**2. Conditions that mimic appendicitis**

## **2.1 Gastrointestinal diseases**

### *2.1.1 Inflammatory bowel disease (IBD)*

Terminal ileitis caused by Crohn's disease and Backwash ileitis associated with Ulcerative colitis both can present with right lower abdominal pain mimicking acute appendicitis. Typical age group is from 15 to 30 years and clinical presentation usually include symptoms of diarrhoea and bloody stool. IBD cannot be diagnosed via a blood test, however routine blood tests checking for pro-inflammatory markers such as raised white cell count (WCC), C-reactive protein (CRP) and Erythrocyte Sedimentation Rate (ESR) may aid in supporting the diagnosis and monitoring the disease activity later on.

Although colonoscopy remains the investigation of choice for confirming the diagnosis, the use of radiological imaging is warranted when colonoscopy is not accessible.

As per imaging choice, IBD is best evaluated with either CT or MRI enterography and classical findings include bowel wall thickening of more than 3 mm, mucosal hyperenhancement, fat stranding and engorged vasa recta known as "Comb" sign. Management of IBD includes both surgical and non-surgical treatment depending on the severity, the extent of the disease and the presence of complications.

### *2.1.2 Infectious enterocolitis*

This refers to bowel inflammation caused by bacteria, viruses or parasites. Patients commonly present with abdominal pain, tenesmus and diarrhoea. Stools are often purulent and mixed with mucous and blood. Commonly implicated organisms include *Campylobacter jujni, Salmonella, Shigella, Escherichia coli, Yersinia enterocolittica, cryptosporidium, Norovirus, Rotavirus and Entamoeba histolytica*. Some infections such as tuberculosis and cryptosporidiosis are very important to consider in immunocompromised patients such as those with HIV infection. Routine blood tests looking for raised inflammatory markers along with stool microscopy and culture may help to support the diagnosis and monitor response to antimicrobial therapy. CT features include bowel long-segment circumferential wall thickening with homogenous enhancement and typically with no adjacent fat stranding. Treatment for infectious enterocolitis depends on the causative organisms.

#### *2.1.3 Radiation enteritis*

This is an inflammation of the bowel that occurs after radiotherapy. Symptoms include diarrhoea, nausea, vomiting and abdominal pain. Most cases of radiation enteritis resolve spontaneously a few weeks after treatment ends however for some it can extend for months and years after the termination of treatment. CT and MRI findings include bowel wall thickening with luminal narrowing, small bowel obstruction and sometimes the presence of a fistula between the bowel and the bladder or the vagina.

#### *2.1.4 Neutropenic colitis*

Also known as Typhlitis is an acute life-threatening condition that affects immunocompromised patients such as patients with HIV disease or those who are on

immunosuppressive therapy. The aetiology involves mucosal damage secondary to ischemia and secondary bacterial infection with a predilection for the caecum and ascending colon. Patients may present with abdominal pain, diarrhoea, vomiting and fever. Typhlitis is commonly associated with Neutropenia. Early diagnosis and management are crucial to prevent complications such as perforation and sepsis. Classical CT findings include dilated caecum with circumferential wall thickening, peri-colic fluid collection and pneumatosis. Management includes bowel rest and antibiotic therapy.

#### *2.1.5 Diverticular disease and diverticulitis*

This is commonly seen in patients over the age of 40, where small bulging pouches also known as diverticula, form at the weakest portion of the bowel. Diverticulitis is the term used when there is associated inflammation of the diverticula. Symptoms include abdominal pain, vomiting and fever. Risk factors include aging, smoking, low fibre diet, obesity and sedentary life. Laboratory blood tests checking for raised inflammatory markers are useful in making the diagnosis of diverticulitis. Classical features of diverticulitis on CT include bowel wall thickening with infiltration of adjacent mesenteric fat. Managing patients with uncomplicated diverticular disease involves the introduction of low-fibre diet and antibiotics. Surgery is reserved for patients with complications such as perforation, diverticular abscess or fistula formation.

#### *2.1.6 Meckel's diverticulitis*

This is caused by congenital anomaly characterised by the presence of the vitelline duct which normally connects the yolk sac to the midgut during the fetal development. It occurs in 2–3% of the general population [10]. Inflammation of Meckel's diverticulum usually caused by enterolith and symptoms include abdominal pain, rectal bleeding and vomiting.

CT findings include the identification of a blind-end tubular structure protruding from the antimesenteric side of the distal ileum, wall thickening, hyperenhancement and fat stranding. Management is surgical resection of the diverticulum.

#### **2.2 Vascular diseases**

#### *2.2.1 Abdominal aortic aneurysm (AAA)*

This is a life-threatening emergency where there is an abnormal dilatation of the abdominal aorta due to vascular wall weakness. This abnormal dilation (1.5 times its normal diameter or greater than 3 cm) of the aorta is commonly seen involving the infrarenal part of the abdominal aorta. AAA is a fatal condition where mortality is about 80% with leaking aneurysm and only half of the patients survive 30 days post emergency repair [11]. AAA is more common in men and the risk factors implicated in the aetiology are the same factors contributing to atherosclerosis such advancing age, diabetes, hypertension, hypercholesterolemia and smoking history. Clinical presentation of AAA includes a variety of symptoms such as abdominal pain, back pain, groin pain, and a pulsating abdominal mass. Ultrasound aorta remains the gold standard for screening patients for AAA in the emergency setting and the UK Royal College of Emergency Medicine (RCEM) recommends that all emergency physicians are to perform ultrasound aorta in all patients who are over the age of 50 presenting with abdominal pain. Disadvantages

#### *Mimickers of Acute Appendicitis DOI: http://dx.doi.org/10.5772/intechopen.96351*

for ultrasound include difficult studies due to the patient's body habitus, or the presence of overlying bowel obscuring the visualisation of the aorta. Another downside to the use of ultrasound is its operator dependability and the inability to exclude any aneurysmal leak. CT aortogram is a highly acute study that can confirm the presence and the size of an aneurysm which aids in planning surgery. Management of AAA involves either open repair or endovascular aneurysm repair (EVAR) depending on the fitness of patients for surgery and the morphology of the aneurysm.

#### *2.2.2 Mesenteric ischemia*

This refers to small bowel injury secondary to insufficient blood supply which can be acute or chronic. Patients with mesenteric ischemia can present with diarrhoea, rectal bleeding, abdominal pain, especially after eating, and unintentional weight loss due to the fear of eating and vomiting. Risk factors include atrial fibrillation, heart failure and chronic kidney disease. Early CT findings include mesenteric oedema, bowel dilation and wall thickening, mesenteric stranding and the presence of an adjacent solid organ infarction. Treatment depends on the cause of ischemia and as such can be medical or surgical however if it is a late presentation the only treatment is surgical since there is a risk of necrotic bowel.

### **2.3 Urological diseases**

## *2.3.1 Urolithiasis*

Urolithiasis or kidney stone disease can present with a right lower abdominal pain mimicking acute appendicitis. Careful consideration for the presence of obstructive uropathy is very important to prevent kidney injury. CT Urinary system is the gold standard imaging when assessing patients with suspected urolithiasis. CT findings include the identification of a high attenuation calculus within the urinary system with or without hydroureter and hydronephrosis, ureteral wall thickening and adjacent fat stranding.

Ultrasound can be used in patients with ureteric colic to identify any features of hydronephrosis. The only disadvantage of ultrasound imaging is its operator dependability. Conservative treatment is indicated for patients with stones measuring less than 4 mm.
