Appendiceal Mucocele: Benign or Malignant?
Jonathan P. Lopez, BS
Department of Surgery
Emad Kandil, MD
Department of Surgery
Alexander Schwartzman, MD
Division of General Surgery
Department of Surgery
Michael E. Zenilman, MD
Clarence and Mary Dennis Professor and Chairman
Department of Surgery
SUNY Downstate Medical Center
Mucocele of the appendix is an uncommon but potentially dangerous pathological entity that presents in a variety of ways. The authors discuss the diagnostic workup of an appendiceal mucocele from computed tomography scanning to resection, emphasizing the influence of pathological diagnosis on the operative procedure. Right hemicolectomy is sufficient for most patients with appendiceal mucocele; however, the significant risk of postoperative complications and concomitant life-threatening conditions has led the authors to recommend careful resection and exploration of the peritoneum.
Appendiceal mucocele is a rare but well-recognized entity that can mimic several common clinical syndromes or present as an incidental surgical or radiological finding. It has a 0.2% to 0.4% prevalence among appendectomies.1,2 The term mucocele is widely used in diagnosing both benign and malignant lesions, but specific criteria are being proposed for definitive diagnosis and surgical management of appendiceal mucocele.3 While some neoplasms with malignant potential may be treated definitively by resection, other seemingly benign lesions must be treated conservatively due to complications that ensue from peritoneal and cecal inoculation and the possibility of progression to malignancy.4,5
Mucocele can result from mucosal hyperplasia, mucinous cystadenoma, or mucinous cystadenocarcinoma. Signs and symptoms occur in fewer than 50% of cases and are generally associated with malignancy.3 These include pain in the right lower abdominal quadrant, an abdominal mass, weight loss, nausea, vomiting, change in bowel habits, anemia, and hematochezia. Depending on the location of the appendix, other signs may be observed, such as hematuria. The most dreaded complication of benign or malignant mucocele is pseudomyxoma peritonei, which is difficult to treat surgically or medically. It has an uncertain prognosis, with a 5-year survival rate between 53% and 75%.5,6
More than half of appendiceal mucoceles are mucinous cystadenomas, most of which can be treated by appendectomy alone, with careful exploratory laparotomy for mucinous peritoneal adhesions typical of pseudomyxoma.7 Wide resection of the ap-pendix, however, is currently the standard for conservative surgical management of unspecified appendiceal mucocele.
A 54-year-old man of Caribbean descent presented with a constant, dull right lower quadrant pain of 2 years' duration. His pain did not radiate and was not affected by any activity. He reported no changes in his eating or bowel habits and no hematochezia or melena, although he noted several years of intermittent abdominal distention and vomiting, which was thought to be due to gastroparesis from uncontrolled diabetes. The patient had no history of surgery. On physical examination, he was afebrile and hemodynamically stable. The abdominal examination was normal except for focal tenderness over McBurney's point without rebound tenderness on palpation.
Laboratory analysis was unremarkable. Axial computed tomography (CT) scanning revealed a 5 x 3 x 3-cm in diameter, blind-ending, tubular, fluid-filled structure that appeared to arise from the cecum, consistent with mucocele of the appendix (Figure 1). Colonoscopy showed evidence of an appendiceal mass covered by cecal mucosa and protruding into the cecum.
The patient underwent elective laparoscopic-assisted right hemicolectomy. Several dilated loops of small bowel were noted proximal to the adhesions, which were most extensive over the liver and gallbladder. Exploration of the peritoneum did not show evidence of malignancy.
Pathological examination of the surgical specimen revealed a fluid-filled, distended appendix measuring 8 cm at its greatest diameter and with a base 4 cm in diameter (Figure 2). The obstructed appendix was found to communicate with a mucus-filled evagination of the cecal wall, arising 1 cm proximal to the ileocecal valve. Six lymph nodes discovered in the mesentery of the specimen revealed no pathological morphology. There were no abnormal peritoneal findings. The tumor was diagnosed on histological section as mucinous cystadenoma (Figure 3).
The patient's postoperative course was uneventful, and he was discharged home on postoperative day 5. Three months after the operation, all symptoms had completely resolved and the patient was doing well.
Mucocele of the appendix was first described by Rokitansky in 1842 and was formally named by Feren in 1876. Since that time, there has been some debate as to the gross diagnosis of mucocele. Some consider the term to encompass a large group of conditions involving the appendix, pancreas, or ovaries, with diverse morphological features and pathogenesis. These conditions share the common feature of obstructive process or hyperplasia of mucinous epithelium, or both, leading to gross mucinous accumulation. Others consider mucocele to be a strictly neoplastic process that can spread to lymph nodes, extend into surrounding tissue, or seed the peritoneum.7 The latter description encompasses most mucocele-related diagnoses, and thus, right hemicolectomy is an appropriate first step in managing suspicious mucinous collections of the appendix. Histopathological findings can confirm whether further tests are needed for workup of malignancy. If a patient has a mucinous cystadenoma of the appendix, as was the case with our patient, then right hemicolectomy is curative (except in cases that are complicated by pseudomyxoma peritonei).
