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Inflammatory myofibroblastic tumor

Last author update: 1 May 2016

Last staff update: 6 June 2023

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PubMed Search: Inflammatory myofibroblastic tumor[TI] lung[TI]

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Cite this page: Wu R. Inflammatory myofibroblastic tumor. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/lungtumorinflammatorypseudotumor.html. Accessed December 22nd, 2024.

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

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

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

Images hosted on other servers:

Myofibroblasts with plump oval nuclei

Lymphoid hyperplasia and lymphocytic infiltration

Nodular lesions and infiltrating lymphocytes

Variable appearance of ALK<br>rearranged IMTs

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)

Differential diagnosis

Amyloid tumor
Benign fibrous histiocytoma, malignant fibrous histiocytoma
Carcinoid tumor
Histoplasmosis: see Am J Clin Pathol 2011;136:410
Lipoid pneumonia
Lymphoma
Lymphoid hyperplasia
Metastatic carcinoma
Mycobacterial pseudotumor
Organizing pneumonia
Plasmacytoma
Solitary fibrous tumor
Tuberculosis: immunosuppressed patients
Other spindle cell tumors

Childhood inflammatory myofibroblastic tumor

Definition / general

Most common isolated lung lesion in children, usually asymptomatic
Mostly neoplastic with frequent ALK gene rearrangements (in inflammatory myofibroblastic tumor)
Benign, although rare cases of malignant behavior have been reported

Essential features

Inflammatory myofibroblastic tumor (IMT) occurs more often in childhood and in young adults and shows morphology similar to the adult form
IMT in children is more often associated with ALK gene rearrangement than in adults

Terminology

Renamed inflammatory myofibroblastic tumor (formerly inflammatory pseudotumor)

Epidemiology

Most common lung tumor in children age 16 and younger

Sites

Lung, mediastinum, trachea, bronchus, abdomen, orbit

Radiology description

Solid masses with homogeneous or heterogeneous enhancement, may contain calcification (Pediatr Radiol 2015;45:1672)

Case reports

3 year old child with cough and recurrent respiratory infections (Diagn Pathol 2012;7:83)
5 year old girl with recurrent pyrexia, dry cough and shortness of breath (Interact Cardiovasc Thorac Surg 2010;10:805)

Treatment

Excision or radiation therapy

Gross description

Solitary, small peripheral nodules, yellow, firm, covered by intact pleura or polypoid bronchial mass

Gross images

Images hosted on other servers:

Right lower lobe

Microscopic (histologic) description

Plasma cells (often abundant), lymphocytes, histiocytes and myofibroblasts
May have vascular proliferation, collagenous or hyalinized stroma, myxoid change, xanthoma cells, hemosiderin
May resemble nodular fasciitis, fibrous histiocytoma or fibromatosis

Microscopic (histologic) images

Images hosted on other servers:

Spindle cells arrayed in fascicles

Proliferation of regular myofibroblasts

ALK1 reactivity

AML reactivity

Molecular / cytogenetics description

More often associated with ALK rearrangement than adult cases

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