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Gastrointestinal Imaging |
1 From the Department of Diagnostic Imaging, Rhode Island Hospital and Women and Infants' Hospital, Brown Medical School, 593 Eddy St, Providence, RI 02903. From the 2004 RSNA Annual Meeting. Received September 21, 2006; revision requested November 21; revision received January 6, 2007; accepted February 19; final version accepted April 3. Address correspondence to E.L. (e-mail: elazarus{at}lifespan.org).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEIMPLICATION FOR PATIENT CAREReferences |
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Materials and Methods: Institutional review board approval was obtained, and the study was HIPAA compliant. Informed consent was waived. Findings of 80 consecutive CT examinations performed in 78 pregnant women (mean age, 25.9 years; range, 17–43 years) for abdominal pain between September 2000 and October 2004 were compared with findings at prior US (n = 52), surgery, and clinical follow-up. Sensitivity and specificity were calculated for the diagnosis of appendicitis. The average fetal radiation dose was 16 mGy (1.6 rad) (range, 4–45 mGy [4–4.5 rad]).
Results: CT findings were normal in 51 examinations (64%) and abnormal in 29 (36%). Abnormal findings were appendicitis (n = 13), urinary tract calculi (n = 6), small-bowel obstruction (n = 2), cholelithiasis (n = 2), pyelonephritis (n = 2), diaphragmatic hernia (n = 1), cecal bascule (n = 1), ileus (n = 1), and metastatic lymphadenopathy (n = 1). One surgically confirmed case of appendicitis was not detected at CT. For diagnosis of appendicitis, sensitivity of CT was 92% (12 of 13 examinations), specificity was 99% (66 of 67), and negative predictive value was 99% (66 of 67). Fifty-two CT studies were performed after US. US findings were normal in 46 patients (88%) and abnormal in six (12%). Abnormal findings were cholelithiasis (n = 3), obstructive hydronephrosis (n = 1), small-bowel dilatation (n = 1), and appendicitis (n = 1). Among 46 patients with normal US findings, CT findings were abnormal in 14, nine of whom required surgery. CT added important diagnostic information in 14 of 46 patients (30%).
Conclusion: CT findings established the diagnosis in 35% of examinations in pregnant women with abdominal pain (28 of 80), with a negative predictive value of 99% for appendicitis; when CT followed negative US findings, CT findings established the diagnosis in 30% of patients.
© RSNA, 2007
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEIMPLICATION FOR PATIENT CAREReferences |
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A delay in the diagnosis of many of the causes of abdominal pain can be threatening to both the mother and fetus (3,5). Therefore, imaging is often used to help clarify a confusing clinical picture. Ultrasonography (US) is widely used as the initial diagnostic modality because of its lack of ionizing radiation. Although infrequently studied in the setting of pregnancy, computed tomography (CT) is a sensitive diagnostic modality in the evaluation of common causes of abdominal pain, such as suspected appendicitis, bowel obstruction, pancreatitis, and urinary tract calculi in the nonpregnant adult patient population (6). CT has also proved effective in increasing the physician's level of certainty and leading to more timely surgical intervention in patients presenting to the emergency room with abdominal pain (7). While CT has traditionally been avoided during pregnancy because it delivers radiation, a timely, accurate preoperative diagnosis of appendicitis is critical because both maternal and fetal morbidity and mortality increase substantially with delayed diagnosis, particularly if appendiceal perforation occurs (8). Magnetic resonance (MR) imaging has also been shown recently to be of use in evaluating abdominal pain during pregnancy (9–11), but its precise role has not yet been defined.
The purpose of our study was to retrospectively determine the sensitivity and specificity of CT for the diagnosis of appendicitis in pregnant women with nontraumatic abdominal pain and to retrospectively compare the findings at CT and US in patients who underwent both examinations, using surgery or clinical follow-up as the reference standard.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEIMPLICATION FOR PATIENT CAREReferences |
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Eighty CT examinations were performed in 78 consecutive patients. The mean age of the patients was 25.9 years (range, 17–43 years). The mean gestational age at the time of CT was 23 weeks (range, 5–40 weeks). Twelve (15%) of the patients were in the first trimester of pregnancy, 41 (53%) in the second trimester, and 26 (33%) in the third trimester. All patients were known to be pregnant before scanning. The clinical indications for CT were presumed appendicitis (n = 55), generalized abdominal pain (n = 13), urinary tract calculi (n = 9), small-bowel obstruction (n = 1), postoperative ileus (n = 1), and gastric cancer metastases (n = 1).
