A 74-year-old female was found to have a round p-GGN measuring 12 mm in diameter in the right middle lobe of the lung on chest HRCT, performed for a preoperative work-up of right breast cancer in May 2008. The patient underwent right mastectomy and sentinel lymph node dissection, and the pathological diagnosis was papillotubular carcinoma without lymph node metastasis. Then she was referred to our department in December 2009, and underwent another HRCT examination in March 2010 (Fig. 1a), and there were no significant changes in size of 11 mm in maximal dimension; however, we could not eliminate the possibility of lung adenocarcinoma. Therefore, we performed surgical resection in order to obtain a pathological diagnosis provide treatment simultaneously. FDG-PET was not performed due to the estimated low diagnostic performance of this modality for a diagnosis of p-GGN. The patient underwent video-assisted thoracoscopic middle lobectomy in April 2009. Since the intraoperative frozen pathological diagnosis revealed the tumor to be an adenocarcinoma, additional mediastinal lymphadenectomy was subsequently performed. Histologically, the tumor located just beneath the visceral pleura exhibited the proliferation of small round to spindle-shaped cells arranged in a spindle cell pattern with finely granular chromatin, inconspicuous nucleoli, and a scant to moderate amount of eosinophilic cytoplasm. Necrosis and mitoses were rarely detected (Fig. 1b). Immunohistochemically, the tumor cells were positive for chromogranin A and synaptophysin (Fig. 1c). These features indicated a typical carcinoid tumor of pT1aN0M0.
Discussion
The term “ground glass opacity (GGO)” is defined as “hazy increased attenuation in the lung that does not obliterate the bronchial and vascular margins” in the lung detected on HRCT, according to the Fleischner Society [2]. This definition is non-specific and does not necessarily reflect the pathological etiology of p-GGN. The presence of p-GGN on HRCT sometimes implies early-stage lung cancer, i.e. adenocarcinoma in situ or so-called bronchioloalveolar adenocarcinoma [3]. With respect to other lung malignancies, Okita et al. reported a rare case of metastatic melanoma in the lung presenting with focal GGO [4]. To our knowledge, this is the first report of a typical carcinoid tumor of the lung that presented with focal p-GGN on HRCT. In general, the appearance of a typical carcinoid tumor on CT is generally a solid nodule [5]. Also, diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) is now considered to be a precursor for pulmonary carcinoid tumors; however, its appearance on HRCT has generally reported to be diffuse, multifocal GGO due to small airways obstruction evidenced by inspiratory mosaic attenuation and expiratory air trapping [6]. In the present case, the tumor was consisted of many small scattered tumor foci even in the central collapsed area (Fig. 1b); thus, the appearance of the tumor on HRCT might have a possibility to be p-GGN.