The coexistence of low-grade mucinous neoplasms of the appendix and appendiceal diverticula: a possible role in the pathogenesis of pseudomyxoma peritonei

Epithelial neoplasms of the appendix

CONTEXT

The appendix gives rise to an array of epithelial neoplasms showing glandular or neuroendocrine differentiation, and some tumors with elements of both cell types. Although some appendiceal neoplasms resemble their counterparts in the small and large intestines (conventional adenocarcinoma and carcinoid tumor), the appendix also gives rise to relatively unique entities including mucinous neoplasms and goblet cell carcinoid tumors, which present a challenge in pathologic classification and clinical management.

OBJECTIVE

To review clinical and diagnostic issues for 3 pathologic types of epithelial neoplasms of the appendix: (1) adenocarcinoma, with specific focus on mucinous neoplasm; (2) goblet cell carcinoid tumor and associated adenocarcinoma; and (3) typical carcinoid tumor.

DATA SOURCES

Case-derived material and literature review.

CONCLUSIONS

The most important issue in pathologic assessment of epithelial tumors of the appendix is to understand the clinical implications inherent in the diagnosis.

Mucinous Neoplasms of the Vermiform Appendix

Most epithelial neoplasms of the vermiform appendix are of mucinous type and can be stratified into 3 main diagnostic categories: (1) adenoma, (2) mucinous neoplasms of uncertain malignant potential or low-grade mucinous neoplasm, and (3) adenocarcinoma. Clinically, appendiceal mucinous adenomas and adenocarcinomas may present as right lower abdominal pain mimicking acute appendicitis, a mass, or pseudomyxoma peritonei. Nomenclature currently in use to describe and diagnose mucinous tumors of the appendix, particularly those of low morphologic grade, varies among surgical pathologists and centers, resulting in different histologic and clinical features being attributed to these entities in the literature. It may be of help, as already attempted by some investigators, to simply apply algorithmic parameters for such lesions (grade of the primary lesion, extensiveness and composite of extra-appendiceal involvement, and so forth), instead of adopting rigid classification categories. This approach allows for more objective data to be collected in hopes that it will provide a more nuanced understanding of the clinical behavior of the spectrum of mucinous appendiceal tumors. Remaining focused on histopathologic parameters of the primary and secondary sites of involvement may help in avoiding circular reasoning.

Appendiceal mucinous neoplasms: clinicopathologic study of 116 cases with analysis of factors predicting recurrence

The classification and nomenclature of appendiceal mucinous neoplasms are controversial. To determine the outcome for patients with appendiceal mucinous neoplasms and further evaluate whether they can be stratified into groups that provide prognostic information, the clinicopathologic features of 116 patients (66 with clinical follow-up) with appendiceal mucinous neoplasms were studied. From a wide variety of histopathologic features assessed, the important predictors that emerged on univariate statistical analysis were presence of extra-appendiceal neoplastic epithelium (P=0.01), high-grade cytology (P<0.0001), architectural complexity (P<0.001), and invasion (P<0.001). Stratification using a combination of these predictors resulted in a 4-tiered classification scheme. All 16 patients with mucinous neoplasms confined to the appendix and lacking high-grade cytology, architectural complexity, and invasion were alive with no recurrences at median 59 months follow-up (=mucinous adenoma). One of 14 patients with low-grade cytology and acellular peritoneal mucin deposits developed recurrent tumor within the peritoneum at 45 months with no patient deaths to date (median, 48-mo follow-up) (=low-grade mucinous neoplasm with low risk of recurrence). None of the 2 patients with acellular peritoneal mucinous deposits outside of the right lower quadrant developed recurrence at 163 and 206 months. Twenty-seven patients with low-grade mucinous neoplasms with extra-appendiceal neoplastic epithelium had 1-year, 3-year, 5-year, and 10-year overall survival rates of 96%, 91%, 79%, and 46%, respectively, at median 53 months follow-up (=low-grade mucinous neoplasm with high risk of recurrence). Three of the 4 patients with extra-appendiceal epithelium limited to the right lower quadrant developed full-blown peritoneal disease at 6, 41, and 99 months follow-up and 1 patient eventually died of disease. Nine patients with appendiceal neoplasms with invasion or high-grade cytology and follow-up showed 1-year, 3-year, and 5-year overall survival rates of 86%, 57%, and 28% (=mucinous adenocarcinoma). At 10 years, all patients with mucinous adenocarcinoma were either dead or lost to follow-up. Appendiceal mucinous neoplasms can be stratified into 4 distinct risk groups on the basis of a careful histopathologic assessment of cytoarchitectural features and extent of disease at presentation.

