Giant Calcified Frontal Lobe Metastasis as the Initial Manifestation of Pulmonary Large-Cell Neuroendocrine Carcinoma: Diagnostic and Surgical Insights From Intraoperative Diagnosis

We present a rare case of pulmonary large-cell neuroendocrine carcinoma (LCNEC) manifesting as a solitary, calcified brain metastasis (CBM) in a 69-year-old woman with no known malignancy or respiratory symptoms. Computed tomography (CT) of the brain revealed a large, heterogeneous left frontal lobe mass with coarse intratumoral calcification and central necrosis. Magnetic resonance imaging (MRI) demonstrated ring-like peripheral enhancement, peritumoral edema, and signal voids on gradient-echo (GRE) sequences, suggesting calcification and/or hemorrhage. A solitary pulmonary nodule was identified in the right upper lobe on preoperative chest CT, and the serum progastrin-releasing peptide (proGRP) level was markedly elevated, suggesting a neuroendocrine tumor. Differential diagnoses included high-grade glioma, particularly oligodendroglioma, based on the lesion's location and calcification. Intraoperatively, the tumor was partially calcified and infiltrated the eloquent cortex, necessitating subtotal resection near the pyramidal tract. Frozen sections revealed a proliferation of atypical large cells with rosette-like structures and nuclear palisading, which are inconsistent with glioma and suggestive of a metastatic neuroendocrine neoplasm. Final pathological examination confirmed metastatic LCNEC. Although CBMs are not exceedingly rare, their imaging features can mimic those of primary brain tumors, potentially delaying diagnosis. This case underscores the importance of considering metastatic LCNEC in the differential diagnosis of solitary calcified brain lesions and highlights the practical impact of intraoperative pathology on surgical decision-making.