Appendicitis: symptoms, diagnosis, treatment

Appendicitis is an acute inflammation of the appendix. It is one of the most common causes of acute abdomen and emergency surgery. The disease progresses along a spectrum: from uncomplicated inflammation to perforation with peritonitis, abscesses, and fistulas. Early diagnosis and proper treatment directly reduce complications and treatment time. [1]

In recent years, tactics have become more flexible. Along with laparoscopic appendectomy, a validated alternative—observed antibiotic therapy—has emerged for selected adult patients with uncomplicated disease. The choice depends on the clinical setting, imaging data, and patient preferences: a "shared decision-making" approach is now standard. [2]

Diagnosis is based on a combination of clinical assessments, laboratory markers, and imaging. Ultrasound is often used as a first-line procedure, especially in children and pregnant women; computed tomography (CT) scanning improves accuracy in adults when in doubt. Laparoscopy remains both a diagnostic and therapeutic option. [3]

Antibiotic prophylaxis protocols and the duration of antibacterial therapy have been revised: antibiotics are not indicated for uncomplicated cases after surgery, and with adequate source control in complicated cases, the course is limited to 3-5 days. This reduces side effects and hospitalization without worsening outcomes. [4]

Code according to ICD-10 and ICD-11

In the International Classification of Diseases, Tenth Revision, appendicitis is coded in blocks K35-K37: K35 - acute appendicitis (with specification of peritonitis, perforation, gangrene), K36 - "other appendicitis" (including chronic/recurrent), K37 - "appendicitis, unspecified." The specifying sublevels of K35 allow for the identification of localized or widespread peritonitis, as well as gangrene with/without perforation. [5]

The International Classification of Diseases, Eleventh Revision, uses the section DB10.0 "Acute appendicitis" with subtypes: with generalized peritonitis (DB10.00), with localized peritonitis (DB10.01), and without localized/generalized peritonitis (DB10.02). ICD-11 supports post-coordination (adding complication modifier codes), which improves the accuracy of statistics and routing. [6]

Table 1. Examples of ICD codes for appendicitis

Clinical situation	ICD-10 (example)	ICD-11 (example)
Acute appendicitis without local/generalized peritonitis	K35.80 / K35.890	DB10.02
Acute appendicitis with localized peritonitis (phlegmon, infiltrate)	K35.3	DB10.01
Acute appendicitis with generalized peritonitis	K35.2	DB10.00
Other/chronic appendicitis	K36	- (Spanish: relevant sections "other diseases" of the appendix)
Appendicitis, unspecified	K37	DB10.0 (NOS if no detail is available)
[7]

Epidemiology

Appendicitis is the most common cause of emergency abdominal surgery in young and middle-aged adults. The lifetime risk is estimated at 6-8 percent, with a peak between ages 10 and 30. Men are affected somewhat more often than women in young adults, but the ratio evens out after age 50. (Review data are consistent with clinical guidelines.) [8]

Acute abdominal pain accounts for 7–10% of all emergency department visits.[9] Acute appendicitis is one of the most common causes of lower abdominal pain for which patients present to the emergency department and is the most common diagnosis given to young patients admitted to the hospital with an acute abdomen.

The incidence of acute appendicitis has been steadily declining since the late 1940s. In developed countries, acute appendicitis occurs at a rate of 5.7–50 patients per 100,000 inhabitants per year, with a peak between the ages of 10 and 30 years. [10], [11]

Geographical differences have been reported, with the lifetime risk of developing acute appendicitis being 9% in the United States, 8% in Europe, and 2% in Africa.[12] Furthermore, there are large differences in the presentation, severity of disease, radiological examination, and surgical treatment of patients with acute appendicitis, which is associated with country income.[13]

The incidence of perforations varies from 16% to 40%, with a higher incidence in younger age groups (40–57%) and in patients over 50 years of age (55–70%).[14]

Some authors report a gender predisposition at all ages, slightly higher among men, with a lifetime incidence of 8.6% for men and 6.7% for women.[15] However, women tend to have a higher rate of appendectomy due to various gynecological diseases that mimic appendicitis.[16]

According to population-based ethnic statistics, appendicitis is more common in white, non-Hispanic, and Latino groups and less common in black and other racial-ethnic groups.[17] However, data show that minority groups are at higher risk for perforation and complications.[18],[19]

In recent years, increased access to ultrasound and computed tomography has reduced the rate of "negative appendectomies" (removal of an intact appendix). At the same time, the rate of early detection of complications, such as abscesses and perforations, has increased. This has improved the selection of patients for conservative treatment and the timing of surgeries. [20]

Antibiotic-versus-surgery programs in research cohorts have shown that by day 90, most patients avoid appendectomy, although some eventually undergo surgery. Over a 3- to 4-year period, approximately half of those initially treated with antibiotics undergo appendectomy, which is important to consider when choosing a strategy. [21]

Health systems report a stable burden of appendicitis on emergency and surgical services, with the transition to laparoscopy and shorter antibiotic regimens reducing hospital stays and complications. [22]

Reasons

The classic cause is obstruction of the appendix lumen (by a fecal stone/appendicolith, lymphoid tissue hyperplasia, or, less commonly, parasites or tumor), which leads to secretion stagnation, increased pressure, ischemia, and bacterial colonization. The result is inflammation with the risk of necrosis and perforation. [23]

