Findings at Appendectomy

Fig. 12.1

Peritoneal implant

Appendiceal adenocarcinoma is a rare cancer with an estimated incidence of 2.6 per one million per year. These tumors are thought to arise from adenomas and are most commonly mucinous or intestinal type though some harbor a variety of elements. Mechanical rupture of these tumors does not necessarily lead to peritoneal metastases, and many will have established metastases prior to symptoms of rupture [21]. The typical pattern of metastasis is to the parietal and visceral peritoneum rather than along lymphatics, particularly in low-grade primary tumors [22]. However, the intestinal type is thought to progress along the adenoma to carcinoma sequence and is comparable to colon cancer, yet solid organ metastases are not common as initial site of metastatic disease [21]. Signet ring cell appendiceal adenocarcinoma is a particularly rare subset of mucinous adenocarcinoma. It is rarely confined at diagnosis and may infiltrate below mucosal surfaces. Unfortunately, the majority of appendiceal cancers may have spread at the time of diagnosis, though estimates vary greatly by series [17, 23–25]. Mucin may be found throughout the abdomen and easily visualized in more advanced cases (Fig. 12.2); in other situations, there may be small mucin deposits which are subtle and are only seen after meticulous inspection. For the low-grade lesions, right hemicolectomy typically does not play a role in staging as lymph node positivity rate may be as low as 5%; however, in higher-grade primary tumors, lymph nodes have been shown to be predictive of recurrence [22, 23]. As a result, given the uncertain nature of the disease at time of index surgery and the more extensive treatment that will likely be required particularly for many appendiceal cancers, right colectomy is best reserved for an elective operation after appropriate pathology review and patient counseling.

../images/465809_1_En_12_Chapter/465809_1_En_12_Fig2_HTML.jpg — Fig. 12.2

Ruptured low-grade appendiceal mucinous neoplasm (LAMN) with peritoneal mucin

A low-grade appendiceal mucinous neoplasm (LAMN) is a well-differentiated tumor which grows slowly and tends to have a fibrotic, sometimes calcified appendiceal wall and is commonly described as a mucocele by radiologist; however, it is important to note that mucocele is not a pathologic diagnosis (Fig. 12.3). LAMNs may extrude mucin on the nearby serosal surfaces. When a mucinous lesion is suspected, it is important to avoid directly grasping it as it may rupture and increase the risk of subsequent recurrence within the peritoneal cavity if the mucin harbors neoplastic epithelium.

../images/465809_1_En_12_Chapter/465809_1_En_12_Fig3_HTML.jpg — Fig. 12.3

Intact low-grade appendiceal mucinous neoplasm (LAMN) opened for pathologic examination

When LAMNs are confined to the mucosa of the appendix, as proven by complete sectioning of the appendix and careful examination of the peritoneum by imaging and during surgery, appendectomy with negative margins is curative, and no specific follow-up is necessary. However, when there is intramural or extra-appendiceal mucin present, further follow-up and, possibly, treatment are necessary. When the mucin is acellular and seen within the wall of the appendix or confined to the serosa of the appendix or periappendicular tissue, the entity is referred to as LAMN of uncertain malignant potential (UMP) and is associated with a 5% risk of subsequent recurrence. However, cellular mucin carries a higher risk of recurrence, and consideration of subsequent treatment at a specialty center should be given [26, 27]. Simple appendectomy is typically sufficient for diagnostic and therapeutic purpose for LAMN and LAMN/UMP. However, partial cecectomy or ileocecectomy is occasionally necessary to clear the margin for neoplastic tissue. Formal right colectomy is unnecessary as the initial treatment as most mucinous neoplasms seen on preoperative imaging do not harbor invasive cancer and are not at risk for lymph node metastases. Baseline serum tumor markers including CEA, CA-125, and CA19-9 may be useful for monitoring LAMN/UMP and can be drawn pre- and postoperatively if a LAMN is suspected. There are no formal guidelines for surveillance of LAMN/UMP; however, imaging and serum markers more frequently than once a year appear unnecessary given the low risk of recurrence and indolent course for those who recur.

While definitive management of appendiceal carcinoma may ultimately include right hemicolectomy and/or intraperitoneal chemotherapy (IPC), the most appropriate course of action upon recognizing this unexpected finding is to remove the appendix, biopsy suspected metastatic disease, and close without additional organ resection. Neither the surgeon nor the patient may be prepared for a more significant undertaking. If the next step in a patient’s treatment involves systemic chemotherapy or cytoreductive surgery, a more extensive operation may delay initiation of that treatment. A right hemicolectomy alone does not provide any survival advantage over appendectomy alone in stage IV disease nor does it particularly help with staging in many cases [22, 28]. Furthermore, studies have suggested improved efficacy of IPC with a lower prior surgical score which is calculated based on extent of previous surgery [29]. Therefore, while it is certainly appropriate to remove the appendix and perform any other necessary biopsies, a more extensive right hemicolectomy is not warranted in most cases.

Carcinoid tumors , also known as neuroendocrine tumors (NET) , of the appendix have an incidence of 0.15 per 100,000 per year (Fig. 12.4) [30, 31]. Approximately 75% occur at the tip of the appendix, 15% in the mid-appendix, and 10% at the base. Size is one of the critical features of staging for carcinoid tumor; fortunately the majority are less than 1 cm at the time of removal, and only 6% are more than 2 cm [32]. With increasing size, penetration of the appendiceal wall and infiltration of the mesoappendix become more likely. However, size is the most significant predictor of prognosis, rather than depth of invasion and lymphatic or perineural invasion. In a carcinoid <1 cm in size, lymph node metastases are rare. In tumors over 2 cm, the risk is approximately 20–30% [33]. Distant metastasis for appendiceal carcinoid is rare at diagnosis. In general, definitive management of non-metastatic appendiceal carcinoids >2 cm, those at the base or with positive margins, or those with adverse histologic features or radiologic evidence or locoregional nodal involvement is right hemicolectomy, though it is important to note that there are no data to address the benefit of this intervention. Nevertheless, pathologic diagnosis must be made; therefore, appendectomy alone is the first treatment. Once the diagnosis of appendiceal NET is made, workup including cross-sectional imaging should be performed. Octreotide scans and serum markers are unnecessary in the absence of symptoms consistent with metastatic disease, such as carcinoid syndrome. Staging right colectomy is recommended for tumors greater than 2 cm, and no specific follow-up is necessary for tumors less than 1.5 cm. The management of tumors between 1.5 and 2 cm after appendectomy remains controversial. The two largest series of appendiceal NET report no cases of lymph node metastases in patients with <2 cm tumors; however, there are only seven patients reported in case series with lymph node metastases and tumors <2 cm. [34–36] Though small bowel NET is associated with synchronous additional small bowel lesions, this has not been described in appendiceal NET.