Aim and objective

Acute appendicitis is one of the most common diseases of abdomen pain [1]. It reveals the inflammation of appendix. The real reason causing this phenomenon is still unknown. Clinic diagnosis usually depends on physical examination and medical image such as ultrasound and computer tomography. However, pregnant women with suspected appendicitis are more difficult to diagnose because obstetric symptoms are similar to those of appendicitis, and computer tomography is not an appropriate tool because of the risk of radiation. The literature indicates the rate of non-detected acute appendicitis on ultrasound imaging is 68%-97% [2-4]. For pregnant women it’s about 64% [5,6]. Magnetic resonance imaging (MRI) is introduced to the process of clinic evaluation. The characteristic of non-radiation makes it possible to replace the role of computer tomography. Another advantage of MRI is to provide better anatomical information. Because of motion artifacts of uncontrolled fetus and limited breath holding, the choice of pulse sequences to reduce this intervention is important on MRI. We aim to take MRI as one important indicator in diagnosing the condition of pregnant women with unsure ultrasound findings.

From October 2015 to Apr 2017, there were 10 pregnant women with suspected acute appendicitis. Since Appendix cannot be clearly identified with ultrasound, further survey with MRI was recommended. Their average age is 33.7 year old, distributed at 29 29 40 28 40 28 33 39 33 38. Two patients were in the first trimester, four patients were in the second trimester, and four patients were in the third trimester. All had ultrasound examination before MRI. We use Siemens Aera 1.5Tesla MRI equipment with 18-channel design body coil. The sequences include True FISP coronal and sagittal with/ without fat-saturated, Haste T2-weighted with/without fat-saturated axial and coronal images and Axial T2 images (Table 1). To avoid uncomfortable reaction of patients, scan time was controlled in less than 10 minutes.

Table 1: Parameters of MRI sequences.

Ten pregnant women underwent MRI examination because of RLQ flank pain. Five were diagnosed with acute appendicitis, one was diagnosed with intraperitoneal hemorrhage. Patients’ data are summarized in Table 2. Among five patients with positive MRI findings of acute appendicitis, four were accepted appendectomy and the other one was recommended following in out-patient department. One patient who was diagnosed with intraperitoneal hemorrhage accepted salpingectomy.

Table 2: MRI findings and clinical treatment of ten patients.

The sensitivity for diagnosed acute appendicitis by MRI was 80% (4 of 5 cases, the other one without medical treatment), compared with 40% of ultrasound. These three cases were confirmed at surgery. The specificity was 100% because 4 cases that had negative MRI findings were discharged from hospital and no other sign of appendicitis.

In general, acute appendicitis is the most common reason of right flank pain for pregnant women. Since it’s of high fatality, early diagnosis and treatment are important. However, accurate diagnosis is challenging because of accompanying obstetric symptoms. As pregnancy progresses, uterus will enlarge and the location of appendix will have some variation. The symptoms like nausea, vomiting are not unusual in gestation period. Medical imaging can provide useful information to confirm patient’s condition. Ultrasound is usually the first step of image modalities. However, ultrasound highly depends on operators’ experience, and will be interfered by intestinal gas and enlarged uterus [7-9]. Computer tomography will not be taken into consideration because of radiation exposure, although present guidelines ensure fetal safety with exposure dose less than 5 rads [10,11].

On MRI, the appendix is a blind-ending tubular structure and about 9-10 cm in length [12,13]. The diameter of normal appendix should be less than 7 mm with wall thickness less than 2 mm [14]. True FISP sequence is less sensitive to the motion artifact, and it can rapidly have morphological images. Coronal True FISP detect intraperitoneal inflammation (Figure 1), and sagittal True FISP images helps tracing the direction of the intestines. The inflamed appendix has thickened wall and alter signal characteristic with increased signal intensity on T2-weighted imaging (Figure 2 and 3) [15]. To date, there is no biological evidence showing that MRI is harmful for the fetus [16,17]. But we still need to reduce the time period in the MRI examination because of noise stimulation and potential heat. In our study, the sensitivity and specificity of MRI for acute appendicitis was 80% and 100% respectively.

Figure 1 (A,B): This is a 38-year-old woman during the third trimester with acute appendicitis. (A) Coronal trufisp images shows the swollen appendix with inflammation (arrow). (B) Sagittal trufisp images show squeezed appendix (arrow). The location of appendix will be variable during pregnancy, sagittal view can detect it even if appendix is squeezed forward or to the back.

Figure 2: Acute appendicitis. Coronal haste T2 spair images show a dilated thick-walled and fluid-filled appendix with surrounding tissues inflammatory reaction.

Figure 3: A 29-year-old woman with right lower quandrant pain during 27th week of pregnancy. Axial T2 haste images show acute appendicitis with presence of appendicoliths, pericecal fluid collection (arrow).

We also found that 4 of 5 patients with positive findings are older than 35 years old, so the pregnant age probably could be one risk factor of acute appendicitis. Due to the limited number of cases, more cases are needed to establish credibility.

In our study, MRI becomes the recommended image modality for pregnant women with suspected acute appendicitis, better morphological resolution and no radiation are the main advantages. Variable anatomic location of the appendix can be better detected in MRI with three plane images. We chose rapid and less sensitive motion sequences to execute the examination. The results reveal that MRI provides valuable information in pregnant patients with acute appendicitis.