INTRODUCTION — Appendicitis, an inflammation of the vestigial vermiform appendix, is one of the most common causes of the acute abdomen and one of the most frequent indications for an emergency abdominal surgical procedure worldwide [1,2].
The clinical manifestations and differential diagnosis of appendicitis in adults will be reviewed here. The diagnostic evaluation and management of appendicitis in adults and appendicitis in pregnancy and children are discussed separately. (See "Acute appendicitis in adults: Diagnostic evaluation" and "Management of acute appendicitis in adults" and "Acute appendicitis in pregnancy" and "Acute appendicitis in children: Clinical manifestations and diagnosis".)
ANATOMY — The vermiform appendix is located at the base of the cecum, near the ileocecal valve where the taenia coli converge on the cecum (figure 1) [3,4]. The appendix is a true diverticulum of the cecum. In contrast to acquired diverticular disease, which consists of a protuberance of a subset of the enteric wall layers, the appendiceal wall contains all of the layers of the colonic wall: mucosa, submucosa, muscularis (longitudinal and circular), and the serosal covering .
The appendiceal orifice opens into the cecum. Its blood supply, the appendiceal artery, is a terminal branch of the ileocolic artery, which traverses the length of the mesoappendix and terminates at the tip of the organ (figure 2) .
The attachment of the appendix to the base of the cecum is constant. However, the tip may migrate to the retrocecal, subcecal, preileal, postileal, and pelvic positions. These normal anatomic variations can complicate the diagnosis as the site of pain and findings on the clinical examination will reflect the anatomic position of the appendix.
The presence of B and T lymphoid cells in the mucosa and submucosa of the lamina propria make the appendix histologically distinct from the cecum . These cells create a lymphoid pulp that aids immunologic function by increasing lymphoid products such as IgA and operating as part of the gut-associated lymphoid tissue system . Lymphoid hyperplasia can cause obstruction of the appendix and lead to appendicitis. The lymphoid tissue undergoes atrophy with age .
EPIDEMIOLOGY — The incidence of acute appendicitis is approximately 100 per 100,000 person-years. The precise rate varies between 98 and 110 per 100,000 person-years in several large population studies from North America [7-9] and Europe . The incidence of acute appendicitis has been decreasing since the 1970s for unknown reasons [8,10,11].
Appendicitis occurs most frequently in the second and third decades of life. The incidence is highest in the 10-to-19-year-old age group and lowest in children ≤9 years [7,8]. It is also higher among men (male-to-female ratio of 1.4:1), who have a lifetime incidence of 8.6 percent compared with 6.7 percent for women .
The incidence of perforated appendicitis is approximately 29 per 100,000 person-years in both the United States and South Korea . There are also more cases of perforated appendicitis in men than women (31 versus 25 per 100,000 person-years) . The incidence of perforated appendicitis has been rising despite a fall in the overall incidence of acute appendicitis .
One report from Washington state suggested that acute appendicitis is not randomly distributed across geographic subunits . Socioeconomic advantages, such as higher income and secondary education, were strongly associated with a lower incidence of acute appendicitis. The geographic clustering of perforated appendicitis is only half as strong as that of acute appendicitis.
PATHOGENESIS — The natural history of appendicitis is similar to that of other inflammatory processes involving hollow visceral organs. Initial inflammation of the appendiceal wall is followed by localized ischemia, perforation, and the development of a contained abscess or generalized peritonitis.
Appendiceal obstruction has been proposed as the primary cause of appendicitis [3,13-16]. Obstruction is frequently implicated but not always identified. A study of patients with appendicitis showed that there was elevated intraluminal pressure in only one-third of the patients with nonperforated appendicitis .
Appendiceal obstruction may be caused by fecaliths (hard fecal masses), calculi, lymphoid hyperplasia, infectious processes, and benign or malignant tumors. However, some patients with a fecalith have a histologically normal appendix, and the majority of patients with appendicitis do not have a fecalith [18,19].
