Lung tumor
Benign tumors
Inflammatory pseudotumor

Topic Completed: 1 May 2016

Revised: 31 January 2019, last major update May 2016

Copyright: (c) 2003-2018,, Inc.

PubMed Search: Inflammatory pseudotumor pulmonary

Related topics: Childhood inflammatory pseudotumor

Roseann Wu, M.D., M.P.H.
Page views in 2018: 7,746
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Cite this page: Wu R. Inflammatory pseudotumor. website. Accessed October 21st, 2019.
Definition / general
  • Category used to designate a variety of benign proliferative lesions forming a lung mass, including neoplastic and nonneoplastic entities
  • Neoplastic: renamed inflammatory myofibroblastic tumor (IMT), may show clonal cytogenetic abnormalities involving 2p23 that encodes ALK gene, typically occurs in children and young adults, well demarcated but non encapsulated, usually solitary mass that replaces underlying lung tissue
  • Nonneoplastic: older age, ill defined or irregular contour due to prominent organizing pneumonia component and fibrosis at edge (Arch Pathol Lab Med 2010;134:417)
  • Essential features
  • Inflammatory pseudotumor is a heterogeneous group of benign lesions that may occur in the lung, with a variable mix of inflammatory cells and fibroblasts / myofibroblasts
  • Inflammatory myofibroblastic tumor is recognized as a neoplastic subset that can be associated with ALK gene rearrangement and is typically seen in the younger age group
  • The differential diagnosis is broad, and diagnosis typically requires surgical excision
  • Terminology
  • Variable definitions in use of "inflammatory pseudotumor"; some use term to describe any circumscribed or irregular inflammatory nodule, mass or consolidation; others favor a more descriptive diagnosis
  • Inflammatory myofibroblastic tumor means neoplastic, fibrohistiocytic, associated with ALK rearrangement
  • Other names used in nonneoplastic lesions: plasma cell granuloma, hyalinizing granuloma, plasma cell pseudotumor, inflammatory myofibrohistiocytic proliferation
  • Epidemiology
  • Incidence unclear since terminology / definition varies
  • M=F, broad age range but usually < 30 if IMT
  • 3% bilateral
  • Sites
  • Typically parenchymal, but may involve pleura
  • Rarely intrabronchial
  • Etiology
  • Unknown, but may be autoimmune (IgG4) related or due to an infectious process
  • Clinical features
  • 50% with cough, shortness of breath, chest pain, hemoptysis
  • Diagnosis
  • Surgical excision with histologic examination
  • Radiology description
  • Xray: single, well defined, round or oval mass
  • CT: may show pleural retraction if lesion involves pleura, may show cavitation or calcification
  • Prognostic factors
  • Usually remains stable or grows very slowly, may spontaneously resolve
  • Poor prognostic factors for IMT: metastases, necrosis > 15% of surface area examined, local recurrence, bizarre giant cells, > 3 mitotic figures / 50 HPF, advanced stage, high cellularity, poor circumscription
  • Case reports
  • 27 year old man with IMT invading into GE junction (Ann Thorac Surg 2010;89:1659)
  • 45 year old man with IMT and progressive dyspnea, cough, wheezing (J Cardiothorac Surg 2010;5:55)
  • 58 year old man with inflammatory pseudotumor from Coxiella burnetti (Microbes Infect 2015;17:795)
  • Treatment
  • Complete excision
  • Rarely causes death due to local extension
  • Clinical images

    Images hosted on other servers:

    Bronchoscopy with biopsy

    Gross description
  • Variable size from <1 cm to very large (> 30 cm)
  • Well circumscribed, non encapsulated, usually solitary, white to gray, firm, fleshy parenchymal nodule
  • May be yellow and friable or show hemorrhage, necrosis, calcification
  • Gross images

    Images hosted on other servers:

    Well demarcated, yellowish white fibrous tumor
    encircles part of left bronchus, involves pleural surfaces

    Microscopic (histologic) description
  • Variable patterns, e.g. fibrohistiocytic, plasma cell granuloma, largely sclerosed, compact spindle cells, hypocellular fibrous, myxoid / vascular, fibroxanthomatous
  • Generally fibroinflammatory with variable numbers of plasma cells, lymphocytes, histiocytes and myofibroblasts
  • May show mast cells, eosinophils, neutrophils, multinucleated cells, hemosiderin, calcification
  • May resemble nodular fasciitis, fibrous histiocytoma or fibromatosis
  • May show features of organizing pneumonia including lymphohistiocytic inflammation and fibrosis with preservation of alveolar architecture in early lesions; also bordering alveoli with foamy macrophages and hyperplastic pneumocytes
  • Lymphoplasmacytic variant with mostly plasma cells and lymphocytes, germinal centers, paucicellular collagen, endothelialitis, fibrinous pleuritis
  • Microscopic (histologic) images

    Images hosted on PathOut server:

    Contributed by Roseann Wu, M.D., M.P.H.

    Images hosted on other servers:

    Various images

    Variable appearance of ALK
    rearranged IMTs

    Positive stains
  • Spindle cells: vimentin, smooth muscle actin
  • ALK1 staining in 40% of IMTs
  • Polyclonal kappa and lamda light chain Ig in plasma cells
  • Negative stains
  • Spindle cells negative for desmin, myogenin, myoglobin, CD117, S100
  • Electron microscopy description
  • Elongated cytoplasmic processes with pinocytotic vesicles, subplasmalemmal plaques, thin filaments, abundant endoplasmic reticulum
  • Molecular / cytogenetics description
  • ~50% of inflammatory myofibroblastic tumor have t(2;17) translocation
  • ROS1 or RET gene rearrangements reported (Am J Surg Pathol 2015;39:957)
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