Mucinous Cystic Neoplasms



Mucinous Cystic Neoplasms


Scott R. Owens, MD





Key Facts


Terminology



  • Mucinous cystic neoplasm



    • Circumferential proliferation of low-grade or high-grade dysplastic, mucin-producing epithelium that may distend appendix and fill it with mucin


  • Pseudomyxoma peritonei



    • Clinical term referring to neoplastic process that fills abdomen with extracellular mucin


  • Mucinous adenocarcinoma is appropriate diagnosis when lesion is clearly invasive


Clinical Issues



  • Simple appendectomy with negative margins is probably sufficient for tumors confined to appendix


  • Truly invasive adenocarcinomas require regional resection with lymphadenectomy (right hemicolectomy)


  • Prognosis tied predominantly to cytological grade of neoplasm


Macroscopic Features



  • Evidence of rupture must be carefully sought


  • Thorough sampling of abdominal tissues in PMP is crucial to adequately search for neoplastic epithelium


Microscopic Pathology



  • So-called epithelial displacement vs. true mural invasion is root of much controversy


Diagnostic Checklist



  • Ovarian involvement common in women, leading to previous belief that pseudomyxoma peritonei often originated in primary ovarian tumors







Gross photograph shows an appendectomy specimen distended into a sausage-like shape by a mucinous cystic neoplasm image.






Hematoxylin & eosin shows a villiform appendiceal mucinous neoplasm. Note the lack of normal mucosal and submucosal lymphoid tissue.


TERMINOLOGY


Abbreviations



  • Mucinous cystic neoplasm (MCN)


  • Pseudomyxoma peritonei (PMP)


Synonyms



  • Appendiceal mucocele


  • Mucinous cystadenoma (MCA)


  • Mucinous tumor of uncertain malignant potential


  • Mucinous tumor of low malignant potential


  • Borderline tumor of appendix


  • Low-grade appendiceal mucinous neoplasm (LAMN)


Definitions



  • Mucinous cystic neoplasm



    • Proliferation of low- or high-grade, dysplastic, mucin-producing epithelium that may distend appendix and fill it with mucin


  • Mucocele results when mucin production distends appendix into spherical or sausage-shaped mass


  • Mucinous cystadenoma



    • Refers generally to low-grade dysplastic epithelial proliferations confined to appendix


  • Pseudomyxoma peritonei



    • Clinical term referring to neoplastic process that fills abdomen with extracellular mucin


    • Often associated with appendiceal mucinous tumors


    • Classification of primary appendiceal tumor particularly controversial in this setting


  • Confusing terminology



    • Disseminated peritoneal adenomucinosis (DPAM), LAMN, borderline tumor, mucinous tumor of uncertain/low malignant potential


    • Reflects longstanding controversies regarding spread of acellular or cellular mucin outside appendix without clear-cut invasive carcinoma



      • Some advocate use of “adenocarcinoma” for any tumor with extraappendiceal spread of mucinous cells


      • Others suggest possibility of noncarcinomatous spread of mucin-producing cells after appendiceal rupture


  • Mucinous adenocarcinoma is appropriate diagnosis when lesion is clearly invasive


ETIOLOGY/PATHOGENESIS


Molecular Abnormalities



  • KRAS mutations in around 70%


  • Loss of heterozygosity (LOH) of chromosome 5q (including locus linked to APC gene) in up to approximately 20%


CLINICAL ISSUES


Epidemiology



  • Incidence



    • Low-grade MCN relatively uncommon (˜ 1 per 100,000 per year)


    • Pseudomyxoma peritonei even rarer (˜ 0.1 per 100,000 per year)


    • Primary appendiceal adenocarcinoma (˜ 0.2 per 100,000 per year in North America)


  • Age



    • Occur in adults of any age, but 3rd to 8th decade most common


  • Gender



    • Occur in both males and females, with female predominance


Presentation



  • Asymptomatic/incidental


  • Deep mass



    • Possible with larger tumors


  • Abdominal pain



    • Possible in abdominal dissemination/PMP



Treatment



  • Options, risks, complications



    • Simple appendectomy with negative margins probably sufficient for tumors confined to appendix


    • Truly invasive adenocarcinomas require regional resection with lymphadenectomy (right hemicolectomy)


  • Surgical approaches



    • Not standardized for low-grade tumors with peritoneal spread


    • Some advocate aggressive approach to tumors that have breached appendix with resultant PMP



      • Omentectomy, splenectomy, peritoneal stripping (“peritonectomy”), cholecystectomy, antrectomy, sigmoid colectomy


      • Intraoperative hyperthermic chemotherapy to treat unresected tumor cells


    • Disseminated high-grade tumor/carcinomatosis may not be amenable to aggressive therapy


  • Adjuvant therapy



    • Additional cycles of intraperitoneal ± systemic chemotherapy may follow aggressive resection


Prognosis



  • Good for lesions confined to appendix and completely resected


  • Outcomes data hampered in extraappendiceal spread by varying diagnostic labels used in different studies



    • Appears to be tied predominantly to cytological grade of neoplasm


    • Low-grade extraappendiceal neoplasm has better prognosis than high-grade/frank carcinomatosis


MACROSCOPIC FEATURES


General Features



  • Dilated mucin-filled appendix



    • Evidence of rupture must be carefully sought


Sections to Be Submitted



  • Entire appendix should be submitted when mucinous lesion is seen grossly



    • Incidental mucinous lesions found after routine appendiceal sampling should prompt complete submission


  • Thorough sampling of abdominal tissues in PMP is crucial to adequately search for neoplastic epithelium


MICROSCOPIC PATHOLOGY


Key Descriptors

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Jul 6, 2016 | Posted by in PATHOLOGY & LABORATORY MEDICINE | Comments Off on Mucinous Cystic Neoplasms

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