The double halo sign: What's behind?

Clinical History

A 67-year-old woman presented in the emergency department with abdominal pain and constipation. On physical examination, she was found to have abdominal pain on palpation of epigastrium and right upper quadrant. The routine blood test showed leukocytosis and high levels of CRP.

Imaging Findings

An acute abdominal series was negative for bowel obstruction.
Abdominal ultrasound was requested to rule out acute cholecystitis. Gallbladder was normal (Fig. 1) but dilated bowel loops with free fluid in pelvis (Fig. 2) were seen.
Computed tomography (CT) scan of abdomen and pelvis showed circumferential wall thickening of the small bowel loops with "double halo" sign regarding submucosal oedema and inflammatory changes in the adjacent mesenteric fat (Fig. 3). A filling defect was displayed at the distal end of the portal vein, splenic and superior mesenteric veins (Fig. 4, 5). Therefore, in our case, the "double halo" sign translated a mesenteric ischaemia caused by mesenteric vein thrombosis (MVT).
The patient underwent surgery. The MVT was shown (Fig. 6), fundamentally affecting an ileum segment which was resected (Fig. 7). A week after that the patient was asymptomatic and was therefore discharged.

Discussion

The "double halo" sign indicates stratification within a thickened bowel wall that consists of two continuous thickened layers. It is composed of a higher-attenuation outer ring (muscularis propria) surrounding a lower-attenuation inner ring (oedematous submucosa). The "double halo" sign is seen in a high variety of diseases. In our case, the filling defect which was seen at the distal end of the portal vein, splenic and superior mesenteric veins (Fig. 4, 5) confirms that this "double halo" sign shows a mesenteric ischaemia caused by superior mesenteric vein thrombosis (MVT).
MVT can result in an uncommon form of acute mesenteric ischaemia (AMI) which includes arterial, venous occlusion as well as non-occlusive causes of ischaemia. As in an arterial thrombosis, MVT has serious complications, for example bowel infarction. For this reason, the early diagnosis of this disease is vital.
Differential diagnosis of the arterial or venous origin of intestinal ischaemia is a big challenge because their clinical and radiologic features are quite similar.
The clinical symptoms of this disease are nonspecific (asymptomatic, abdominal pain…), so imaging techniques are very important. Nowadays, Multidetector Computer Tomography (MDCT) is the modality of choice, because technical advances allow a better visualization of mesenteric vessels. MDCT has a sensitivity of 95% [1, 2].
MDCT signs of bowel ischaemia can be divided in mural, vascular and extramural signs.
Mural signs: Abnormal wall enhancement and "double halo"/"target" sign [3].
An increase of normal wall enhancement may be the consequence of venous congestion or the preservation of arterial inflow in the setting of impaired venous drainage. Decreased normal wall enhancement is secondary to venous bowel infarction [4]. "Double halo" or “target” sign is the mural stratification into two or three layers (Fig. 2, 3). In the "target" sign the inner (mucosa) and outer (muscularis propria) rings of high attenuation are separated by a ring of low attenuation (submucosal oedema).
Vascular signs: Venous filling defect (thrombotic material) (Fig. 4, 5), venous engorgement secondary to venous congestion due to thrombosis, venous collateral circulation, intestinal pneumatosis and porto-mesenteric venous gas.
Extramural signs: Mesenteric fat oedema (Fig. 3), bowel dilatation (Fig. 2, 3) and free intraperitoneal air, this last feature resulting from perforation.
Abnormal wall enhancement, mesenteric fat oedema and bowel dilatation are more pronounced in venous occlusion than in arterial occlusion [2, 5]. In our case the combination of these findings and the venous filling defect led to the early diagnosis of a dangerous disease like MVT.

Differential Diagnosis List

Final Diagnosis

Mesenteric ischaemia caused by superior mesenteric vein thrombosis.

URL:	https://www.eurorad.org/case/14152
DOI:	10.1594/EURORAD/CASE.14152
ISSN:	1563-4086