Pulmonary inflammatory pseudotumor

Pulmonary inflammatory pseudotumours (PIP's) are solid, non-neoplastic masses which can mimic pulmonary malignancy. They should not be confused with pulmonary pseudotumours which usually refer to loculated collections of pleural fluid mimicking a pulmonary mass on chest radiography.

Pathology

Thought to occur from an uncontrolled response to lung tissue injury. Lesions are typically solitary with a lower lobe predilection.

Pathologically, pulmonary inflammatory pseudotumours are typically well-defined, firm, lobulated parenchymal nodules or masses with a whorled and often heterogeneous appearance on cross-section.

Histologically, there is proliferation of spindle-shaped fibroblasts and permeation of collagen with lymphocytes, fibrosis, granulomatous inflammation, lymphoid hyperplasia, and intra-alveolar fibrosis at the edge of the lesion.

Radiographic features

Plain radiograph

Features on chest radiographs can vary but frequently mimics a solitary, well circumscribed, peripheral lung mass with calcifications in situ. May have an anatomical bias for the lower lobes.

CT

CT most commonly shows a well-marginated, lobulated mass of heterogeneous attenuation with variable patterns of contrast enhancement and calcification. Cavitation and lymphadenopathy are rare.

Treatment and prognosis

• some authors advocate resection ⁴

Differential diagnosis

The differential can be quite wide, specific considerations include

• solitary metastases from an osteosarcoma or mucinous tumour
• intra-thoracic soft tissue sarcoma
• pulmonary hamartoma