Cavitary pulmonary metastasis from renal pelvic urothelial carcinoma with pathological evidence of bronchiolar obstruction supporting a check-valve mechanism: a case report.

Approximately 4% of metastatic lung tumors exhibit cavitation. Cavitary pulmonary metastases arising from urothelial carcinoma are rare. Renal pelvic cancer accounts for only 3%-5% of all urothelial carcinomas; cavitary pulmonary metastasis from renal pelvic cancer is rare. This report describes pulmonary metastasis from renal pelvic cancer with cavitation. A man in his 50s underwent laparoscopic left nephroureterectomy with hilar lymph node dissection for left renal pelvic cancer 2 years earlier. During follow-up, chest computed tomography (CT) revealed a gradually enlarging lesion with internal cavitation in the right lower lobe. Chest CT demonstrated a 17-mm cavitary nodule in segment 7 of the right lung, enlarged from 4 mm over 1 year. Cavitation was evident even when the lesion was small; tumor diameter and cavity size also increased. The cavity wall remained thin, measuring 1.5 mm in most areas, up to 4 mm, without progressive thickening. Given the rarity of cavitary metastasis from renal pelvic cancer, a surgical biopsy was performed. Thoracoscopic wedge resection revealed a nodular lesion with a grayish-white cavity. Immunohistochemical staining demonstrated GATA3 positivity, confirming pulmonary metastasis. Microscopically, the tumor proliferated while destroying the lung architecture, with small tumor cell clusters within the alveolar spaces. Tumor extension into a bronchiole lacking cartilage resulted in partial luminal obstruction. Here, radiological progression and pathological findings supported cavity formation via a check-valve mechanism. This case provides radiological and pathological evidence supporting a check-valve mechanism of cavitation in pulmonary metastasis and contributes to the differential diagnosis of thin-walled cavitary pulmonary nodules.