MRI of appendicitis in the pregnant female

Abstract

Acute appendicitis is the most common non-obstetric emergency during pregnancy. Clinical presentation is often atypical, leading to diagnostic dilemma. Delayed diagnosis and treatment can lead to significant morbidity and mortality for both the mother and fetus. The aim of imaging is to provide early and definitive diagnosis, to reduce the incidence of negative laparotomy and clinical complications. This lecture will discuss appropriate imaging pathways for the diagnosis of appendicitis in pregnancy. The RANZCR guidelines for MRI safety in pregnancy will be reviewed. The variation in appendix location in relation to the gravid uterus will be highlighted. Example cases will be used to illustrate the diagnostic criteria for acute appendicitis. Imaging of other acute causes of abdominal pain in pregnancy will also be presented. Learning objectives: 1 Review the RANZCR guidelines for MRI safety in pregnancy. 2 Discussion of an MRI protocol for the detection of appendicitis in pregnancy. 3 Demonstration of the variable locations of the appendix during pregnancy. 4 Diagnostic imaging criteria for acute appendicitis. 5 Review imaging of other causes of acute abdominal pain in pregnancy. Main: Appendicitis is the most common surgical cause for acute abdominal pain during pregnancy. The classical clinical signs are often confounded by the altered anatomy and physiology of pregnancy. The enlarging uterus progressively displaced the appendix superiorly out of the right lower quadrant, and can shield it from palpation. Mildly elevated leukocyte levels are often seen during normal pregnancy. These features can lead to delayed presentation and diagnostic uncertainty. Perforated appendicitis is more common in pregnancy and leads to increased morbidity and mortality, when compared to non-perforated appendicitis. Surgical removal of a perforated appendix is associated with higher rates of fetal demise. A negative laparotomy can also be detrimental to the fetus. It is therefore vital that diagnostic accuracy is maximized to guide appropriate treatment, and that delays are avoided. Ultrasound and MRI both provide imaging without the potential negative effects of ionizing radiation to the fetus. Ultrasound should be performed as the first-line imaging test for the investigation of suspected appendicitis in pregnancy. MRI can be considered as a second- line test, if the initial ultrasound proves equivocal. MRI is presumed to be safe in pregnancy, with no deleterious effects to the fetus seen in short-term studies. However, concerns remain about the effects of noise and heating on the fetus. The RANZCR MRI safety guidelines state that a proposed MRI study during pregnancy should be needed to guide management before the end of pregnancy, provide information not available by other non-ionising means, and be justified by risk-benefit balance, with waiting not clinically prudent. Gadolinium chelates are known to reach the amniotic fluid, with unknown effects on the fetus. Therefore Gadolinium contrast use should be avoided during pregnancy, if able. The single-shot fast spin echo sequence (SSFSE or HASTE), with or without fat-saturation, forms the mainstay of the MRI imaging protocol used to investigate suspected acute appendicitis. This sequence has a fast acquisition time, largely eliminates motion artefact, and can be acquired either at end expiration or during free breathing. Initially, 3-plane large field-of-view images are obtained of the abdomen and pelvis. These images should be reviewed immediately by the supervising radiologist, to both localize and assess the appendix. If required, further sequences can be protocoled at this point. Examples include small field-of-view fat-saturated SSFSE sequences of the appendix to assess for peri-appendiceal oedema, or time-of-flight imaging to distinguish between an elongated appendix and enlarged adjacent veins. A morphologically normal appendix has a diameter of <6 mm and a mural thickness of <2 mm. The diagnostic features of acute appendicitis include an appendix diameter of >7 mm, mural th ckness of >2 mm, luminal fluid signal, mural oedema and peri-appendiceal fat oedema and/or fluid collection. An appendix with a diameter between 6-7 mm, but without the abnormal luminal, mural or peri-appendiceal signal changes described above, is considered indeterminate and warrants clinical observation, with or without interval re-imaging. In cases of acute abdominal pain in pregnancy with normal MRI appearances of the appendix, alternative causes should be searched for on the provided imaging. Examples include renal obstruction/infection, biliary colic, cholecystitis, ovarian torsion, ectopic pregnancy and caecal volvulus.L618976951 <br />