Synchronous lung adenocarcinoma in situ and type B2-B3 thymoma in a frozen hemithorax: a case report and multidisciplinary approach.

BACKGROUND: Synchronous primary lung cancer and mediastinal thymoma represent a rare clinical entity. While 18F-FDG PET/CT serves as a cornerstone modality for differentiating benign from malignant thoracic neoplasms, hypermetabolic activity secondary to severe localized inflammation can frequently masquerade as highly aggressive malignancies. Such radiologic-pathologic discordance significantly elevates the risk of misdiagnosis, thereby adding substantial complexity to clinical decision-making and patient management.

CASE PRESENTATION: A 73-year-old woman with prior tuberculosis and stented coronary artery disease presented with a hypermetabolic right upper lobe (RUL) nodule (2.3 cm, SUVmax 5.0) and an anterior mediastinal mass (SUVmax 3.0) on PET/CT. Due to the patient's cardiovascular comorbidities, the multidisciplinary team (MDT) initially recommended a percutaneous biopsy. As the pathology revealed only adenocarcinoma in situ (AIS) in the context of a persistent cough and a hypermetabolic lesion, empirical broad-spectrum antibiotics were administered. A two-month follow-up HRCT showed substantial shrinkage of the right lung lesion and absorption of its solid component. The patient subsequently underwent elective uniportal video-assisted thoracoscopic surgery (VATS) for a right upper lobe posterior segmentectomy and an anterior mediastinal tumor resection. Intraoperatively, dense pan-pleural adhesions from the prior tuberculosis were evident, compounded by localized adhesions from the recent biopsy. Following sharp adhesiolysis, both lesions were successfully resected. Final pathology revealed a diagnostic masquerade: the true AIS measured only 0.66 cm, obscured by surrounding organizing pneumonia, occurring synchronously with a B2-B3 thymoma (Ki-67 >30%). The postoperative course was uneventful. The patient was discharged on postoperative day 6 after chest tube removal, and is scheduled for regular radiological follow-up.

CONCLUSION: This report highlights a critical diagnostic pitfall: the "hypermetabolic inflammatory trap" on PET/CT can easily mimic or obscure true micro-carcinomas. In medically high-risk cohorts, leveraging an MDT approach with upfront tissue diagnosis, diagnostic anti-infective management, and dynamic imaging is paramount to avoiding surgical overtreatment. Crucially, we validate that despite the technical hurdles of extensive pleural adhesions, uniportal VATS remains a highly secure and advantageous strategy for resecting synchronous thoracic neoplasms.