When obstruction of the appendix is the cause of appendicitis, the obstruction leads to an increase in luminal and intramural pressure, resulting in thrombosis and occlusion of the small vessels in the appendiceal wall and stasis of lymphatic flow. As the appendix becomes engorged, the visceral afferent nerve fibers entering the spinal cord at T8 to T10 are stimulated, leading to vague central or periumbilical abdominal pain . Well-localized pain occurs later in the course when inflammation involves the adjacent parietal peritoneum.
The mechanism of luminal obstruction varies depending upon the patient's age. In the young, lymphoid follicular hyperplasia due to infection is thought to be the main cause. In older patients, luminal obstruction is more likely to be caused by fibrosis, fecaliths, or neoplasia (carcinoid, adenocarcinoma, or mucocele). In endemic areas, parasites can cause obstruction in any age group. (See "Well-differentiated neuroendocrine tumors of the appendix".)
Once obstructed, the lumen becomes filled with mucus and distends, increasing luminal and intramural pressure. This results in thrombosis and occlusion of the small vessels and stasis of lymphatic flow. As lymphatic and vascular compromise progresses, the wall of the appendix becomes ischemic and then necrotic.
Bacterial overgrowth occurs within the diseased appendix. Aerobic organisms predominate early in the course, while mixed infection is more common in late appendicitis . Common organisms involved in gangrenous and perforated appendicitis include Escherichia coli, Peptostreptococcus, Bacteroides fragilis, and Pseudomonas species . Intraluminal bacteria subsequently invade the appendiceal wall and further propagate a neutrophilic exudate. The influx of neutrophils causes a fibropurulent reaction on the serosal surface, irritating the surrounding parietal peritoneum . This results in stimulation of somatic nerves, causing pain at the site of peritoneal irritation .
During the first 24 hours after symptoms develop, approximately 90 percent of patients develop inflammation and perhaps necrosis of the appendix, but not perforation. The type of luminal obstruction may be a predictor of perforation of an acutely inflamed appendix. Fecaliths were six times more common than true calculi in the appendix, but calculi were more often associated with perforated appendicitis or periappendiceal abscess (45 percent) than were fecaliths (19 percent). This is presumably due to the rigidity of true calculi compared with the softer, more crushable fecaliths .
Once significant inflammation and necrosis occur, the appendix is at risk of perforation, which leads to localized abscess formation or diffuse peritonitis. The time course to perforation is variable. One study showed that 20 percent of patients developed perforation less than 24 hours after the onset of symptoms . Sixty-five percent of patients in whom the appendix perforated had symptoms for longer than 48 hours.
History — Abdominal pain is the most common symptom and is reported in nearly all confirmed cases of appendicitis [23,24]. The clinical presentation of acute appendicitis is described as a constellation of the following classic symptoms:
●Right lower quadrant (right anterior iliac fossa) abdominal pain
●Nausea and vomiting
In the classic presentation, the patient describes the onset of abdominal pain as the first symptom. The pain is typically periumbilical in nature with subsequent migration to the right lower quadrant as the inflammation progresses . Although considered a classic symptom, migratory pain occurs only in 50 to 60 percent of patients with appendicitis [13,25]. Nausea and vomiting, if they occur, usually follow the onset of pain . Fever-related symptoms generally occur later in the course of illness.
In many patients, initial features are atypical or nonspecific and can include:
Because the early symptoms of appendicitis are often subtle, patients and clinicians may minimize their importance. The symptoms of appendicitis vary depending upon the location of the tip of the appendix (figure 1) (see 'Anatomy' above). For example, an inflamed anterior appendix produces marked, localized pain in the right lower quadrant, while a retrocecal appendix may cause a dull abdominal ache . The location of the pain may also be atypical in patients who have the tip of the appendix located in the pelvis, which can cause tenderness below McBurney's point. Such patients may complain of urinary frequency and dysuria or rectal symptoms, such as tenesmus and diarrhea.
Physical examination — The early signs of appendicitis are often subtle. Low-grade fever reaching 101.0°F (38.3°C) may be present. The physical examination may be unrevealing in the very early stages of appendicitis since the visceral organs are not innervated with somatic pain fibers.
