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ECR 2018 / C-1576
Overview of CT evaluation in acute appendicitis: an illustrated semiological guide
Congress: ECR 2018
Poster No.: C-1576
Type: Educational Exhibit
Keywords: Inflammation, Education and training, Acute, Technical aspects, Structured reporting, Education, CT-Angiography, CT, Gastrointestinal tract, Emergency, Abdomen, CT-Colonography
Authors: M. E. Ispas, R. Dumitru, I. G. Lupescu; Bucharest/RO
DOI:10.1594/ecr2018/C-1576

Background

INTRODUCTION

 

Right lower quadrant pain is a common clinical presentation in the emergency room [1]. Acute appendicitis is one of the most common causes of right lower quadrant pain and the most common condition that requires surgery in childhood. Because of low costs and availability, ultrasound is sometimes preferred as the initial imaging modality, but it is often inconclusive. Spiral CT is more sensitive and specific, therefore  is the imaging modality of choice in adult patients presenting with right lower quadrant pain [2], [3].

 

CLINICAL ISSUES

 

  • Clinical presentation

 

Acute appendicitis affects patients of all age groups, regardless of gender (M:F = 1:1), although some studies have shown a male preponderence (M:F = 1.4:1) [4], [5]. Patients with acute appendicitis often present with periumbilical pain migrating to right lower quadrant, but because of the variation in the position of the appendix, the age of the patient and the degree of inflammation, many  of the patients have atypical symptoms. Other signs and symptoms are anorexia, nausea, vomiting, diarheea, possible fever [1], [2], [4], [5]. The clinical examination can reveal peritoneal inflammation at the McBurney point, but MDCT scans have shown that the base of the appendix was located at the McBurney point in only 4% of the cases [6]. Therefore the most specific physical findings are rebound tenderness, pain on percussion, rigidity and guarding. The clinical profile is often unreliable, but in some cases white blood cells can be elevated [4], [5]. 

 

  • Stages of acute appendicitis [7]

 

  • Early stage appendicitis

     - Obstruction of the appendiceal lumen leads to edema

  • Suppurative appendicitis

    - Increasing intraluminal pressure leads to transmural spread of bacteria

  • Gangrenous appendicitis

    - Intramural venous and arterial thrombosis

  • Phlegmonous appendicitis or abscess

    - An inflammed or perforated appendix can be walled off by the adjacent peritoneum or small-bowel loops leading to phlegmonous appendicitis

  • Spontaneously resolving appendicitis

    - Occurs when the intraluminal pressure is relieved

  • Recurrent appendicitis
  • Chronic appendicitis

 

  • Treatment

Acute appendicitis is the most common abdominal surgical emergency worldwide, with a lifetime risk of 8.6% in male population and 6.9% in female population [5]. For many decades, appendectomy was the standard of care, but nowadays the management of acute appendicitis has evolved: laparoscopic appendectomy is preferred over open appendectomy, some patients with perforated appendicitis may benefit from initial antibiotic therapy followed by interval appendectomy, abscesses benefit from percutaneous drainage before surgery and antibiotic therapy only is given to patients with periappendicular soft tissue inflammation and no abscess [8], [9], [10].

Imaging findings are essential for the correct management of the patients with acute appendicitis. 

 

 

COMPLICATIONS

 

 

Table 1. Complications of acute appendicitis

 

Complications

Terminology

Imaging findings

Perforation

Ischemia of the appendiceal wall [11]

 

-the presence of one or more appendicoliths in association with periappendiceal inflammation is virtually diagnostic of perforation

-the presence of extraluminal air, extraluminal appendicolith, abscess, phlegmon and a defect in the enhancing appendiceal wall – excellent sensitivity and specificity [2]

Abscess

The most frequent complication of perforation [2]

 

-rim-enhancing fluid collection that may have mass effect on the adjacent bowel loops [11]

-depending on the size of the abscess (>4 cm), percutaneous drainage is preffered in the first place, followed by delayed appendectomy [2], [8]

Peritonitis

Complication of early appendiceal rupture; more common in children [2]

 

-enhancement and thickening of peritoneal reflection, inflammatory changes in mesentery and omentum, engorgement of mesenteric vessels, hyperemic changes in bowel segments, associated with free-fluid (common sites pelvis, paracolic gutters subhepatic, subphrenic, hepatorenal spaces) [2], [11]

 

Bowel obstruction

-mechanical obstruction secondary to entrapment of the distal ileum in a periappendiceal inflammatory mass

-more commonly is a late complication of appendectomy caused by postoperative fibrosis [2]

 

-dilated bowel loops with air/fluid levels upstream a periappendiceal      inflammatory mass or fibrosis [12]

