Diagnostic value of 3D T1-weighted gradient-echo and 2D T1-weighted in-phase and out-of-phase gradient-echo sequences for appendicitis diagnosis in pregnant women

INTRODUCTION

Acute appendicitis is the most common cause of abdominal pain requiring emergency surgical intervention in pregnant women, with an incidence of 0.05–0.07%.^[1-3] Radiology plays a crucial role in its diagnosis due to the limitations of clinical examination and other laboratory tests. While ultrasonography is considered the modality of choice in these cases, it depends on the physician’s experience and is limited by the positional changes of abdominal organs during pregnancy. Magnetic resonance imaging (MRI) has been used routinely to diagnose pregnancy appendicitis for nearly two decades.

Numerous studies have shown MRI’s outstanding value in this area.^[4-8] Each study used a different sequence protocol. Choosing sequences with high diagnostic values is more important than taking a series of different sequences, reducing examination time and minimizing discomfort due to the poor breath-holding ability of pregnant women, especially those with high fetal weight and gestation weeks. Therefore, this study compared the diagnostic value of 3D T1-weighted (T1W) gradient-echo (GRE) and 2D T1W in-phase and out-of-phase GRE sequences for diagnosing appendicitis in pregnant women.

MATERIALS AND METHODS

Image analysis

The appendix was observed through MRI in the 25 enrolled patients, of which four had an MRI-based appendicitis diagnosis. These four patients underwent surgery and were confirmed to have appendicitis by surgery and pathology. The remaining 21 cases with no MRI-based appendicitis diagnosis were monitored clinically. Of these, one case was later diagnosed with peritonitis surgically due to ruptured appendicitis (3 days post-MRI); all others were confirmed non-appendicitis cases. Therefore, based on pathological results and clinical follow-up, this study had five appendicitis cases and 20 non-appendicitis cases.

Four radiologists with >5 years of experience in gastroenterology independently interpreted the MRI images on the INFINITT PACS system (Infinitt Healthcare, Seoul, South Korea). The radiologists were blinded to information about surgical, pathological, and clinical follow-up results. Each used a separate set of images. There were four image groups: A (only T2W sequences), B (T2W and 3D T1W GRE), C (T2W and T1W in-phase and out-of-phase GRE), and D (T2W, 3D T1W GRE, and T1W in-phase and out-of-phase GRE). Radiologists were asked to determine whether appendicitis was present based on the provided images. In a pregnant woman, the appendix, which has a double-layer wall thickness and a diameter of around 6 mm, is frequently seen on T2W image of the pelvis. The appendix’s lumen sometimes showed hyposignal in the in-phase compared to the out-phase GRE image, indicating the presence of air inside the lumen [Figure 1].

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Figure 1:

Normal appendix in a 28-year-old pregnant woman at 12 weeks gestation. The appendix size was small, without surrounding infiltration on all sequences (arrow). (a) Axial T2-weighted image. (b) Axial 3D T2-weighted gradient-echo (GRE). (c) Out-of-phase GRE. (d) Axial in-phase GRE. Her final diagnosis was non-appendicitis based on clinical follow-up.

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The standard criteria for defining appendicitis were an increase in appendiceal size (diameter ≥7 mm) and periappendiceal fatty infiltration [Figure 2]. We considered such cases negative predictive value (NPV) for appendicitis, regardless of appendix size. In cases where there was disagreement on the diagnostic conclusion in the combined groups (B, C, and D) based on images from different sequences, the radiologists used the results based on the 3D T1W GRE sequence (for group B) and in-phase and out-of-phase GRE sequences (for Group C). For Group D, the radiologists made a majority conclusion (diagnosis from 2/3 sequences).

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Figure 2:

Appendicitis in a 41-year-old woman at 32 weeks pregnant. (a) Axial T2-weighted image shows an enlarged appendix with intraluminal fluid but unclear surrounding infiltrates (arrow). (b) Axial 3D T2-weighted gradient-echo shows an enlarged appendix with surrounding infiltrates (arrow); this case was later diagnosed with appendicitis after surgery and pathology.

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RESULTS

DISCUSSION

Acute appendicitis is the most common cause of non-obstetric abdominal pain requiring surgical emergency treatment during pregnancy.^[10,11] During pregnancy, the maternal body experiences decreased immunity, increasing steroid hormone levels. Therefore, they are more prone to infectious diseases. In addition, clinical appendicitis symptoms during pregnancy are non-specific and complicated due to natural physical and anatomical changes in the appendix’s location. Consequently, diagnosing pregnancy appendicitis is challenging. The risk of complications, such as rupturing and developing peritonitis, in this population is higher than in the average population. Accurately diagnosing the appendix’s inflamed condition in pregnant women early is crucial in providing them with the best treatment strategy.^[12] MRI is an accepted imaging diagnosis modality for appendiceal inflammation during pregnancy.

