Neuroendocrine tumors of the lung: clinical, pathologic, and imaging findings

Neuroendocrine tumors of the lung arise from Kulchitzky cells of the bronchial mucosa and comprise typical carcinoid, atypical carcinoid, large cell neuroendocrine carcinoma (LCNEC), and small cell lung cancer (SCLC). At histopathologic analysis, these tumors demonstrate a progressive increase in the number of mitotic figures per 10 high-power fields of viable tumor and in the extent of necrosis, with typical carcinoid having the lowest values and SCLC having the highest. Typical carcinoid is less aggressive than atypical carcinoid, although these tumors have similar gross pathologic and radiologic features; LCNEC has a prognosis between that of atypical carcinoid and that of SCLC. SCLC is the most aggressive pulmonary neuroendocrine tumor and has the most specific imaging feature: mediastinal or hilar lymphadenopathy. At CT, carcinoid tumors appear as a spherical or ovoid nodule or mass with a well-defined and slightly lobulated border. When nonspherical, the tumor is elongated with its long axis parallel to adjacent bronchi. Calcification or ossification is seen in up to 30% of cases. The CT findings of LCNEC are nonspecific and are similar to those of other non-small cell lung cancers. Although there are some overlapping features between these tumors, integration of the clinical and imaging features may be helpful in differentiation of pulmonary neuroendocrine tumors.