MRI协助诊断怀孕女性急性盲肠炎


  March 3, 2009 — 根据一项发表于2009年3月放射学期刊的回溯性研究结果,核磁共振(MR)造影协助诊断怀孕女性的急性盲肠炎,且可能可以减少计算机断层扫描(CT)的需求,以及在这个情况下不理想的放射线暴露。
  
  研究团队假设MR造影具有降低负面剖腹机率(NLR),且维持可接受的穿孔机率(PR)。目前,超音波是检验腹痛怀孕女性偏好使用的方法,而CT扫描则留给超音波检验未得到结论的病患。这项研究是第一项用于检验MR造影在一大群被怀疑罹患急性盲肠炎怀孕女性,对于手术预后的影响。
  
  Ivan Pedrosa医师与其麻州波士顿哈佛大学、贝丝以色列女执事医院的同事们表示,我们的研究目的在于评估MR造影对于这群病患的影响,以及使用NLR和PR作为预后客观评量与评估这个情况下CT的需求。
  
  在这个收纳148位连续、且有代表急性盲肠炎临床症状的怀孕病患单一中心病历回顾研究中,受试者平均年龄为29岁(范围从15-42岁),平均怀孕周数为20周(范围从4-37周),所有受试者都在2002年3月到2007年8月之间接受MR造影;140位受试者在MR造影之前接受超音波检验,仅4位(3%)病患接受CT检查。
  
  14位病患(10%)被诊断罹患急性盲肠炎,MR造影正确地侦测到所有罹患急性盲肠炎的病患。相对的,14位病患中仅有5位(36%)超音波检验呈阳性,但7位(50%)急性盲肠炎病患被超音波判断为正常。14位急性盲肠炎有3位发生穿孔,急性盲肠炎最严重的并发症,PR率为21%。
  
  在134位没有急性盲肠炎患者中,MR对125位病患为阴性结果,而9位病患为伪阳性结果。MR造影并未有伪阴性结果,代表这在排除急性盲肠炎上是个可靠的技术。在那些没有急性盲肠炎的病患中,超音波在126个病例中可以侦测到2例正常的盲肠(<2%),MR造影则可在134个病例中侦测到116例(87%)。
  
  作者们写到,MR造影可以改善侦测正常盲肠的能力是辅助临床决定最重要的贡献。
  
  其中27位(18%)病患进行外科剖腹,其中8位剖腹结果是阴性的,换算NLR率为30%。作者们表示,如果以造影阴性结果来作为避免探索性剖腹的决定根据,NLR率将可以降到7%,但维持可以接受的PR率21%。作者们期待当外科医师与妇产科医师对于MR造影侦测正常盲肠阴性预测值具有信心后,将可以进一步降低NLR。
  
  这项研究有许多限制,包括急性盲肠炎的样本数目少、因为回溯性病例回顾的试验设计限制、以及无法将这些结果应用到不是随时都有MR造影技术的中心。其次,值班住院医师判读部分超音波结果,而放射科医师判读MR造影结果,这些都可能有利于MR结果。
  
  作者写到,结论是,当检验临床上怀疑急性盲肠炎的怀孕女性时,使用MR造影,比过去在文献中所报告的,NLR与PR合并结果较好。当使用MR造影时,许多病例将可以避免与CT检查有关的放射线暴露。
  
  作者们表示没有相关资金上的往来。

MRI Helpful in Diagnosing Acute Appendicitis in Pregnant Patients

By Alice Goodman
Medscape Medical News

March 3, 2009 — Magnetic resonance (MR) imaging aids in the diagnosis of acute appendicitis in pregnant patients and may be able to obviate the need for computed tomography (CT) and itsundesirable radiation exposure in this situation, according to a retrospective study reported in the March 2009 issue of Radiology.

The investigators hypothesized that MR imaging has the potential to reduce the negative laparotomy rate (NLR) while maintaining an acceptable perforation rate (PR). Currently, ultrasound is the favored technique for examination of women with abdominal pain, and CT scan is reserved for patients with inconclusive ultrasound examinations. The present study is the first to examine the impact of MR imaging on surgical outcomes in a large series of pregnant women suspected of having acute appendicitis.

"[T]he aim of our study was to assess the effects of MR imaging [in this group of patients,] using the NLR and PR as objective measures of outcome and to assess the need for CT in this setting," write Ivan Pedrosa, MD, and colleagues at Beth Israel Deaconess Medical Center and Harvard Medical School in Boston, Massachusetts.

In this single-center retrospective review of 148 consecutive pregnant patients with clinical symptoms suggesting acute appendicitis, mean age was 29 years (range, 15 – 42 years). Mean gestational age was 20 weeks (range, 4 – 37 weeks). All subjects underwent MR imaging between March 2002 and August 2007; 140 subjects underwent ultrasonography before MR imaging. CT was performed on 4 patients (3%).

Fourteen patients (10%) had acute appendicitis, and MR imaging correctly identified all of these patients. In contrast, ultrasound was positive for acute appendicitis in 5 (36%) of 14 patients, while ultrasound was interpreted as normal in 7 (50%) of the 14 acute appendicitis patients. Perforation — the most serious consequence of acute appendicitis — occurred in 3 of the 14 patients with acute appendicitis, for a PR rate of 21%.

Of the 134 patients without acute appendicitis, MR yielded negative results for 125 patients and false-positive results for 9 patients. There were no false-negative results for MR imaging, suggesting that it is a valid technique for ruling out acute appendicitis. In those without acute appendicitis, ultrasound was able to visualize the normal appendix in 2 (<2%) of 126 cases compared with 116 (87%) of 134 cases for MR imaging.

"The improved visualization of the normal appendix with MR imaging is a major attribute that assists in clinical decision making," write the authors.

Surgical exploration was performed in 27 patients (18%), and 8 had negative laparotomy results, for an NLR of 30%. The authors note that if the decision to avoid exploratory laparotomy had been based on negative MR findings, the NLR would have declined to 7%, while maintaining an acceptable PR of 21%. The authors expect further declines in NLR as surgeons and obstetricians gain confidence in the negative predictive value of a normal appendix visualized by MR imaging.

The study had several limitations, including the small number of patients with acute appendicitis, the potential for bias inherent in a retrospective review, and the inability to generalize results to centers that do not have MR imaging available at all times. Also, residents on call interpreted some of the ultrasound studies, while radiologists read the MR images, which may have led to more favorable MR results.

"In conclusion, when examining pregnant patients for clinically suspected [acute appendicitis], the use of MR imaging yields favorable combinations of the NLR and the PR compared with values previously reported in the literature," the authors write. "With use of MR imaging, the radiation exposure associated with CT examinations can be minimized and in many cases avoided."

The authors have disclosed no relevant financial relationships.

Radiology. 2009;250:749–757.

    
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