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The use of MRI to demonstrate small bowel obstruction during pregnancy

Departments of ¹Radiology ²Surgery, University College Hospital, Newcastle Road, Galway, Republic of Ireland

Correspondence: David A McKenna, Department of Radiology, University College Hospital Galway, Hillside, Windgate Road, Howth, Dublin, Co. Dublin, Ireland. E-mail: radiologyresident{at}hotmail.com

	Abstract

Top Abstract Introduction Case report Discussion Conclusion References

 
Patients who present during pregnancy with acute abdominal symptoms often present a significant diagnostic challenge. Although ultrasound is often the first mode of abdominal imaging, in complex cases further imaging is often necessary. MRI of the small bowel has been made possible with the development of rapid scanning techniques. This has increased the attractiveness of a modality whose benefits include multiplanar imaging, excellent soft tissue contrast and the avoidance of ionizing radiation. With these capabilities MRI has been shown to be a useful adjunct when imaging the small bowel in pregnancy. Although MRI has been employed to investigate small bowel obstruction in the obstetric setting, to date there have been no reports of MR identifying small bowel obstruction secondary to extrinsic compression from a gravid uterus. During pregnancy, small bowel obstruction is most commonly attributed to adhesions. However, there are also antenatal occurrences of small bowel obstruction secondary to uterine compression. We present the MRI findings of an unusual case of small bowel obstruction occurring secondary to compression from a 32-week gravid uterus, in a patient with an end ileostomy. Furthermore, while clinical history and examination are fundamental to diagnosis of intestinal obstruction, the following case highlights the value of MRI in pregnancy as a confirmatory test.

	Introduction

Top Abstract Introduction Case report Discussion Conclusion References

 
Patients who present during pregnancy with acute abdominal symptoms often present a significant diagnostic challenge. Although ultrasound is often the first mode of abdominal imaging, in complex cases, further imaging is often necessary. MRI of the small bowel has been made possible with the development of rapid scanning techniques. This has increased the attractiveness of a modality whose benefits include: multiplanar imaging, excellent soft tissue contrast and the avoidance of ionizing radiation. With these capabilities MRI has been shown to be a useful adjunct when imaging the small bowel in pregnancy [1].

Although MRI has been employed to investigate small bowel obstruction in the obstetric setting [2], to date there have been no reports of MR identifying small bowel obstruction secondary to extrinsic compression from a gravid uterus. During pregnancy, small bowel obstruction is most commonly attributed to adhesions. However, there are also antenatal occurrences of small bowel obstruction secondary to uterine compression. We present the MRI findings of an unusual case of small bowel obstruction, occurring secondary to compression from a 32-week gravid uterus, in a patient with an end ileostomy. Furthermore, while clinical history and examination are fundamental to diagnosis of intestinal obstruction, the following case highlights the value of MRI in pregnancy as a confirmatory test.

	Case report

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The patient was a 28-year-old woman in the 32nd week of her first pregnancy, admitted via the emergency department. She complained of vomiting clear fluid and a reduced ileostomy output for 24 h, associated abdominal cramps and backache. At 11 weeks gestation she had undergone a subtotal colectomy with end-ileostomy formation for management of fulminant ulcerative colitis. At the current presentation, she was apyrexial, with normal heart rate and blood pressure readings. Abdominal examination revealed a soft palpable uterus, fundal height equivalent to dates, with cephalic presentation. Her abdomen was non-tender and bowel sounds were increased. An initial working clinical diagnosis of gastroenteritis was adopted.

The patient was rehydrated intravenously and blood samples drawn for full blood count and renal profile. Urine and stoma effluent were collected for bacteriological analysis. Analgesia was provided in the form of intramuscular pethidine, 50 mg. Anticipating the possibility of metabolic disturbance prematurely precipitating labour, intravenous dexamethasone was also given, to promote fetal lung maturation. First-line investigations proved unremarkable, apart from a mild leukocytosis, of 11 000. Cultures of urine and stool yielded no organisms. Over the course of the following 3 days, bile-stained vomiting continued, with minimal passage of faeces or flatus via the stoma.

