Atypical carcinoid localized at the bronchus accompanied by diffuse idiopathic pulmonary neuroendocrine cell hyperplasia in the distal lung: a rare case report.

Diffuse idiopathic pulmonary neuroendocrine cell hyperplasia (DIPNECH) is hyperplasia of noninvasive neuroendocrine cells originating from Kultchitsky cells. This is a rare pathological condition, suspected to be a precursor lesion of carcinoid, together with tumorlet. In the WHO histological classification (4th edition) revised in 2015, DIPNECH was added to the category that includes neuroendocrine tumors. Our patient was a 77-year-old woman who initially visited another doctor because of coughing. Chest CT revealed a mass occluding the right intermediate bronchial trunk, and bronchial carcinoid was suspected from biopsy findings, leading to referral of this patient to our department. The tumor was excised under a rigid bronchoscope for the purpose of making a definitive histological diagnosis and determining the extent of spread. The stalk portion of the tumor extended from the bifurcation of the middle and lower lobe bronchi in the membranous part of the intermediate trunk to the central side. The airway appeared to be almost completely occluded under bronchoscopy, but aeration from the periphery was maintained. Histopathologically, there was hyperplasia of oval atypical cells with relatively poor cytoplasm beneath the bronchial mucosa on HE staining, suggesting neuroendocrine tumor. Immunostaining revealed that these cells were positive for CD56, chromogranin A, and synaptophysin, and that there was moderate mitosis, leading to a diagnosis of atypical carcinoid. At a later date, radical surgery comprised of right pulmonary middle and lower lobectomy and lymph node dissection was performed. The final histopathological diagnosis was atypical carcinoid of the bronchus (pT1aN0M0, stage IA). There were multiple aggregations of atypical cells, measuring approximately 1-3 mm, along the airway around the bronchioles in the excised lung, indicating concomitant DIPNECH. The patient currently has no evidence of either recurrence or metastasis at 12 months after surgery, but we will continue meticulous follow-up.