Fifty-two US examinations were performed in our cohort of 78 patients. The mean age of the patients who underwent US was 26.3 years (range, 17–43 years). The mean gestational age in this cohort was 24 weeks (range, 5–40 weeks).
CT Examinations
Before the CT examinations were performed, informed consent was obtained. The CT examination protocols were established by a radiologist who had the choice of performing the study with or without oral or intravenous contrast material. According to our institutional policy, only an attending referring physician can order a CT examination for a pregnant woman, and only for high clinical suspicion of surgically relevant diagnoses. A radiologist verbally screened all CT requests for pregnant patients and recommended US as a first-line test in all cases of presumed appendicitis. At our institution, MR imaging was not routinely performed for the evaluation of abdominal pain in pregnant women during the period of our study.
During our study period, the CT hardware at our institution changed. The CT examinations were performed with either a single–detector row scanner (CTI; GE Healthcare, Waukesha, Wis), a four–detector row scanner (Lightspeed; GE Healthcare), or a 16–detector row scanner (Somatom; Siemens, Malvern, Pa). The specific scanning parameters varied depending on the scanner used, but general parameters included a helical acquisition with a kilovolt peak of 140 kVp and variable milliampere-second. For generalized abdominal pain, collimation of 5–7.5 mm was used. When there was a clinical question of appendicitis or renal stones, a collimation of 5 mm was used.
Scanning was started after a delay of 80 seconds following the start of intravenous contrast bolus administration, with an additional 180-second delay between abdominal and pelvic scanning. Our departmental policy is to reduce the radiation as much as allowable. To accomplish this, we shield the abdomen and pelvis of all pregnant patients when they are undergoing CT examinations of other body parts, alter CT technique to minimize dose (increase pitch), and record CT dose index, kilovolt peak, milliampere-second, and section thickness on a form sent to the departmental physicist, who then reviews dosimetry at a monthly departmental quality assurance conference.
Forty-nine of the CT examinations were performed with both intravenous contrast material (100 mL of iohexol [130 mg of iodine per milliliter]; GE Healthcare) and oral contrast material (900 mL of 2.1% wt/vol barium sulfate; E-Z-Em, Long Island, NY). Low-osmolarity intravenous contrast material was administered without reaction or complication. Twenty examinations were performed with the oral contrast material only, and 11 examinations were performed with no contrast material.
The dose delivered to the female pelvis was estimated from the CT dose index of the pelvic portion of the CT examination, as calculated on the CT scanner. Although in the third trimester a portion of the fetus typically lies above the maternal pelvis, the majority of the fetus, and in particularly the fetal head, usually remains in the pelvis. Therefore, our departmental policy is to use the pelvic CT dose index as our best estimate of fetal dose, which can be compared between scans and vendors regardless of fetal gestational age. We chose the CT dose index method of determining the estimated dose as it is an industry standard, available to all radiologists from all CT manufacturers. The fetus was within the field of view for all 80 CT scans. The mean dose delivered was 16 mGy (1.6 rad) (range, 4–45 mGy [0.4–4.5 rad]).
US Examinations
The US examinations were performed on US machines manufactured by a variety of vendors (Logiq 9, GE Healthcare; HDI 5000, Philips, Washington, DC; and Acuson XP, Siemens). All of the US examinations were performed by a sonographer supervised by a radiologist. As most of the studies were performed in an emergent "on-call" setting, examinations were performed by more than 10 registered sonographers and more than 10 board-certified radiologists, with posttraining experience ranging from 1 year to more than 20 years. All US examinations were performed no more than 48 hours before the CT examination (range, 1–48 hours).
The organs studied in the US examinations varied depending on the indication for the examination. Twenty-two studies were performed of the pelvic organs, including the right lower quadrant, 20 were performed of the abdomen and pelvis, six were performed of the abdomen only, and four were performed of only the kidneys and bladder.
Record Review and Outcome
The CT examination findings were tabulated from the original reports and compared with US findings by one author (E.L.), a board-certified radiologist. Any positive findings were recorded. An imaging study was considered diagnostic for appendicitis only if the term appendicitis was included in the report impression. Both US and CT findings were considered normal if they were notable for hydronephrosis due to pregnancy only.
