Appendicitis

Acute appendicitis

Definition

• Acute inflammation of appendix, which may be precipitated by obstruction of lumen

General Features

○ By ultrasound

– Thick-walled noncompressible appendix (outer diameter ≥ 7 mm),  Lumen may or may not be distended

– Periappendiceal edema seen as echogenic fat

– Increased vascularity on power Doppler

○ By CT

– Distension &/or wall thickening; single wall thickness > 3 mm . Wall thickening more reliable than maximum outer diameter

– Hyperenhancement of wall

– Periappendiceal inflammation seen as fat stranding

○ Additional findings include appendicolith, periappendiceal fluid

○ Increased caliber alone is not reliable indicator: Must be considered alongside history and other imaging findings

• Location

○ Base between ileocecal valve and cecal apex . Position of tip variable, depending upon length and direction

• Size

○ Length ranges between 2-20 cm

○ Wall thickening when inflamed

• Morphology

○ Blind-ending, worm-like extension of cecum

Ultrasonographic Findings

• Grayscale ultrasound

• ·         Thickened noncompressible appendix :
• ·         Outer diameter > 7 mm
• ·         single wall thickness > 3 mm
• ·         May or may not be distended
• ·         Echogenic periappendiceal fat
• ·         Mural stratification seen in early stages
• ·         Sonographic McBurney sign over inflamed appendix
• ·         Gangrenous appendicitis: Loss of mural stratification
• ·         "Tip appendicitis": Changes involving only tip
• ·          Appendicolith may be present: Echogenic focus, with distal acoustic shadowing , Seen in obstructive type .when present, increased risk of perforation

·         Perforated appendicitis
–      Identifying appendix can be difficult
–      Marked periappendiceal inflammatory change
–      Fluid collection/abscess (thick echogenic fluid } gas)
–      Loose appendicolith may be seen in collection
·         Additional findings: Dilated adynamic small bowel loops in right lower quadrant (RLQ), associated thickening of adjacent bowel
·         False-negative US: Aberrant location of appendix, appendiceal perforation, early inflammation limited to appendix tip
·         False-positive US: Distended noninflamed appendix from gas, fluid, and feces; thickened appendix from lymphoid hyperplasia

Doppler

ü   Increased flow on power Doppler within wall of appendix and periappendiceal inflamed fat

Transvaginal US: For visualization of pelvic appendix

Radiographic Findings

v  Infrequently diagnostic

v  Appendicolith may be visible in 5-10% of patients

CT Findings

CECT

•    Wall thickening: May or may not be distended
• u  Hyperenhancement of appendiceal wall
• u  Mural stratification: seen in early stages
• u  Periappendiceal fat stranding and fluid .
• u  Appendicolith : Can be seen as incidental finding .In isolation not diagnostic of appendicitis
• u  Arrowhead sign :Focal symmetric thickening of medial cecal wall at base of appendix . Entire appendix should be scrutinized
• u  "Tip appendicitis" may be early manifestation
• u  Excellent for identifying complications

MR Findings

• Overlap with CT findings

Imaging Recommendations

Best imaging tool

•     US method 1st choice in children, thin young adults, and pregnant patients
•     CT performed for patients with inconclusive US, if complications suspected, or in obese patients
•     MR helpful during pregnancy; alternative to CT in children/young adults

• Protocol advice

v  US: Transabdominal scan with graded compression

v  CT: Optimal CT technique controversial

v  MR: Adding DWI improves reader sensitivity

DIFFERENTIAL DIAGNOSIS

Mesenteric Adenitis

•    Enlarged and clustered lymph nodes in mesentery and right lower quadrant .
•    Normal appendix
•    May have ileal/cecal wall thickening due to GI involvement
•    Diagnosis of exclusion, as other inflammatory conditions
•    may show enlarged reactive mesenteric nodes

Cecal Diverticulitis

•    Focal pericecal inflammatory changes
•    Mild cecal wall thickening
•    Visualization of thickened cecal diverticulum

Ileocolitis

•    Mural thickening of cecum and terminal ileum; increased mural flow on color Doppler
•    Crohn disease
•    Infectious (e.g., Campylobacter, Yersinia, tuberculosis)

Appendicular Mucocele

F  Well-encapsulated cystic mass,  wall calcification

F  No periappendiceal inflammation

F  Onion skin appearance of mucus in lumen

Normal Appendix With Mucosal Lymphoid Hyperplasia

F  Associated with infectious/inflammatory GI tract conditions

F  Appendix may be thick walled; thick, smooth, inner hypoechoic band; no luminal distension

F  Absent periappendiceal inflammatory changes/no hyperenhancement in wall

Appendiceal/Cecal Carcinoma

F  Soft tissue density mass infiltrating &/or occluding appendicular lumen

F  Usually little surrounding inflammatory infiltration

F  Local and regional enlarged lymph nodes

Pelvic Inflammatory Disease

F  Complex adnexal/tubo-ovarian mass

F  Dilated fallopian tube with fluid-fluid level (pyosalpinx)

Ruptured Right Adnexal Ectopic Pregnancy

F  Echogenic tubal ring and increased tubal mural vascularity, fetal pole with or without cardiac activity

Segmental Omental Infarction (SOI)/Epiploic Appendagitis (EA)

F  Mass-like echogenic omentum in SOI, smaller echogenic mass in EA with focal tenderness

