Appendectomy is one of the most commonly performed emergency operations. On occasion, the surgeon is faced with unexpected findings mimicking the presentation of appendicitis, which require specific treatments. Tumors are found in approximately 0.1 % of appendectomies. Carcinoid tumors are the most frequent type, followed by adenocarcinoma of the appendix and by benign tumors. It is important to point out that all tumors of the appendix may be accompanied by synchronous disease, making a full exploration of the abdomen imperative [1].

Carcinoid tumors are neuroendocrine neoplasms derived from the Kulchitsky cells, present in the epithelium of the GI tract. These cells participate in the regulation of enteric motility, secretion, and permeability through the production of serotonin and other mediators. The appendix is the most common site of carcinoid tumors in the GI tract, followed by the small intestine and rectum. The incidence of appendiceal carcinoid tumors in appendectomy specimens is as high as 1 in 200. Currently, most appendiceal carcinoid tumors are found during surgery for acute appendicitis. Carcinoid syndrome is a late presentation of disease, associated with hepatic and pulmonary involvement. The degree of invasiveness correlates well with the size of the tumor. Tumors smaller than two centimeters, with no involvement of the appendiceal base, are best treated by appendectomy with complete mesoappendiceal excision. Larger tumors or those involving the base or the mesoappendix require a right hemicolectomy. Carcinoid tumors have high association with adenocarcinoma of the GI tract [2–6].

Primary adenocarcinomas of the appendix are rare neoplasms constituting only 0.5 % of all GI malignancies. They are often unrecognized at the time of surgery and identified during the pathologic analysis of the specimen. The ideal treatment consists of right hemicolectomy. Appendectomy alone may result in increased mortality and reoperation for a completion hemicolectomy is appropriate, especially in cases that are poorly differentiated, invade the mucosa, or have nodal involvement [7–9].

Appendiceal mucoceles are associated with benign and malignant processes (mucinous cystoadenocarcinoma). Proper management is imperative, due to the risk of development of pseudomyxoma peritonei. In the past, right hemicolectomy was advocated for all appendiceal mucoceles, but currently this operation is reserved for tumors confirmed by frozen section that are involving the base of the appendix and local nodes. In all cases encountered laparoscopically, conversion to an open procedure is recommended to reduce the risk of tumor seeding and subsequent development of pseudomyxoma peritonei [10].

Cystic duplication of the cecum is a congenital malformation usually identified during childhood, typically presenting as an abdominal mass associated with intussusception, obstruction, or bleeding. These masses are found in the mesenteric side of the bowel, with which they intimately share their blood supply, making segmental en bloc resection necessary [11, 12].

Torsion of appendices epiploica (epiploic appendagitis) may mimic acute appendicitis. Resection of the infarcted appendix epiploica is indicated. High-resolution CT scanners help make this diagnosis in a vast majority of patients. Performing a simultaneous appendectomy is controversial [13].

The main blood supply of the appendix comes from the appendicular artery, which is the end branch of the superior mesenteric artery. The appendicular artery represents the distal extension of the ileocolic artery. This artery courses within the mesoappendix giving multiple perpendicular branches to the appendix. The appendix may receive additional blood supply from small branches derived from the cecal artery [14].

During pregnancy, the uterus displaces the cecum laterally and superiorly. During early pregnancy, patients with appendicitis may complain of right lower quadrant pain, but later on appendicitis may present as right upper quadrant or right flank pain [15].

The appendiceal tip may be located in any position in relation to the cecum; however, the base of the appendix can be reliably found at the confluence of the taenia coli, which is the preferred landmark for its localization. The location of the appendix has not been shown to increase the risk for appendicitis. However, it may change the clinical presentation of acute appendicitis and in some cases result in delayed diagnosis and increased morbidity (Fig. 14.1).

The psoas and obturator signs are mutually exclusive. Both are caused by irritation of the adjacent muscle due to contact with the inflamed appendix. This manifests as pain during stretching. The psoas sign is typical of retrocecal appendicitis, whereas the obturator sign is present when the appendix is located in the anterior pelvis.

As a general rule, perforation of hollow abdominal organs leads to pneumoperitoneum; however, appendiceal perforation is an exception to this rule. Appendices perforate distal to the point of obstruction, which impedes the passage of gas from the cecum to the peritoneal cavity. Furthermore, the capacity of the normal appendix is only 0.2–0.5 ml, a volume too small to produce pneumoperitoneum. Rarely, pneumoperitoneum may be present if the perforation happens at the base of the appendix, allowing direct leakage from the cecum (Fig. 14.2).