Acute Appendicitis

Leyla Azmoun, MD
Piran Aliabadi, MD
B Leonard Holman, MD

December 12, 1995

Presentation

A 29-year-old woman presented to the emergency room with nausea, vomiting and abdominal pain. The pain was initially in the periumbilical area and later localized to the right lower quadrant. On physical exam, her temperature was 38 degrees Celsius. She had guarding and mild rebound tenderness in the right lower quadrant of her abdomen. On pelvic examination, there is right adnexal tenderness. Her white blood cell count (WBC) is 12K/痞 and her urine B-HCG is negative.

Imaging Findings

Supine and upright radiographs of the abdomen

Ultrasound

Supine and upright plain radiographs of the abdomen show a relative paucity of bowel gas on the left side of the abdomen. There is mild irregularity and thickening of the folds in a loop of bowel in the right lower quadrant (arrow). Several gas-fluid levels are seen in this region (arrows). No appendicolith or free intraperitoneal air is seen. These findings are consistent with an inflammatory process in the right lower quadrant resulting in a localized small bowel ileus.

Ultrasound shows a thick-walled, non-compressible tubular structure in the right lower quadrant arising from the cecum (arrow). It measures 2.2 cm in its outer anteroposterior diameter and represents an inflamed appendix (arrow). A small amount of periappendiceal fluid (arrow) may represent a possible perforation. No appendicolith or periappendiceal abscess is visible. The uterus and ovaries are normal.

Diagnosis

Acute appendicitis

Discussion

In 70% of patients with acute appendicitis, the diagnosis is made clinically based on classic signs and symptoms. In the remaining 30% of patients with uncertain clinical findings, radiologic imaging is needed to establish the diagnosis. Both graded compression sonography or CT can be utilized to evaluate patients with suspected appendicitis. Advantages with sonography include lower cost and real-time observation of bowel peristalsis. Ultrasound is also superior to CT in diagnosing gynecologic diseases which may mimic appendicitis. CT is performed in patients with marked obesity, tense ascites or severe pain in whom sonography may be technically difficult or non-diagnostic. CT is also preferred in patients likely to have an abscess.

Sonographic criteria for acute appendicitis include a noncompressible appendix with an outer AP diameter of at least 7 mm, mural thickness of 3 mm or greater, or presence of an appendicolith in an appendix of any size. Presence of a hypoechoic fluid collection containing an appendicolith or a fluid collection adjacent to a gangrenous appendix is diagnostic of a periappendiceal abscess. Percutaneous drainage of large periappendiceal abscesses prior to appendectomy can be performed under both CT or ultrasound guidance.

In experienced hands, graded compression sonography has a greater than 90% accuracy for diagnosing acute appendicitis. False-negative diagnoses may occur in retrocecal appendicitis, perforated appendicitis or in pregnant patients. False-positive results may be seen in women with a dilated fallopian tube or in inflammatory conditions such as tubo-ovarian abscess or Crohn's disease, which may secondarily affect the appendix.

The majority of patients imaged for right lower quadrant pain do not have acute appendicitis. In up to 70% of these patients, sonography may detect alternative diagnoses such as salpingitis, Crohn's disease, bowel obstruction, ureteral calculi or degenerating uterine leiomyomas.

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