Other mesenchymal tumors

Inflammatory myofibroblastic tumor

Editor-in-Chief: Debra L. Zynger, M.D.
Jennifer A. Bennett, M.D.

Topic Completed: 23 May 2019

Minor changes: 30 November 2021

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PubMed search: Uterus inflammatory myofibroblastic tumor

Jennifer A. Bennett, M.D.
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Cite this page: Bennett J. Inflammatory myofibroblastic tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/uterusinflammpseudo.html. Accessed December 7th, 2021.
Definition / general
  • Rare mesenchymal neoplasm of myofibroblastic / fibroblastic origin with variable amounts of myxoid stroma and lymphoplasmacytic inflammation
Essential features
  • Best classified as a neoplasm of uncertain malignant potential, as histologically bland uterine confined tumors may recur
  • Comprised predominantly of spindle cells with hypercellular (fascicular / storiform) and hypocellular (myxoid rich) areas admixed with a variably prominent lymphoplasmacytic infiltrate
  • Most express ALK, CD10, smooth muscle actin and desmin but with variable staining intensity and distribution
  • Multiple fusion partners have been identified, some with complex genetic rearrangements, which might result in false negative FISH testing
  • Inflammatory myofibroblastic tumor (IMT)
  • Inflammatory pseudotumor
  • Plasma cell granuloma
ICD coding
  • ICD-10: D39.0 - neoplasm of uncertain behavior of uterus
  • ICD-10: C54.9 - malignant neoplasm of corpus uteri, unspecified
  • ICD-O: 8000 / 1 - neoplasm, uncertain whether benign or malignant
  • ICD-O: 8000 / 3 - neoplasm, malignant
  • ~80 cases reported to date (corpus and cervix)
  • Most commonly present at age 30 - 60 (range: 6 - 78)
  • Uterine corpus most common site in gynecologic tract
    • Rarely cervix (6 cases), ovary, fallopian tube, cul de sac, broad ligament, placenta
  • Unknown
  • Unknown
Clinical features
  • Generally present with nonspecific gynecologic symptoms (abnormal uterine bleeding, abdominal / pelvic pain) or presumed fibroids (Mod Pathol 2017;30:1489)
  • May be incidentally discovered at cesarean section
  • Occasionally present with constitutional symptoms (may be related to IL6 production by tumor) (Am J Obstet Gynecol 2003;189:890)
Radiology description
  • No defining features to distinguish from other uterine mesenchymal neoplasms on imaging
Radiology images

Images hosted on other servers:

CT shows intrauterine mass

Axial MRI shows local lesion

Prognostic factors
  • Not well defined since only a small subset (~20%) have recurred or metastasized
    • Large size (> 7 cm), moderate to severe atypia, high mitotic activity (> 10 per 10 high power fields), tumor cell necrosis and infiltrative border have been associated with more aggressive behavior (Adv Anat Pathol 2017;24:354)
    • Often fascicular / compact predominant, although one study showed myxoid dominant tumors had worse outcome (Am J Surg Pathol 2015;39:157)
  • Can recur years after original diagnosis
Case reports
Gross description
  • Variable and resemble other mesenchymal lesions (Am J Surg Pathol 2015;39:157, Mod Pathol 2017;30:1489)
  • Typically submucosal or intramural but may be polypoid
  • Tan, white, pink, solid and cystic mass, often soft and gelatinous / myxoid
  • May have whorling, hemorrhage, necrosis
Gross images

Images hosted on other servers:

Polypoid lesion within endometrial cavity

Microscopic (histologic) description
  • Borders range from well circumscribed to focally irregular to infiltrative
  • 3 main growth patterns: myxoid, fascicular / compact, hyalinized (Mod Pathol 2017;30:1489)
    • Myxoid: loosely arranged spindle cells (nodular fasciitis-like) in a myxoid background, hypocellular
    • Fascicular / compact: densely arranged spindle cells with fascicular or storiform architecture, may have a smooth muscle appearance or myxoid stroma, hypercellular
    • Hyalinized (infrequent): sparsely cellular collagen resembling a scar
  • Variable degree of lymphoplasmacytic inflammation, occasionally lymphocyte predominant
    • Lymphoid aggregates, foamy histiocytes, neutrophils, eosinophils and Touton giant cells may be seen
  • Thin walled and elongated vessels, occasional thick walled (leiomyoma-like) or staghorn vessels (Mod Pathol 2017;30:1489, Am J Surg Pathol 2019;43:64)
  • Spindle cells have open vesicular nuclei with variable atypia (rarely severe)
  • Ganglion-like cells (abundant eosinophilic cytoplasm, eccentric nuclei, prominent nucleoli) may be seen and typically comprise a minority of the tumor
  • Spindle cells may show a decidualized appearance during pregnancy (Mod Pathol 2017;30:1489)
  • Mitotic index is usually low and tumor cell necrosis uncommon
Microscopic (histologic) images

Contributed by Jennifer Bennett, M.D.

Hyper and hypocellular areas

Myxoid pattern

Acellular myxoid areas

Myxoid areas resemble nodular fasciitis

Plasma cell aggregates

Compact pattern

Severe nuclear atypia

Ganglion-like cells

Spindle cells with decidualized appearance


Positive stains
Negative stains
Electron microscopy description
  • Spindle cells show features of myofibroblasts and are focally surrounded by basal lamina-like material (Int J Gynecol Pathol 1987;6:275)
    • Nondilated rough endoplasmic reticulum
    • Thin filaments with peripheral dense bodies
    • Pinocytic vesicles, occasional Golgi bodies, lipid droplets
Molecular / cytogenetics description
Molecular / cytogenetics images

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FISH: classic ALK rearrangement

Sample pathology report
  • Uterus, hysterectomy:
    • Inflammatory myofibroblastic tumor with (list any atypical features here, including tumor cell necrosis, > 7 cm, moderate to severe atypia, > 10 mitoses per 10 high power fields, infiltrative borders)
    • Surgical margins, negative for tumor
Differential diagnosis
Board review style question #1
A 44 year old woman presents with an infiltrative spindle cell neoplasm in the myometrium that has prominent myxoid stroma and a dense lymphoplasmacytic infiltrate. It is positive for desmin, smooth muscle actin and ALK by immunohistochemistry and shows ALK rearrangement by FISH. What is the most likely diagnosis?

  1. BCOR rearranged endometrial stromal sarcoma
  2. Inflammatory myofibroblastic tumor
  3. Myxoid endometrial stromal sarcoma
  4. Myxoid leiomyosarcoma
  5. Postoperative spindle cell nodule
Board review style answer #1
B. Inflammatory myofibroblastic tumor

Comment Here

Reference: Inflammatory myofibroblastic tumor
Board review style question #2
Which gene is rearranged in the majority of uterine inflammatory myofibroblastic tumors?

  1. ALK
  2. BCOR
  3. RANB2
  4. RRBP1
  5. STAT6
Board review style answer #2
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