F  Absent or minimal adjacent bowel wall changes

Meckel Diverticulitis

F  Imaging findings may overlap with acute appendicitis

F  No association with cecum

PATHOLOGY

Etiology

F  Multifactorial : Ischemic mucosal damage, bacterial overgrowth, luminal obstruction (appendicolith or Peyer patches)

F  Secondary/reactive appendicitis : Crohn disease, reactive to adjacent inflammation

Staging, Grading, & Classification

• Could be obstructive or nonobstructive

• Gangrenous when there is necrosis

CLINICAL ISSUES

Presentation

@   Periumbilical pain migrating to RLQ; peritoneal irritation at McBurney point; atypical signs in 1/3 patients

@  Anorexia, nausea, vomiting, diarrhea, fever

Clinical profile

White blood cells may or may not be elevated

Age

 All ages affected

Gender

M = F

Epidemiology

 7% of all individuals in Western world develop appendicitis during their lifetime

Treatment

S  Surgery if nonperforated or if minimal perforation

S  Antibiotic therapy alternative to surgery in nonobstructive appendicitis in some centers

S  Percutaneous drainage if well-localized abscess > 3 cm

S  Antibiotic therapy if periappendiceal soft tissue inflammation and no abscess

Complications

N  Gangrene and perforation; abscess formation

N  Peritonitis; septicemia; liver abscess, pyelophlebitis

N  Bowel obstruction; hydronephrosis

Prognosis

 Excellent with early surgery

DIAGNOSTIC CHECKLIST

@  Appendicitis in right clinical context when inflamed fat is seen in RLQ

@  Use graded compression to identify inflamed appendix

@  Nonvisualization of inflamed appendix does not rule out appendicitis

@  Other possible causes when no features to suggest appendicitis

@  Perforated appendicitis when there is inflamed echogenic fat with fluid collection in right iliac fossa

@  Blind-ended, aperistaltic, thick-walled tubular structure with gut signature

@  May or may not be distended

@  Sonographic McBurney sign with focal pain over appendix

@ Presence of appendicolith associated with periappendiceal inflammation is diagnostic of appendicitis

Imaging gallery

                                                    

ultrasound through the right iliac fossa shows a thick walled blind-ending tubular structure representing an inflamed appendix. Note the mural stratification and the base invaginating into the medial cecal wall.

blind-ending tip and mural stratification  

Power Doppler ultrasound of the inflamed appendix shows increased flow 

Axial ultrasound through an inflamed appendix demonstrates a target-like st appearance due to the preservation of mural stratification. Note the surrounding echogenic inflamed fat and thickened inflamed parietal layer of the peritoneum which is in contact with the inflamed appendix.

Axial ultrasound of an inflamed appendix demonstrates increased mural flow on power Doppler. Note the surrounding echogenic inflamed fat and thickened parietal peritoneum .

In this ultrasound of obstructive appendicitis, note the distended appendix with an appendicolith at the base, curvilinear echogenicity with posterior acoustic shadowing and lumen distended with purulent exudate and debris.

Transvaginal ultrasound depicts a distended inflamed pelvic appendix with an appendicolith within the lumen, representing acute pelvic appendicitis. Note the stratified mural appearance to the appendicular wall.

Sagittal CECT reconstruction shows a thickened appendix with periappendicular fat  stranding representing retrocecal acute appendicitis; ultrasound has a limited role in identifying these.

Sagittal NECT reconstruction shows a distended appendix with an appendicolith at the base and surrounding fat stranding representing acute appendicitis. Note the focus of gas within the lumen 

Axial NECT through the right iliac fossa in the previous patient demonstrates the inflamed, distended appendix . Note the poor definition of the wall and gas within the lumen.

Coronal MPR NECT in the previouspatient shows the increased density and stranding in the surrounding fat st and a tiny focus of extra luminal gas , appearances representing gangrenous appendicitis on CT.

Ultrasound through the right iliac fossa in a patient with previous appendectomy shows an inflamed, distended appendicular stump containing luminal purulent exudate . Note the reactive thickening of the cecal pole  surrounding echogenic fat.

Coronal CECT shows an inflamed appendicular stump with an appendicolith at the base. Note the surrounding inflammatory fat stranding and reactive thickening of the cecum . The ileocecal valve is seen.

ultrasound through the right iliac fossa depicts phlegmonous appendicitis with a central collection containing a loose appendicolith secondary to appendicular perforation.

Axial CECT from the previous patient shows the phlegmon with a central loose calcific appendicolith 

 an appendicular tip with loss of the stratified mural appearance representing gangrenous "tip appendicitis." Note the surrounding echogenic inflamed fat st.

ultrasound in the previous patient shows a more proximal part of the appendix with an inflamed thickened wall and surrounding inflamed echogenic fat

ultrasound through the right flank shows an abscess with debris and an appendicolith at the dependent part from perforated appendicitis. Note the abscess extending cranially anterior to the right kidney.

 ultrasound in the previous  patient (at a lower level) shows the proximal part of the inflamed appendix , the adjacent collection from tip perforation, and the surrounding inflamed fat.

Sagittal CECT shows an inflamed, distended appendix st with surrounding periappendicular inflammatory changes. Note soft tissue at the base of the appendix that is causing the obstruction.

Axial CECT through the appendicular base from the same patient shows the soft tissue at the appendicular base in continuity with eccentric soft tissue thickening involving the posterior wall of the cecum. At surgery, there was an infiltrative cecal carcinoma, causing obstruction and infection.