Non-contrast multidetector computed tomography in the evaluation of acute abdomen: is this a new paradigm in first-aid clinics?

EDITORIAL

Non-contrast multidetector computed tomography in the evaluation of acute abdomen: is this a new paradigm in first-aid clinics?

Marcos Roberto de Menezes^I; Fernando Uliana Kay^II

^IMD, Assistant, Head at the Emergency Radiology Service of the Clinics Hospital Radiology Institute, Faculty of Medicine of the Universidade de São Paulo

^IIMD, Preceptor at Clinics Hospital Radiology Department, Faculty of Medicine of the Universidade de São Paulo

Historically and almost in a dogmatic way, the acute abdomen radiographic series has been used as an universal diagnostic tool for evaluating patients with acute abdominal pain in many emergency departments worldwide. There is a certain resistance, both from the part of radiologists and surgeons, to give an opinion on any case if an abdomen radiographic series is not performed. Contrarily to this way of thinking, current scientific studies call this paradigm into question: would the plain radiograph be necessary in the age of the multidetector computed tomography (CT) yet? Several studies have shown that CT scan, combined with physical examination and laboratory tests, provides relevant diagnostic information in cases of acute abdomen admitted to emergency medical services. The acute abdomen is defined as a syndrome characterized by a sudden onset of diffuse abdominal pain demanding urgent clinical or surgical intervention^(1–4). The etiological diagnosis is extremely relevant, since a delayed diagnosis may result in a delayed treatment and the consequential patients prognosis worsening. The acute abdomen differential diagnosis includes an array of diseases, many times confounding clinicians and surgeons.

Generally speaking, one knows that the clinical laboratory diagnosis is non-specific, so invasive procedures like exploratory laparotomy have been preconized in a great number of cases. At the end, a great part of these procedures revealed non-surgical diseases (white laparotomies), emphasizing the relevance of developing less invasive diagnostic methods. In a literature review, Dombal has collected data on 10,682 cases of acute abdominal pain % with undetermined cause in 34.0%, appendicitis in 8.0%, acute cholecystitis in 9.7%, small bowel obstruction in 4.1%, gynecologic disease in 4%, acute pancreatitis in 2.9%, renal colic in 2.9%, perforating peptic ulcer in 2.5%, cancer in 1.5% and diverticular disease in 1.5%⁽⁴⁾. As observed, a minority of conditions required surgical treatment. For not a very long time ago, surgeons would accept an index between 8% and 30% of white laparotomies under penalty of not diagnosing diseases with imminent death risk.

It is in this context that the CT is inserted. Clinical examinations, laboratory tests and abdomen plain x-ray series (anteroposterior in dorsal decubitus, in orthostatic position and diaphragmatic domes x-ray) were part of the classic algorithm for acute abdomen evaluation. In the daily practice, abdomen x-rays have been useful for identifying obstructive and perforating (pneumoperitoneum) conditions with a sensitivity considered as reasonable. However, these methods in conjunction do not prove sensitive and specific enough to determine diseases like appendicitis and acute pancreatitis. Studies demonstrate that the additional cost (US$ 136.00–184.00) and the 2.44 mSv dose, despite their relative significance, would not justify the generalized use of this technique as a single way for evaluating acute abdominal pain, as its poor performance may imply a subdiagnosis of diseases with severe negative impact on the patients' prognosis^(4,5).

With the arrival, improvement and increased availability of CT as diagnostic method, it could be demonstrated that CT is an accurate method for determining these several conditions. Not only the CT is more specific for definition of the acute abdomen etiology but it is also more sensitive than x-ray for determining the presence, the level and the causes of obstructive conditions. The CT is, at least, as sensitive as x-ray for demonstrating the presence of perforation, also allowing the definition of the perforation level in specific cases.

Additionally, the method has become faster and more easily available with the technological development. The new multidetector CT devices are able to scan the patients abdomen and pelvis during only one apnea, quickly providing high resolution thin slices. The volumetric acquisition also proves ideal for generating reformatted images at coronal, sagittal and oblique plans and in curve multiplanar reconstructions, contributing to the diagnosis of several conditions (for example, the utility of the coronal plan for evaluation of urinary lithiasis and cases of appendicitis) by demonstrating a more anatomical shape. Additionally, CT provides slices plans which both clinicians and surgeons are more used to in their work. The optimization of the radiological work has also contributed to the expansion of CT applicability. The presence of a radiologist prepared to analyze tomographic studies 24 hours a day, has optimized the diagnosis and therapeutic processes. This is a trend currently and universally being implemented.

There are several tomographic protocols for acute abdomen evaluation. Some screening protocols do not include the use of intravenous, rectal or oral iodine contrast agents, increasing even more the quickness of the method (for example, the use of oral diluted contrast media delays the beginning of the examination for about one hour % that is the period required for an adequate opacification of the intestinal loops). Another advantage of the non-contrast-enhanced screening protocols would be the possibility of this procedure universalization, extending it to patients with allergic antecedents or other contraindications (for example, renal failure). As usually, the use of this method in cases of pregnant women and children should be weighted. The ionizing radiation dose, as well as the multidetector CT costs, have been considered as factors difficulting the universalization of the method. MacKersie et al. have demonstrated doses of 12 mSv for men and 17 mSv for women in multidetector CT examinations, comparing to doses of 2.4 mSv for abdominal radiographic series⁽⁵⁾.

On the other hand, studies demonstrate the effectiveness of the method both in terms of costs and in terms of irradiation doses^(4,5). Additionally, the multidetector CT offers the theoretical benefit of increasing the diagnostic accuracy due its intrinsic qualities of a better axial spatial resolution and an almost isotropic resolution in other plans.

In Brazil, differently from the American literature, the ultrasound plays a relevant role in the diagnosis of diseases frequently appearing in emergency services, such as evaluation of biliary tracts, gynecologic emergencies and appendicitis, and in the initial evaluation of polythraumatized patients. In our experience in the HC-FMUSP first-aid clinic, the ultrasound optimizes and rationalizes the use of multidetector CT in cases not resolved or screened by ultrasound, resulting in a general cost reduction due to the low cost of this examination method.

Up to the present time there is not a consensus on the best approach for patients presenting acute abdomen. We think that the active participation of the emergency radiologist in the choice of the best imaging method for investigation rationalizes and optimizes the patients flow, principally in high volume emergency services. Many authors, however, imagine a scenario in which patients are routinely submitted to multidetector CT scans replacing the acute abdomen x-ray series as a screening way for classifying cases into surgical or non-surgical. Taking the costs into consideration, the use of multidetector CT may allow the screening of these patients in a faster, safer and more decisive way towards an optimized treatment.

REFERENCES

1. Federle MP. CT of the acute (emergency) abdomen. Eur Radiol Suppl 2005;15(Suppl 4).

2. Leschka S, Alkadhi H, Wildermuth S, Marincek B. Multi-detector computed tomography of acute abdomen. Eur Radiol 2005;15:2435–2447.

3. Marincek B. Nontraumatic abdominal emergencies: acute abdominal pain: diagnostic strategies. Eur Radiol 2002;12:2136–2150.

4. Mindelzun RE, Jeffrey RB. Unenhanced helical CT for evaluating acute abdominal pain: a little more cost, a lot more information. Radiology 1997;205:43–47.

5. MacKersie AB, Lane MJ, Gerhardt RT, et al. Nontraumatic acute abdominal pain: unenhanced helical CT compared with three-view acute abdominal series. Radiology 2005;237:114–122.

Publication Dates

• Publication in this collection
  25 May 2006
• Date of issue
  Apr 2006