However, as the inflammation progresses, involvement of the overlying parietal peritoneum causes localized tenderness in the right lower quadrant and can be detected on the abdominal examination. Rectal examination, although often advocated, has not been shown to provide additional diagnostic information in cases of appendicitis . In women, right adnexal area tenderness may be present on pelvic examination, and differentiating between tenderness of pelvic origin versus that of appendicitis may be challenging. High-grade fever (>101.0°F/38.3°C) occurs as inflammation progresses. (See "Causes of abdominal pain in adults".)
Patients with a retrocecal appendix may not exhibit marked localized tenderness in the right lower quadrant since the appendix does not come into contact with the anterior parietal peritoneum (figure 1) . The rectal and/or pelvic examination is more likely to elicit positive signs than the abdominal examination. Tenderness may be more prominent on pelvic examination and may be mistaken for adnexal tenderness.
Several findings on physical examination have been described to facilitate diagnosis, but these findings predated definitive imaging for appendicitis, and the wide variation in their sensitivity and specificity suggests that they be used with caution to broaden, or narrow, a differential diagnosis. There are no physical findings, taken alone or in concert, that definitively confirm a diagnosis of appendicitis.
Commonly described physical signs include:
●McBurney's point tenderness is described as maximal tenderness at 1.5 to 2 inches from the anterior superior iliac spine (ASIS) on a straight line from the ASIS to the umbilicus  (sensitivity 50 to 94 percent; specificity 75 to 86 percent [30-32]).
●Rovsing's sign refers to pain in the right lower quadrant with palpation of the left lower quadrant. This sign is also called indirect tenderness and is indicative of right-sided local peritoneal irritation  (sensitivity 22 to 68 percent; specificity 58 to 96 percent [31,34-36]).
●The psoas sign is associated with a retrocecal appendix. This is manifested by right lower quadrant pain with passive right hip extension. The inflamed appendix may lie against the right psoas muscle, causing the patient to shorten the muscle by drawing up the right knee. Passive extension of the iliopsoas muscle with hip extension causes right lower quadrant pain (sensitivity 13 to 42 percent; specificity 79 to 97 percent [34,37,38]).
●The obturator sign is associated with a pelvic appendix. This test is based on the principle that the inflamed appendix may lie against the right obturator internus muscle. When the clinician flexes the patient's right hip and knee, followed by internal rotation of the right hip, this elicits right lower quadrant pain (sensitivity 8 percent; specificity 94 percent ). The sensitivity is low enough that experienced clinicians no longer perform this assessment.
Laboratory findings — Mild leukocytosis (white blood cell [WBC] count >10,000 cells/microL) is present in most patients with acute appendicitis . Approximately 80 percent of patients have leukocytosis and a left shift (increase in total WBC count, bands [immature neutrophils], and neutrophils) in the differential [40-42]. The sensitivity and specificity of an elevated WBC count in acute appendicitis are 80 and 55 percent, respectively.
Acute appendicitis is unlikely when the WBC count is normal, except in the very early course of the illness [42,43]. In comparison, mean WBC counts are higher in patients with a gangrenous (necrotic) or perforated appendix :
●Acute − 14,500±7300 cells/microL
●Gangrenous − 17,100±3900 cells/microL
●Perforated − 17,900±2100 cells/microL (see 'Perforated appendix' below)
Mild elevations in serum bilirubin (total bilirubin >1.0 mg/dL) have been noted to be a marker for appendiceal perforation with a sensitivity of 70 percent and a specificity of 86 percent . However, the test is not discriminatory and generally not helpful in the evaluation of patients suspected of acute appendicitis
Imaging examinations — Representative images of appendicitis are shown in this section. The choice of imaging examination for the diagnosis of acute appendicitis is discussed in detail separately. (See "Acute appendicitis in adults: Diagnostic evaluation", section on 'Imaging'.)
●Enlarged appendiceal diameter >6 mm with an occluded lumen
●Appendiceal wall thickening (>2 mm)
●Periappendiceal fat stranding
●Appendiceal wall enhancement
●Appendicolith (seen in approximately 25 percent of patients)
Plain radiograph findings — Plain radiographs are usually not helpful for establishing the diagnosis of appendicitis (image 5).