In adults, the presence of appendicolith increases the likelihood of failure of conservative management and early surgery. Studies have shown this factor to be associated with a nearly twofold increase in the risk of appendectomy in the first 30 days with the initial choice of antibiotics. [24]

Some cases present as "primarily complicated"—with an abscess or phlegmon; in these cases, a stepwise strategy is often chosen: antibacterial therapy ± drainage with delayed appendectomy when indicated. The decision depends on the size of the abscess and the patient's condition. [25]

Microbiological aspects (mixed aerobic-anaerobic flora) and the characteristics of the immune response are also important. These factors are taken into account when choosing empirical antibiotics and the duration of courses. [26]

Risk factors

Research on the risk factors associated with acute appendicitis is limited. However, some factors that may potentially influence the likelihood of developing this disease include demographic factors such as age, gender, family history, and environmental and nutritional factors. Research suggests that acute appendicitis can affect people of all ages, although it appears to be more common among adolescents and young adults, with a higher incidence observed in men.[27],[28] As with many other diseases, family history plays a significant role in acute appendicitis; evidence suggests that people with a positive family history of acute appendicitis are at increased risk of developing the disease.[29] Several dietary risk factors have been associated with appendicitis, such as a low-fiber diet, increased sugar intake, and decreased water intake. [30] Environmental factors involved in the development of appendicitis include exposure to air pollution, allergens, cigarette smoke, and gastrointestinal infections. [31], [32], [33]

Age under 30 years marks the peak epidemiological incidence, but complicated forms are more common in the elderly and patients with comorbidities. The latter have a higher risk of perforation and postoperative complications. [34]

The presence of appendicolith on computed tomography (CT) is an independent predictor of poor outcome when attempting conservative treatment. Increased appendicular diameter on imaging also correlates with failure of the antibiotic-only strategy. [35]

Immunodeficiency states, taking glucocorticosteroids, late presentation, and pregnancy impose limitations on diagnosis and increase the risk of complications, requiring an individual protocol. [36]

In children and adolescents, a rapid course is more common; in pregnant women, the altered anatomy and the acceptable range of imaging (ultrasound, then magnetic resonance imaging) dictate a special algorithm. [37]

New evidence suggests a potential correlation between elevated temperature and acute appendicitis, suggesting that high temperatures may increase the likelihood of developing this condition due to dehydration.[38]

Studies have also shown that patients with mental disorders who are prescribed high doses of antipsychotic drugs daily are at increased risk of developing complicated appendicitis.[39]

Pathogenesis

Lumen obstruction → secretion congestion and venous stasis → wall ischemia → bacterial invasion and purulent inflammation is the basic sequence. With progression, necrosis and perforation with localized or widespread peritonitis develop. [40]

Localized forms are accompanied by inflammation of the surrounding tissue and mesoappendix, and infiltration and abscess formation are possible. In some cases, the body "limits" the process, opening the door for conservative management and drainage. [41]

Microbiologically, intestinal enterobacteria and anaerobes are the most common, so empirical regimens always cover both. After adequate source control (removal of the appendix, sanitation), long-term antibiotic courses provide no benefit. [42]

Inflammatory biomarkers (leukocytes, C-reactive protein) reflect the activity of the process and help in risk stratification according to clinical scales, but in themselves do not replace visualization. [43]

Symptoms

The classic scenario: dull pain around the navel, then migrating to the right iliac region, fever, loss of appetite, and nausea. The pain intensifies with walking and coughing, and localized tenderness and muscle tension are possible. [44]

Symptoms include diarrhea (especially in children), dysuria if located close to the bladder, and mild symptoms in the elderly. Rupture may cause increasing, diffuse pain, signs of peritonitis, and deterioration in well-being. [45]

In pregnant women, the location of pain may shift higher as the uterus grows; with a high appendix, pain in the right hypochondrium is possible. This complicates the clinical picture and increases the role of ultrasound/magnetic resonance imaging. [46]

Symptoms are always assessed in conjunction with laboratory and scales (AIR, AAS), which allows to classify the patient into low/intermediate/high probability and choose the appropriate imaging or treatment path. [47]

Anatomical aspects of acute appendicitis

The appendix is a tubular structure attached to the base of the cecum at the site of entry of the taeniae coli. In adults, it is approximately 8–10 cm long and represents the underdeveloped distal end of the large cecum, similar to that observed in other animals. In humans, it is considered a vestigial organ, and acute inflammation of this structure is called acute appendicitis.

Retrocecal/retrocolic (75%) – pain in the right lumbar region is often present, with tenderness on examination. Muscle rigidity and tenderness on deep palpation are often absent due to the protection of the overlying cecum. In this position, the psoas muscle may become irritated, leading to hip flexion and increased pain with hip extension (a sign of a psoas strain).

Subcecum and pelvic region (20%) – suprapubic pain and frequent urination may predominate. Diarrhea may result from rectal irritation. Abdominal tenderness may be absent, but pain in the right rectum or vagina may be present. Urinalysis may reveal microscopic hematuria and white blood cells.

Pre- and post-ileal (5%) – signs and symptoms may be absent. Vomiting may be more severe, and diarrhea may result from irritation of the distal ileum.

