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Three Part Question

In [an infant with bilious vomiting] is [a Doppler ultrasound superior to an UGI contrast study] for the [diagnosis of malrotation]?

Clinical Scenario

Three-day-old twins are reported to have persistent bilious vomiting on the postnatal ward. You suspect midgut malrotation and it is suggested by a colleague that a Doppler ultrasound might be a better investigation than an upper gastrointestinal (UGI) contrast study, as it does not involve radiation and is non-invasive. You are uncertain which test is best.

Search Strategy

An Ovid Medline (1950–2010) search was performed
A search of the Cochrane database of systematic reviews and BestBETS website identified no relevant articles.
using the search terms: Intestinal Volvulus/or malrotation.mp. AND ultrasound.mp. Searches were limited to English language, human, infant (birth–23 months).

Search Outcome

Medline:A total of 37 articles were retrieved, and the abstracts were reviewed. Four relevant studies were identified

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Dufour et al, 1992	427 patients referred for UGI contrast study underwent ultrasonography	Prospective cohort study Reference was UGI contrast study (1b)	US indicates malrotation	Sensitivity: 70% (95% CI 50 to 85) Specificity: 96% (95% CI 93 to 98) PPV: 62% (95% CI 44 to 77) NPV: 97% (95% CI 95 to 99) LKR+: 17.5 (95% CI 9.9 to 31.8) LKR−: 0.3 (95% CI 0.2 to 0.5) Accuracy: 94%	67/427 (15.6%) had an unsuccessful US due to bowel gas. There were 30 malrotations. US correctly identified malrotation in 21/30 patients and correctly identified no malrotation in 317/330 patients US missed diagnosis in 30% (false negative) False positive rate: 38%
Zerin and DiPietro, 1991	9 patients with malrotation confirmed by UGI and surgery underwent US examination	Prospective consecutive study, limited population (3b)	US demonstrates inverted superior mesenteric artery and vein	Inverted SMA/SMV in 67%, normal 33%	1/3 of patients with confirmed malrotation did not have abnormal findings at US US missed diagnosis in 33% (false negative) No comparison group
Orzech et al, 2006	252 patients had both an UGI contrast study and US for investigation of malrotation	Retrospective cohort study Reference was UGI contrast study (2b)	US indicates malrotation	Sensitivity: 87%* (95% CI 72 to 95) Specificity: 76%* (95% CI 68 to 82) PPV: 44%* (95% CI 33 to 57) NPV: 96% (95% CI 91 to 99) LKR+: 3.6 (95% CI 2.7 to 4.8) LKR−: 0.2 (95% CI 0.1 to 0.4) Accuracy: 94%	36/252 (14.3%) had an unsuccessful US compared with 5/252 (2.0%) unsuccessful UGI contrast study. US correctly identified malrotation in 34/39 patients (including 2 with normal UGI) and correctly identified no malrotation in 130/135 patients US missed diagnosis in 14%† (false negative) False positive rate: 55%
Weinberger et al, 1992,	337 patients undergoing US for suspected pyloric stenosis had retrospective analysis of SMA/SMV position	Retrospective case series, non-independent reference standard (4)	US demonstrates inverted or ventral position of SMV to SMA	Abnormal SMA/SMV position in 9 (2.6%) patients referred for suspected pyloric stenosis. Malrotation was confirmed or excluded by UGI contrast series in 7/9 patients and 2/9 at surgery	17% could not have assessment of SMA/SMV position due to bowel gas. 9 patients had abnormal SMA/SMV position, 6 had confirmed malrotation False positive rate: 33%

Comment(s)

Malrotation of the midgut is a congenital abnormality reportedly affecting 1:500 infants (Williams). The condition is often suspected in an infant with bilious vomiting, but can present with non-bilious vomiting, feeding intolerance or abdominal pain. Volvulus, the life-threatening complication, can result in bowel necrosis and peritonitis (Torres).In malrotation, there is abnormal fixation of the duodenojejunal loop and cecocolic loop of the developing bowel. Disordered attempts to fix the caecum lead to the observation of fibrous bands of tissue, ‘Ladd's bands', extending from the caecum and right colon, crossing the duodenum to the retroperitoneum of the right upper quadrant (Millar). These compressive bands, combined with torsion at the base of the midgut mesentery give rise to the clinical manifestations of obstruction and volvulus. The abnormal position of the gut, in particular the duodenojejunal junction, can be identified by UGI contrast studies and this has been the mainstay of diagnosis (Sizemore).

