of the bowel, predisposing the bowel to twisting and subsequent obstruction, as supported by recent case reports [8, 16]. This hypothesis warrants further investigation to elucidate the precise etiological pathways underlying this rare anomaly, which may inform targeted diagnostic and therapeutic strategies.

The diagnostic utility of prenatal ultrasound in this context cannot be overstated, as this modality facilitates the early identification of a condition prone to rapid progression toward severe complications, including intestinal necrosis, atresia, perforation, and meconium peritonitis. The universal presence of bowel dilation (85.2% of examinations) served as an early indicator of detailed ultrasonographic scrutiny, while ascites (66.7%) and the coffee bean sign (7.4%) emerged as critical markers of advanced pathology, such as strangulated obstruction or perforation, as evidenced in cases 2 and 7 (Table 3). The prenatal detection of the coffee bean sign, observed in two cases, is a critical indicator of strangulated obstruction, underscoring the need for urgent multidisciplinary perinatal collaboration to expedite delivery and surgical management, thereby mitigating the risk of irreversible complications such as perforation [9]. These findings align with recent studies emphasizing the specificity of the whirlpool sign in detecting volvulus and the prognostic significance of secondary signs, such as ascites and pseudocysts [9]. Meanwhile, compared to magnetic resonance imaging (MRI), which offers enhanced anatomical resolution but is constrained by cost and limited dynamic assessment, ultrasound real-time visualization of bowel dynamics and vascular patterns renders this imaging platform the modality of choice for routine prenatal monitoring. The high sensitivity of the whirlpool and vascular spiral signs in our cohort (100% case detection) advocates for their integration into standardized obstetric ultrasound protocols, particularly when bowel dilation is detected, to expedite diagnosis and mitigate adverse outcomes [8, 9, 17].

The prognostic implications of our findings are profound because the severity of ultrasonographic abnormalities is closely correlated with postnatal outcomes. All seven cases exhibited intestinal necrosis, with five complicated by intestinal atresia (four type III), a severe form associated with significant bowel loss and protracted recovery [18]. The presence of ascites and the coffee bean sign observed in cases with the most severe complications, such as perforation in case 7, which resulted in neonatal demise, underscores their utility as predictors of poor prognosis. These observations align with larger case series, such as those reported by Taşdemir et al. [10] and Montironi et al. [1], which highlight the prognostic heterogeneity of fetal volvulus and the critical role of early diagnosis in optimizing surgical planning. The timely identification of volvulus in our cohort enabled successful resection and enterostomy in five of six live births, demonstrating the clinical impact of prenatal ultrasound in facilitating prompt postnatal intervention. However, the neonatal death in case 7, predicted by worsening ascites and loss of peristalsis, illustrates the limitations of the current management strategies in mitigating the consequences of advanced pathology, emphasizing the need for refined therapeutic approaches.

The absence of malrotation in our cases challenges conventional paradigms that associate volvulus with rotational anomalies, suggesting that mechanical factors such as mesenteric torsion or localized ischemia may precipitate volvulus in otherwise normally rotated intestines. This hypothesis is supported by previous reports of volvulus without malrotation, which propose that intrauterine events, such as transient obstructions or vascular insults, may trigger torsion [8]. The high incidence of intestinal atresia in our cohort (71.4%) further suggests a mechanistic link wherein volvulus-induced ischemia impairs bowel development, leading to atresia as a secondary consequence [16, 18]. This interplay between volvulus and atresia warrants further investigation as the interaction may inform prenatal risk stratification and surgical planning. Additionally, the genetic analyses in cases 4 and 5, which identified variants of uncertain significance, revealed no definitive association with volvulus, consistent with the paucity of evidence in the literature linking this condition to specific genetic aberrations [4]. Thus, routine genetic testing in isolated cases of volvulus may be of limited utility, although larger studies are required to clarify this.

