Diffuse reticulonodular shadows in bilateral lungs mimicking metastatic lung tumors and carcinomatous lymphangiomatosis

A 52-year-old woman with an unremarkable medical history was referred to our hospital for the evaluation of diffuse reticulonodular shadows in the lungs (Fig. 1A). Her main symptom was a mild cough. She was a never-smoker and worked as an office clerk for several years, with minimal to no occupational hazard exposure. A chest computed tomography (CT) showed diffuse reticulonodular shadows with nodular septal thickening but no pulmonary nodules or masses, pleural effusion, and lymphadenopathy (Fig. 1B, C). Imaging findings suggested the presence of an infection, interstitial pneumonia, pulmonary edema, metastatic lung tumors, and carcinomatous lymphangiomatosis. Laboratory blood test results showed no abnormalities in the blood counts. Moreover, biochemical test results, including C-reactive protein levels, showed no abnormal values. Since the patient was afebrile, had an oxygen saturation of 97%, and had no rales on auscultation, infection, interstitial pneumonia, and pulmonary edema were unlikely. Thus, we considered the possibility of a metastatic lung tumor or carcinomatous lymphangiomatosis and decided to perform tumor marker tests. Results revealed that the patient had elevated carcinoembryonic antigen levels (1498 ng/mL, normal value <5 ng/mL). Although she underwent a neck-chest-abdomen-pelvis contrast-enhanced CT, upper and lower gastrointestinal endoscopy, and gynecologic examination, the primary tumor site was undetected. Thus, a random transbronchial lung biopsy was performed. Histopathological examination showed that the tumor was an adenocarcinoma immunohistochemically positive for both CK7 and TTF-1 (Fig. 2). These findings suggest that the primary site of the carcinoma was the lungs. In addition, the specimens were found to harbor Epidermal growth factor receptor exon 21 L858R mutations.