CT

DR SAKHER-ALKHADERICONSULTANT RADIOLOGIST AMC

IMAGING OF ACUTE APPENDICITIS

Gross anatomy

The appendix arises from the posteromedial surface of the caecum, approximately 2-3 cm inferiorly to the ileocaecal valve, where the taena coli converge. It is a blind diverticulum, which is variable in length from 2-20 cm. The appendix lies on its own mesentery, the mesoappendix . 

The tip of the appendix can have a variable position within the abdominal cavity :-retro-caecal (65-70%)-pelvic (25-30%)-pre- or post-ileal (5%)

CT scan after oral contrast administration in 32-year-old woman with normal appendix. Note normal appendix with intraluminal enteric contrast material and gas (arrows). Appendix wall is nearly imperceptibly thin.

34-year-old healthy volunteer with a normal appendix. A and B, longitudinal (A) and transverse (B) sonogram, showing the appendix (arrowheads) with a diameter less than the 7 mm cut-off point, surrounded by normal noninflamed fat.

NORMAL APPENDIX CT SCAN ULTRASOUND

AppendicitisIs inflammation of the appendix

Pathology:Appendicitis is typically caused by obstruction of the appendiceal lumen, with resultant build up of fluid, secondary infection, venous congestion, ischaemia and necrosis. Obstruction may be caused by:-lymphoid hyperplasia (~60%)-appendicolith (~33%)-foreign bodies (~4%)-Crohn disease or other rare causes, e.g. stricture, tumour, parasite

Common signs of Appendicitis •Right lower quadrant pain on palpation (the single most important sign )•Low –grade fever (38 C { or 100.4 F} absence of fever or high fever can occur. peritoneal signs . -Localized tenderness to percussion . -Guarding .* Other confirmatory peritoneal signs (absence of these signs does not exclude appendicitis ) .•Psoas sign – pain on extension of right thigh (retroperitoneal retrocecal appendix ) .•Obturator sign- pain on internal rotation of right thigh (pelvic appendix ) .•Rovsing `s sign – pain in right lower quadrant with palpation of left lower quadrant .•Dunphy`s sign - increased pain with coughing .•Flank tenderness in right lower quadrant (retroperitoneal retrocecal appendix ).Patient maintains hip flexion with knees drawn up for comfort.

Radiographic features

Ultrasound

Findings supportive of the diagnosis of appendicitis include :-Aperistaltic, noncompressible, dilated appendix ( >6 mm outer diameter)-Appendicolith-Distinct appendiceal wall layers-Echogenic prominent pericaecal fat-Periappendiceal fluid collection-Target appearance (axial section)

CT scan : CT is highly sensitive (94-98%) and specific (up to 97%) for the diagnosis of acute appendicitis and allows for alternative causes of abdominal pain to also be diagnosed.The need for contrast (IV, oral or both) is debatable and varies from institution to institution. Findings include :-Dilated appendix with distended lumen ( >6 mm diameter) -Thickened and enhancing wall-Thickening of the caecal apex (up to 80%): caecal bar sign, arrowhead sign-Periappendiceal inflammation, including stranding of the adjacent fat and thickening of the lateroconal fascia or mesoappendix.-Extraluminal fluid-Inflammatory phlegmon-Abscess formation-Appendicolith may also be identified

Caecal bar signThe caecal bar sign is a secondary sign in acute appendicitis. It refers to the appearance of inflammatory soft tissue at the base of the appendix, separating the appendix from the contrast-filled caecum.

Arrowhead signThe arrowhead sign refers to the focal caecal thickening centered on the appendiceal orifice, seen as a secondary sign in acute appendicitis. The contrast material in the cecal lumen assumes an arrowhead configuration, pointing at the appendix.  The arrowhead sign is applicable only when enteric contrast distends the caecum.

CT Technique

-The most commonly used CT technique for studying the appendix is a scan of the entire abdomen and pelvis after both oral and IV administration of contrast material-It is generally accepted that appendiceal CT should incorporate thin-section scanning (5 mm) through the right lower quadrant (RLQ) to improve identification of the appendix,

CT has high accuracy for the noninvasive assessment of patients with suspected appendicitis, with reported sensitivities of 88–100%, specificities of 91–99%

CASES OF ACUTE

APPENDICITIS

38-year-old man with early, acute appendicitis. Unenhanced CT scan shows inflamed appendix measuring 10 mm in transverse diameter (arrows). Note low-attenuation edema in submucosal layer of appendix. No appendicoliths, free air, adjacent fluid collection, or fat stranding is seen. Surgery confirmed early, nonperforated appendicitis.

20-year-old man with acute appendicitis. Oral and IV contrast-enhanced CT scan shows thickened, fluid-filled appendix (arrows).

15 year old boy presented with symptoms and signs of acute appendicitis. Ultrasound of the right lower quadrant demonstrated a thickened fluid filled appendix containing an echogenic shadowing appendicolith. 

ULTRASOUND

An inflamed appendix has a diameter larger than 6 mm, and is usually surrounded by hyperechoic inflamed fat at sonography

NORMAL APPENDIX

ULTRASOUND

The appendix is distended showing mural thickening and enhancement, with surrounding edema.