In a retrospective study of 135 patients with appendiceal mucocele, 55% were women; other reports have shown a distinct male predominance (4:1).3,8 Indications for removal of appendiceal mucocele are evolving as diagnostic procedures that lead to surgery for a wide variety of concomitant conditions improve. Forty percent of patients in the 135-patient study went into the operating room specifically for treatment of symptoms or to confirm a diagnosis, while the remaining 60% had their appendiceal mucocele removed on incidental finding. Although CT scanning is usually accurate in imaging a fluid-filled appendix, the appendix was often missed on CT scans for workup of coexisting conditions. This may explain the high incidence of surgical diagnosis for other conditions (although CT scanning was not available for a number of patients in that study). Still, in the workup for a patient's symptoms of right lower quadrant abdominal pain or a palpable abdominal mass, CT scanning has high sensitivity and specificity for detecting an abnormal appendix.
Ultrasonography and endoscopy are becoming the standards for confirming CT findings before taking the patient to the operating room. Endoscopic biopsy and pathological determination can further guide the operative procedure if hemicolectomy is contraindicated or otherwise undesirable. CT scanning has the advantage of allowing precise observation of the relationship between the lesion and adjacent organs (Figure 1B) and any other abnormalities associated with mucocele. This diagnostic modality should be used before a patient undergoes endoscopy, colonoscopy, or ultrasonography. In suspected cases of appendiceal mucocele, fine needle aspiration should be avoided to preserve integrity of the appendix and prevent tumor inoculation.1,6-11
Although complications from appendiceal mucocele are minimal, there is evidence that complications are associated with concomitant neoplasms. These occurred in about one third of patients in the retrospective study and undoubtedly contributed to the high number of incidental findings of mucocele. While the incidence of ovarian and uterine neoplasms might be explained in part by the high number of gynecologic procedures reported, the association between appendiceal mucocele and colonic neoplasms is well established.3,12,13 This additional evidence makes a strong case for the use of surveillance colonoscopy and removal of polyps in any patient with an appendiceal mucocele. Most investigators agree that the adenoma-adenocarcinoma sequence is similar to the colonic polyp-adenocarcinoma sequence.14
No cystadenomas smaller than 2 cm have been reported, which suggests that all mucoceles larger than 2 cm should be removed to eliminate the chance of progression to malignancy. Furthermore, all patients, whether they have benign or malignant appendiceal mucocele, should be evaluated for pseudomyxoma peritonei. Although the condition is more common in malignant appendiceal mucocele (95% occurrence rate as opposed to 13% in patients with nonmalignant appendiceal mucocele), the grave consequences of pseudomyxoma peritonei and the somewhat better prognosis for patients whose condition is diagnosed and treated early should challenge the view that simple surgical resection sans careful exploration for every diagnosed appendiceal mucocele is sufficient.5
Appendiceal mucocele presents a challenge to the surgeon who does not appreciate the effect of pathological diagnosis on the operative procedure. Appendectomy alone should be performed only on mucinous lesions that are determined to be non-neoplastic after biopsy. If appendectomy is performed, precautions should be taken to minimize the risk of seeding the peritoneal cavity with tumorous mucin during manipulation. In our patient's case, simple appendectomy could have allowed spillage of fluid from the small collection between the obstruction and the cecal mucosa, and because of the multiple suspicious adhesions, it would have been inappropriate. Although these adhesions were not suspicious for malignancy on imaging studies, they did raise suspicion of malignancy because our patient had never undergone surgery before. In other instances, it has been shown that induration of the appendix, a spontaneous appendiceal perforation, or mucus extravasation emanating from the appendiceal lumen strongly suggest malignancy.4 These features, however, also may be present with benign tumors, which makes the gross diagnosis of neoplastic process difficult, at best.
Although laparoscopic techniques have been described that minimize the prohibitive risk of seeding mucinous tumor implants during laparoscopic manipulation, appendectomy alone?whether open or laparoscopic?does not guarantee the removal of all neoplastic tissue, including extensions into surrounding tissue and lymph nodes.2,15 We recommend right hemicolectomy for cases in which the pathological diagnosis has not been established and for any cases suspicious for adenocarcinoma or complicated by concomitant adenocarcinomatous disease or pseudomyxoma peritonei.
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