Magnetic resonance imaging — Magnetic resonance imaging (MRI) can assist with the evaluation of acute abdominal and pelvic pain during pregnancy (image 6) [51,52]. A normal appendix is visualized as a tubular structure less than or equal to 6 mm in diameter and filled with air and/or oral contrast material . An enlarged fluid-filled appendix (>7 mm in diameter) is considered an abnormal finding, while an appendix with a diameter of 6 to 7 mm is considered an inconclusive finding . (See "Approach to acute abdominal/pelvic pain in pregnant and postpartum patients" and "Acute appendicitis in pregnancy".)
DIAGNOSIS — Appendicitis is suspected in patients who present acutely with right lower quadrant pain/tenderness and leukocytosis but only confirmed on histologic finding of a surgical specimen. The diagnostic evaluation of appendicitis is discussed in detail in a separate topic. (See "Acute appendicitis in adults: Diagnostic evaluation", section on 'Imaging'.)
DIFFERENTIAL DIAGNOSIS — A variety of inflammatory and infectious conditions in the right lower quadrant can mimic the signs and symptoms of acute appendicitis. (See "Causes of abdominal pain in adults".)
Perforated appendix — During the first 24 hours after the onset of abdominal pain and associated symptoms, approximately 90 percent of patients develop inflammation and perhaps necrosis of the appendix, but not perforation. Once significant inflammation and necrosis occur, the appendix is at risk for perforation, which leads to localized abscess formation or diffuse peritonitis. The time course to perforation is variable. One study showed that 20 percent of patients developed perforation less than 24 hours after the onset of symptoms . Sixty-five percent of patients in whom the appendix perforated had symptoms for longer than 48 hours.
A perforated appendix must be considered in a patient whose temperature exceeds 103.0°F (39.4°C), whose WBC count is greater than 15,000 cells/microL, and whose imaging studies reveal a fluid collection in the right lower quadrant. (See 'Pathogenesis' above and 'Laboratory findings' above and 'Imaging examinations' above and "Acute appendicitis in adults: Diagnostic evaluation".)
Cecal diverticulitis — Cecal diverticulitis usually occurs in young adults and presents with signs and symptoms that can be virtually identical to those of acute appendicitis. Right-sided diverticulitis occurs in only 1.5 percent of patients in Western countries but is more common in Eastern populations (accounting for as many as 75 percent of cases of diverticulitis). Patients with right-sided diverticulitis tend to be younger than those with left-sided disease and often are misdiagnosed with acute appendicitis. Computed tomographic (CT) scanning of the abdomen with intravenous and oral contrast is the diagnostic test of choice in patients suspected of having acute diverticulitis. (See "Clinical manifestations and diagnosis of acute colonic diverticulitis in adults" and "Acute colonic diverticulitis: Medical management", section on 'Right-sided (cecal) diverticulitis'.)
Meckel's diverticulitis — Meckel's diverticulitis presents in a fashion similar to acute appendicitis. A Meckel's diverticulum is a congenital remnant of the omphalomesenteric duct and is located on the small intestine two feet from the ileocecal valve [54,55]. Meckel's diverticulitis should be included in the differential diagnosis as the small bowel may migrate into the right lower quadrant and mimic the symptoms of appendicitis. If an inflamed appendix is not found on abdominal exploration for acute appendicitis, the surgeon should search for an inflamed Meckel's diverticulum. (See "Meckel's diverticulum", section on 'Clinical presentations'.)
Acute ileitis — Acute ileitis, due most commonly to an acute self-limited bacterial infection (Yersinia, Campylobacter, Salmonella, and others), should be considered when acute diarrhea is a prominent symptom. Other clinical manifestations of acute yersiniosis include abdominal pain, fever, nausea, and/or vomiting. Yersiniosis cannot be readily distinguished clinically from other causes of acute diarrhea that present with these symptoms. However, localization of abdominal pain to the right lower quadrant along with acute diarrhea may be a diagnostic clue for yersiniosis. (See "Yersiniosis: Infection due to Yersinia enterocolitica and Yersinia pseudotuberculosis", section on 'Acute yersiniosis'.)
