Appendicular abscess overview
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Appendicular abscess is defined as a collection of pus resulting from necrosis of the tissue superimposed with infection in an inflamed appendix. It is unusual and rare entity; appendicular abscess is a life-threatening complication of acute appendicitis (preoperatively) or appendectomy (postoperatively). It is observed in 2-7% of population presenting with appendicitis. Complications arise if appendicitis is not treated promptly. The abscess develops and is limited by the inflamed coils of intestine. The abscess can spread to pelvis leading to peritonitis if the abdominal wall is ruptured. In most of the patients, the intestinal coils and omentum in the abdominal cavity tend to cover the inflamed appendix forming an appendicular mass. 
Appendicitis was first described by Reginald J. Fitz of Harvard University in 1886. He also coined the term appendix. Since then, the appendectomy has become one of the most common surgical procedures. The laparoscopic appendectomy was invented in the 1980s, and has led to reduced length of hospital stay a decreased risk of infection, and a reduction in post-operative pain. 
There is no classification system established for appendicular abscess.
An appendicular abscess is a complication of acute appendicitis. It is resulted due to the invasion of the appendix by bacteria following an obstruction. The appendix exists at the junction of the small and large intestine and is a natural habitat of wide variety of bacteria. It is, therefore, prone to develop complications when blocked. Coupled with an infection, acute appendicitis can be life threatening. Other serious complications which may develop as a result of neglected appendicitis or appendicular abscess include gangrene, appendicular masses, rupture, and general peritoneal infections. Obstruction of the tubular space inside the appendix is the main inciting event, this initial problem leads to the inflammation of the appendix, obstruction of the blood vessels supplying it, and finally infection. Inflammatory mediators along with various bacterial toxins and proteolytic enzymes from the neutrophils are released, resulting in the formation of an abscess in the appendix. 
Microbiology responsible for appendicular abscess includes a mixture of aerobic and anaerobic organisms that are natural habitat of gut. The most commonly isolated aerobic organism is Escherichia coli, and the most commonly observed anaerobic organism is Bacteroides fragilis. The type and density of aerobic and anaerobic bacteria isolated from appendicular abscesses depends upon the organism that dominates the habitat and degree of obstruction.
Appendicular abscess should be diagnosed early and treat promptly not only to reduce morbidity and mortality, but it is also important to differentiate from other abdominal diseases presenting with RLQ pain, fever, nausea, and vomiting such as psoas abscess, cellulitis, torsion of testis and ovaries, and ectopic pregnancy as the undrained abscess carries high risk of mortality.
Identifying risk factors that predict the likelihood of complications of appendicitis is a crucial step in managing appendicular abscess. Appendicitis is most common risk factor of developing abscess; it is more common among people in the age group of 10 to 30 years old. Appendicitis is a medical emergency that requires proper attention, especially more than any other abdominal causes if symptoms are not conclusive.
According to the Guidelines by the Surgical Infection Society and the Infectious Diseases Society of America, there is insufficient evidence to recommend routine screening for appendicular abscess.
Natural History, Complications, and Prognosis
Without treatment, the patient will likely develop symptoms of diffuse abdominal pain, which is different from typical appendicitis pain, starting centrally (in the periumbilical region) before localizing to the right iliac fossa in the right lower quadrant of the abdomen. During the final stage of the untreated disease process, the appendix will rupture, and this may eventually lead to death if peritonitis develops. Complications that can develop as a result of the untreated appendicular abscess include:septicemia, rupture, peritonitis, hemorrhage and death. Prognosis of the abscess is good with antibiotics and percutaneous drain and resolves without the need for appendectomy, but it is recommended to follow and appendicular abscess by interval appendectomy after 8-12 weeks to prevent recurrence.
History and Symptoms
The key to an efficient and accurate diagnosis is a detailed and thorough history. The onset, location, radiation, and duration of pain, aggravating or relieving factors, severity of pain (constant or intermittent), characteristics of the pain should be obtained in helping out the cause of abdominal pain. Symptoms of appendicular abscess are mostly atypical compared to appendicitis and include include high grade fever, constant pain in the right iliac fossa, prolonged diarrhea associated with nausea and vomiting and increased micturition and tenesmus.
Physical examinations mostly focus on abdominal findings. The patient may appear toxic with diffuse abdominal pain and high grade fever and tachycardia. Even minimal pressure on the abdomen can elicit a marked response from the patient due to pain. Typical signs of appendicitis may not be elicited.
Hematologic parameters suggestive of infection-like leukocytosis, anemia, abnormal platelet counts, and abnormal liver function frequently are present in patients with appendicular abscess. Patients who are debilitated or elderly often fail to mount reactive leukocytosis or fever. Blood cultures indicating persistent polymicrobial bacteremia strongly implicate the presence of an abscess. Common electrolyte and bio-marker indicators of appendicitis include leukocytosis and a shift to the left in the segmented neutrophils.
In general, whenever available, CT scans are preferred over ultrasounds for diagnosing appendicular abscess. Ultrasound imaging presents the least amount of radiation and is therefore the investigation of choice for young patients. Findings include fluid collection (hypoechoic) in the appendicular region which may be well circumscribed with dilated appendicular wall.
CT scans are the diagnostic test of choice for detecting appendicular abscess. They can provide critical information regarding the size of the abscess. CT scans are preferred over ultrasounds for the detection of abscess but is contraindicated in children due to risk of exposure. Findings include Appendiceal wall thickening (wall ≥ 3mm), appendiceal wall hyperenhancement, mural stratification of the appendiceal wall.
Magnetic resonance imaging (MRI) has become the common technique for diagnosing abscess in children and pregnant patients. On an MRI, a periappendiceal stranding appears as an increased fluid signal on the T2 weighted sequence.
Findings of appendicular abscess on ultrasound include fluid collection in the appendicular region.
No universal standard treatment exists for appendicitis complicated by abscess. The mainstay of treatment includes abscess drainage along with empiric antibiotics. Antibiotics should be started immediately once the diagnosis of abscess is made. The duration of treatment with intravenous antibiotics ranges from 5 to 10 days, until fever resolves. Monotherapy with a beta-lactam/beta-lactamase inhibitor is the preferred choice of drugs. Combination third generation cephalosporins plus metronidazole is also employed. Percutaneous drainage can be performed under ultrasound or CT guidance, using either the Seldinger or trocar technique. When an abscess is deep in the pelvis, depending on the specific location of the fluid collection, access may be obtained via transgluteal, transvaginal, or transrectal approaches.
Following drain and antibiotics an interval appendectomy is recommended for patients after six to eight weeks, it is done to prevent recurrence of appendicitis and to exclude neoplasms as a cause (such as carcinoid, adenocarcinoma, mucinous cystadenoma, and cystadenocarcinomas). The surgical approach can be either laparoscopic or open (laparotomy)
There are no primary preventive measures available for appendicular abscess. Secondary prevention strategies following appendicular abscess include treatment of appendicitis in order to prevent significant morbidity.
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