GENERAL CONSIDERATION
Acute appendicitis is very common, with a lifetime risk of 7-8% that favors males slightly. Appendectomy is the most commonly performed emergency operation in the world. the reported incidence has dropped by more than 50% in the past three decades for unknown reason. Over 250.000 patients per year are admitted for management of appendicitis in the United States, with the highest incidence in the second and third decades of life. The rate of appendiceal perforation may be up to 80%. Mortality has dropped to less than 1% with more timely and accurate diagnosis in high risk groups and advancements in imaging techniques.
The pathogenesis of acute appendicitis is bacterial proliferation secondary to luminal obstruction due to one of multiple disorders, including cytomegalovirus or adenovirus enteritis, Crohn disease, stone, foreign body, or tumor. The presentation of appendicitis depends on the patient's age, appendiceal length, body habitus and trimester of pregnancy. The "classic" presentation (acute periumbilical pain migrating to McBurney point, followed by nausea and vomiting occurs in only 30-60% of patients. The perforation rate may reach 50-70% and is directly proportional to a delay in diagnosis of more than 24 hours. The elderly experience a mortality rate from appendicitis that is eightfold greater than that of the general population and accounts for 50% af all detahs from this disorder. Increased body mass index and smoking have also recently been implicated as risk factors for a complicated course.
Diagnosis is particularly challenging in the young and elderly, as well as during pregnancy.
CLINICAL FINDING
A. Symptoms and Signs
The history and abdominal examination may vary depending on the location of the appendix. Diagnosis is delayed, and thus perforation occurs more commonly, in very young (<3 years), pregnant, and elederly (>64 years old) patents, the latter presenting atypically over 70% of the time. Socioeconomic status, but not race, may also influence perforation rate. The atypical location of the appendix in the third trimester of pregnancy represents a particular diagnostic challenge. Fever may be low grade.
B. Laboratory findings
Routine laboratory studies have limited value in the diagnosis of acute appendicitis. Leukocytosis may be modest or absent. Chemistry studies and urinalysis are usually normal. A pregnancy test must always be ordered in a woman of childbearing age.
C. Imaging studies
1. Issues and controversies, The pathophysiology and imaging abnormalities of acute appendicitis are due to luminal obstruction, regardless of etiology. The advantage of preoperative imaging compared with clinical assessment alone continues to be challenged by some studies. Several centers have reported increased time to the operating room, operating time, length of stay and cost without a reduction in negative appendectomy rate in patients whose surgery is postponed for the performance of CT (or ultrasound). On the other hand, even in patients with a high clinical probabilty of appendicitis, almost one third of those imaged will be found to have another diagnosis or a normal scan. We beleive the preceding discrepancies are largely due to variability in institutional experience and recommend that cross-sectional imaging (CT, MRI, or Ultrasound) be performed in all patients suspected of having acute appendicitis, even those patients with high-probability clinical presentations.
CT scan with an appendicitis protocol is appropriate in the majority of patients. The advantage of rectal contrast remains a matter of continued discussion.
2. Ultrasound, Ultrasound has a sensitivity and negative predictive value of nearly 98% and 100%, respectively, with a specificity of 70-100%. Result are highly operator dependent.
Finding suggestive of acute appendicitis include a thickened, blind-ended lumen (as opposed to an open-ended salpinx or gonadal vein) with a diameter greater than 6 mm that is noncompressible and fluid-filled, and the presence of appendicolith. There may be tenderness on compression. Ultrasound should be used as the sole imaging modality only for patients with a high probability of the disorder. False-positive findings occur commonly (33% of the time) in patients with inflammatory bowel disease, cecal diverticulitis and pelvic inflammatory disease. The value of ultrasound is limited in morbidly obese patients, in the presence of perforation or retrocecal position, and when there is inability to compress the right lower quadrant (RLQ).
Ultrasound should be considered as the study of choice in groups most vulnerable to ionizing radiation, especially children and women of childbearing age. The additional information gained about the female pelvic anatomy can also be clinically valuable.
3. CT SCAN- A contrast enhanced helical CT scan performed for acute appendicitis is 96098% sensitive and 83-89% specific, particularly with the demonstration of an appendicolith. MDCT may improve specificity even more. Positive findings include a diamter greater than 6mm, thickened wall with enhancement, periappendiceal fat stranding, and appendicolith. An air-filled appendix on CT essentially excludes acute appendicitis.