Septic seeding

Ascending infection along the draining mesenteric-portal venous system complicates with pylephlebitis, hepatic abscess  [2]

 

Pylephlebitis - inflammed thrombotic occlusion of the portal vein

Hepatic abscess - central low attenuating  lesion with rim enhancement associated with hepatic perfusion abnormalities [13]

Gangrenous appendicitis

The result of intramural and arterial thrombosis [2]

 

-pneumatosis, shaggy appendiceal wall, patchy areas of mural non-perfusion [2]

 

 

 

DIFFERENTIAL DIAGNOSIS

 

 

Table 2. Differential diagnosis of acute appendicitis

 

Differential diagnosis

Imaging findings

Mesenteric adenitis

- usually caused by Yersinia enterocolitica or Campylobacter jejuni

CT: enlarged and clustered lymphadenopathy in the mesentery and RLQ (small axis > 5mm), thickening of adjacent cecum and ileum may appear , normal appendix [14], [15]

Ilecolitis

- Crohn disease or infectious causes

CT: submucosal edema of the cecum and terminal ileum; surrounding cecal inflammation; in Crohn disease skip lesions, proeminent vessels, fistulas or abscesses are frequently found [2], [14]

Epiploic appendagitis

- inflammation, torsion or ischemia of an epiploic appendage

CT: small fat-attenuation mass contiguos with the colon with a hyperattenuating rim; may have a hyperdense center (thrombosed central vein); can associate focal thickening of the adjacent bowel, infiltration of mesenteric fat, focal thickening of the surrounding peritoneum [16]

Omental infarction

- segmental infarction of some portion of the omentum; very rare  

CT: well-circumscribed region of inflammed omental fat with haziness and areas of inflammatory stranding [15], [16]

Cecal diverticulitis

- rare location; 5% of all diverticulitis cases

CT: cecal diverticulum with mural thickening associating pericecal inflammatory changes (+/- abscess) and normal appendix [2], [14]

Appendiceal carcinoma

- malignant causes are extremely rare in young patients, usually occur in elderly patients

CT: soft tissue mass infiltrating or obstructing the appendix with  minimal surrounding infiltration [2], [14]

Appendiceal mucocele

CT: well-capsulated cystic mass in the pericecal region (that represents the distended appendiceal lumen caused by abnormal mucus accumulation) without periappendicular inflammation; focal nodular thickening in the wall suggests the presence of a mucinous cystadenocarcinoma [2]

 

 

IMAGING MODALITIES

 

  • Radiography [14]

-        Appendicolith in 5-10% of patients;

-        Air-fluid levels in the right lower quadrant;

-        Loss of right psoas margin;

-        Free peritoneal air is very uncommon.

  • Barium enema [14]

-       Non-filling of the appendix;

-     Focal mural thickening of the medial wall of the cecum (“arrowhead”  sign).

  • Ultrasound [14]

-        Best imaging tool for pregnant patients and children;

-      Non-compressible appendix; sonographic “McBurney” sign with focal pain;

-        Echogenic appendicolith;

-        Right lower quadrant fluid or abcess;

-        Abnormal Color Doppler flow within the wall of the appendix.

  • CT [14]

-       Best imaging tool for adult patients, especially for the elderly;

-        Dilated appendix;

-        Periappendicular fat stranding;

-        Appendicolith;

-        Perippendicular abscess.

 

 

Table 3. Common CT techniques in acute appendicitis [2], [17], [18], [19], [20]

 

 

Common CT techniques

Advantages

Disadvantages

Low-dose NECT

Eliminates patient preparation and contrast injection risks

Depends on the visceral fat content

Focused CT (scans only on RLQ)

Less radiation

Many false negatives

Enteral contrast

Better characterization of acute appendicitis

Opacification of appendix has a high NPV

Inconsistent opacification ot the ileum

Intravenous contrast

Better for complications and other causes of abdominal pain

Contrast injection risks

NECT with selective use of contrast material

Conclusive: no contrast injection

Inconclusive: additional radiation

 

 

The imaging algorithm for acute appendicitis in adult and pediatric population, is depicted in Table 4.

        

  Table 4. Imaging algorithm for acute appendicitis [21], [22], [23]

  

Adult population

- US upon admission in patients with suspicion of acute appendicitis and appropriate BMI;

- If US is inconclusive, LDCT may be be used to asses acute appendicitis; if inderminate, standard dose CT with intravenous contrast media;

- In the elderly patients or adult patients where important differential diagnosis have to be considered, conventional CT is the fist-line imaging tool. 

Pediatric population

- Graded-compression US is the first-line imaging tool, with similar accuracy as CT;

- CT/MRI can be used in a small number of cases, where US is inconclusive.

Pregnant population

- US is the first-line imaging tool;

- If US is inconclusive, MRI can be used.

 

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