Symptoms of appendicitis in children

In children, appendicitis has a variability in presentation depending on age groups.[48] It is rare and difficult to diagnose in neonates and infants.[49] They typically present with abdominal distension, vomiting, diarrhea, a palpable abdominal mass, and irritability.[50] On physical examination, they often reveal dehydration, hypothermia, and respiratory failure, making a diagnosis of appendicitis unlikely for the physician. Preschool-aged children up to 3 years of age typically present with vomiting, abdominal pain, predominantly diffuse fever, diarrhea, difficulty walking, and right groin stiffness.[51] Evaluation may reveal abdominal distension, rigidity, or a mass on rectal examination.[52] Children aged 5 years and older more often present with classic symptoms, including migratory abdominal pain, anorexia, nausea, and vomiting. Clinical evaluation reveals fever and tachycardia, decreased bowel sounds, and right lower quadrant tenderness, which increases the likelihood of the diagnosis in this age group.[53] The presentation of acute appendicitis in young children is usually atypical, with overlapping symptoms mimicking other systemic diseases, often leading to misdiagnosis and complications leading to morbidity. Furthermore, younger age is a well-known risk factor for adverse outcomes due to complicated appendicitis.[54]

The typical presentation of appendicitis in adults includes migratory pain in the right iliac fossa, anorexia, nausea with or without vomiting, fever, and localized muscle rigidity/generalized rigidity.[55],[56] The classic symptom sequence includes vague umbilical pain, anorexia/nausea/short-lived vomiting, migratory pain to the right lower quadrant, and low-grade fever.

Atypical signs and symptoms of appendicitis

In addition to the typical presentation of appendicitis, atypical signs and symptoms may also be observed. These may include left-sided abdominal pain localized to the left upper quadrant. Although left-sided appendicitis is relatively rare, occurring in approximately 0.02% of the adult population, it is more common in individuals with intestinal malrotation or inverted bowel position.[57] Appendicitis is also associated with diarrhea as an atypical symptom in disseminated appendicitis, particularly in patients with interintestinal abscesses.[58]

In children, the symptoms are generally vague, making diagnosis difficult based on history and examination. An atypical presentation of appendicitis in children may include pain and tenderness throughout the right flank, extending from the right upper quadrant to the right iliac fossa. This may result from an arrest of the cecal descent of the appendix when the cecum is in a subhepatic position.[59] In adult men, atypical symptoms of appendicitis may be observed, such as severe pain in the right hemisphere, which later becomes mild diffuse abdominal pain. In contrast, women may present with genitourinary complaints, such as tenderness in the thigh region with a mass and diarrhea.[60],[61] In the elderly, appendicitis may present atypically as an incarcerated inguinal hernia with non-specific symptoms.[62]

Pregnant patients are more likely to present with atypical complaints such as gastroesophageal reflux, malaise, pelvic pain, epigastric discomfort, indigestion, flatulence, dysuria, and change in bowel habits.[63] Furthermore, physical examination findings are challenging and abnormal because the abdomen is distended, increasing the distance between the inflamed appendix and the peritoneum, resulting in masking of rigidity and decreased tenderness. In late pregnancy, the appendix may displace cranially into the upper abdomen due to the enlarging uterus, resulting in RLQ pain.[64] However, regardless of gestational age, RLQ pain remains the most common clinical manifestation of acute appendicitis during pregnancy. [65] Leukocytosis may not be a reliable indicator of acute appendicitis in pregnant women due to the physiological leukocytosis during pregnancy. Studies have shown that pregnant women have a lower incidence of appendicitis than non-pregnant women. However, there is a higher risk of developing acute appendicitis in the second trimester. [66]

Classification, forms and stages

Clinically, appendicitis is divided into uncomplicated and complicated. Complicated appendicitis includes perforation, abscess, phlegmon, and generalized peritonitis. This distinction determines the choice between immediate surgery and, possibly, conservative management. [67]

ICD-11 specifies the degree of peritonitis (localized/generalized), which reflects its severity. Intraoperative classifications help standardize descriptions, but key decisions are usually made preoperatively, based on CT/ultrasound data. [68]

Children and pregnant women formally have the same categories, but diagnostic algorithms and thresholds for surgery differ due to physiological characteristics and limitations of radiation exposure. [69]

In case of “complex” appendicitis (abscess/phlegmon), a two-stage approach is possible: antibacterial therapy ± drainage followed by (or selectively without) interval appendectomy. The choice is individual. [70]

Complications and consequences

Early complications include perforation with peritonitis, abdominal/pelvic abscess, and sepsis. These require urgent source control—surgery and/or drainage. Delayed diagnosis increases the risk of complications. [71]

Postoperative complications include surgical site infections and intra-abdominal collections. The laparoscopic approach reduces pain and the risk of superficial infection compared with the open approach. Drains are not routinely placed. [72]

With conservative treatment, the main "delayed" risk is recurrence of inflammation and delayed appendectomy (approximately half of patients by 3-4 years of age). The presence of appendicolith increases the likelihood of early surgery. [73]

After an episode in adults, especially if the presentation is atypical, it is important to exclude rare causes of inflammation (eg, tumor) - this is usually done using CT scan data and, if necessary, colonoscopy. [74]

When to see a doctor

Immediately - if you experience persistent, increasing pain in the right lower abdomen, fever, nausea/vomiting, especially if the pain has radiated downwards. This is typical of acute appendicitis and requires urgent evaluation. [75]