Clinical outcome information was obtained from evaluation of the electronic medical records of all patients by one author (E.L.). All surgical and pathologic evaluation findings were recorded. For those patients who did not undergo surgery, final clinical diagnoses were defined as discharge diagnoses obtained from the hospital information system. We also searched the medical records to establish whether the patient was readmitted for abdominal pain during the remainder of the pregnancy and whether the pregnancy resulted in a live birth.
Two of the 78 patients underwent two CT examinations each. The first patient had an initial CT examination that demonstrated ileus only, but CT was repeated because of increased pain. The second CT examination demonstrated small-bowel obstruction and venous thrombus requiring laparotomy. The second patient underwent repeat CT 2 weeks after the original CT examination demonstrated appendicitis and the patient's appendix was removed. The repeat CT examination was performed for postoperative abdominal pain and demonstrated a small-bowel obstruction.
Statistical Analysis and Reference Standard
With surgery or clinical follow-up used as the reference standard, the sensitivity and specificity of CT were calculated for the most common surgical indication, appendicitis. All 80 CT examinations were considered adequate to enable a diagnosis of appendicitis even if performed for other clinical indications. We also calculated the negative predictive value of CT for all diagnoses and for the diagnosis of appendicitis. For patients in whom CT was performed after a US examination with negative findings, the additional diagnostic yield of CT was calculated.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEIMPLICATION FOR PATIENT CAREReferences |
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Two patients had gallstones identified at CT. In two additional patients, US demonstrated cholelithiasis that was not visible at CT. None of these patients required surgical intervention, and no patients with cholecystitis were encountered in our study.
One patient had CT findings of a diaphragmatic hernia complicated by gastric volvulus requiring emergent surgical repair. One patient had CT findings indicative of a cecal bascule, which did not require surgical intervention. An additional patient with known gastric cancer and abdominal pain had a CT examination that demonstrated abdominal lymphadenopathy consistent with metastatic disease.
Of the 51 CT examinations with normal findings, two were in patients who had findings of gallstones at US, which did not require surgery. One patient with US and CT findings interpreted as normal underwent an appendectomy for acute appendicitis 24 hours later. All other patients with normal CT findings did not require surgical intervention for abdominal pain. Thus, the overall negative predictive value of CT in our study was 94% (48 of 51 examinations) and the negative predictive value for appendicitis was 99% (66 of 67 examinations).
No patient was readmitted for abdominal pain during the remainder of her pregnancy. Fetal outcome was available for 55 of the 78 pregnant patients (71%). Fifty-one of 55 patients (93%) had a live infant born at or near term. One patient had a premature delivery of a live 30-week infant, 3 days after CT demonstrated metastatic disease from known gastric cancer. Two patients had spontaneous vaginal delivery of a nonviable fetus, at 18 and 22 weeks gestation. In the first patient, delivery was triggered by unexplained sepsis 7 days after CT with normal findings and 3 days after laparotomy, also with normal findings, performed because of continued concern about appendicitis. The second patient had a delivery triggered by chorioamnionitis, 5 days after a CT examination with normal findings. Finally, in one patient the fetus died in utero at 26 weeks gestation, 4 weeks after a CT examination with normal findings.
Comparison of CT and US Findings
Fifty-two CT examinations were performed after US. US findings were normal in 46 patients (88%) and abnormal in six patients (12%) (Table 2). Abnormal findings included gallstones (n = 3), hydronephrosis secondary to obstruction (n = 1), small-bowel dilatation (n = 1), and possible appendicitis (n = 1). Among the 46 patients with negative US findings, CT provided important diagnostic information in 14 (30%). Nine of these 14 patients (64%) with positive CT findings required surgical intervention for treatment.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEIMPLICATION FOR PATIENT CAREReferences |
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We found that for pregnant women with abdominal pain and normal US findings, CT findings provided important diagnostic information in 30%. CT demonstrated many surgically relevant findings, such as appendicitis, small-bowel obstruction, mesenteric venous obstruction, urinary tract calculi, diaphragmatic hernia, and cecal bascule in patients with normal US findings. Given the high negative predictive value of CT, negative CT findings also provide useful information for patient care and disposition.