Acute yersiniosis presenting with right lower abdominal pain, fever, vomiting, leukocytosis, and understated diarrhea may be confused with acute appendicitis. At surgery, findings include visible inflammation around the appendix and terminal ileum and inflammation of the mesenteric lymph nodes; the appendix itself is generally normal. Yersinia can be cultured from the appendix and involved lymph nodes. (See "Yersiniosis: Infection due to Yersinia enterocolitica and Yersinia pseudotuberculosis", section on 'Pseudoappendicitis'.)
Crohn's disease — Crohn's disease can present with symptoms similar to appendicitis, particularly when localized to the distal ileum. Fatigue, prolonged diarrhea with abdominal pain, weight loss, and fever, with or without gross bleeding, are the hallmarks of Crohn's disease. An acute exacerbation of Crohn's disease can mimic acute appendicitis and may be indistinguishable by clinical evaluation and imaging.
Crohn's disease should be suspected in patients who have persistent pain after surgery, especially if the appendix is histologically normal. (See "Clinical manifestations, diagnosis, and prognosis of Crohn disease in adults".)
Gynecologic and obstetrical conditions — The following gynecologic diseases may present with symptoms and/or clinical findings that are included in the differential of acute appendicitis:
Tubo-ovarian abscess — A tubo-ovarian abscess (TOA) is an inflammatory mass involving the fallopian tube, ovary, and, occasionally, other adjacent pelvic organs (eg, bowel, bladder). These abscesses are found most commonly in reproductive-age women and typically result from upper genital tract infection. Tubo-ovarian abscess is usually a complication of pelvic inflammatory disease. The classic presentation includes acute lower abdominal pain, fever, chills, and vaginal discharge. However, fever is not present in all patients, some patients report only low-grade nocturnal fevers or chills, and not all women present in an acute fashion. Clinical history and CT imaging can help differentiate TOA from acute appendicitis (picture 1). (See "Epidemiology, clinical manifestations, and diagnosis of tubo-ovarian abscess", section on 'Clinical presentation'.)
Pelvic inflammatory disease — Lower abdominal pain is the cardinal presenting symptom in women with pelvic inflammatory disease (PID), although the character of the pain may be quite subtle. The recent onset of pain that worsens during coitus or with jarring movement may be the only presenting symptom of PID; the onset of pain during or shortly after menses is particularly suggestive. On physical examination, only approximately one-half of patients with PID have fever. Abdominal examination reveals diffuse tenderness greatest in the lower quadrants, which may or may not be symmetrical. Rebound tenderness and decreased bowel sounds are common. On pelvic examination, the finding of a purulent endocervical discharge and/or acute cervical motion and adnexal tenderness with bimanual examination is strongly suggestive of PID. Clinical history and CT imaging can help differentiate PID from acute appendicitis. (See "Pelvic inflammatory disease: Clinical manifestations and diagnosis".)
Ruptured ovarian cyst — Rupture of an ovarian cyst is a common occurrence in women of reproductive age and may be associated with the sudden onset of unilateral lower abdominal pain. The right lower quadrant is most commonly affected, possibly because the rectosigmoid colon protects the left ovary from the effects of abdominal trauma. The pain often begins during strenuous physical activity, such as exercise or sexual intercourse, and may be accompanied by light vaginal bleeding due to a drop in secretion of ovarian hormones and subsequent endometrial sloughing. Blood from the rupture site may seep into the ovary, which can cause pain from stretching of the ovarian cortex, or it may flow into the abdomen, which has an irritant effect on the peritoneum. Serous or mucinous fluid released upon cyst rupture is not very irritating; the patient may remain asymptomatic despite accumulation of a large volume of intraperitoneal fluid. On the other hand, spillage of sebaceous material upon rupture of a dermoid cyst causes a marked granulomatous reaction and chemical peritonitis, which is usually quite painful. Intra-abdominal hemorrhage may be associated with Cullen's sign (ie, periumbilical ecchymoses). Clinical history and CT imaging can help differentiate a ruptured ovarian cyst from acute appendicitis (image 7 and image 8). (See "Evaluation and management of ruptured ovarian cyst".)
