| Summary: | Introduction: Pulmonary Neuroendocrine tumors have been categorized into high, intermediate and low grade. The distinction between low grade typical carcinoid from atypical carcinoid depends on mitotic count and presence of punctate necrosis. Case presentation: The patient is a 60 year old female with past medical history of diabetes mellitus, hyperlipidemia, gastrointestinal reflux disease and cervical myelopathy. An incidental right upper lobe nodule was discovered during hospitalization for post-total knee arthroplasty sepsis. Follow-up CT and PET scans demonstrated size stability with mild hypermetabolic activity. The tumor was excised by a robotic thoracoscopic right upper lobectomy and mediastinal lymph node dissection. A lobulated, tan-yellow, well demarcated firm mass, measuring 1.2 × 1 × 1 cm was grossly identified. Microscopically, the well circumscribed mass demonstrated near complete infarct-like central necrosis with a peripheral viable cellular rim consisting of nests of tumor cells that stained positively with TTF-1, Synaptophysin, Chromogranin, and CD56; and was negative for calcitonin and monoclonal CEA. The mitotic figure count was negligible and met the WHO criteria for typical carcinoid. The proliferative index (Ki-67) was slightly high at 9.29%. Discussion: The unusual central necrosis seen in the tumor and the relatively high proliferative index created a pathological diagnostic dilemma discussed in this report. Keywords: Lung, Neuroendocrine tumors, Carcinoid
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