US remains the initial diagnostic imaging test for the examination of pregnant women with abdominal pain because of its lack of radiation and ability to demonstrate obstetric and gynecologic origins of abdominal pain. A sizable proportion of our patients underwent CT without a preceding US examination. As we screen all requests from attending referring physicians and recommend US as a first-line test in cases of appendicitis, many of these patients may have undergone US examinations outside of our institution, possibly at their obstetrician's office, that were inaccessible to us. In cases of pain from presumed small-bowel obstruction, postoperative ileus, or metastatic disease, our department would not require that US precede CT, as US is not as sensitive as CT to these diagnoses (14–16).
Findings of several studies have shown that MR imaging is helpful in pregnant patients (8–10). The majority of these publications were published after the time period of our study. Diagnostic criteria for the use of MR imaging in this patient population were not established or disseminated during that period. Additionally, at many institutions (including ours at the time of our study), MR imaging was not readily available for emergent evaluation of these patients. The use of gadolinium-based contrast material in pregnancy is not advised owing to the lack of safety data, unlike the situation for iodinated CT contrast agents (17). The ability to administer contrast agents may confer an advantage to CT for diagnosis of vascular abnormalities. The single vascular abnormality in our study, a mesenteric venous thrombosis, was easily identified on CT images. Additionally, MR imaging does not allow one to readily identify calcifications, and small stones in the urinary tract may be missed (18), as well as appendicoliths in the setting of acute appendicitis. CT can be used to identify both the location and size of calcifications (19).
A mean radiation dose of 16 mGy (1.6 rad) (range, 4–45 mGy [0.4–4.5 rad]) was delivered to the pelvis at CT, as estimated from the CT dose index. While our maximum radiation dose is below the threshold dose for deterministic effects of developmental neurologic impairment, there is no threshold dose for the stochastic effects of radiation, and there is therefore a theoretical risk for increasing the chance of the fetus to develop childhood cancer (20). Unfortunately, these risks are hard to detect, as the effects may occur years after exposure. Due to its lack of radiation, MR imaging may be a preferable test when available and appropriate to the clinical history. However, if MR imaging is not available, CT does impart very useful information, and failure to diagnose the mother's medical problems correctly can pose a much greater risk to the fetus than the radiation from a diagnostic examination. The risk of fetal loss in the setting of perforated appendix approaches 20% (5).
Our study had limitations, which included its retrospective design and the selection bias caused by limiting entry to pregnant patients who underwent CT. Thus, we were not able to include all the patients who underwent only US for evaluation of their abdominal pain and did not require an additional study. The record keeping of the CT division is rigorous, as mandated by the radiation safety committee at our institution, and these data were interrogated. There is no database at our institution to allow us to reliably identify pregnant patients who presented with abdominal pain but did not undergo CT. Because we examined patients who had undergone CT, our study had a selection bias for sick patients with unrevealing US examination findings. Nevertheless, the sizable diagnostic yield for CT in patients with negative US findings in our study suggests that CT is a useful diagnostic test in the setting of pregnancy and unremitting abdominal pain. An additional limitation of our study is that many of the US examinations were focused on specific body parts but were compared with findings of CT, which offers a more comprehensive examination of the abdomen and pelvis.
Our results show that CT provided important diagnostic information in 30% of pregnant women whose US examination findings were normal. The sensitivity and specificity of CT for appendicitis were 92% and 99%, respectively.
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ADVANCES IN KNOWLEDGE |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEIMPLICATION FOR PATIENT CAREReferences |
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IMPLICATION FOR PATIENT CARE |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEIMPLICATION FOR PATIENT CAREReferences |
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FOOTNOTES |
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Author contributions:Guarantor of integrity of entire study, E.L.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, E.L.; clinical studies, E.L.; statistical analysis, E.L.; and manuscript editing, all authors
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References |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEIMPLICATION FOR PATIENT CAREReferences |
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  K. S. Lee, N. M. Rofsky, and I. Pedrosa Localization of the Appendix at MR Imaging during Pregnancy: Utility of the Cecal Tilt Angle Radiology, October 1, 2008; 249(1): 134 - 141. [Abstract] [Full Text] [PDF]
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 M. M. Chen, F. V. Coakley, A. Kaimal, and R. K. Laros Jr Guidelines for Computed Tomography and Magnetic Resonance Imaging Use During Pregnancy and Lactation Obstet. Gynecol., August 1, 2008; 112(2): 333 - 340. [Abstract] [Full Text] [PDF]
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