It has been observed that abnormally positioned superior mesenteric vessels frequently coexist with malrotation. In this situation, the superior mesenteric vein and superior mesenteric artery are inverted, or the vein lies ventral to the artery. This abnormal position can be identified using colour Doppler assessment during abdominal ultrasound.

The non-invasive nature and lack of ionising radiation makes ultrasound an attractive modality for the diagnosis of malrotation in children. However, given the potentially disastrous and life-threatening consequences of missing the diagnosis, any test must have a very low false negative rate.

Dufour et al describe three outcomes of the ultrasound assessment in their study: normal, intermediate and inversion.All 16 patients with inversion had confirmed malrotation, compared with 5/18 with intermediate vessel position. As no patient with inverted vessels did not have malrotation, the likelihood ratio of this situation would reach ∞ – truly pathognomonic. However, inverted vessels in the context of normal rotation have been described elsewhere (Zerin). In the analysis above, both inverted and intermediate results were combined to reflect a result suggestive of malrotation.

The studies by Dufour et al, Orzech et al and Weinberger et al report a similar failure rate of approximately 15% for ultrasound due to the presence of bowel gas obscuring assessment of the superior mesenteric vessels; this contrasts with 2% for the UGI contrast study. A high rate (one in six) of test failure can result in unnecessary delay to diagnosis.

The Dufour et al and Ozrech et al reports are similar in their demonstration that ultrasound has both low sensitivity (70% and 87%) and a high type 2 error rate (false negative) of 14–33%. This arises from the inconsistent relationship between the presence of abnormal superior mesenteric vessels and malrotation. This is crucial, as clinicians may be falsely reassured by a negative test, with potentially disastrous consequences. The study by Weinberger et al s least suited to the posed question because of its inconsistent application of an appropriate reference standard; its premise was to assess the utility of mesenteric artery position as an adjunct to the assessment of infants referred with suspected pyloric stenosis. This contrasts with the studies by Dufour et al and Ozrech et al in which study patients had both tests.

The combined data suggest that ultrasound assessment of the superior mesenteric vessels is not an appropriate test to exclude malrotation in infants, due to inadequate sensitivity. However, if inverted superior mesenteric vessels are identified during any ultrasound examination, malrotation is likely.

Editor Comment

# * Corrected from published paper for two patients who had an abnormal ultrasound and normal UGI, subsequently identified as having malrotation at surgery.

† Type 2 error (false negative) incorrectly reported as 2% on original paper.

LKR+ positive likelihood ratio; LKR−, negative likelihood ratio; NPV, negative predictive value; PPV, positive predictive value; SMA, superior mesenteric artery; SMV, superior mesenteric vein; UGI, upper gastrointestinal; US, ultrasound.

Clinical Bottom Line

Ultrasound is an inappropriate first line investigation for malrotation as it misses the diagnosis in 15–30% of patients.

The identification of inverted superior mesenteric artery and superior mesenteric vein position during any ultrasound is highly suggestive of malrotation (although not pathognomonic) and warrants further investigation and management.

Upper gastrointestinal contrast study remains the first line investigation for suspected malrotation.

References

1. Williams H . Green for danger! Intestinal malrotation and volvulus. Arch Dis Child Educ Pract Ed 2007;92:ep87–91.
2. Torres AM, Ziegler MM . Malrotation of the intestine. World J Surg 1993;17:326–31.
3. Millar AJ, Rode H, Cywes S . Malrotation and volvulus in infancy and childhood. Semin Pediatr Surg 2003;12:229–36.
4. Sizemore AW, Rabbani KZ, Ladd A, et al . Diagnostic performance of the upper gastrointestinal series in the evaluation of children with clinically suspected malrotation. Pediatr Radiol 2008;38:518–28.
5. Dufour D, Delaet MH, Dassonville M, et al . Midgut, malrotation the reliability of sonographic diagnosis. Pediatr Radiol 1992;22:21–3.
6. Zerin JM, DiPietro MA . Mesenteric vascular anatomy at CT: normal and abnormal appearances. Radiology 1991;179:739–42.
7. Orzech N, Navarro OM, Langer JC . Is ultrasonography a good screening test for intestinal malrotation? J Pediatr Surg 2006;41:1005–9.
8. Weinberger E, Winters WD, Liddell RM, et al . Sonographic diagnosis of intestinal malrotation in infants: importance of the relative positions of the superior mesenteric vein and artery. AJR Am J Roentgenol 1992;159:825–8.
9. Zerin JM, DiPietro MA . Superior mesenteric vascular anatomy at US in patients with surgically proved malrotation of the midgut. Radiology 1992;183:693–4.