Key words: appendicitis, CT scan.

The purpose of this study was to evaluate the diagnostic accuracy of the spiral-CT in patients with clinically suspected acute appendicitis and to determine the impact on patient management and overall costs and to exclude or confirm appendicitis in patients who presented with equivocal symptoms and signs of appendicitis, such as surgery for pain in the right lower quadrant of the abdomen, remains a clinical dilemma.

Appendiceal computed tomography was performed in 124 consecutive patients with acute appendicitis in the differential diagnosis, and whose clinical findings were insufficient to perform surgery or to discharge from the hospital. The primary CT criteria for diagnosing acute appendicitis was the identification of an appendix with a transverse diameter of 7 mm and larger with associated periappendiceal inflammatory changes (Table 1). However, appendicitis was not diagnosed in such patients unless an enlarged appendix was definitely identified. Final diagnoses were established by surgical or clinical follow-up and were compared with the original CT reports.

Appendiceal computed tomography was performed in 124 consecutive patients with acute appendicitis in the differential diagnosis, whose clinical findings were insufficient to perform surgery or to discharge from the hospital. Each scan was obtained in a single breath hold from the lower abdomen to the upper pelvis using a 5-mm collimation. Computed tomography results were correlated with surgical and pathologic findings after appendectomy or clinical follow-up. The criteria used to diagnose acute appendicitis were: (a) a thickened appendix of more than 7 mm or (b) inflammatory changes in the periappendiceal fat. If the CT findings were negative for acute appendicitis and surgery not performed, the results were correlated with other corroborating diagnostic investigations or clinical follow-up. Computed tomography signs of acute appendicitis included fat stranding (100%), enlarged appendix (> 7 mm) (97%), adenopathy (55%), appendicoliths (30%), abscess (7%), and phlegmon (12%)-(Table 3). tomography (92% sensitivity, 93% specificity).

Appendiceal spiral-CT was performed in 124 patients (51 women and 73 men) with clinically suspected acute appendicitis. Scans were obtained from the L4 level to the symphysis pubis using 5 mm collimation without i.v., oral, or rectal contrast material. Prospective diagnoses based on CT findings were compared with surgical (and histopathological) results and clinical follow-up. The effect of spiral-CT on patient management and clinical resources was assessed. Patients with negative CT findings were followed up clinically.

Eighty-eight of the 96 patients with acute appendicitis were correctly diagnosed by computed tomography, and 26 of the 28 patients (93%) without acute appendicitis were correctly diagnosed by computed tomography. Computed tomography signs of acute appendicitis included fat stranding (100%), enlarged appendix (> 7 mm) (97%), adenopathy (55%), appendicoliths (30%), abscess (7%), and phlegmon (12%) (Table3). Appendicitis was diagnosed by CT in 96 patients. Acute appendicitis was identified during surgery in 88 patients (89 per cent). Prospective interpretation of CT images yielded a sensitivity of 92 per cent and a specificity of 93 per cent for the diagnosis of acute appendicitis. There were eight false-negative scans. In 26 of 28 patients without signs of appendicitis on CT, the scan established negative signs for appendicitis or the presence of other pathology. A total of 124 patients were scanned, of which 28 were excluded (Table 4). Of the total final there were 88 true positives, 26 true negatives, 8 false negatives and no false positives, (51 women and 73 men) underwent appendectomies. The normal appendix was identified in most of the cases. The negative findings included torsion ovarian cyst (two patients), urinary tract disease (three patients), mesenteric lymphadenopathy (two cases), and one case was negative.

Appendicitis is a disease afflicting young patients. Appendicitis affects 1 in 500 people each year. Appendicitis should be considered in any person with undiagnosed abdominal pain. The incidence peaks between the ages 15 and 24. The concept is that right lower quadrant pain in women of childbearing age is a more complex clinical problem than in men. Women have historically had higher rates of negative laparotomy (1). Anderson reported decreased diagnostic accuracy for appendicitis among women, particularly in the third decade of age (2). The need for improved diagnostic testing in the evaluation of patients with appendicitis is suggested by this study, both from the perspective of the delay encountered in women as well as the extremely high perforation rate in men. A variety of approaches have been investigated including ultrasound, WBC scanning, helical CT, clinical scoring systems, and neural network (3).

Clinical diagnosis of appendicitis is usually made on the basis of history, physical examination (Table 2) and laboratory studies, but approximately 20-35% of patients with suspected appendicitis present with a diagnostic dilemma (4) mainly in the extremes of life, and in ovulating females and young children. There is a high incidence of a false negative appendectomy rate in the pediatric population and it reaches up to 25 %(4).

