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Histoplasma-associated pulmonary inflammatory pseudotumor

Pulmonary inflammatory myofibroblastic tumor associated with histoplasmosis

Saturday 8 May 2010

Only three reports exist in the medical literature suggesting an association of IMT with histoplasmosis [2010].

In the report by Frey and associates, the fungal organisms were found only in associated lymph nodes and not within the IMT lesion itself.

Gariépy and colleagues describe an elderly female with a left lower lobe IMT and positive histoplasmosis serology. However, no organisms were isolated in culture or able to be observed histologically in the specimen following curative left lower lobectomy.

The case presented represents the only published account of IMT with intralesional histoplasma organisms isolated.

Synopsis

- immunocompetent man or woman in a non-endemic area
- round mass
- inflammatory pseudotumour of the lung combined with histoplasmosis of the hilar lymph glands (9833193)
- inflammatory pseudotumour of the lung in conjunction with histoplasmosis of the hilar lymph glands (9833193)
- IMT with intralesional histoplasma organisms isolated (17670634)

Nota bene: Inflammatory myofibroblastic tumors of the lung in children are a non-neoplastic process characterized by an unregulated proliferation of inflammatory cells. The etiology of these ‘tumors’ is not certain and often difficult to ascertain.

Inflammatory myofibroblastic tumor (IMT), also frequently referred to as inflammatory pseudotumor or plasma cell granuloma, is the most common benign primary lung tumor encountered in children.

Typically this non-neoplastic process is distinguished by an unregulated proliferation of inflammatory cells. Often the etiology of this inflammatory phenomenon is uncertain or difficult to determine.

The incidence of pulmonary IMT has been reported to be as high as 0.7% of thoracic surgical resections.

IMT can be a neoplastic process and manifesting as a soft-tissue/mesenchymal tumor with an indeterminate or low malignant potential.

In few cases of IMT, cytogenetic analysis has demonstrated the presence of clonal chromosomal aberrations indicating that IMT may be a neoplastic proliferation. One-third to one half of IMT cases present with a 2p23 rearrangement involving anaplastic lymphoma kinase (ALK) often fused with tropomyosin genes TPM3 and TPM4 and the clarithrin heavy chain gene (CLTC).

However, the lack of p53 detection in IMT coupled with the low proliferation index (Ki67 @<@10%) suggests that IMT may be a low-grade sarcoma, if at all. Nonetheless, Donner and colleagues have described progression of IMT to sarcoma in 7% of pulmonary occurrences.

Inflammatory myofibroblastic tumors are uncommon with at least 50% occurring in patients under the age of 16 years. IMT is the most frequently diagnosed primary lung tumor in the pediatric population. It has not shown any sex predilection, affecting boys as often as girls. Symptoms are generally non-specific, with up to 40% of reported cases occurring without any discernible symptoms.

Chest radiography typically demonstrates a solitary, well-demarcated peripheral lung mass. Previously reported lesions have ranged in size from 1 to 15 cm in diameter.

Calcifications are more commonly found in children and can be punctate, curvilinear, dense or dispersed in nature. Cavitation is exceedingly rare. Hilar and mediastinal adenopathy is also very uncommon.

The etiology of IMT is thought to be an uncontrolled response to tissue damage or chronic inflammation. It has been previously suggested that the process leading to IMT of the lung originates as an organizing intra-alveolar pneumonia.

References

- Pulmonary inflammatory myofibroblastic tumor associated with histoplasmosis. Cassivi SD, Wylam ME. Interact Cardiovasc Thorac Surg. 2006 Aug;5(4):514-6. PMID: 17670634

- Frey A, Eichfeld U, Schubert S, Friedrich T, Schonfelder M. Inflammatorischer pseudotumor der lunge bei hiluslymphknotenhistoplasmose. Chirurg 1998; 69:1101–1104. PMID: 9833193

- Gariépy G, Poitras P, Charbonneau R. Granulome plasmocytaire du poumon. Union Med Can 1975; 105:77–81.