Diverticulosis and diverticulitis of the appendix

Diverticulosis of the appendix is a relatively rare pathological finding. The majority are acquired pseudodiverticula. True congenital diverticula are very rare. Appendiceal diverticulosis is usually an incidental finding and clinically asymptomatic. When symptomatic, it is usually complicated by acute or chronic diverticulitis with or without acute appendicitis. It presents with atypical abdominal signs and symptoms, mostly in adult males. Appendiceal diverticulitis is a distinct entity with several clinical and pathological differences from acute appendicitis. It has a more rapid progression to perforation and a higher rate of mortality. Therefore, appendiceal diverticulitis should be considered in the clinical differential diagnosis, especially in adult males with chronic abdominal pain. Appendiceal diverticulosis demonstrates a significant association with obstructing or incidental appendiceal neoplasms. It may play an important role in the development of pseudomyxoma peritonei, which is associated with appendiceal mucinous tumors. Therefore, meticulous gross examination and thorough histological examination of the entire appendicectomy specimen are essential. When discovered either by preoperative radiological investigations or during an exploratory operation, prophylactic appendicectomy is advocated to prevent the risk of complications and to rule out the possibility of a coexisting neoplasm.

Diverticular disease of the vermiform appendix: a diagnostic clue to underlying appendiceal neoplasm

Acquired diverticula of the vermiform appendix are rare and arise as a result of different pathogenetic mechanisms. One of the etiologies includes proximally located, often unsuspected small neoplasms. Although the association of appendiceal diverticulosis and neoplasia is known, it remains underemphasized in the teaching and practice of surgical pathology. To investigate the frequency of appendiceal neoplasms with acquired diverticulosis, we conducted a retrospective analysis of all appendectomy specimens received in our institution for a 55-month period (January 2002-July 2006). A total of 1361 appendectomy specimens were identified. Diverticulosis was diagnosed in 23 (1.7%) of all cases. Eleven (48%) appendectomy specimens with diverticulosis also harbored an appendiceal neoplasm. The association of appendiceal neoplasms with diverticulosis was statistically significant (P < .0001, 2-sided Fisher exact test). Neoplastic processes included 5 well-differentiated neuroendocrine tumors (carcinoids), 3 mucinous adenomas, 1 tubular adenoma, and 2 adenocarcinomas. In one case, routine representative sections sampled only a small focus of carcinoma, which originally went undiagnosed. We stress the need for meticulous gross assessment with histologic examination of the entire appendectomy specimen in cases of appendiceal diverticulosis. Thorough examination is required to rule out an underlying neoplasm as a cause of diverticulosis. As acquired diverticula represent a rare finding, examination of the entire appendix in this setting does not create a significant impact on the workload within the pathologic laboratory.

Appendiceal diverticulitis: diagnosis and differentiation from usual acute appendicitis using computed tomography

OBJECTIVE

To describe the computed tomographic findings of appendiceal diverticulitis.

METHODS

Computed tomography (n = 20) and clinical findings in 23 patients with appendiceal diverticulitis were retrospectively reviewed and compared with those in 23 patients with usual acute appendicitis.

RESULTS

Computed tomography visualized the inflamed diverticula (up to 4 per patient) mostly as small (median, 7.5 mm) round cystic outpouchings at the distal appendix with contrast enhancement at the cyst wall in 16 (80%) patients with appendiceal diverticulitis. In 50% of appendiceal diverticulitis patients, computed tomographic diagnosis of accompanying appendicitis was false positive. Appendicolith was rarely observed in the appendiceal diverticulitis group (5% vs 48%, P = 0.002). No significant difference was observed in the clinical findings except for the patient age (median, 45 vs 31 years; P = 0.001).

CONCLUSIONS

Most appendiceal diverticulitis can be differentiated from usual acute appendicitis at computed tomography by visualization of the inflamed diverticulum.

Appendiceal neoplasms and pseudomyxoma peritonei: a population based study

BACKGROUND

Pseudomyxoma peritonei (PMP) is a rare disease with an estimated incidence of 1 per million per year, and is thought to originate usually from an appendiceal mucinous epithelial neoplasm. However it is not known exactly how often these neoplasms lead to PMP. The aim of this study is to investigate the incidence of both lesions and their relation.

METHODS

The nationwide pathology database of the Netherlands (PALGA) was searched for the incidence of all appendectomies, the incidence of primary epithelial appendiceal lesions and the incidence and pathology history of patients with PMP. All regarded the 10-year period of 1995-2005.

