# Pulmonary sclerosing pneumocytoma mimicking a low-grade primary malignancy: A case report

## TL;DR

A rare benign lung tumor called pulmonary sclerosing pneumocytoma can mimic low-grade cancer due to its fast growth rate, making diagnosis challenging.

## Contribution

This case report highlights the rare occurrence of a short volume doubling time in pulmonary sclerosing pneumocytoma, resembling low-grade malignancies.

## Key findings

- PSPs can grow rapidly with a volume doubling time of 249 days, similar to low-grade malignancies.
- Histopathological analysis confirmed the diagnosis of PSP despite the rapid growth pattern.
- Diagnostic testing beyond growth rate is essential for accurate identification of PSPs.

## Abstract

Pulmonary sclerosing pneumocytoma (PSP) is a rare benign tumor classified as a pulmonary adenoma. It presents as a solitary pulmonary nodule without any specific findings, often posing a diagnostic challenge. We herein present a case of a PSP with a short volume doubling time (VDT) comparable to low-grade pulmonary malignancies.

A 27-year-old female presented to the emergency department with a fever that had persisted for the past two days. An incidental finding on chest screening computed tomography (CT) revealed a 9 mm pulmonary nodule with a round shape and smooth margin, suggestive of a benign etiology.

Follow-up CT one year later revealed an enlarged nodule exhibiting a VDT of 249 days. A thoracoscopic lingulectomy was performed, and the histopathological examination revealed papillary and diffuse proliferation of epithelial-like cells. The epithelial cells were positive for cytokeratin (CKAE1/AE3) and thyroid transcription factor 1 (TTF1), whereas the stromal cells were positive for TTF1 but negative for CKAE1/AE3. Those results were consistent with the diagnosis of a PSP.

PSPs typically present as incidental pulmonary nodules with no specific findings, often posing a diagnostic challenge. The radiographic features of PSPs have mainly been explored based on the morphological findings and metabolic activity, with limited research on their growth rate, represented by the VDT.

PSPs may exhibit rapid growth, demonstrating a short VDT similar to that of low-grade pulmonary malignancies. Comprehensive diagnostic testing not based solely on the growth rate for this rare condition is essential.

•Pulmonary sclerosing pneumocytomas (PSPs) is difficult to diagnose due to the lack of specific radiological findings.•Radiographic features of PSPs have mainly been limited research on their growth rate.•Solitary pulmonary nodules with a rapid growth pattern typically indicate a primary malignancy.•PSPs may exhibit a short volume doubling time similar to that of low-grade pulmonary malignancies.

Pulmonary sclerosing pneumocytomas (PSPs) is difficult to diagnose due to the lack of specific radiological findings.

Radiographic features of PSPs have mainly been limited research on their growth rate.

Solitary pulmonary nodules with a rapid growth pattern typically indicate a primary malignancy.

PSPs may exhibit a short volume doubling time similar to that of low-grade pulmonary malignancies.