Thoracic Endometriosis Mimicking a Lung Mass: Management With Single-Stage Biopsy and Microwave Ablation

A 31‐year‐old woman with a history of endometrial hyperplasia and previous hysteroscopic polypectomy was referred for a pulmonary nodule incidentally detected on chest radiography during a routine health examination in December 2024. She was asymptomatic, without respiratory or menstruation‐related symptoms, and had no previous diagnosis of endometriosis. Chest computed tomography (CT) in January 2025 revealed a 1.8‐cm solid nodule in the right lower lobe (RLL) (Figure  1A ). Follow‐up CT in April 2025 demonstrated interval enlargement to 2.1 cm. The centrally located lesion was in close proximity to the pulmonary artery supplying the RLL, with a minimum distance of approximately 2 mm. (A) Chest computed tomography demonstrating a 1.8 cm solitary pulmonary nodule in the right lower lobe (RLL) (red arrow). (B) Image‐guided biopsy of the RLL nodule. (C) Image‐guided microwave ablation (MWA) of the lesion. (D) Follow‐up chest CT obtained 6 months after ablation, demonstrating post‐ablation scar formation without obvious radiological evidence of local recurrence (red arrow). Given the documented interval growth and inability to exclude malignancy, a shared decision was made to proceed with single‐stage image‐guided percutaneous biopsy (Figure  1B ) and microwave ablation (MWA) (Figure  1C ) in June 2025. No preliminary pathological assessment was performed before ablation. MWA was performed using a 16‐gauge, 200‐mm ablation antenna (ECO‐100CL22C; ECO Medical Instruments Co. Ltd., Nanjing, China). Two consecutive ablation cycles were delivered through a single antenna placement at 40 W for 8 and 6 min, respectively, for a total ablation time of 14 min. The lesion was located approximately 2 mm from the pulmonary artery supplying the RLL. No clinically significant postoperative complications occurred, and the patient was discharged on postoperative Day 1. Pathological evaluation of the biopsy specimen showed a biphasic lesion consisting of bland spindle cells and epithelial components (Figure  2A ). Immunohistochemical (IHC) staining confirmed the diagnosis of endometriosis, showing: Positive: oestrogen receptor (ER) in both components, PAX8 in the epithelial component and CD10. Negative: thyroid transcription factor‐1 (TTF‐1) and STAT6 (Figure  2B–E ). (A) Haematoxylin and eosin (H&E) stain (×200) showing a biphasic lesion composed of spindle and epithelial components. (B–E) Immunohistochemical staining of the lesion. (B) Thyroid transcription factor‐1 (TTF‐1), negative. (C) CD10, positive. (D) PAX8, positive. (E) Oestrogen receptor (ER), positive. Follow‐up chest CT examinations in December 2025 and June 2026, approximately 6 and 12 months after ablation, respectively, demonstrated post‐ablation changes without obvious evidence of local recurrence (Figure  1D ). No hormonal therapy or additional treatment was administered during the follow‐up period.

Min Hsieh: data curation, investigation, visualization, writing – original draft, writing – review and editing. Shun‐Mao Yang: conceptualization, investigation, writing – review and editing, supervision, resources. Hsien‐Neng Huang: investigation, validation, resources.

The authors have nothing to report.

TES occurs in approximately 1.5% of women with endometriosis and most frequently involves the pleura [ 3 ]. Parenchymal involvement is particularly rare and often presents as catamenial haemoptysis. While radiological findings typically include ground‐glass opacities, a solitary solid nodule, as seen in this patient, can raise suspicion of malignancy [ 4 ]. Histological confirmation is essential in these cases. The biphasic pattern and immunohistochemical profile (ER+, PAX8+, TTF‐1−) help distinguish pulmonary endometriosis from other lesions, including synovial sarcoma, which may also demonstrate TLE1 positivity. Standard management generally involves hormonal therapy or surgical resection. In this case, single‐stage biopsy and MWA were selected following shared decision‐making because of the documented interval growth and indeterminate nature of the pulmonary nodule. This approach enabled tissue diagnosis and local treatment during the same intervention, potentially avoiding a second percutaneous procedure. However, ablation before definitive pathological confirmation carries diagnostic uncertainty and cannot replace the comprehensive pathological assessment provided by surgical resection. Additional oncological evaluation and treatment would have been necessary if malignancy had been identified. The lesion's central location and proximity to the pulmonary artery, with a minimum distance of approximately 2 mm, presented potential technical challenges, including vascular thermal injury. Although no clinically significant procedural complications occurred, detailed documentation of the specific precautions taken to protect adjacent pulmonary vessels and bronchi was unavailable, limiting a comprehensive assessment of procedural safety. While MWA has been reported for abdominal wall endometriosis, its application in pulmonary endometriosis remains poorly established [ 5 ]. In this patient, no obvious radiological evidence of local recurrence was observed during 12 months of follow‐up without additional treatment. Nevertheless, a single case with limited follow‐up cannot establish the safety or long‐term efficacy of MWA for pulmonary endometriosis. Further clinical evidence is required. Thoracic endometriosis may rarely present as a solitary pulmonary nodule mimicking malignancy, even without catamenial symptoms. This case describes the use of single‐stage image‐guided biopsy and MWA in a selected patient, with no obvious radiological evidence of local recurrence during 12 months of follow‐up. Further evidence is needed to establish the safety, efficacy and long‐term outcomes of this approach.

The authors declare that written informed consent was obtained for the publication of this manuscript and accompanying images and attest that the form used to obtain consent from the patient(s) complies with the Journal requirements as outlined in the author guidelines.

Thoracic endometriosis syndrome (TES) is a rare condition involving the presence of endometrial tissue within the thoracic cavity [ 1 ]. Predominantly affecting women of reproductive age, it typically manifests as catamenial pneumothorax, haemoptysis or chest pain [ 2 ]. However, when TES presents as a solitary solid pulmonary nodule, it can mimic primary or metastatic malignancy, posing a significant diagnostic challenge. We present a rare case managed through a single‐stage, minimally invasive percutaneous approach.

The authors declare no conflicts of interest.