Pathology of Inflammatory Pseudotumor of the Lung

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Inflammatory pseudotumor (plasma cell granuloma) of the lung is an uncommon benign, slowly growing lesion of unknown origin.

As the origin and pathology of inflammatory pseudotumor is not clearly understood, there has recently been some confusion regarding the diagnosis of inflammatory pseudotumor.

Because it is difficult to make a preoperative diagnosis of inflammatory pseudotumor by radiological findings or histological findings using specimens obtained by transbronchial lung biopsy, surgical resection, such as video-assisted thoracic surgery or open lung biopsy, is required to differentiate inflammatory pseudotumors from primary or metastatic lung cancers.

Although inflammatory pseudotumors constitute less than 1% of all lung tumors, they are reported to be the most common cause of solitary lung masses in children.

Patients with inflammatory pseudotumor are usually asymptomatic. It can behave as a malignant tumor both clinically and radiologically.

The tumour can present with symptoms secondary to obstruction when arising in a endobronchial location.

This tumour typically manifests as a solitary, peripheral, and sharply circumscribed mass. Multiple lesions are seen in about 5% of cases.

Cough, fever, dyspnea, and hemoptysis are the usual presenting symptoms.

Histologically the two main variants are:

- Plasma cell granuloma variant: Characterized by hyalinized fibroconnective tissue, sheets of plasma cells together with plump fibroblasts, histiocytes, mast cells and lymphocytes.

- Fibrohistiocytic variant: Characterized by proliferation of spindle cells arranged in whorled or storiform pattern. (Differential diagnosis: Sarcoma).

Mitotic figures may be present. No abnormal mitotic figures are present.

Complete surgical excision is the treatment of choice and should be performed as early as possible. Relapse after incomplete resection and recurrence of aggressive forms have been described.

It has been suggested that probably these lesions are neoplastic and related to inflammatory myofibroblastic tumours located at other sites.