MRI協助診斷懷孕女性急性盲腸炎

作者：Alice Goodman  
出處：WebMD醫學新聞

　　March 3, 2009 — 根據一項發表於2009年3月放射學期刊的回溯性研究結果，核磁共振（MR）造影協助診斷懷孕女性的急性盲腸炎，且可能可以減少電腦斷層掃描（CT）的需求，以及在這個情況下不理想的放射線暴露。
　　
　　研究團隊假設MR造影具有降低負面剖腹機率（NLR），且維持可接受的穿孔機率（PR）。目前，超音波是檢驗腹痛懷孕女性偏好使用的方法，而CT掃描則留給超音波檢驗未得到結論的病患。這項研究是第一項用於檢驗MR造影在一大群被懷疑罹患急性盲腸炎懷孕女性，對於手術預後的影響。
　　
　　Ivan Pedrosa醫師與其麻州波士頓哈佛大學、貝絲以色列女執事醫院的同事們表示，我們的研究目的在於評估MR造影對於這群病患的影響，以及使用NLR和PR作為預後客觀評量與評估這個情況下CT的需求。
　　
　　在這個收納148位連續、且有代表急性盲腸炎臨床症狀的懷孕病患單一中心病歷回顧研究中，受試者平均年齡為29歲（範圍從15-42歲），平均懷孕週數為20週（範圍從4-37週），所有受試者都在2002年3月到2007年8月之間接受MR造影；140位受試者在MR造影之前接受超音波檢驗，僅4位（3%）病患接受CT檢查。
　　
　　14位病患（10%）被診斷罹患急性盲腸炎，MR造影正確地偵測到所有罹患急性盲腸炎的病患。相對的，14位病患中僅有5位（36%）超音波檢驗呈陽性，但7位（50%）急性盲腸炎病患被超音波判斷為正常。14位急性盲腸炎有3位發生穿孔，急性盲腸炎最嚴重的併發症，PR率為21%。
　　
　　在134位沒有急性盲腸炎患者中，MR對125位病患為陰性結果，而9位病患為偽陽性結果。MR造影並未有偽陰性結果，代表這在排除急性盲腸炎上是個可靠的技術。在那些沒有急性盲腸炎的病患中，超音波在126個病例中可以偵測到2例正常的盲腸（<2%），MR造影則可在134個病例中偵測到116例（87%）。
　　
　　作者們寫到，MR造影可以改善偵測正常盲腸的能力是輔助臨床決定最重要的貢獻。
　　
　　其中27位（18%）病患進行外科剖腹，其中8位剖腹結果是陰性的，換算NLR率為30%。作者們表示，如果以造影陰性結果來作為避免探索性剖腹的決定根據，NLR率將可以降到7%，但維持可以接受的PR率21%。作者們期待當外科醫師與婦產科醫師對於MR造影偵測正常盲腸陰性預測值具有信心後，將可以進一步降低NLR。
　　
　　這項研究有許多限制，包括急性盲腸炎的樣本數目少、因為回溯性病例回顧的試驗設計限制、以及無法將這些結果應用到不是隨時都有MR造影技術的中心。其次，值班住院醫師判讀部分超音波結果，而放射科醫師判讀MR造影結果，這些都可能有利於MR結果。
　　
　　作者寫到，結論是，當檢驗臨床上懷疑急性盲腸炎的懷孕女性時，使用MR造影，比過去在文獻中所報告的，NLR與PR合併結果較好。當使用MR造影時，許多病例將可以避免與CT檢查有關的放射線暴露。
　　
　　作者們表示沒有相關資金上的往來。

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.