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Lung tumor

Benign tumors

Inflammatory pseudotumor

Reviewer: Deepali Jain, M.D. (see Reviewers page)
Revised: 7 January 2013, last major update September 2012
Copyright: (c) 2003-2013, PathologyOutlines.com, Inc.

General
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● Also called inflammatory myofibroblastic tumor, plasma cell granuloma
● Neoplastic: clonal cytogenetic abnormalities involving 2p23 that encodes ALK gene, typically occurs in children and young adults, well-demarcated but nonencapsulated, 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)
● IgG4-related immunopathologic processes may be involved
● Usually age < 30 years; most common lung tumor in children age 16 and younger

Poor prognostic factors
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● Metastases, necrosis >15% of surface area examined, local recurrence, bizarre giant cells, > 3 mitotic figures/50 HPF, advanced stage, high cellularity, poor circumscription

Treatment
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● Excision
● Rarely causes death due to local extension

Gross description
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● Well circumscribed, non-encapsulated, usually solitary, white, firm, parenchymal nodule
● 3% bilateral
● May have hemorrhage, necrosis or calcification

Micro description
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● Plasma cells, 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

Micro images
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Various images


Spindle cells in collagenous stroma

Positive stains
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● Spindle cells: vimentin, smooth muscle actin

Electron microscopy description
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● Elongated cytoplasmic processes with pinocytotic vesicles, subplasmalemmal plaques, thin filaments, abundant endoplasmic reticulum

Differential diagnosis
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● Amyloid tumor
● Benign and malignant fibrous histiocytoma
● Carcinoid tumor
● Hemangiopericytoma
● Histoplasmosis see Am J Clin Pathol 2011;136:410
● Lipoid pneumonia
● Metastatic carcinoma
● Mycobacterial pseudotumor
● Organizing pneumonia
● Plasmacytoma
● Tuberculosis (immunosuppressed patients)
● Other spindle cell tumors

Childhood inflammatory pseudotumor

General
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● Most common isolated lung lesion in children, usually asymptomatic
● Benign, although rare cases of malignant behavior have been reported

Treatment
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● Excision or radiation therapy

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

Micro description
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● 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

Micro images
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3 year old child

End of Lung tumor > Benign tumors > Inflammatory pseudotumor

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