Author: Eric Funk, MD (@efunkEM)

How common is appendicitis in pregnancy?

Appendicitis during pregnancy is relatively uncommon.  Most studies show that approximately 0.1% of pregnancies are affected by appendicitis. (1,2) However, the low incidence is of little consolation when one of these patients presents to your Emergency Department. Besides intrauterine complications, appendicitis is the most frequent surgical problem during pregnancy. (1,2,3,4) It is most common during the second trimester. (1) In fact, a perforated appendix is the leading surgical cause of fetal loss during pregnancy. The incidence of fetal loss increases 3-fold once perforation of the appendix occurs. (5) One study showed an 8% fetal mortality, all occurring in cases of appendiceal perforation. (2) Once perforation occurs, fetal mortality is 35-40%, but maternal mortality is exceedingly rare. (2)

Unfortunately, the presentation of appendicitis can be very non-specific. Many of the symptoms that occur as a result of appendicitis (nausea, vomiting, abdominal discomfort) may be normal for a pregnant patient. In light of the serious complications and vague presentation, is important to have a good understanding of the unique aspects of the diagnosis and care of the pregnant patient in whom appendicitis is suspected.

What parts of the history and physical are important?

One of the most persistent myths about maternal appendicitis is that the patient will have pain in the right upper quadrant.  A single study conducted in 1932 by Baer provided the basis for this idea. (6) The subjects of his study were pregnant but did not have appendicitis. The paper showed that the uterus will slowly displace the abdominal contents superiorly into the upper abdomen.  While it is true that pregnancy results in upward migration of the appendix, it has a minimal bearing on the location of the pain in pregnant patient with appendicitis.  About 70-80% of these patients will primarily have right lower quadrant pain. (1, 2). Only 7% of patients with histologically-proven appendicitis report right upper quadrant pain. (1) Additionally, only 1/3 of patients had rebound tenderness on exam.  Another important element of the history is the length of time from onset of symptoms to presentation to the ED, which is directly correlated with the likelihood of perforation. (2)

Physical exam may reveal a fever, but this finding is not helpful in making the diagnosis. Patients often report nausea and vomiting. As discussed previously, these common manifestations of appendicitis have significant overlap with normal pregnancy. (3) Similar to non-pregnant patients, appendicitis can be associated with anorexia. New onset abdominal pain should trigger the ED physician to consider appendicitis, but no singular finding provides definitive confirmation. Clinical exam alone is very inaccurate for identifying appendicitis in pregnancy (3,4).

What lab testing is helpful?

Lab testing is actually not very useful in diagnosing appendicitis during pregnancy. Leukocytosis has limited utility in non-pregnant appendicitis patients. The picture is even further muddied in pregnant patients due to physiologic leukocytosis. (1) One study found an increase in the leukocyte count (16.4 as compared to 14.0), but the clinically utility of this is limited. (1) Leukocyturia is similarly unhelpful. (2)  In a rare circumstance, obtaining a beta-HCG will be critical if it reveals a new diagnosis of pregnancy in a patient with suspected appendicitis.

Occasionally, lab testing will be more useful for managing complications of appendicitis on a case-by-case basis. For example, a sepsis panel including blood cultures and a lactate are important for the pregnant patient who is in septic shock as a result of a ruptured appendicitis.

What type of imaging does the patient need?

Imaging that does not involve radiation exposure is obviously preferred in order to avoid causing fetal harm. Ultrasound and MRI have been the most extensively studied. Ultrasound is operator dependent and can be inhibited by the presence of bowel gas. (4) In non-pregnant patients, the generally accepted sensitivity and specificity are 86% and 81%, respectively. (3) Studies addressing pregnant patients with appendicitis have lower sample sizes, but ultrasound was 100% specific and 48% sensitive in one study (2). While radiation exposure should be minimized if possible, Wallace et al proposed ultrasound followed by CT if inconclusive.  The rate of negative appendectomy was 54% based on clinical exam alone, 36% based on ultrasound alone, and 8% based on ultrasound followed by CT if needed. (3) These results illustrate the challenges of diagnosing appendicitis based on physical exam alone and the importance of selecting appropriate imaging techniques. Unfortunately, this study did not consider MRI.

Using MRI to diagnose appendicitis in pregnancy is a feasible option in those facilities that have 24/7 MRI capability. The scanner time is much lower than many other MRI scans, and can be as low as 20 minutes. There is no standardized approach to using MRI for appendicitis, so the length of scan and utility of the images may vary widely from institution to institution. One challenge is that the appendix is not always identified using this modality, and might not be seen in up to 31% of patients. It has been suggested that nonvisualization likely excludes appendicitis. (7) Despite the rate of nonvisualization, MRI appears to be very useful for diagnosing appendicitis, with sensitivity of 92% and specificity of 95%. (7)

Given these findings, a reasonable approach is to use ultrasound followed by MRI if needed. However, this approach has not been validated using large patient datasets. Collaboration with the surgical service and obstetics will play an important role in managing these patients. If the appendix has not ruptured and the case is otherwise not complicated, appendectomy is generally indicated. If perforation has already occurred, utility of surgical vs. medical management is less clear. (5)

Conclusion:

Appendicitis during pregnancy is uncommon but can have severe consequences, especially for the fetus. Poor outcomes, including fetal death, are more likely once perforation of the appendix has occurred. A thorough history and physical exam provide little assistance in determining which patients have appendicitis. The pain is most likely to be located in the lower right quadrant, regardless of the length of gestation. Labs have scant utility. The preferred imaging modalities are ultrasound and MRI. Positive imaging results are fairly reliable, but there are frequent inconclusive or negative results that are less reliable. A multidisciplinary approach that includes obstetrics and surgical evaluation is appropriate. Despite the challenges in identifying and treating these patients, a good understanding of the appropriate history, physical, and workup allows the EM physician to provide excellent care of pregnant patients with appendicitis.

References

1. Mourad J, Elliott JP, Erickson L, Lisboa L. Appendicitis in pregnancy: new information that contradicts long-held clinical beliefs. Am J Obstet Gynecol. 2000;182(5):1027-9.
2. Yilmaz HG, Akgun Y, Bac B, Celik Y. Acute appendicitis in pregnancy--risk factors associated with principal outcomes: a case control study. Int J Surg. 2007;5(3):192-7.
3. Wallace CA, Petrov MS, Soybel DI, Ferzoco SJ, Ashley SW, Tavakkolizadeh A. Influence of imaging on the negative appendectomy rate in pregnancy. J Gastrointest Surg. 2008;12(1):46-50.
4. Cobben LP, Groot I, Haans L, Blickman JG, Puylaert J. MRI for clinically suspected appendicitis during pregnancy. AJR Am J Roentgenol. 2004;183(3):671-5.
5. Young BC, Hamar BD, Levine D, Roqué H. Medical management of ruptured appendicitis in pregnancy. Obstet Gynecol. 2009;114(2 Pt 2):453-6.
6. Baer JL, Reis RA, Arens, RA. Appendicitis in pregnancy with changes in position and axis of the normal appendix in pregnancy. Journal of the American Medical Association. 1932;98(16):1359-1364.
7. Theilen LH, Mellnick VM, Longman RE, et al. Utility of magnetic resonance imaging for suspected appendicitis in pregnant women. Am J Obstet Gynecol. 2015;212(3):345.e1-6.

Image by Shutterstock used with permission.

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