We present four cases at the 2nd and 3rd trimester, featuring different imaging presentations of the same pathology: Cystic Fibrosis.

Case Descriptions

Case 1:  Imaging at 33 weeks gestation shows meconium ileus with bowel volvulus secondary to cystic fibrosis.

Ultrasound examination revealed bowel dilation with fluid and isoechoic content, lack of peristalsis, ascites and polyhydramnios (Image 1, Video 1 and 2). MRI showed dilated distal bowel with meconial content, a whirlpool sign pathognomonic of a bowel volvulus (Image 2), walled-off meconial ascites with thickened peritoneum (Image 3) consistent with meconium peritonitis secondary to bowel perforation. Normal non-distended bowel could be seen distally. The colon looked small, with a thin tiny rectal pouch barely visible (Image 5), as expected in obstructive bowel conditions. Amniotic fluid analysis revealed Cystic Fibrosis (F508 deletion, homozygous). The parents chose to pursue the pregnancy. Neonatal surgery at Day 2 found a bowel volvulus with perforation. After surgical resection and anastomosis, there was 20cm of healthy jejunal bowel proximally and 60cm of healthy ileal bowel distally for a total of 80cm of small bowel.

Case 2: Imaging at 31 weeks gestation shows meconium ileus with bowel volvulus likely occurring a few weeks prior and seen at late stage, secondary to Cystic Fibrosis

Case 2 is a similar to Case 1, and shows bowel volvulus at a later stage. Ultrasound (Images 6-8, Video 3-4) revealed bowel dilation, lack of peristalsis, ascites and a unilateral hydrocele secondary to ascites. Interestingly, there was a mass-like cluster of some bowel loops with neither a lumen, peristalsis nor whirlpool sign visible. There was no polyhydramnios and the stomach was not distended. Fetal MRI (Images 9-11) was performed a few days later, and showed bowel dilation with meconial content, proximal to a few tiny bowel loops in circles, without the pathognomonic whirlpool sign. Some normal bowel loops could be seen distally in the right flank. There was a microcolon as expected. The ascites seemed mild, less marked than on the US. We diagnosed meconium ileus, with likely a bowel volvulus occurring a few weeks prior, which had healed. Bowel atresia secondary to volvulus, if any, can only be diagnosed at autopsy or surgery. Amniotic fluid analysis revealed Cystic Fibrosis (F508 deletion, homozygous) and the parents chose medical abortion. No autopsy was done.

Case 3: Imaging at 32 to 35 weeks gestation showing hyperechoic small bowel and small gallbladder secondary to Cystic Fibrosis

Prenatal ultrasound (Image 12 and 13) showed hyperechoic bowel, without significant dilation, and a small gallbladder. Amniotic fluid analysis revealed Cystic Fibrosis (heterozygous state, with a Y122X mutation on one copy of the CFTR gene, and a deletion of the exons 17a-18 on the other copy of the CFTR gene). The parents chose to pursue the pregnancy.

Case 4: Imaging at 22 weeks gestation showed mildly dilated, hyperechoic small bowel with non-visualization of the gallbladder, secondary to Cystic Fibrosis

Prenatal ultrasound (Images 14-15, Video 5-6) showed hyperechoic bowel with mild dilation. The gallbladder was not seen. This is known as the classic triad of cystic fibrosis signs on ultrasound. Amniotic fluid analysis revealed Cystic Fibrosis (heterozygous state, with a Y122X mutation on the one copy of the CFTR gene, and an F508 deletion on the other copy of the CFTR gene). The parents chose to abort the pregnancy.

Discussion

In bowel obstructive conditions, one finding can hide the other. In small bowel atresias for example, the first atresia may hide other atresias or an apple-peel syndrome. There is currently no reliable way on prenatal imaging, ultrasound or MRI, to predict multiple atresias [1]. There has been discussion of whether or not the visibility/absence of the distal bowel, and the visibility/absence of a microcolon on imaging could be used as predictive factors. That said in cystic fibrosis, bowel atresia is not expected but rather meconium ileus: the lack of progression of the meconium due to its thickness. However, volvulus can also occur with secondary atresia.

On MRI, the meconium signal is unusual in cystic fibrosis. In normal conditions, the meconium is expected to feature marked T1 hyperintensity compared to the liver. In cases 1 and 2, the meconium shows mild hyperintensity, almost isointensity, compared to the liver.  Our MRI findings are consistent with other prenatal MR findings in cystic fibrosis reported in the literature in which 4 fetuses with echogenic bowel on ultrasound are retrospectively analyzed: 2 with ileal atresia without cystic fibrosis, and 2 with meconial Ileus and cystic fibrosis [2]. Regarding this peculiar MR characteristic of meconium, one theory speculates that what makes meconium hyperintense on T1 sequences, is the rich content in bile acids. In cystic fibrosis, the bile acids are less concentrated, hence less T1 signal intensity [3,4].

References:

[1] Rubio EI, Blask AR, Badillo AT, et al. Prenatal magnetic resonance and ultrasonographic findings in small-bowel obstruction: imaging clues and postnatal outcomes. Pediatr Radiol. 2017 Apr;47(4):411-421. PMID: 28116474

[2] Carcopino X, Chaumoitre K, Shojai R, et al. Use of fetal magnetic resonance imaging in differentiating ileal atresia from meconium ileus. Ultrasound Obstet Gynecol, 28: 976-977. Publish date 11/2006. https://doi.org/10.1002/uog.3827

[3] Righetti C, Peroni DG, Pietrobelli A, et al. Proton nuclear magnetic resonance analysis of meconium composition in newborns. J Pediatr Gastroenterol Nutr. 2003 Apr;36(4):498-501. PMID: 12658044.

[4] Zizka J, Elias P, Hodik K, et al. Liver, meconium, haemorrhage: the value of T1-weighted images in fetal MRI. Pediatr Radiol. 2006 Aug;36(8):792-801. PMID: 16799788.