Mittelschmerz — Mittelschmerz refers to midcycle pain in an ovulatory woman caused by normal follicular enlargement just prior to ovulation or to normal follicular bleeding at ovulation. The pain is typically mild and unilateral; it occurs midway between menstrual periods and lasts for a few hours to a couple of days. Fluid or blood is released from the ruptured egg follicle and can cause irritation of the lining of the abdominal wall. (See "Normal menstrual cycle".)
Ovarian and fallopian tube torsion — Ovarian torsion refers to the twisting of the ovary on its ligamentous supports, often resulting in impedance of its blood supply (picture 2 and picture 3). Isolated fallopian tube torsion is uncommon (picture 4). Expedient diagnosis is important to preserve ovarian function and prevent adverse sequelae. However, the diagnosis can be challenging because the symptoms are relatively nonspecific.
The most common symptom of ovarian torsion is sudden-onset lower abdominal pain, often associated with waves of nausea and vomiting. Fever, although an uncommon finding in ovarian torsion, may be a marker of necrosis, particularly in the setting of an increased white blood cell count. Clinical history and CT imaging can help differentiate the diagnosis from acute appendicitis. (See "Ovarian and fallopian tube torsion".)
Endometriosis — Endometriosis is defined as the presence of endometrial glands and stroma at extrauterine sites. These ectopic endometrial implants are usually located in the pelvis but can occur nearly anywhere in the body (picture 5).
Common symptoms of endometriosis include pelvic pain (which is usually chronic and often more severe during menses or at ovulation), dysmenorrhea, deep dyspareunia, cyclical bowel or bladder symptoms, abnormal menstrual bleeding, and infertility. There are often no abnormal findings on physical examination; when findings are present, the most common is tenderness upon palpation of the posterior fornix. Ultrasound is mostly useful for diagnosing ovarian endometriomas; it lacks adequate resolution for visualizing adhesions and superficial peritoneal/ovarian implants, which are more common than endometriomas. (See "Endometriosis in adults: Pathogenesis, epidemiology, and clinical impact".)
Ovarian hyperstimulation syndrome — Ovarian hyperstimulation syndrome (OHSS) is an iatrogenic complication of ovulation induction therapy and may be accompanied by or mistaken for cyst rupture. Clinical findings include bloating, nausea, vomiting, diarrhea, lethargy, shortness of breath, and rapid weight gain.
Severe ovarian hyperstimulation syndrome is characterized by large ovarian cysts; ascites; and, in some patients, pleural and/or pericardial effusion, electrolyte imbalance (hyponatremia, hyperkalemia), hypovolemia, and hypovolemic shock. Marked hemoconcentration, increased blood viscosity, and thromboembolic phenomena, including disseminated intravascular coagulation, occur in the most severe cases. (See "Pathogenesis, clinical manifestations, and diagnosis of ovarian hyperstimulation syndrome".)
Ectopic pregnancy — Ectopic pregnancy has clinical symptoms and sonographic features similar to those of a ruptured ovarian cyst. In women with acute pelvic pain or abnormal vaginal bleeding, a positive pregnancy test strongly suggests the presence of an ectopic pregnancy if an intrauterine pregnancy cannot be visualized sonographically. If an intrauterine pregnancy is visualized, then pelvic pain and intraperitoneal fluid could be due to a ruptured ovarian cyst (eg, corpus luteum cyst, theca lutein cyst) or heterotopic pregnancy. (See "Ectopic pregnancy: Clinical manifestations and diagnosis", section on 'Heterotopic pregnancy'.)
Acute endometritis — Acute endometritis occurs after an obstetrical delivery or, rarely, after an invasive uterine procedure. The diagnosis is largely based upon the presence of fever, gradual onset of uterine tenderness, foul uterine discharge, and leukocytosis in an at-risk setting. (See "Postpartum endometritis" and "Endometritis unrelated to pregnancy".)
Renal colic — Pain is the most common symptom and varies from a mild and barely noticeable ache to discomfort that is so intense that it requires parenteral analgesics. The pain typically waxes and wanes in severity and develops in waves or paroxysms that are related to movement of the stone in the ureter and associated ureteral spasm. Paroxysms of severe pain usually last 20 to 60 minutes. Pain is thought to occur primarily from urinary obstruction with distention of the renal capsule. (See "Kidney stones in adults: Diagnosis and acute management of suspected nephrolithiasis" and "Kidney stones in children: Acute management".)