Call emergency medical help immediately if you experience increasing, diffuse pain, abdominal muscle rigidity, severe weakness, or cold sweat—these are signs of peritonitis. Any delay increases the risk of complications. [76]

Pregnant women, the elderly, and patients with immunodeficiency should be consulted if their symptoms are milder: their clinical picture may be “blurred,” and the threshold for visualization is lower. [77]

If appendicitis has already been diagnosed and you have chosen antibiotics, seek immediate medical attention if the pain increases, fever, vomiting, or chills appear - this may be a sign that conservative treatment has failed. [78]

Diagnostics

The Alvarado score can be used to stratify patients with symptoms suspected of appendicitis; the reliability of the score in specific patient groups and at different points remains unclear. The Alvarado score is a useful diagnostic "rule-out" score with a cutoff of 5 for all patient groups. This score is well calibrated in men, inconsistent in children, and overpredicts the likelihood of appendicitis in women across all risk groups. [79]

The Alvarado score allows risk stratification in patients with abdominal pain by relating the likelihood of appendicitis to recommendations for discharge, observation, or surgery.[80] Further investigations, such as ultrasound and computed tomography (CT), are recommended when the likelihood of appendicitis is in the intermediate range.[81] However, the time lag, high cost, and variable availability of imaging procedures mean that the Alvarado score may be a valuable diagnostic aid when appendicitis is suspected to be the underlying cause of an acute abdomen, particularly in low-resource settings where imaging is not available.

Although the Alvarado score lacks specificity for the diagnosis of AA, a cutoff score of <5 is sufficiently sensitive to exclude acute appendicitis (99% sensitivity). Thus, the Alvarado score may be used to reduce the length of emergency department stay and radiation exposure in patients with suspected acute appendicitis. This is supported by a large retrospective cohort study that found that 100% of men with an Alvarado score of 9 or greater and 100% of women with an Alvarado score of 10 had acute appendicitis confirmed by surgical pathology. Conversely, 5% or less of female patients with an Alvarado score of 2 or less and 0% of male patients with an Alvarado score of 1 or less were diagnosed with acute appendicitis at surgery.[82]

However, the Alvarado scale does not differentiate complicated from uncomplicated acute appendicitis in elderly patients and appears less sensitive in HIV-positive patients.[83],[84]

The RIPASA (Raja Isteri Pengiran Anak Saleh appendicitis) score showed better sensitivity and specificity than the Alvarado score in Asian and Middle Eastern populations. Malik et al. recently published the first study evaluating the utility of the RIPASA score for predicting acute appendicitis in a Western population. With a value of 7.5 (a score indicative of acute appendicitis in an Eastern population), RIPASA demonstrated reasonable sensitivity (85.39%), specificity (69.86%), positive predictive value (84.06%), negative predictive value (72.86%), and diagnostic accuracy (80%) in Irish patients with suspected AA and was more accurate than the Alvarado score.[85]

The Adult Appendicitis Score (AAS) stratifies patients into three groups: high, intermediate, and low risk for developing acute appendicitis. This score has been shown to be a reliable tool for stratifying patients for selective imaging, resulting in a low rate of negative appendectomies. In a prospective study of 829 adults with clinical suspicion of acute appendicitis, 58% of patients with histologically confirmed acute appendicitis had a score of at least 16 and were classified as high-probability with a specificity of 93%. Patients with a score below 11 were classified as low-probability for acute appendicitis. Only 4% of patients with acute appendicitis had a score below 11, and none of them had complications of acute appendicitis. In contrast, 54% of non-AA patients had a score below 11. The area under the ROC curve was significantly larger with a new score of 0.882 compared with an Alvarado score AUC of 0.790 and an AIR of 0.810.[86]

The Alvarado score may be higher in pregnant women due to higher white blood cell counts and the incidence of nausea and vomiting, especially in the first trimester, resulting in lower accuracy compared to the non-pregnant population. Studies show that the sensitivity of the Alvarado score (cutoff 7 points) is 78.9% and the specificity is 80.0% in pregnant women.[87],[88] The specificity of the RIPASA score (cutoff 7.5 points) is 96%, but this needs to be verified in larger studies. There are no studies on the Alvarado score that can differentiate between uncomplicated and complicated AA during pregnancy.

If classic symptoms and signs are present, the diagnosis is made clinically. In such patients, delaying laparotomy due to additional instrumental investigations only increases the risk of perforation and subsequent complications. In patients with atypical or questionable findings, instrumental investigations should be performed without delay.

Contrast-enhanced CT has reasonable accuracy in diagnosing appendicitis and can also verify other causes of acute abdomen. Graded compression ultrasound can usually be performed more quickly than CT, but the examination is sometimes limited by the presence of intestinal gas and is less informative in the differential diagnosis of causes of non-appendiceal pain. The use of these studies has reduced the rate of negative laparotomies.

Laparoscopy can be used for diagnosis; the examination is particularly useful in women with mild lower abdominal pain of unknown etiology. Laboratory tests usually reveal leukocytosis (12,000-15,000/μL), but these findings are highly variable; the leukocyte count should not be used as a criterion for excluding appendicitis.

