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    • Surgical Pathology Criteria

    Gastric Plexiform Fibromyxoma

    Definition

    • Multinodular myxoid tumor involving gastric antrum

    Alternate/Historical Names

    • Gastric fibromyxoma
    • Plexiform angiomyxoid myofibroblastic tumor

    Diagnostic Criteria

    • Plexiform multinodular growth pattern
      • 1-7 mm nodules
    • Myxoid or fibromyxoid stroma
      • Alcian blue positive
        • PASd negative
      • Prominent arborizing capillaries
      • Some nodules may have dense collagenous stroma
    • Cytologically bland oval nuclei
      • 0-4/50 hpf mitotic count
      • Indistinct cell borders
        • May have clear cytoplas
    • Generally hypocellular
      • May have areas or nodules of increased cellularity
        • More commonly seen in extramural involvement
    • All cases involve the muscularis propria
      • Frequent extension into submucosa and mucosa
      • 50% extend into adjacent soft tissue or duodenum
        • Pushing border without plexiform pattern in areas of extragastric involvement
        • May form subserosal nodules
    • All cases reported in gastric antrum
      • May extend into duodenum
    • Ulceration, mucosal invasion and vascular invasion may be seen
      • None has any clinical significance
    • Absent features
      • Tumor cell necrosis and calcification
      • Nuclear palisading and skeinoid fibers

    Robert V Rouse MD
    Department of Pathology
    Stanford University School of Medicine
    Stanford CA 94305-5342

    Original posting/updates: 12/6/09, 11/26/11

    Supplemental studies

    Immunohistology

    • Smooth muscle actin 80%
    • CD10 focal positive in one case
    • Desmin variable
    • Negative markers
      • KIT, DOG1, CD34
      • S100, Heavy caldesmon
      • Keratin, EMA

    Genetic Studies

    • All studied cases to date show no mutations in KIT and PDGFRA

    Differential Diagnosis

    GIST (spindled, bland) Gastric Plexiform Fibromyxoma
    Usually solitary nodule Multinodular, plexiform
    Myxoid pattern rare Myxoid pattern predominates
    KIT and/or DOG1 74-95% KIT and DOG1 negative
    CD34 frequently positive CD34 negative

    Inflammatory Fibroid Polyp Gastric Plexiform Fibromyxoma
    Usually solitary nodule Multinodular, plexiform
    Usually a pedunculated polyp Intramural
    Centered on submucosa Centered on muscularis propria
    Frequent inflammatory infiltrate No intrinsic inflammatory infiltrate
    May have concentric perivascular pattern of spindle cells Lacks concentric pattern
    CD34 frequently positive CD34 negative

    Plexiform Neurofibroma Gastric Plexiform Fibromyxoma
    S100 positive S100 negative

    GI Leiomyoma, Myxoid Gastric Plexiform Fibromyxoma
    Usually contains at least focal collections or fascicles of cells with distinct eosinophilic cytoplasm Indistinct or clear cytoplasm, no fascicles
    Myxoid pattern rare Myxoid pattern predominates
    Desmin usually positive Desmin negative

    Fibromatosis, Mesenteric or Retroperitoneal and Pelvic Gastric Plexiform Fibromyxoma
    Long fascicles of cells No fascicles
    Myxoid pattern rare Myxoid pattern predominates
    Areas of dense collagen frequent Lacks dense collagen
    Usually extrinisc mass invading bowel wall Intrinsic to bowel wall
    CD117 frequently negative, variable reports of focal/weak staining CD117 74-95% positive
    DOG1 negative DOG1 87-94%

    Clinical

    • Usually presents with bleeding
    • Median age 41 years
      • Range 7-75
    • Apparently benign
      • No reported recurrence or metastasis
    • No features of Carney complex have been reported

    Bibliography

    • Bosman FT, Carneiro F, Hruban RH, Thiese ND (Eds). WHO Classifiication of Tumors of the Digestive System, IARC, Lyon 2010
    • Miettinen M, Makhlouf HR, Sobin LH, Lasota J. Plexiform fibromyxoma: a distinctive benign gastric antral neoplasm not to be confused with a myxoid GIST. Am J Surg Pathol. 2009 Nov;33(11):1624-32.
    • Rau TT, Hartmann A, Dietmaier W, Schmitz J, Hohenberger W, Hofstaedter F, Katenkamp K. Plexiform angiomyxoid myofibroblastic tumour: differential diagnosis of gastrointestinal stromal tumour in the stomach. J Clin Pathol. 2008 Oct;61(10):1136-7.
    • Takahashi Y, Shimizu S, Ishida T, Aita K, Toida S, Fukusato T, Mori S. Plexiform angiomyxoid myofibroblastic tumor of the stomach. Am J Surg Pathol. 2007 May;31(5):724-8.
    • Sing Y, Subrayan S, Mqadi B, Ramdial PK, Reddy J, Moodley MS, Bux S. Gastric splexiform angiomyxoid myofibroblastic tumor. Pathol Int. 2010 Sep;60(9):621-5.
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