A surgical opinion was sought, at which time it was considered that both the extended duration of symptoms and the clinical findings were now more indicative of small bowel obstruction, possibly attributable to adhesions arising from the recent laparotomy. Non-surgical management was continued, with fasting, nasogastric tube drainage and maintenance of optimal fluid and electrolyte balance with intravenous fluids. However, there was no resolution of the obstructive picture over the ensuing 48 h.

An MR study of the small bowel was performed without administration of oral or intravenous contrast. Multiplanar TruFISP images demonstrated multiple loops of dilated small intestine. The point of transition was identified in the right iliac fossa, just proximal to the stoma, with the gravid uterus seen clearly abutting small bowel loops. No focal lesion could be identified as the likely cause of obstruction. There was no evidence of bowel wall thickening or mucosal abnormality. There was no sign of stomal complications such as stenosis or a parastomal hernia. The biliary system, urinary tract, liver and spleen were normal. In this setting, the consensus was to recommend delivery by urgent elective caesarean section. The patient was counselled accordingly and consented to this course of action.

Intraoperatively, dilated loops of bowel were found. There was no evidence of adhesions, infarction or volvulus at the point of change in bowel dimensions. Immediate post-operative recovery was uneventful and within 24 h, loose stools had appeared in the stoma bag. The patient's recuperation continued without incident and after 2 weeks in the neonatal intensive care unit, a 2.12 kg baby boy returned home with mother.

	Discussion

Top Abstract Introduction Case report Discussion Conclusion References

 
Small bowel obstruction is an important, if unusual, complication during pregnancy. It is the second most common non-obstetric reason for surgical intervention in the pregnant patient. Estimates of incidence have varied from 1 case in 3000 to 1 in 16 000 pregnancies [3, 4]. Abdominal pain, vomiting and obstipation are the most common presenting symptoms. The most common aetiology for mechanical obstruction is adhesions from previous abdominal surgery, implicated in 60–70% of cases. An additional 25% result from volvulus and intussusception causes 5% of presentations. There are three time periods which are thought to confer increased likelihood of obstruction. The first is between the 16th and 20th weeks, when the uterus becomes an abdominal organ. The next is at the 36th week of gestation, when the fetal presenting part engages, and finally in the immediate puerperium due to a sudden decrease in uterine size. Less than half of patients included in a large study of bowel obstruction in pregnancy, presented during these time periods. Only one third of patients complete full term pregnancies following operative resolution of small bowel obstruction. Published rates of maternal and fetal mortality range from 6% to 20%, with fetal loss rate as high as 50% [5]. Therefore, early diagnosis and successful treatment are paramount in order to maintain both maternal and fetal wellbeing. This is achieved by thorough clinical assessment and, when necessary, appropriate imaging.

Where highly suggestive symptoms of intestinal obstruction are present in a pregnant patient, the diagnosis can be confirmed by a number of modalities.

Ultrasound may demonstrate fluid-filled bowel loops, while also excluding alternative causes in the biliary and renal systems. Plain abdominal radiography should not be dismissed out of hand as it may reveal highly suggestive appearances, although the reported sensitivity in pregnant patients has been found to be low [4]. The patient must first, of course, be advised regarding the justifiable risk of the fetal radiation dose in the context of evaluating an undiagnosed ongoing acute abdominal condition.

In the non-pregnant patient, CT is the mainstay of management of small bowel obstruction. However, owing to the inherent fetal radiation dose involved, MRI, where available, is a justifiable cross-sectional imaging technique.

While research in this area is understandably limited by ethical constraints, the international standard of care is founded on the ongoing failure to demonstrate deleterious effects produced by the use of clinical MRI during pregnancy [6]. Most radiologists would offer MRI where indicated, in the 2nd and 3rd trimesters, when concerns of early term radiofrequency bioeffects have receded. The safety committee for the Society of Magnetic Resonance Imaging has indicated that MR procedures should be carried out when other non-ionizing methods are inadequate or when the MR study will provide information that would otherwise necessitate radiation exposure [6].

