Appendix
Other nonneoplastic
Mucocele
Authors: Matt Andrew M. Paz, D.O., Aastha Chauhan, M.D.
Editorial Board Member: Maryam Kherad Pezhouh, M.D., M.Sc.
Deputy Editor-in-Chief: Aaron R. Huber, D.O.
Last author update: 22 August 2023
Last staff update: 22 August 2023
Copyright: 2003-2024, PathologyOutlines.com, Inc.
PubMed Search: Appendiceal mucocele
Table of Contents
Definition / general | Essential features | Terminology | ICD coding | Epidemiology | Sites | Pathophysiology | Etiology | Clinical features | Diagnosis | Laboratory | Radiology description | Radiology images | Prognostic factors | Case reports | Treatment | Gross description | Gross images | Microscopic (histologic) description | Sample pathology report | Differential diagnosis | Additional references | Board review style question #1 | Board review style answer #1 | Board review style question #2 | Board review style answer #2Cite this page: Paz MAM, Chauhan A. Mucocele. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/appendixmucocele.html. Accessed December 26th, 2024.
Definition / general
- Appendiceal mucocele is a clinical term referring to a mucus filled, distended appendix
Essential features
- Asymptomatic distension of the lumen due to the accumulation of mucin
- Surgical treatment is dependent on dimensions and the histology of the mucocele
Terminology
- Mucocele, obstructive mucocele, inflammatory mucocele, simple retention cyst
ICD coding
Epidemiology
- Mucoceles of the appendix are rare, encountered in 0.2 - 0.3% of appendectomies
- Usually diagnosed in patients ~50 - 60 years old, with a slight female predominance (Acta Chir Scand 1973;139:392)
Sites
- Rupture of a mucocele can present as acute peritonitis
Pathophysiology
- Pathogenesis of appendiceal mucocele is dependent on its etiology
- Natural history is strongly influenced by anatomic peculiarities of the vermiform appendix that predispose to perforation and subsequent mucinous spillage into the peritoneal cavity
Etiology
- Retention or obstruction cyst; nonneoplastic lesions are < 2 cm (Emerg Radiol 2014;21:535, Chirurgia (Bucur) 2014;109:788)
- Appendicitis: case series highlighting neoplastic mucinous lesions, including cases of appendicitis resected as mucoceles (Int J Surg Oncol 2015;2015:139461)
- Fecalith: case report of superinfection of an obstructive lesion due to an appendicolith (Cureus 2022;14:e23974)
- Cystic fibrosis due to inspissated succus (Emerg Radiol 2014;21:535)
- Enrometriosis: case report of endometriosis causing an obstructive lesion of the appendix (World J Gastroenterol 2013;19:5021)
- Focal scarring and obstruction: case report of patient with endometriosis of appendix and scarring of appendix and cecum (Cureus 2023;15:e37825)
- Nonappendiceal malignancy causing obstruction
Clinical features
- Most patients with appendiceal mucoceles are asymptomatic (Pan Afr Med J 2017;28:106)
- Patients with symptoms can present with right lower quadrant pain or generalized abdominal pain, similar to acute appendicitis (J Surg Case Rep 2020;2020:rjaa344)
- Patients with a ruptured mucocele may present with symptoms of acute abdomen (Surg Gynecol Obstet 1992;175:401)
- Palpable pelvic mass (World J Gastroenterol 2005;11:4761)
Diagnosis
- Asymptomatic mucoceles are often diagnosed incidentally on imaging or endoscopic procedures
- Unexpected finding during surgical procedures performed for acute appendicitis or various nonappendiceal pathologies (Am J Case Rep 2014;15:355)
Laboratory
- Mucoceles have nonspecific laboratory findings
- Appendiceal mucoceles with a neoplastic etiology may have elevated tumor markers, such as carcinoembryonic antigen (Int J Surg Case Rep 2013;4:886)
Radiology description
- Mucoceles of any etiology present as a tubular cystic mass in the expected location of the appendix (AJR Am J Roentgenol 1992;159:69)
- Barium enema: usually nonfilling or partial filling of the appendix with contrast (AJR Am J Roentgenol 1985;144:923)
- Ultrasound findings are nonspecific: porcelain appendix may be appreciated; onion skin sign, signifying concentric layers of lamellated mucin, may be present (Abdom Radiol (NY) 2018;43:2913)
- CT finding of a right lower quadrant cyst with curvilinear wall calcifications is suggestive of a mucocele (AJR Am J Roentgenol 1992;159:69)
- Pseudomyxoma peritonei presents as peritoneal implants on CT scan (AJR Am J Roentgenol 1992;159:69)
- Atypical imaging findings for appendiceal mucoceles include intussusception and small bowel obstruction (Abdom Radiol (NY) 2018;43:2913)
Radiology images
Images hosted on other servers:
Hypodense ovoid structure
Prognostic factors
- Prognosis is dependent on the underlying etiology of the lesion
- Simple mucoceles are benign; they have an excellent prognosis (91 - 100% 5 year survival) and do not recur after standard appendectomy (Dig Dis 1998;16:183)
Case reports
- 24 year old woman with 8 month history of right lower quadrant pain (Cureus 2023;15:e37825)
- 43 year old woman with recurrent right lower abdominal pain during her menstrual periods (World J Gastroenterol 2013;19:5021)