Enlarged appendix with wall thickening and enhancement, appendicolith. Features of acute appendicitis. 

Major Complications1.Perforation

If appendicitis is allowed to progress, portions of the appendiceal wall eventually become ischemic or necrotic and the appendix perforates.

CT findings—extraluminal air, extraluminal appendicolith, abscess, phlegmon, and a defect in the enhancing appendiceal wall—allows excellent sensitivity (95%) and specificity (95%) for perforation in patients with known appendicitis who underwent preoperative CT. In that study, the individual finding with highest sensitivity was a mural enhancement defect (64%).

32-year-old man with acute appendicitis. Unenhanced CT shows appendicolith (arrowhead), periappendiceal fat stranding (black arrows), lateral conal fascia thickening (white arrow), and periappendiceal fluid. Perforation was confirmed on surgery

2.Periappendiceal Abscess

Abscess is the most frequent complication of perforation. The abscess remains localized if periappendiceal fibrinous adhesions develop before rupture. CT shows a loculated, rim-enhancing fluid collection that may have mass effect on adjacent bowel loops. If the abscess is large (> 4 cm), percutaneous drainage followed by delayed appendectomy is the preferred treatment .

47-year-old man with periappendiceal abscess. Helical CT after IV contrast injection shows periappendiceal abscess extending into psoas muscle (arrowheads).

3.Peritonitis

4.Bowel Obstruction

5.Septic Seeding of Mesenteric Vessels6.Gangrenous Appendicitis

Differential Diagnosis1.Mesenteric Adenitis Mesenteric adenitis is

the most common alternative condition identified at negative appendectomy. It is a benign inflammation of the ileocolic lymph nodes that is usually caused by Yersinia enterocolitica, Y. pseudotuberculosis, or Campylobacter jejuni. CT findings include enlargement (> 5 mm) of mesenteric lymph nodes, thickening of the adjacent cecum and ileum, and a normal appendix

2.Cecal Diverticulitis

51-year-old man with right-sided colonic diverticulitis. A, Unenhanced CT shows extensive with fat-standing along the cecal wall (arrowheads), and a normal appendix (arrow). B, Sonography reveals the cause of the inflammation by depicting an inflamed cecal diverticulum (arrow) centred in the hyperechoic fat.

3.Epiploic AppendagitisEpiploic appendagitis is an uncommon condition caused by inflammation, torsion, or ischemia of an epiploic appendage. On CT, there is a small fat-attenuation mass contiguous with the colon and having a hyperattenuating rim. A round or linear hyperdense focus in the center of the mass thought to represent a thrombosed central vein is characteristic but is not always present

4.Omental InfarctionOmental infarction is a rare condition in which there is segmental infarction of some portion of the omentum. CT features include a well-circumscribed region of inflamed omental fat with haziness and streaklike areas of inflammatory stranding

NB : usually larger than in epiploic appendagitis and lacking a hyperattenuating ring on CT.

5.Crohn's DiseaseCrohn's disease is a chronic granulomatous inflammatory condition that can involve any segment of the gastrointestinal tract but most commonly involves the terminal ileum and right colon. CT helps exclude appendicitis and shows features characteristic of Crohn's disease. Affected bowel usually shows prominent circumferential wall thickening. In acute and subacute cases, IV contrast administration shows bowel wall mural stratification (target sign). Characteristically, skip lesions are present. Local proliferation of mesenteric fat around the affected bowel, prominent vessels in the hypertrophied fat, fistulas, sinus tracts, and abscesses are frequently found . Importantly, Crohn's disease may involve the appendix and cause a chronic granulomatous appendicitis, which is usually managed conservatively.

28-year-old man with acute ileocecal Crohn disease.A and B, Sonography shows transmural wall thickening of the terminal ileum (arrows) in longitudinal (A) and transverse (B) section, with hyperechoic inflammatory changes of the surrounding fat (arrowheads).C, Contrast-enhanced CT confirms the wall thickening and luminal narrowing of the terminal and pre-terminal ileum (arrowheads), with regional fat-stranding.

6.Bacterial ileocecitisThis presentation may occur in bacterial ileocecitis, caused by Yersinia, Campylobacter, or Salmonella. Imaging studies show mural thickening of the terminal ileum and cecum without inflammation of the surrounding fat and moderate mesenteric adenopathy.

US typically shows submucosal wall thickening (arrowheads) of the terminal ileum and cecum without inflammation of the surrounding fat.

Conclusion-Helical CT with oral and IV

contrast is an accurate, effective technique for diagnosing acute appendicitis. -Sonography will continue to play an important role. And probably should be performed first in children, adolescents, thin young adults, and women of reproductive age with possible gynecologic causes of pain.-The correct diagnosis of acute appendicitis, differentiation of appendicitis from other entities, and identification of complications are the major role of radiology.

Treatment with antibiotics alone can be a safe and effective alternative to surgery for children with uncomplicated acute appendicitis, according to a new study.

UPDATES IN ACUTE APPENDICITIS

THE END