The emergency department physician should refrain from prescribing any pain medications to the patient until they have been seen by a surgeon. Analgesics can mask peritoneal signs and lead to a delay in diagnosis or even appendiceal rupture.

Laboratory testing

Laboratory measurements, including the total white blood cell (WBC) count, percentage of neutrophils, and C-reactive protein (CRP) concentration, are necessary to continue the diagnostic workup in patients with suspected acute appendicitis.[89] Classically, an elevated white blood cell (WBC) count with or without a left shift or bandemia is present, but up to a third of patients with acute appendicitis have normal WBC counts. Ketones are commonly detected in the urine, and C-reactive protein levels may be elevated. The combination of normal WBC and CRP results has a specificity of 98% for excluding acute appendicitis. Furthermore, WBC and CRP results have a positive predictive value for differentiating between non-inflamed, uncomplicated, and complicated appendicitis. Both elevations in CRP and WBC levels correlate with a significantly increased likelihood of complicated appendicitis. The likelihood of developing appendicitis in a patient with normal WBC and CRP levels is extremely low.[90] A WBC count of 10,000 cells/mm^3 is quite predictable in patients with acute appendicitis; however, the level will increase in patients with complicated appendicitis. Accordingly, a WBC count equal to or greater than 17,000 cells/mm^3 is associated with complications of acute appendicitis, including perforated and gangrenous appendicitis.

Visualization

Appendicitis is traditionally a clinical diagnosis. However, several imaging techniques are used to guide the diagnostic process, including abdominal CT, ultrasound, and MRI.

Computed tomography

Abdominal CT is more than 95% accurate for diagnosing appendicitis and is increasingly used. CT criteria for appendicitis include an enlarged appendix (more than 6 mm in diameter), thickened appendiceal wall (more than 2 mm), periappendiceal fat accumulation, enhanced appendiceal wall, and the presence of appendicoliths (approximately 25% of patients). It is unusual to see air or contrast in the lumen of appendicitis due to lumen dilation and possible obstruction in most cases of appendicitis. Failure to visualize the appendix does not rule out appendicitis. Ultrasound is less sensitive and specific than CT but may be useful for preventing ionizing radiation exposure in children and pregnant women. MRI may also be useful in pregnant women with suspected appendicitis and an indeterminate ultrasound result. Traditionally, the best way to diagnose acute appendicitis is a good history and a thorough physical examination by an experienced surgeon; however, a CT scan can easily be performed in the emergency department. It has become common practice to rely primarily on CT scans when diagnosing acute appendicitis. Appendicoliths are sometimes discovered incidentally during routine X-rays or CT scans.

Computed tomography shows an inflammatory mass in the right iliac fossa caused by acute appendicitis.

The primary concern when performing CT of the abdomen and pelvis is radiation exposure; however, the average radiation exposure from a typical CT scan will not exceed 4 mSv, which is slightly higher than the background radiation of nearly 3 mSv. Despite the higher resolution of CT images obtained with a maximum radiation dose of 4 mSv, lower doses will not affect clinical outcomes. Furthermore, performing CT of the abdomen and pelvis with intravenous contrast in patients with suspected acute appendicitis should be limited to an acceptable glomerular filtration rate (SFR) equal to or greater than 30 mL/min. These patients are at higher risk of developing appendicitis than the general population. Prophylactic appendectomy should be considered in these patients. Studies have also shown that the incidence of appendicoliths in appendectomy specimens performed for acute appendicitis ranges from 10% to 30%. [91], [92], [93]

Ultrasound echography

Abdominal ultrasound is a widely used and accessible initial evaluation of patients with acute abdominal pain. A specific compressibility index (SCI) of less than 5 mm in diameter is used to exclude appendicitis. Conversely, certain findings, including an anteroposterior diameter greater than 6 mm, appendicoliths, and abnormally increased echogenicity of periappendiceal tissue, suggest acute appendicitis. The main challenges in using abdominal ultrasound to evaluate a potential diagnosis of acute appendicitis include the inherent limitations of sonography in obese patients and operator dependence in detecting suggestive features. Furthermore, patients complicated by peritonitis have difficulty tolerating graded compression.[94]

MRI

Despite the high sensitivity and specificity of MRI for detecting acute appendicitis, there are significant challenges associated with performing abdominal MRI. Abdominal MRI is not only expensive but also requires a high level of expertise to interpret the results. Therefore, its use is generally limited to specific patient groups, including pregnant women, who are at unacceptable risk of radiation exposure. [95]

Table 2. Diagnostic methods and their role

Method	Strengths	Limitations/When not suitable
AIR/AAS scales	Rapid risk stratification	Do not replace visualization when in doubt
Ultrasound	No radiation, first line in children/pregnant women	Depends on the operator, worse in obesity/atypia
CT with contrast	High accuracy, detects complications	Radiation exposure; avoid in pregnant women
MRI (pregnant women)	Accurate without radiation	Less availability, price
Diagnostic laparoscopy	Diagnosis and treatment in one stage	Invasive, requires surgery
[96]

Differential diagnosis

In adults, right-sided renal colic, mesadenitis, terminal ileitis, Crohn's disease, ileocecal tuberculosis, ulcer perforation, cholecystitis with irradiation, and gynecological causes (ectopic pregnancy, torsion/rupture of a cyst). Imaging and a pregnancy test help narrow the range. [97]

