US FINDING FOR GANGRENOUS APPENDICITIS

Clinical History

US examinations shows enlarged (diameter 13 mm) noncompressible, appendix with periappendiceal fluid as well as fluid within the pouch of Douglas.

Imaging Findings

A previously healthy 29 year old woman presents to the emergency department with acute abdominal pain in the right lower quadrant of 32 hours' duration. She has fever, and her examination is remarkable for right lower quadrant tenderness with peritoneal signs. The three factors with the highest predictive value for acute appendicitis are right lower quadrant pain, abdominal rigidity, and migration of pain from the periumbilical region to the right lower quadrant. US examinations shows enlarged (diameter 13 mm) noncompressible, appendix with periappendiceal fluid as well as fluid within the pouch of Douglas. Enlargement of the appendix is a sign of suppurative or gangrenous appendicitis. The inflamed appendix appears as a sausage-shaped, blind-ending structure on longitudinal, or as a target lesion on transverse sections. An appendicolith, was seen as an intraluminal hyperechoic structure with accustic shadow. When an appendicolith is detected, the thickness and compressibility are not important in making the diagnosis of appendicitis. In addition, an irregular hypoechoic mass is identified surrounding the appendix, this represents periappendiceal inflammation.

Discussion

Acute appendicitis is the most common indication for emergency laparotomy. Perforation, although still uncommon, occurs with a much greater frequency in the pediatric and oldery population. The pathogenesis generally begins with luminal obstruction. Continued natural secretions of mucus within the appendix leads to distention. Luminal bacteria multiply as venous engorgement develops secondary to the elevated intraluminal pressure causing vascular compromise. Finally, arterial compromise ensues and perforation occurs with the development of a periappendiceal abscess. The usual initial symptoms are vague visceral abdominal pain secondary to the distention of the appendix. After 4 to 6 hours, as the inflammation spreads to the parietal peritoneum, the pain increases in intensity and becomes somatic in nature localized at "McBurney's Point" in the RLQ. Nausea, vomiting, and anorexia are frequently associated. The typical historical and physical findings are found in approximately 2/3 of patients eventually determined to have appendicitis. The clinical diagnosis is not always entirely straightforward especially in children who may not be able to communicate their symptoms adequately. Imaging methods must be used in patients with indeterminate clinical findings to avoid unnecessary laparotomies. On the US exam the mucosa, if seen, will appear as a thin hyperechoic line surrounding the lumen. The wall of the appendix is hypoechoic and is usually <2 mm in thickness with an overall cross-sectional diameter of less than or equal to 6mm. A recent study has shown that any appendix measuring >6 mm at its greatest point will be inflamed 93% of the time. Enlargement of the appendix is a sign of suppurative or gangrenous appendicitis. A cross-sectional diameter measurement of greater than 6 mm along with noncompressibility in a patient with persistent RLQ pain is considered reliable evidence of appendicitis. It is extremely important that the entire appendix is visualized because inflammation may be localized to the distal tip. Associated findings include loss of the echogenic submucosal layer which may reflect extension of the inflammation through the muscularis propria. There may be a fluid-filled lumen which will be anechoic and/or a hyper echoic appendicolith with acoustic shadowing. There may also be associated periappendiceal fluid collections or mass which may displace adjacent structures. These latter findings are more likely to be seen in association with perforation. The inflamed appendix can usually be identified medial and inferior to the cecum. It appears as a sausage-shaped, blind-ending structure on longitudinal, or as a target lesion on transverse sections. The lumen of the appendix may be hyperechoic or, if fluid filled, anechoic. An appendicolith, gas, or inspissated feces can be seen as an intraluminal hyperechoic structure with or without shadow. The diameter of the lumen is between 3 and 10 mm. When an appendicolith is detected, the thickness and compressibility are not important in making the diagnosis of appendicitis. If, in addition, an irregular hypoechoic mass is identified surrounding the appendix, this represents periappendiceal inflammation.

Differential Diagnosis List

Final Diagnosis

Acute Gangrenous Appendicitis

URL:	https://www.eurorad.org/case/4437
DOI:	10.1594/EURORAD/CASE.4437
ISSN:	1563-4086