Unmasking a Hidden Mimic: Pulmonary Papillary Adenoma - a Diagnostic Challenge

Document Type

Conference Proceeding

Publication Date

5-15-2026

Publication Title

Am J Respir Crit Care Med

Keywords

General & Internal Medicine, Respiratory System

Abstract

Introduction: Pulmonary papillary adenoma (PPA) is an extremely rare benign lung tumor arising from type II pneumocytes, with fewer than 50 cases reported. Because of its rarity and nonspecific radiologic features, PPA often poses a diagnostic dilemma, mimicking low-grade adenocarcinoma or carcinoid tumor. We present a case with mild FDG avidity, highlighting the diagnostic pitfalls and the importance of histologic confirmation. Case A 66-year-old man with a smoking history was followed for a right upper lobe lung nodule first noted incidentally in 2007. Over time, he developed chronic cough and intermittent wheezing, which were attributed to his underlying COPD. Serial imaging demonstrated slow interval growth of the nodule from 1.4 cm to 2.7 cm. A PET/CT performed in August 2024 revealed mild FDG uptake, raising concern for low-grade malignancy. The patient elected to proceed with video-assisted thoracoscopic surgery (VATS) wedge resection and mediastinal lymph node sampling.Gross examination showed a 2.5-cm well-circumscribed papillary lesion. Histopathology demonstrated papillary fronds lined by bland cuboidal pneumocytes without necrosis or mitotic activity. Immunohistochemistry showed positivity for TTF-1, KRTAE1/AE3, and EMA, and absence of a round-cell component, ruling out sclerosing pneumocytoma. Margins and all lymph nodes were negative for tumor.Postoperatively, the patient’s chronic cough and wheezing completely resolved, and he remains asymptomatic and doing well. Discussion: This case highlights unique aspects of pulmonary papillary adenoma. The 17-year radiologic course represents one of the longest documented natural histories of this tumor, underscoring its indolent and benign behavior. Despite slow growth, the lesion showed mild FDG avidity, raising concern for malignancy. This reinforces that low-level PET uptake does not exclude benign pathology, as chronic pneumocyte hyperplasia or focal inflammation can yield false positives. Histologically, PPA can closely mimic sclerosing pneumocytoma or papillary adenocarcinoma, requiring immunohistochemical confirmation. Notably, the patient’s chronic respiratory symptoms resolved after tumor excision, suggesting a local inflammatory effect of the lesion. This case also emphasizes the role of shared decision-making in managing indeterminate pulmonary nodules, where growth and metabolic activity warranted resection, leading to both diagnosis and symptom resolution. Conclusion: PPA is a benign lesion that can mimic malignancy radiographically and metabolically. Awareness of its indolent growth pattern, potential for mild FDG uptake, and overlapping histology with malignant papillary neoplasms is essential for accurate diagnosis and appropriate management. Complete surgical excision is curative, and long-term prognosis is excellent.

Volume

212

First Page

1

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