The appendix is obstructed by a fecal concretion in 50-80% of all cases. The position of the appendix is retrocecal or retroperitoneal in 30% of the cases and intraperitoneal in 70% of the cases.

In retro peritoneal appendicitis, the inflammation invades retroperitoneal fat and can permeate fasciae and fatty tissue by means of inflammation, which eventually leads to abscess formation. In intraperitoneal appendicitis, the inflammation causes localized adhesion of peritoneal membranes and intraperitoneal abscess(5). Radiological examination can reduce the number of misdiagnoses and negative laparotomies and help in treatment of appendiceal abscesses and in post-operative complications.

Continuous improvements in technology, technique and interpretation achieved over the past 15 years have increased the accuracy of imaging methods substantially. CT has gained acceptance as a primary imaging technique for acute appendicitis by virtue of its ability to image the appendix ,adjacent fat and gut directly.(8) CT for suspected appendicitis is a widely accepted technique because CT examinations are rapidly performed and are usually straightforward to interpret by radiologists with varying degrees of experience from residents (9) to more subspecialized abdominal radiologists. All these features have led to a steady increase in use of appendiceal CT (10-11).

The radiation exposure is the main disadvantage of using CT technique. While the sonographic disadvantages are that they are operator dependant for which intestinal peristalsis, iliac artery pulsations, deep respiration in a non-cooperative patient may give a false impression, and difficulty in maintaining the probe at the same location for a long time, is another disadvantage (8).

With a high resolution CT, an abnormal appendix can be observed and variable CT findings can be evaluated in patients with acute appendicitis(Table 1)(6). The mortality rate in appendicitis is about 1%.

The differential diagnosis includes :colitis, gastroenteritis, small bowel obstruction, duodenal ulcer, pancreatitis, intussusception, Crohn's disease, mesenteric lymphadenitis, pancreatitis, ovarian torsion, urinary tract problems, and pelvic inflammatory disease. The prognosis is more serious if there is perforated appendicitis. In such a case, the patient may require more extensive surgery and antibiotics, and the convalescence is much longer.

In infiltrative phases, the normally readily demonstrable retrocecal fatty tissue is seen on CT scan as a streaky, reticulated area which becomes more demarcated when abscesses are present .

A retrocecal appendix can sometimes be identified as a finger shaped soft tissue structure. Calcified densification corresponding to fecal concretion may be seen in the central region. Intraperitoneal abscesses are fluid collections that are demonstrated as sharply marginated, hypodense areas. While the masking of the surrounding fat is initially less pronounced, the amount of masking can increase as the disease progresses. Protracted processes can cause wall thickening in the pole of the cecum.(5).

Contrast studies are not necessary in reaching a diagnosis nor is there any value in performing an ultrasound examination in acute appendicitis(6) but it is of value in demonstrating complications or an alternative diagnosis.

Appendicular abscess appears as a well -demarcated fluid collection in the right lower quadrant of the pelvis, while appendicitis appears as a dilated, thickened wall appendix or ceacum with periappendicular edema and "dirty fat" may be present(7).

Prompt diagnosis of appendicitis ensures timely treatment and prevents complications. Obvious cases of appendicitis require urgent surgical consultation.

* The use of spiral computed tomography in patients with equivocal clinical presentations suspected of having acute appendicitis lead to a significant improvement in the preoperative diagnosis and a lower negative appendectomy rate.

*Helical CT has been shown to be an excellent imaging tool for differentiating appendicitis from most acute gynecological conditions, thus challenging the use of ultrasonography in women. The accuracy of CT relies in part on its ability to reveal a normal appendix better than ultrasonography.

* When the appendix measures less than 9 mm alone, the likelihood of appendicitis is much smaller

*Non-contrast CT is an accurate, reliable and efficacious method in the diagnosis of acute appendicitis and it has the advantage of showing other pathologies mimicking the symptoms of acute appendicitis

* Appendiceal computed tomography is an accurate, reliable and a safe technique to diagnose or to exclude acute appendicitis even if performed in daily routine scanning; on the other hand it can improve medical care and reduce the overall costs for patients suspected of having acute appendicitis.

CT is highly accurate for diagnosing acute appendicitis in both men and women, although there was a slight decrease in sensitivity in thin women.

Developing experience with the technique and understanding the subtleties of interpretation can further improve diagnostic accuracy.