Despite the contributions of this study, limitations exist, including the small sample size of seven cases, which reflects the rarity of fetal intestinal volvulus without malrotation, with an estimated incidence of related conditions of approximately 1 in 6000 [12, 17, 19, 20]. This limitation, acknowledged as acceptable given the rarity of the condition, underscores the value of case series in elucidating rare anomalies [12, 17, 19, 20]. The single-center retrospective design may introduce information bias, although this was mitigated by employing a standardized ultrasound protocol, expert validation, and corroboration of postnatal findings. The variability in detection rates of the whirlpool and vascular spiral signs (74.1% across examinations) may reflect the dynamic nature of volvulus, wherein prolonged ischemia leads to necrosis and adhesion, obscuring these signs, as noted in prior studies [15]. Nevertheless, our detailed ultrasonographic and clinical characterization provides a robust foundation for future research, particularly in the context of this rare entity. Multicenter studies with larger cohorts are imperative to validate our findings, refine the diagnostic criteria, and explore the genetic and environmental factors contributing to volvulus without malrotation. Additionally, the development of advanced imaging techniques, such as high-resolution Doppler or fetal MRI, may enhance diagnostic precision and prognostic accuracy, further improving the clinical outcomes.

In summary, this study underscores the instrumental role of prenatal ultrasound in the early diagnosis and management of fetal intestinal volvulus without malrotation, with whirlpool and vascular spiral signs serving as reliable diagnostic markers. The correlation between ultrasonographic findings and prognostic outcomes highlights the importance of vigilant monitoring and timely intervention to mitigate severe complications. By elucidating the characteristics of a rare condition, our findings contribute to the evolving landscape of prenatal diagnostics, paving the way for enhanced counseling and therapeutic strategies to optimize fetal and neonatal outcomes.

This investigation elucidates the pivotal role of prenatal ultrasound in the early and precise diagnosis of fetal intestinal volvulus without malrotation, which is a rare yet potentially life-threatening condition. The consistent identification of the whirlpool and vascular spiral signs across all seven cases, as detailed in the results, underscores their diagnostic reliability, enabling timely detection in the absence of malrotation. Prenatal ultrasound, through the identification of these characteristic signs, provides a critical foundation for timely intervention decisions, facilitating multidisciplinary perinatal collaboration and improving neonatal outcomes by expediting postnatal surgical management. Nonspecific ultrasonographic findings, such as bowel dilation and ascites, further corroborate the diagnosis, whereas the presence of ascites and the coffee bean sign serve as critical predictors of severe complications, including necrosis and intestinal atresia, which were prevalent in our cohort. Specific findings, such as the coffee bean sign, underscore the importance of multidisciplinary collaboration in perinatal care to optimize outcomes for high-risk cases. These findings facilitated informed prenatal counseling and expedited postnatal surgical intervention, resulting in favorable outcomes in five of six live births. The high incidence of type III atresia (four of five cases with atresia) highlights the prognostic significance of early diagnosis, as delayed intervention may exacerbate adverse outcomes, as evidenced by the neonatal death in case 7. Despite the inherent limitations of a small, single-center cohort, this study provides a robust foundation for understanding the ultrasonographic and clinical profiles of this rare entity, contributing valuable insights to the limited literature. Future multicenter studies are imperative to validate these findings and refine the diagnostic protocols, potentially incorporating advanced imaging modalities to enhance precision. By delineating the diagnostic and prognostic utility of prenatal ultrasound, this study advances the paradigm of fetal medicine, fostering improved prenatal management and optimized neonatal outcomes for fetal intestinal volvulus without malrotation.

The datasets used and analyzed during the current study are available from the corresponding author upon reasonable request, subject to institutional data-protection policies.

SZ and XH contributed equally to this work by performing ultrasound examinations, data collection, and drafting the initial manuscript. ML and JZ conducted the data analysis and interpretation, contributing to the methodology and results sections of the manuscript. XZ contributed to data visualization and literature review. All authors contributed to editorial changes in the manuscript. All authors read and approved the final manuscript. All authors have participated sufficiently in the work and agreed to be accountable for all aspects of the work

This study was approved by the Institutional Ethics Committee of the Women and Children’s Hospital, School of Medicine, Xiamen University (Approval No. KY-2024-079-K01). Written informed consent was obtained from all participants prior to their inclusion in the study in accordance with the Declaration of Helsinki.

This research received no external funding.

The authors declare no conflict of interest.