MRI of the small bowel has now become commonplace. Indeed, MR enteroclysis has been shown to be equivalent in providing functional information when compared with conventional enteroclysis [7]. In addition, MR small bowel studies have exhibited additional benefits in the detection of extraintestinal processes [8]. The requirement to avoid image degradation by respiratory, fetal and gastrointestinal motion demands rapid pulse sequence techniques. It is our practice to use a fat-suppressed true-FISP sequence for MR of the small bowel.

In high-grade small bowel obstruction, the small intestinal lumen is distended with fluid and readily imaged. Intermittently or partially obstructed small bowel presents greater diagnostic difficulty as the affected bowel loops may not be dilated at the time of imaging. Adhesions, the most common cause for small bowel obstruction in pregnancy, are frequently not visible on static MRI cross sectional images. Indirect evidence for the presence of adhesions may be inferred by demonstration of obstructed bowel loops in the absence of a defined obstructing lesion. Some authors maintain that volume distension produced, for example during conventional enteroclysis, and which provokes colicky pain, can distinguish symptomatic adhesions from the asymptomatic, incidental variety. However, the availability of MRI spares the pregnant patient and fetus the considerable associated ionizing radiation dose.

The patient we have described had undergone subtotal colectomy with end ileostomy formation, some 20 weeks earlier in the pregnancy. In this context, post-operative adhesions would be a reasonable putative cause for her subsequent small intestinal obstruction. However, neither the imaging appearances nor the intraoperative findings supported this hypothesis. Indeed, the prompt return, following delivery, to normal stoma output certainly implies that the gravid 32-week uterus had contributed to the evolution of obstruction. There were no abnormalities of the ileostomy to suggest hernia, prolapse or stenosis. In pregnant patients with normal bowel anatomy, the terminal ileal loops remain relatively mobile, allowing them to move aside when abutted by the enlarging uterus, and thereby maintain normal patency and function. We postulate that the surgical fixation of the distal ileum to the abdominal wall has resulted in a pre-disposition of the small bowel to obstruction when compressed by the adjacent gravid uterus. This would account for the absence of findings at imaging and laparotomy, as well as the prompt return to normal stoma output following delivery, and unremarkable post-operative course. In the only other comparable case on record [9], a 17-year-old girl with ileal pouch-anal anastomosis had presented at 36 weeks with complete small bowel obstruction. Conservative management proved unsuccessful, so labour was induced to relieve the obstruction or simplify surgery. Immediately following spontaneous vaginal delivery, the patient began to pass copious amounts of stool and flatus, and within hours her bowel obstruction had resolved. There is a further report of intussusception in ileostomy in a pregnant woman [10].

	Conclusion

Top Abstract Introduction Case report Discussion Conclusion References

 
Small bowel obstruction is an uncommon but important cause of acute abdomen in the pregnancy. It is often difficult to diagnose. Imaging, and particularly MR techniques, allows early diagnosis and trial of conservative treatment, as well as facilitating operative planning when required. In analysing this case, we have demonstrated the usefulness of rapid MRI techniques in pregnant patients with abdominal symptoms, both for delineating anatomy and excluding a variety of candidate pathological processes giving rise to small bowel obstruction. Continuing innovation in the development of rapid MR pulse sequences offers further improvements in image quality and patient outcomes.

View larger version (80K): [in this window] [in a new window]   Figure 1. (a) Coronal T2 weighted images identify dilated loops of small bowel (indicated by the white arrow) from the left upper quadrant down to the level of the ileostomy in the right iliac fossa (indicated by the black arrow). (b) Axial image at the level of the stoma identifies a change in calibre, (indicated by the white arrow) from dilated small bowel to collapsed bowel adjacent to the uterus indicating the compressive effect of the uterus to be the cause of obstruction. (c) Dilated loops of small bowel in the midline posterior to the uterus (indicated by the white arrow).

	References

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