Mean maternal age did not differ significantly between the non-appendicitis (30.4 ± 7.1 years) and appendicitis (30.4 ± 7.1 years) groups (P = 0.500). In addition, their gestation weeks distribution was similar (P = 0.730). These findings are consistent with Shin et al.^[13] and Theilen et al.^[14] However, Andersen and Nielsen^[1] and Guttman et al.^[10] reported that appendicitis was most common in the second trimester.

In this study, white blood cell levels were significantly higher in patients in the appendicitis group than in the non-appendicitis group, consistent with Shin et al.^[13] and Cardall et al.^[15] However, Mourad et al.^[16] and Stone^[17] found that high white blood cell levels were not informative for diagnosing appendicitis during pregnancy. Their appendiceal inflamed patients had white blood counts >10,000/mm³, but so did 50% (10/20) of patients with normal appendices. Pritchard and Rowland^[18] found that white blood cell counts can fluctuate from 6,000 to 16,000/mm³ and even as high as 20,000–30,000/mm³ during normal pregnancy.

To the best of our knowledge, no previous study has assessed the diagnostic efficacy of 3D T1W GRE sequence and in-out phase images or the diagnostic value of in-out phase images solely in diagnosing pregnancy appendiceal inflammation. Only Jang et al.^[19] sought to determine the diagnostic value of 3D T1W images. Our study indicates a moderate agreement between T2W image analysis alone or combined with in-out phase images of the final appendicitis diagnosis (κ = 0.600). Similarly, Jang et al.^[19] found agreement between T2W image analysis results and pathological diagnoses (κ = 0.571), indicating good agreement. Our analyses found excellent agreement between final diagnosis and pathological findings in groups using 3D T1W images (κ = 0.865). These results are higher than those of Jang et al.,^[19] illustrating a good within-group agreement (κ = 0.673). This disagreement between our study and Jang et al.^[19] in using 3D T1W combined with T2W might be due to our use of 3D T1W sequences with a 2.5 mm slide thickness, while Jang et al.^[19] used a 3 mm slide thickness. Using in-out phase images for diagnosis disagreed with MRI final diagnosis and final pathological diagnosis.

Jang et al.^[19] showed that adding 3D T1W-GRE images to T2WI helps identify the appendix and improves diagnostic confidence compared to T2W image analysis. This study’s 3D T1W-GRE images assisted and increased diagnostic ACC from 88% to 96%. However, adding in-out phase images did not add value to the diagnostic process. Adding 3D T1W GRE images to T2WI provided 80% Se, 100% Sp, 100% PPV, and 95.2% NPV. These results are consistent with Pedrosa et al.,^[4] Vu et al.,^[7] Duke et al.,^[8] and Wi et al.^[20] These studies used different protocols and had sensitivities of 50–97%, specificities of 92–100%, and accuracies of up to 96%. Our study’s use of 3D T1W GRE images with a thinner slide thickness (<3 mm) could explain these differences since it increases image quality and shortens acquisition time.

Intra-appendiceal T1W hyperintensity due to fecal accumulation could be determined by reducing water content through self-absorption.^[21] It accounted for 92.3% and 51.0% of T1W hyperintensity in normal appendices in Jang et al.^[19] and Shin et al.,^[13] respectively. In addition, during this study, we discovered that periappendiceal infiltration signs were more accessible on 3D T1W images than on T2W pictures with or without fat saturation since both water and fat show hypersignal intensity in T2W images. 3D T1W images could provide clues to distinguish true from false-positive cases due to periappendiceal fluid collection.

One case was misdiagnosed with appendicitis based on T2W images showing periappendiceal hypersignal intensity with fatty stranding without any suggestion signs in 3D T1W images. This case underwent surgical intervention with intrasurgical confirmation of the right ovarian torsion, which caused secondary fluid collection in the right iliac region. In addition to diagnosing appendicitis, the 3D T1W sequence can also aid radiologists in uncovering other abnormalities. For example, one case in our study population was diagnosed with a normal appendix using T2W images but failed to specify the leading cause of pain. The 3D T1W images showed a cystic lesion in the left iliac region with intralesional fluid, and pelvis fluid collection showed T1W hypersignal intensity. The patient underwent emergency surgical treatment, and the final result was hemorrhage ovarian cyst rupture, consistent with MRI detection.

This study had several limitations. First, since our study population was relatively small, it might only partially represent part of it. Second, in-out phase and 3D T1W images were obtained with 4 mm and 3 mm slice thicknesses, respectively. Therefore, image quality could cause differences in volume effect. Finally, differences in enrolled patient numbers in appendicitis and non-appendicitis groups might influence our results.

CONCLUSION

Our study showed that adding a 3D T1W GRE sequence to the diagnostic protocol facilitated the accurate diagnosis of appendicitis during pregnancy better than analyzing T2W images alone. Moreover, 3D T1W images played a pivotal role in diagnosing another abnormality that might cause pain during pregnancy. However, in-out phase sequences had limited value in imaging analyses for pregnancy appendicitis.