In children, gastroenteritis, mesadenitis, and pneumonia of the lower lobe of the right side are present. Ultrasound and laboratory markers can differentiate these conditions; if in doubt, observation with repeated assessment is used. [98]

In the elderly, right-sided colon diverticulitis, ischemic colitis, and cecal tumors are common. Here, the threshold for CT scanning is lower, and clinical interpretation is more difficult due to the "obscured" symptoms. [99]

During pregnancy, differentiate with acute pyelonephritis, cholecystitis and obstetric pathology; if unclear after ultrasound, magnetic resonance imaging is recommended. [100]

Treatment

The goal of non-operative management (NOM) is to allow patients to avoid surgery by using antibiotics.[101] Early studies in the 1950s reported successful treatment of acute appendicitis with antibiotics alone and recommended treatment for appendicitis with symptoms lasting less than 24 hours.[102],[103] In recent years, there has been renewed interest in NOM of uncomplicated acute appendicitis, with several studies reporting successful treatment of approximately 65% of cases using antibiotics alone. However, studies such as APPAC, ACTUAA, and meta-analyses have shown mixed results, with short- and long-term NOM failure rates ranging from 11.9% to 39.1%. [104] Furthermore, studies on the use of NOM in complicated appendicitis are limited but have shown that although it can be successful, it is associated with increased readmission rates and longer hospital stays. [105], [106]

Treatment for acute appendicitis involves removal of the inflamed appendix. Since mortality increases with delayed treatment, a 10% negative appendectomy rate is considered acceptable. The surgeon typically removes the appendix, even if it is perforated. Sometimes, locating the appendix is difficult: in these cases, the appendix is usually located behind the cecum or ileum, as well as the mesentery of the right colon.

Inflammatory bowel disease involving the cecum is a contraindication to appendectomy. However, in cases of terminal ileitis with an intact cecum, the appendix must be removed.

Appendix removal should be preceded by intravenous antibiotics. Third-generation cephalosporins are preferred. In uncomplicated appendicitis, further antibiotic administration is not required. If perforation occurs, antibiotic therapy should be continued until the patient's temperature and white blood cell count return to normal (approximately 5 days). If surgery is not possible, antibiotics, although not a cure, significantly improve survival. Without surgery or antibiotic therapy, mortality reaches over 50%.

In the emergency department, the patient should be kept on oral fluids (NPO) and hydrated intravenously with crystalloids, and antibiotics should be administered intravenously as directed by the surgeon. Responsibility for consent lies with the surgeon. The gold standard treatment for acute appendicitis is appendectomy. Laparoscopic appendectomy is preferred over the open approach. Most uncomplicated appendectomies are performed laparoscopically. Several studies have compared the outcomes of a laparoscopic appendectomy group with patients who underwent open appendectomy. The results showed a lower rate of wound infections, a reduced need for postoperative analgesics, and a shorter postoperative hospital stay in the former group. The main disadvantage of laparoscopic appendectomy is a longer operative time.[107]

Operation time

A recent retrospective study found no significant difference in complications between early (less than 12 hours after presentation) and late (12–24 hours) appendectomy.[108] However, this does not take into account the actual time from symptom onset to presentation, which may influence the perforation rate.[109] After the first 36 hours from symptom onset, the average perforation rate is 16% to 36%, and the risk of perforation is 5% for every subsequent 12 hours.[110] Therefore, once the diagnosis is made, appendectomy should be performed without unnecessary delay.

Laparoscopic appendectomy

In cases of abscess or advanced infection, an open approach may be necessary. A laparoscopic approach offers less pain, a faster recovery, and the ability to explore a larger portion of the abdominal cavity through small incisions. Situations involving a known abscess of a perforated appendix may require a percutaneous drainage procedure, typically performed by an interventional radiologist. This stabilizes the patient and allows the inflammation to subside over time, allowing for a less complex laparoscopic appendectomy at a later stage. Practitioners also prescribe broad-spectrum antibiotics to patients. There is some controversy regarding the preoperative use of antibiotics for uncomplicated appendicitis. Some surgeons believe that routine antibiotic use in these cases is inappropriate, while others routinely prescribe them.

In patients with appendiceal abscess, some surgeons continue antibiotics for several weeks and then perform an elective appendectomy. In the case of a ruptured appendix, the procedure can be performed laparoscopically, but extensive irrigation of the abdomen and pelvis is necessary. In addition, trocar sites may need to be left open. A significant number of patients with suspected acute appendicitis can be treated without any complications using a laparoscopic approach. However, several factors predict the demand for conversion to an open approach. The only preoperative independent factor predicting conversion to laparoscopic appendectomy is the presence of comorbidities. Moreover, certain intraoperative findings, including the presence of a periappendiceal abscess and diffuse peritonitis, are independent predictors of not only a higher conversion rate but also a significant increase in postoperative complications.[111]

Open appendectomy

Although laparoscopic appendectomy is widely used as the preferred surgical treatment for acute appendicitis in many centers, open appendectomy may still be a practical option, particularly in the treatment of complicated appendicitis with phlegmon and in patients who have undergone a surgical transition from the laparoscopic approach, primarily due to potential problems associated with poor visibility.