Testicular torsion — Testicular torsion is a urologic emergency that is more common in neonates and postpubertal boys, although it can occur at any age. Testicular torsion results from inadequate fixation of the testis to the tunica vaginalis. If fixation of the lower pole of the testis to the tunica vaginalis is insufficiently broad based or absent, the testis may torse (twist) on the spermatic cord, potentially producing ischemia from reduced arterial inflow and venous outflow obstruction. (See "Causes of scrotal pain in children and adolescents", section on 'Testicular torsion' and "Acute scrotal pain in adults".)
Epididymitis — Epididymitis occurs more frequently among late adolescents but also occurs in younger boys who deny sexual activity and is the most common cause of scrotal pain in adults in the outpatient setting. Several factors may predispose postpubertal boys to develop subacute epididymitis, including sexual activity, heavy physical exertion, and direct trauma (eg, bicycle or motorcycle riding). Bacterial epididymitis in prepubertal boys is associated with structural anomalies of the urinary tract. In acute infectious epididymitis, palpation reveals induration and swelling of the involved epididymis with exquisite tenderness. More advanced cases often present with testicular swelling and pain (epididymo-orchitis) with scrotal wall erythema and a reactive hydrocele. (See "Causes of scrotal pain in children and adolescents", section on 'Epididymitis' and "Acute scrotal pain in adults".)
Torsion of the appendix testis or appendix epididymis — The appendix testis is a small vestigial structure on the anterosuperior aspect of the testis (an embryologic remnant of the Müllerian duct system). The appendix epididymis is a vestigial remnant of the Wolffian duct that is located at the head of the epididymis. The pedunculated shape of these appendages predisposes them to torsion, which can produce scrotal pain that ranges from mild to severe. Most cases of torsion of the appendix testis occur between the ages of 7 and 14 years, and it rarely occurs in adults. (See "Causes of scrotal pain in children and adolescents", section on 'Torsion of the appendix testis or appendix epididymis' and "Acute scrotal pain in adults", section on 'Other etiologies'.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Appendicitis in adults".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Basics topics (see "Patient education: Appendicitis in adults (The Basics)").
SUMMARY AND RECOMMENDATIONS
●Epidemiology – Appendicitis is one of the most common causes of the acute abdomen and one of the most frequent indications for an emergency abdominal surgical procedure worldwide. (See 'Epidemiology' above.)
●Anatomy – The tip of the appendix can be found in a retrocecal or pelvic location, as well as medial, lateral, anterior, or posterior to the cecum. Anatomic variability can complicate the diagnosis as clinical presentation will reflect the anatomic position of the appendix. (See 'Anatomy' above.)
●Pathogenesis – Appendiceal obstruction plays a role in the pathogenesis of appendicitis, but it is not required for the development of appendicitis. (See 'Pathogenesis' above.)
●Clinical manifestations – The classic symptoms of appendicitis include right lower quadrant abdominal pain, anorexia, fever, nausea, and vomiting. The abdominal pain is initially periumbilical in nature with subsequent migration to the right lower quadrant as the inflammation progresses (see 'Clinical manifestations' above). Patients with appendicitis can also present with atypical or nonspecific symptoms, such as indigestion, flatulence, bowel irregularity, and generalized malaise; not all patients will have migratory abdominal pain.
●Diagnosis – Appendicitis is suspected in patients who present acutely with right lower quadrant pain/tenderness and leukocytosis but only confirmed on histologic finding of a surgical specimen. The diagnostic evaluation of appendicitis is discussed in detail in a separate topic. (See "Acute appendicitis in adults: Diagnostic evaluation", section on 'Imaging'.)
●Differential diagnosis – The differential diagnosis of right lower quadrant abdominal pain includes inflammatory disease processes (eg, Crohn's disease, ruptured cyst), infectious diseases (eg, acute ileitis, tubo-ovarian abscess), and obstetrical conditions (eg, ectopic pregnancy). (See 'Differential diagnosis' above.)
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