Focal thickening of the terminal ileum or cecum may be confused with Crohn disease and appendical dilation may be falsely attributed to an infected right fallopian tube. An ovoid fat-attenuation focus with hyperattenuating rim near the colonic serosa distinguishes epiploic appendagitis, infectious enteritis should be easily differentiated by the diffuse nature of bowel thickening and enhancement in the presence of a normal appendix. Less common mimics include mucocele of the appendix, ovarian disorders, and endometriosis. Advantage of CT over ultrasound are its ability to visualize the entire abdomen, demonstrating an alternative diagnosis in 15% of cases. An additional 15% of patients will be found to be normal.
A high clinical index of suspicion for acute appendicitis mandates the use of dedicated appendicitis protocol with intravenous and rectal contrast alone, reducing the time of study to only 15 minutes by elimintaing the administration of oral contrast. CT scan during pregnancy must be used with great discretiom; ultrasound or MRI is recommended. The lack of reduction in the published rate of negative appendectomy since the introduction of CT most likely reflect inconsistent performance standards.
DIFFERENTIAL DIAGNOSIS
The differential diagnosis of acute appendicitis is broad. reflecting classic and atypical presentations of the disorder. It includes mesenteric, lymphadenitis, bacterial enteritis, acute diverticulitis, ureteral calculus, Crohn disease, Cholecystitis, appendagitis epiploica, Meckel diverticulitis and several gynecologic disorders including acute salpingitis (pelvic inflammatory disease), ruptured ovarian follicle (mit-telshmerz), and ruptured ectopic pregnancy.
SOURCE :
Current Diagnosis & Treatment: Gastroenterology, Hepatology & Endoscopy. United States of America; McGraw-Hill Lange: 2009; P 6-7
Acute appendicitis is very common, with a lifetime risk of 7-8% that favors males slightly. Appendectomy is the most commonly performed emergency operation in the world. the reported incidence has dropped by more than 50% in the past three decades for unknown reason. Over 250.000 patients per year are admitted for management of appendicitis in the United States, with the highest incidence in the second and third decades of life. The rate of appendiceal perforation may be up to 80%. Mortality has dropped to less than 1% with more timely and accurate diagnosis in high risk groups and advancements in imaging techniques.
The pathogenesis of acute appendicitis is bacterial proliferation secondary to luminal obstruction due to one of multiple disorders, including cytomegalovirus or adenovirus enteritis, Crohn disease, stone, foreign body, or tumor. The presentation of appendicitis depends on the patient's age, appendiceal length, body habitus and trimester of pregnancy. The "classic" presentation (acute periumbilical pain migrating to McBurney point, followed by nausea and vomiting occurs in only 30-60% of patients. The perforation rate may reach 50-70% and is directly proportional to a delay in diagnosis of more than 24 hours. The elderly experience a mortality rate from appendicitis that is eightfold greater than that of the general population and accounts for 50% af all detahs from this disorder. Increased body mass index and smoking have also recently been implicated as risk factors for a complicated course.
Diagnosis is particularly challenging in the young and elderly, as well as during pregnancy.
CLINICAL FINDING
A. Symptoms and Signs
The history and abdominal examination may vary depending on the location of the appendix. Diagnosis is delayed, and thus perforation occurs more commonly, in very young (<3 years), pregnant, and elederly (>64 years old) patents, the latter presenting atypically over 70% of the time. Socioeconomic status, but not race, may also influence perforation rate. The atypical location of the appendix in the third trimester of pregnancy represents a particular diagnostic challenge. Fever may be low grade.
B. Laboratory findings
Routine laboratory studies have limited value in the diagnosis of acute appendicitis. Leukocytosis may be modest or absent. Chemistry studies and urinalysis are usually normal. A pregnancy test must always be ordered in a woman of childbearing age.
C. Imaging studies
1. Issues and controversies, The pathophysiology and imaging abnormalities of acute appendicitis are due to luminal obstruction, regardless of etiology. The advantage of preoperative imaging compared with clinical assessment alone continues to be challenged by some studies. Several centers have reported increased time to the operating room, operating time, length of stay and cost without a reduction in negative appendectomy rate in patients whose surgery is postponed for the performance of CT (or ultrasound). On the other hand, even in patients with a high clinical probabilty of appendicitis, almost one third of those imaged will be found to have another diagnosis or a normal scan. We beleive the preceding discrepancies are largely due to variability in institutional experience and recommend that cross-sectional imaging (CT, MRI, or Ultrasound) be performed in all patients suspected of having acute appendicitis, even those patients with high-probability clinical presentations.