RESULTS

In the 10-year period 167,744 appendectomies were performed in the Netherlands. An appendiceal lesion was found in 1482 appendiceal specimens (0.9%). Nine percent of these patients developed PMP. Coincidentally, an additional epithelial colonic neoplasm was found in 13% of patients with an appendiceal epithelial lesion. A mucinous epithelial neoplasm was identified in 0.3% (73% benign, 27% malignant) of appendiceal specimens and 20% of these patients developed PMP. For mucocele and non-mucinous neoplasm the association with PMP was only 2% and 3%, respectively. From the nationwide database 267 patients (62 men and 205 women) with PMP were identified, which demonstrates an incidence of PMP in the Netherlands approaching 2 per million per year. The primary site was identified in 68% and dominated by the appendix (82%).

CONCLUSIONS

Primary epithelial lesions of the appendix are rare. One third of these lesions are mucinous epithelial neoplasms and especially these tumours may progress into PMP. The incidence of PMP seems to be higher than thought before. Furthermore there is a considerable risk of an additional colonic epithelial neoplasm in patients with an epithelial neoplasm at appendectomy.

Laparoscopic resection of mucinous cystadenoma of appendix: a careful decision

Appendiceal mucoceles are mainly due to cystadenoma or cystadenocarcinoma. Definite diagnosis is difficult preoperatively and is usually peroperatively. Surgical excision, either by laparoscopy or by laparotomy, is the mainstay of treatment. Rupture of the lesion causes pseudomyxoma peritonei. We present a case to highlight this point and especially deplore the use of laparoscopy if the tumor clearly extends beyond the appendix.

Pseudomyxoma peritonei

Pseudomyxoma peritonei (PMP) is a rare condition, which is known for its high mortality when not treated properly. The first step to improve prognosis of these patients is to recognize this clinical syndrome preferably in an early stage. Knowledge of pathogenesis and common diagnostic tools is essential in this regard. Treatment strategy for PMP should pursue complete cytoreduction and prevention of recurrence or progression. Combined modality treatment, consisting of cytoreductive surgery with hyperthermic intraperitoneal chemotherapy, seems very efficient in this regard. This approach is currently carried out in many centers throughout the world with promising results and seems to win ground as the standard treatment approach.

Pseudomyxoma peritonei of appendiceal origin: a clinicopathologic analysis of 101 patients uniformly treated at a single institution, with literature review

Pseudomyxoma peritonei is a clinical term for gelatinous ascites, usually secondary to an appendiceal tumor. The pathologic classification of pseudomyxoma peritonei and its associated appendiceal tumors has been plagued with controversy and confusing terminology. In an effort to clarify this, we reviewed the pathology of 101 patients, all treated at our institution from 1993 to 2005, with pseudomyxoma peritonei of appendiceal origin. All patients were uniformly treated with our standardized protocol. This is the largest pathologic series solely devoted to appendiceal neoplasia with gelatinous ascites. The cases were assigned, according to previously published criteria, to the categories of disseminated peritoneal adenomucinosis (DPAM), peritoneal mucinous carcinomatosis (PMCA), or PMCA with intermediate (well differentiated) features (PMCA-I), with the exception that any case with a signet-ring cell component was considered as PMCA and not PMCA-I. By histologic category, 58 patients had DPAM, 23 were PMCA, and 20 were PMCA-I.One-year, 3-year, and 5-year survival outcomes were not significantly different between DPAM and PMCA-I. DPAM and PMCA-I also exhibited a roughly equal incidence of parenchymal (beyond the serosa) organ invasion. Survival outcomes were significantly worse for PMCA, compared with PMCA-I and DPAM. After reviewing our data and the literature, mucinous carcinoma peritonei-low grade was applied to the low-grade histology of pseudomyxoma peritonei, including those cases referred to by some as DPAM in the same category as PMCA-I. Cases that are moderately differentiated to poorly differentiated are classified as mucinous carcinoma peritonei-high grade.

Appendiceal mucinous tumors and pseudomyxoma peritonei: histologic features, diagnostic problems, and proposed classification

Pseudomyxoma peritonei is an overused and underspecified condition that has garnered much attention in the historic literature. In recent years, this condition has been convincingly linked to appendiceal mucinous neoplasms, yet there has been insufficient attention to the histologic characteristics, classification, and differential diagnostic considerations of these neoplasms when encountered by the surgical pathologist. This review provides a coherent approach to the diagnosis and classification of appendiceal mucinous tumors and the peritoneal implants associated with the pseudomyxoma peritonei syndrome with emphasis on differential diagnostic considerations and recommendations for the final pathology report.

