Pulmonary Hyalinizing Granuloma and Diagnostic Pitfalls

Key Takeaways

• Incidentally detected pulmonary nodules in a 71-year-old man were described as mimicking metastatic disease on imaging.
• Surgical pathology identified fibrocollagenous nodules with perivascular inflammatory infiltrates, and immunohistochemistry with special stains helped exclude malignancy and infection.
• The authors described pulmonary hyalinizing granuloma as typically benign and suggested the name may be misleading because the lesions are fibrosing rather than true granulomas.

The pulmonary findings emerged during an abdominal evaluation rather than a planned assessment for lung disease or thoracic symptoms. Their radiologic appearance raised concern for metastatic disease and complicated the diagnostic picture early in the workup. That initial framing set a benign process against a malignant explanation before adequate tissue clarification was available. The case illustrates how this lesion can present a malignancy-like imaging pitfall despite its nonmalignant nature.

The authors note that the nodules came to attention during imaging for acute appendicitis rather than evaluation of pulmonary complaints. The incidental discovery shifted attention to lung findings with a concerning radiologic profile from the start. Because the scans suggested metastatic disease, the pulmonary abnormalities became the central diagnostic uncertainty during early evaluation. Biopsy samples were reported as inadequate, preventing firm classification in the initial workup. With imaging pointing toward one possibility and sampling not resolving the question, the nature of the nodules remained unsettled.

Pathologic evaluation after surgical resection provided the basis for classification, demonstrating fibrocollagenous nodules with perivascular inflammatory infiltrates within the pulmonary lesions. This was the first adequate tissue assessment after earlier sampling left the findings indeterminate. Ancillary studies further narrowed the differential by adding layers of exclusion to the workup. Taken together, the morphologic findings and reported immunohistochemistry and special stains supported the diagnosis by excluding malignancy and infection. The diagnosis was therefore established through pathology rather than radiologic appearance alone.

Investigators describe pulmonary hyalinizing granuloma as typically benign in its clinical course. The authors state that surgery is described as the treatment of choice for solitary lesions. The discussion also questions whether the established name matches the underlying lesion. According to the authors, the term can be misleading because these nodules are fibrosing lesions rather than true granulomas. The case closes by linking diagnostic difficulty to both imaging appearance and terminology that may blur pathologic identity at the time of interpretation.