CT scan with an appendicitis protocol is appropriate in the majority of patients. The advantage of rectal contrast remains a matter of continued discussion.
2. Ultrasound, Ultrasound has a sensitivity and negative predictive value of nearly 98% and 100%, respectively, with a specificity of 70-100%. Result are highly operator dependent.
Finding suggestive of acute appendicitis include a thickened, blind-ended lumen (as opposed to an open-ended salpinx or gonadal vein) with a diameter greater than 6 mm that is noncompressible and fluid-filled, and the presence of appendicolith. There may be tenderness on compression. Ultrasound should be used as the sole imaging modality only for patients with a high probability of the disorder. False-positive findings occur commonly (33% of the time) in patients with inflammatory bowel disease, cecal diverticulitis and pelvic inflammatory disease. The value of ultrasound is limited in morbidly obese patients, in the presence of perforation or retrocecal position, and when there is inability to compress the right lower quadrant (RLQ).
Value of preoperative imaging in acute appendicitis
|
Final operative diagnosis
|
Low Probability
(n=109)
|
Clinical presentatiom Intermediate Probability
|
Clinical Presentation
High Probability
(n=144)
|
|
Acute appendicitis
|
11 (10%)
|
23 (24%)
|
99 (65%)
|
|
Other
|
34 (31%)
|
37 (38%)
|
26 (18%)
|
|
Inflammatory bowel
disesase
|
7 (6%)
|
9 (9%)
|
6 (4%)
|
|
Enteritis
|
15 (14%)
|
8 (8%)
|
1 (<1%)
|
|
Right-sided
diverticulitis
|
0 (0%)
|
1 (1%)
|
5 (3%)
|
|
Ovarian cyst
|
3 (3%)
|
3 (3%)
|
1 (<1%)
|
|
Normal findings
|
63 (59%)
|
37 (38%)
|
24 (17%)
|
Ultrasound should be considered as the study of choice in groups most vulnerable to ionizing radiation, especially children and women of childbearing age. The additional information gained about the female pelvic anatomy can also be clinically valuable.
3. CT SCAN- A contrast enhanced helical CT scan performed for acute appendicitis is 96098% sensitive and 83-89% specific, particularly with the demonstration of an appendicolith. MDCT may improve specificity even more. Positive findings include a diamter greater than 6mm, thickened wall with enhancement, periappendiceal fat stranding, and appendicolith. An air-filled appendix on CT essentially excludes acute appendicitis.
Focal thickening of the terminal ileum or cecum may be confused with Crohn disease and appendical dilation may be falsely attributed to an infected right fallopian tube. An ovoid fat-attenuation focus with hyperattenuating rim near the colonic serosa distinguishes epiploic appendagitis, infectious enteritis should be easily differentiated by the diffuse nature of bowel thickening and enhancement in the presence of a normal appendix. Less common mimics include mucocele of the appendix, ovarian disorders, and endometriosis. Advantage of CT over ultrasound are its ability to visualize the entire abdomen, demonstrating an alternative diagnosis in 15% of cases. An additional 15% of patients will be found to be normal.
A high clinical index of suspicion for acute appendicitis mandates the use of dedicated appendicitis protocol with intravenous and rectal contrast alone, reducing the time of study to only 15 minutes by elimintaing the administration of oral contrast. CT scan during pregnancy must be used with great discretiom; ultrasound or MRI is recommended. The lack of reduction in the published rate of negative appendectomy since the introduction of CT most likely reflect inconsistent performance standards.
DIFFERENTIAL DIAGNOSIS
The differential diagnosis of acute appendicitis is broad. reflecting classic and atypical presentations of the disorder. It includes mesenteric, lymphadenitis, bacterial enteritis, acute diverticulitis, ureteral calculus, Crohn disease, Cholecystitis, appendagitis epiploica, Meckel diverticulitis and several gynecologic disorders including acute salpingitis (pelvic inflammatory disease), ruptured ovarian follicle (mit-telshmerz), and ruptured ectopic pregnancy.
SOURCE :
Current Diagnosis & Treatment: Gastroenterology, Hepatology & Endoscopy. United States of America; McGraw-Hill Lange: 2009; P 6-7
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