Alternative surgical approaches

Several other alternative surgical approaches have recently been introduced, including natural orifice transluminal endoscopic surgery (NOTES) and single incision laparoscopic surgery (SILS). The concept of using a flexible endoscope to enter the gastrointestinal or vaginal tract and then transect the gastrointestinal tract to enter the abdominal cavity is an attractive alternative for patients who are sensitive to the cosmetic aspects of the procedure. It was later tested in a successful transgastric appendectomy in a group of ten Indian patients. The main potential advantages of NOTES-assisted appendectomy are the absence of scars and limited postoperative pain. Given the limited number of patients who have undergone NOTES-assisted appendectomy, a detailed comparison of postoperative outcomes is not yet possible. Therefore, the main drawback of using this technique is the need to combine it with a laparoscopic approach to ensure adequate retraction during the procedure and confirm entry-site closure. [112], [113], [114] As a surgical technique, SILS for appendectomy is performed through an umbilical incision or a pre-existing abdominal scar. Potential advantages of SILS include reduced postoperative pain, postprocedural wound-related complications, and resulting shorter periods of sick leave. [115] However, up to 40% of patients still convert to traditional laparoscopy at some point during the procedure. The main disadvantage of SILS for appendectomy is a higher long-term complication associated with incisional hernia.

In case of detection of a large inflammatory space-occupying lesion involving the appendix, distal ileum and cecum, resection of the entire lesion and ileostomy are preferable.

In advanced cases, when a pericolic abscess has already formed, it is drained with a tube inserted percutaneously under ultrasound guidance or by open surgery (followed by delayed appendectomy). The Meckel diverticulum is removed simultaneously with appendectomy, but only if the inflammation around the appendix does not interfere with this procedure.

Table 3. Comparison of strategies for uncomplicated appendicitis (adults)

Criterion	Laparoscopic appendectomy	Antibiotics under observation
Short-term security	High	High (no worse in quality of life for 30 days)
Risk of reoperation	Short	~49% undergo surgery by 3-4 years
Hospitalization and recovery	Often shorter with stable flow	Repeat visits/hospitalizations are possible
Suitable for appendicolitis	Yes	Usually no (higher risk of failure)
[116]

Table 4. Antibiotics: principles and duration

Situation	Recommendation	Note
Preoperative prophylaxis	Single dose broad spectrum	Coverage of aerobes and anaerobes
After surgery, uncomplicated	Do not use	No gain in reducing infections
Postoperative, complicated (adequate source control)	3-5 days	Early clinical and laboratory monitoring
Without adequate source control	Up to 5-7 days and re-evaluation	Consider the need for re-sanitation
[117]

Prevention

There is no specific prevention for the initial episode, but prompt treatment for typical symptoms is the best way to prevent perforation and peritonitis. On a population scale, the availability of ultrasound/CT and standardization of routes contribute to a reduction in complications. [118]

Prevention after an episode primarily involves informing the patient of "red flags" and a clear plan for contact in the event of pain recurrence, especially if antibiotic treatment was initially chosen. Early imaging of recurrent complaints reduces the risk of complications. [119]

Inpatient prevention of site-of-care infections involves adherence to antibiotic prophylaxis protocols and avoiding unnecessary long courses. This reduces resistance and complications. [120]

Elderly patients and those with comorbidities benefit from "rapid diagnostic routes"—a low threshold for CT scanning in case of doubt and an early decision on surgery. This reduces the incidence of perforations. [121]

Forecast

With uncomplicated treatment and timely management, the prognosis is favorable. Laparoscopic surgery provides rapid recovery and a low recurrence rate. The risk of serious postoperative complications is low. [122]

In complicated cases, the outcome depends on the speed of source control and the patient's overall condition. Modern approaches with short courses of antibiotics after adequate sanitation provide results no worse than longer regimens. [123]

In patients initially choosing antibiotics, the rate of transition to surgery increases over time, reaching approximately half by 3–4 years, but with proper monitoring, this does not compromise long-term safety outcomes. Awareness and easy access to follow-up care are important. [124]

Overall, standardization of diagnostics (scales + imaging) and the prevalence of laparoscopic technologies continue to reduce complications and length of hospital stay compared to the past decade. [125]

FAQ

Antibiotics instead of surgery – is it safe? Yes, in carefully selected adults with uncomplicated disease without appendicitis, this is an acceptable strategy: at 30 days, quality of life is no worse than after surgery. However, almost half will require appendectomy within 3-4 years. [126]

Are antibiotics necessary after a "routine" appendectomy? If appendicitis is uncomplicated and the source has been removed, postoperative antibiotics are not recommended. In complicated cases, the standard is 3-5 days after adequate debridement. [127]

Which imaging method is better: ultrasound or CT? Ultrasound is the first-line method in children, pregnant women, and those with intermediate probabilities; in adults, if there is any doubt, CT becomes the "gold standard." In pregnant women, magnetic resonance imaging is preferred after an uninformative ultrasound. [128]

Is urgent surgery always necessary? If clinical/CT scan findings are highly suggestive or complications arise, yes. In uncomplicated cases, adults may have a choice between surgery and antibiotics; the decision is made in consultation with a doctor. [129]

What increases the risk of antibiotic treatment failure? The presence of an appendicolith and a large appendix diameter on CT. These factors double the chances of early surgery. [130]

Additional tables

Table 5. AIR scale (abbreviated structure and thresholds)

