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CT of the Right Lower Quadrant. Rajul Pandit, M.D. Acute Abdominal Pain (AAP). In 34% of cases, the cause of abdominal pain is not established Acute appendicitis is seen in 28% of AAP Acute GI and GU conditions are the most common causes of AAP

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Ct of the right lower quadrant l.jpg

CT of the Right Lower Quadrant

Rajul Pandit, M.D.


Acute abdominal pain aap l.jpg
Acute Abdominal Pain (AAP)

  • In 34% of cases, the cause of abdominal pain is not established

  • Acute appendicitis is seen in 28% of AAP

  • Acute GI and GU conditions are the most common causes of AAP

  • In approximately 66% of patients with AAP diagnosis may be made on imaging findings

  • CT of the RLQ has effectively replaced exploratory laparotomy as the primary means of evaluating patients with a “surgical abdomen”


Acute appendicitis aa l.jpg
Acute Appendicitis (AA)

  • Atypical presentations result in diagnostic confusion and delay in treatment

  • High morbidity if perforation occurs

  • The diagnosis should be considered in any patient with RLQ pain unless prior appendectomy

  • Unusual presentations at extremes of age, pregnant patient, when appendix is distant from anterior parietal peritoneum

  • Diagnostic accuracy varies by sex

  • Negative appendectomy rates of 9% in men, 19% in women


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Pathophysiology of AA

  • Obstruction of appendiceal lumen from fecolith, lymphoid hyperplasia, foreign bodies, parasites or tumors

  • Continued secretion of mucus results in elevated intraluminal pressure, venous engorgement, arterial compromise, tissue ischemia

  • Luminal bacteria invade the wall with transmural inflammation, perforation

  • Mild cases resolve if obstruction is relieved (8%)

  • Recurrent and chronic appendicitis seen in 1-10%



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CT Technique

  • Thin-section (</= 5 mm), helical CT of abdomen and pelvis

  • Controversy over use of oral/IV contrast

  • IV contrast may help in mild cases of AA, minimal fat and perforating appendicitis

  • Oral contrast may limit false positive cases

  • Rectal contrast


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CT Criteria for AA

  • Distended, fluid-filled, thick-walled, tubular structure > 6mm in diameter (nl wall thickness <1-2mm)

  • Calcified appendicolith

  • Mural enhancement

  • Entire appendix should be seen

  • Periappendiceal inflammation (absent in 2-22% of cases)

  • Severe cases- phlegmon, abscess, extraluminal gas, ileocecal thickening, peritonitis, small bowel obstruction


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Clinical Value of CT

  • Negative appendectomy rates have reduced to as low as 4-6 %

  • Cost-effective, prevents unnecessary surgery

  • CT differentiates abscess from phlegmon

  • Road-map for percutaneous abscess drainage


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Right-sided Colonic Diverticulitis

  • Uncommon, misdiagnosed as AA

  • Incidence highest in Asian populations

  • Abnormal thickening of colon wall, pericolonic inflammation, inflamed diverticulum with marked enhancement, abscess formation

  • DDx difficult if normal appendix not seen


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Perforated Cecal Carcinoma

  • 10% colorectal cancers arise in the cecum

  • May cause secondary appendicitis, SBO, intussusception, perforation with abscess

  • Large soft-tissue mass that outweighs the inflammatory component

  • Contiguous organ invasion, regional lymph nodes, peritoneal implants, distant mets


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Cecal Infarction

  • Acute colonic ischemia in elderly due to low-flow states, small vessel dx

  • Splenic flexure most common, rare in the cecum

  • Cecal wall thickening, pneumatosis



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Neutropenic Colitis

  • AKA typhlitis or ileo-cecal syndrome

  • Cecum mostly involved

  • Seen in immuno-suppressed pts.

  • Thickened wall, low-attenuation in the bowel wall due to edema/necrosis, pneumatosis coli, pericolonic fluid

  • DDx: pseudomembranous colitis, colitides by opportunistic infections like CMV



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Mesenteric Adenitis and Terminal Ileitis

  • Mesenteric adenitis: self-limiting inflammation of the lymph nodes in children, young adults

  • Usually due to Campylobacter, Yersinia

  • Cluster of moderately enlarged lymph nodes +/- ileocecal wall thickening

  • DDx: Crohn’s dx


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Epiploic Appendagitis

  • Spontaneous torsion of an epiploic appendage of the large bowel

  • Sudden onset of acute abdominal pain, self-limiting

  • Seen in 1% of patients undergoing CT for AA

  • Small , pedunculated, round, fat-containing mass with a hyperattenuating rim at the serosal surface of the colon

  • Small linear or round focus in the center of the lesion may be vascular thrombosis


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Omental Infarction

  • Localized acute right abd pain, spontaneously resolving

  • Inflamed omental fat located between the right anterolateral abdominal wall and ascending colon, at or above the level of the umbilicus

  • High density streaks in the fat

  • Adjacent colon, TI and appendix are normal


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Other Differentials

  • Sigmoid diverticulitis: LLQ pain, also in ddx for RLQ pain where the apex of the sigmoid colon may reside

  • Acute urinary disorders:ureteral calculi, acute pyelonephritis

  • Gyn conditions: ovarian cysts, torsion, PID, ectopic pregnancy