Primary epithelial neoplasms and other epithelial lesions of the appendix (excluding carcinoid tumors)

Epithelial tumors of the appendix range from low-grade mucosal-based tumors which, when confined to the appendix, have an excellent prognosis but, once outside the appendix, have a fair prognosis and often a prolonged disease course, to high grade invasive carcinomas that are rapidly fatal. Low grade mucinous neoplasms may rupture and spread to the peritoneum as pseudomyxoma peritonei, and the nomenclature of these tumors has been the subject of considerable disagreement among pathologists; the designation "low grade appendiceal mucinous neoplasm" has recently been proposed for reasons discussed herein. Demonstrating rupture of these neoplasms may require particularly diligent gross and microscopic evaluation as the rupture site often heals over leaving only subtle evidence of its presence. Invasive adenocarcinomas are often mucinous and may also spread to the peritoneum. Against this backdrop, the clinical and pathologic features of low grade appendiceal mucinous neoplasms and mucinous adenocarcinomas, as well as other types such as typical colorectal type and signet-ring cell type, are reviewed. In addition, emerging entities, serrated polyps and serrated adenomas, whose significance is only beginning to be understood, are considered. Retention cysts, hyperplastic polyps, and diffuse mucosal hyperplasia, although not necessarily neoplastic, are reviewed here as they may enter into the differential diagnosis of appendiceal mucinous neoplasms.

Appendiceal mucinous neoplasms: a clinicopathologic analysis of 107 cases

The classification of appendiceal mucinous tumors is controversial and terminology used for them inconsistent, particularly when they lack overtly malignant features but are associated with extra-appendiceal spread. We reviewed 107 appendiceal mucinous neoplasms and classified them as low-grade appendiceal mucinous neoplasm (LAMN) (n = 88), mucinous adenocarcinomas (MACAs) (n = 16), or discordant (n = 3) based on architectural and cytologic features. LAMNs were characterized by a villous or flat proliferation of mucinous epithelium with low-grade atypia. Thirty-nine tumors were confined to the appendix, but 49 had extra-appendiceal tumor spread, including 39 with peritoneal tumor characterized by mucin pools harboring low-grade mucinous epithelium, usually dissecting in a hyalinized stroma. Eight of the 16 MACAs lacked destructive invasion of the appendiceal wall and eight showed an infiltrative pattern of invasion. Extra-appendiceal tumor spread was present in 12 MACAs (four peritoneum, seven peritoneum and ovaries; one ovaries only). In MACAs with an infiltrative pattern, peritoneal tumor consisted of glands and single cells in a desmoplastic stroma. The peritoneal tumor in the remaining cases consisted of mucin pools that contained mucinous epithelium with high-grade atypia and, in some cases, increased cellularity compared with that seen in peritoneal spread in cases of LAMN. Three cases were classified as discordant because the appendiceal tumors were LAMNs but the peritoneal tumors were high-grade. Follow-up was available for 49 LAMNs, 15 MACAs, and 2 discordant cases. None of the patients with LAMNs confined to the appendix experienced recurrence (median follow-up 6 years). LAMNs with extra-appendiceal spread were associated with 3-, 5-, and 10-year survival rates of 100%, 86%, and 45%, respectively. Patients with MACA had 3- and 5-year survival rates of 90% and 44%, respectively (p = 0.04). The bulk of peritoneal disease correlated with prognosis among patients with MACA (p = 0.04) and, to a lesser degree, among patients with LAMNs (p = 0.07). We conclude that: 1) appendiceal mucinous neoplasms can be classified as either low-grade mucinous neoplasms or mucinous adenocarcinoma based on architectural and cytologic features; 2) tumors that can be confidently placed in the low-grade group (which requires rigorous pathologic evaluation of the appendix) and are confined to the appendix are clinically benign in our experience to date; 3) low-grade tumors confined to the appendix are morphologically identical to those with extra-appendiceal spread (except for the usual identification of breach of the wall in the latter cases) and the same designation is appropriate for the appendiceal neoplasia in each situation; 4) the long-term outlook for patients with low-grade tumors and peritoneal spread is guarded with just over half dying of disease after 10 years; 5) appendiceal mucinous tumors with destructive invasion of the appendiceal wall, complex epithelial proliferations, or high-grade nuclear atypia generally pursue an aggressive clinical course and should be classified as mucinous adenocarcinomas; 6) peritoneal tumor can be classified as involvement by LAMN or MACA, and this distinction is of prognostic significance; 7) bulky peritoneal tumor worsens prognosis; and 8) LAMNs associated with high-grade peritoneal tumor behave as adenocarcinoma.

Sonographic appearance of an appendiceal diverticulum

The increasing use of sonography for evaluating acute abdomen has brought greater recognition of appendicular abnormalities. We present an incidental finding of an appendiceal diverticulum during a sonographic examination of a 4-year-old child with acute appendicitis. Abdominal sonography showed an enlarged, swollen appendix with a diameter of 1.1 cm and a small, fingerlike lateral projection approximately 2.0 cm from its tip. The specimen, resected during an appendectomy, was 5.5 cm long and 1.0 cm in diameter and had a 0.3-cm outpouching. Microscopic examination revealed a pseudodiverticulum composed of mucosa and muscularis mucosa.