Parameters (symptoms + examination + laboratory)	Interpretation
Points 0-4	Low probability - observation/re-evaluation
Points 5-8	Intermediate - ultrasound/CT according to the algorithm
Points ≥9	High probability - surgical tactics
(Detailed scores: vomiting, right iliac fossa pain, rigidity/rebound, temperature ≥38.5°C, neutrophil count, white blood cell count, C-reactive protein.) [131]

Table 6. Visualization algorithm by groups

Group	First line	If it is not informative
Children	Ultrasound	CT (as indicated)
Pregnant women	Ultrasound	MRI
Adults, intermediate risk	Ultrasound	CT
Adults, high probability/severity	CT scan or laparoscopy immediately
[132]

Table 7. When which tactics are optimal

Clinical situation	Preferred approach	Comment
Uncomplicated appendicitis without appendicolith (adults)	Surgery or antibiotics	Joint decision; consideration of risk of relapse
Presence of appendicolith	Laparoscopic appendectomy	High risk of failure of conservative tactics
Abscess/cellulitis	Antibiotics ± percutaneous drainage; delayed surgery if indicated	Personalization by size and response
Generalized peritonitis/perforation	Urgent surgery + short course of antibiotics	Source control is primary
[133]

Anatomy of the appendix

The official name of the appendix is "Appendix Vermiformis". The appendix is a true diverticulum arising from the posteromedial margin of the cecum, located in close proximity to the ileocecal valve. The base of the appendix can be reliably located near the convergence of taeniae coli at the apex of the cecum. The term "vermiformis" is Latin for "worm-shaped" [134] and is explained by its long tubular architecture. Unlike the acquired diverticulum, it is a true colonic diverticulum containing all layers of the colon: mucosa, submucosa, longitudinal and circular muscular coat, and serosa. The histological distinction between the colon and the appendix depends on the presence of B and T lymphoid cells in the mucosa and submucosa of the appendix. [135]

Structure and functions

The appendix can have a variable length from 5 to 35 cm, with an average of 9 cm. [136] The function of the appendix has traditionally been a subject of debate. Neuroendocrine cells in the mucosa produce amines and hormones that help carry out various biological control mechanisms, while lymphoid tissue is involved in the maturation of B lymphocytes and the production of IgA antibodies. There is no clear evidence of its function in humans. The presence of gut-associated lymphoid tissue in the lamina propria has led to the belief that it serves an immune function, although the specific nature of this has never been established. As a result, the organ has largely retained its reputation as a vestigial organ. However, as the understanding of intestinal immunity has improved in recent years, a theory has emerged that the appendix serves as a "sanctuary" for symbiotic gut microbes. [137] Severe bouts of diarrhea, which can clear the intestines of commensal bacteria, can be replaced by drugs contained in the appendix. This suggests an evolutionary advantage in retaining the appendix and weakens the theory that this organ is vestigial. [138]

Physiological variants

Although the location of the appendiceal orifice at the base of the cecum is a stable anatomical feature, the position of its tip is not. Positional variations include retrocecal (but intraperitoneal), subcecal, pre- and post-ileal, pelvic, and even reaching the hepatorenal pouch. Furthermore, the position of the appendix can be influenced by factors such as posture, respiration, and distention of the adjacent bowel. The retrocecal position is the most common. This can cause clinical confusion in the diagnosis of appendicitis, as changes in position can cause various symptoms. Agenesis of the appendix, as well as its duplication or triplication, are rarely described in the literature. As pregnancy progresses, the enlarging uterus displaces the appendix cranially so much that by the end of the third trimester, pain with appendicitis may be felt in the right upper quadrant.

Clinical significance

The pathogenesis of acute appendicitis is similar to that of other hollow viscous organs and is thought to be most often caused by obstruction. A gallstone, and sometimes a gallstone, tumor, or worms, obstruct the orifice of the appendix, causing increased intraluminal pressure and impaired venous outflow. In young adults, obstruction is more often caused by lymphoid hyperplasia. The appendix receives its blood supply from the appendiceal artery, which is the terminal artery. Because intraluminal pressure exceeds perfusion pressure, ischemic injury occurs, promoting bacterial overgrowth and triggering an inflammatory response. This requires urgent surgical intervention, as perforation of the inflamed appendix can result in the release of bacterial contents into the peritoneal cavity.[139]

When the appendiceal wall becomes inflamed, visceral afferent fibers are stimulated. These fibers enter the spinal cord at T8-T10, causing the classic diffuse periumbilical pain and nausea seen at the onset of appendicitis. As the inflammation progresses, the parietal peritoneum becomes irritated, stimulating somatic nerve fibers and causing more localized pain. The location depends on the position of the appendiceal apex. For example, a retrocecal appendix may cause pain in the right flank. Extending the patient's right hip may also elicit this pain. Pain resulting from stretching the iliopsoas muscle due to hip extension while lying on the left side is known as the "psoas sign." Another classic sign of acute appendicitis is McBurney's sign. This is detected by palpating the abdominal wall at McBurney's point (two-thirds of the distance from the umbilicus to the right anterior superior iliac spine) when pain occurs. Unfortunately, these signs and symptoms are not always present, making clinical diagnosis difficult. The clinical picture often includes nausea, vomiting, low-grade fever, and a slightly elevated white blood cell count.