Usually presents in children with a recent history of upper respiratory infection.
Pain in the abdomen is usually diffuse with tenderness not localized to the right lower quadrant.
Guarding may be present, but rigidity is usually absent.
Generalized lymphadenopathy may be noted.
There is no specific test to confirm the diagnosis.
Relative lymphocytosis in WBC differential counts is suggestive.
Negative ultrasound or CT findings help exclude other diagnoses.
Common in children; caused by viruses, bacteria, or toxin.
Characterized by profuse watery diarrhea, nausea, and vomiting.
Crampy abdominal pain often precedes the diarrhea, and no localizing signs are present.
If caused by typhoid fever, intestinal perforation may cause localized abdominal pain and/or generalized and rebound tenderness. In this scenario, associated maculopapular rash, inappropriate bradycardia, and leukopenia will differentiate from appendicitis.
No specific test unless due to typhoid ( Salmonella typhi from stool or blood will confirm the diagnosis).
Only 20% of the patients present with diverticulitis, and 50% of this group are age <10 years. 
Clinical presentation of diverticulitis is similar to acute appendicitis.
Technetium pertechnetate scan may show the enhancement of diverticulum if gastric mucosa is present.
Occurs in young children (age <2 years).
Sudden onset of colicky pain; between episodes of pain the child is calm.
A sausage-shaped mass may be palpable in the right lower quadrant.
Barium enema may demonstrate the intussusception with a coil-spring sign at the point of bowel invagination.
Young adult with fever, nausea, vomiting, diarrhea, right lower quadrant pain, and localized tenderness.
CT scan may show intra-abdominal abscess.
Contrast study of the small bowel and colon may show stricture or a series of ulcers and fissures (cobblestone appearance) of mucosa.
May or may not have a history of peptic ulcer disease.
Pain is abrupt, severe in intensity, and may be localized to right lower quadrant.
Erect CXR and abdominal x-ray may show free air under the diaphragm
Pain is usually colicky in nature and severe in intensity. May be referred to the labia, scrotum, or penis and associated with hematuria.
Fever usually absent.
Urinalysis positive for blood.
Leukocytosis usually absent.
Abdominal x-rays or tomogram may show calcified stone.
Pyelography and CT scan without oral and intravenous contrast confirm the diagnosis.
Pain and tenderness are usually in the right upper quadrant. In one third of patients the gallbladder can be palpable. 
Abdominal ultrasound shows thick wall with pericholecystic collection, and tenderness is present over gallbladder area (Murphy sign).
Hepatobiliary iminodiacetic acid (HIDA) scan will show nonvisualization of gallbladder at >4 hours.
Pain and tenderness is usually in suprapubic area associated with burning micturition.
Acute right-sided pyelonephritis may present with fever, chills, and tenderness at the right costovertebral angle.
Urine microscopy and culture confirm presence of bacteria.
Most patients present with abrupt abdominal pain, fever, distension, and rebound tenderness.
History of advanced cirrhosis or nephrosis.
CT scan may show fluid in the abdomen.
Peritoneal fluid shows >500/microliter count and >25% polymorphonuclear leukocytosis.
Occurs in females usually aged between 20 and 40 years.
Presents with bilateral lower quadrant tenderness, usually within 5 days of the last menstrual period.
Purulent discharge from cervical os.
Endocervical swab may confirm the pelvic inflammatory disease due to Chlamydia trachomatis . 
Midmenstrual cycle, brief period of lower abdominal pain not usually associated with nausea and vomiting and fever.
Tenderness is usually diffused not localized.
Clinical diagnosis. No investigation indicated.
Female within childbearing age presents with missed menstrual period, right lower quadrant pain, or pelvic pain with some degree of vaginal bleeding or spotting. Cervical motion tenderness may be present on pelvic examination.
HCG hormone level is high in serum and in urine.
Ultrasound reveals presence of mass in fallopian tubes.
Female with right lower quadrant pain. Occasionally presents with mass in the right lower quadrant.
Ultrasonography shows ovarian cyst and decreased blood flow.
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