- 47 year old man with an appendiceal orifice protrusion noted incidentally during colonoscopy (World J Clin Cases 2021;9:3936)
- 68 year old man with a 10 hour history of mild pain in the right iliac and periumbilical region (Cureus 2022;14:e23974)
Treatment
- Appendectomy for nonneoplastic mucoceles is curative
Gross description
- Mucus filled, distended appendix
- Nonneoplastic mucoceles exhibit less dramatic distention, often measuring < 2 cm across the short axis (Cancer 1995;75:757)
Gross images
Images hosted on other servers:
Distended appendix with intact wall
Microscopic (histologic) description
- Microscopic features of mucocele depend on the underlying pathology
- Crypts may be decreased in the lamina propria but otherwise show no atypia (PLoS One 2017;12:e0179216)
- Acellular mucin may dissect into the wall even in simple mucoceles (Turk J Gastroenterol 2020;31:649)
- May have a dilated lumen with thinned epithelium (Chirurgia (Bucur) 2014;109:788)
- May have degenerated epithelium with no evidence of hyperplasia or neoplasia (Chirurgia (Bucur) 2014;109:788)
- Transmural fibrosis may be present from previous mucin extravasation (PLoS One 2017;12:e0179216)
- Entire appendix should be examined microscopically to rule out dysplastic epithelium (Chirurgia (Bucur) 2014;109:788)
Sample pathology report
- Appendix, appendectomy:
- Dilated appendix due to endometriosis and focal scarring
Differential diagnosis
- Serrated polyp:
- Exhibits serrated features akin to colonic serrated polyps and does not invade into the muscularis mucosa (Am J Surg Pathol 2016;40:14)
- Low grade appendiceal neoplasm (LAMN):
- Exhibits loss of muscularis mucosae, pushing invasion and dissection of mucin into the appendiceal wall (Am J Surg Pathol 2016;40:14)
- High grade appendiceal neoplasm (HAMN):
- Exhibits the architectural features of LAMN in addition to high grade cytological atypia (Am J Surg Pathol 2016;40:14)
- Mucinous adenocarcinoma:
- Characterized by infiltrative invasion and destructive invasion of the appendiceal wall (Am J Surg Pathol 2016;40:14)
- High grade mucinous adenocarcinoma may have signet ring cells (Am J Surg Pathol 2016;40:14)
- Ruptured appendiceal diverticulum:
- Reactive as opposed to neoplastic epithelial changes; preserved lamina propria
- May be associated with neural or Schwann cell proliferations (Am J Surg Pathol 2009;33:1515)
Additional references
Board review style question #1
A 32 year old woman with history of hematuria coinciding with her menstruation underwent an appendectomy for an incidentally discovered dilated appendix. On gross exam, the appendix appeared dilated. Sectioning revealed a dilated mucin filled lumen with no evidence of neoplasms. What histological findings are supportive of an endometriosis involving an appendix?
- Complex villous proliferation of appendiceal epithelium
- Flat proliferation of mucinous epithelial cells
- Monotonous infiltration of small round cells with speckled nuclei
- Unremarkable appendiceal epithelium with focal fibrosis and nests of endometrial stroma
Board review style answer #1
D. Unremarkable appendiceal epithelium with focal fibrosis and nests of endometrial stroma. This patient is presenting with signs of endometriosis. Endometriosis and focal scarring may obstruct the appendix, causing dilation of the lumen and mucus build up. Answer B is incorrect because flat proliferation of mucinous epithelial cells suggests a mucinous neoplasm, likely a low grade appendiceal neoplasm (LAMN). Answer C is incorrect because monotonous infiltration of small round cells with speckled nuclei suggests a neuroendocrine tumor. Answer A is incorrect because complex villous proliferation of appendiceal epithelium refers to a high grade mucinous neoplasm.
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Reference: Mucocele
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Board review style question #2
A 54 year old man with a history of acute appendicitis managed conservatively with antibiotics alone presented for an elective appendectomy after his appendix was incidentally found to be dilated in a recent hospital visit. The resected appendix appeared pink-tan with no gross signs of infection. Sectioning revealed focal scarring with no signs of necrosis of neoplasms. Microscopic exam noted focal fibrosis of the mucosa and focal lymphoid aggregates. No other abnormality was identified. What other treatment, if any, is appropriate for this patient?
- Intraperitoneal chemotherapy is appropriate
- No further treatment is necessary
- Right sided hemicolectomy with lymph node dissection
- Tumor debulking
Board review style answer #2
B. No further treatment is necessary. This patient presents with an incidentally dilated appendix likely due to scarring from his previous history of acute appendicitis. His clinical picture does not suggest any evidence of an appendiceal neoplasm. Answers A, C and D are incorrect because intraperitoneal chemotherapy, tumor debulking and right sided hemicolectomy with lymph node dissection are not warranted.
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Reference: Mucocele
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