Pituitary metastasis as the initial presentation of small cell lung carcinoma diagnosed by endobronchial ultrasound-guided transbronchial needle aspiration

Pituitary metastasis as the initial presentation of small cell lung carcinoma (SCLC) is rare, occurring in <1% of symptomatic pituitary lesions, and poses a significant diagnostic challenge when the primary malignancy is unknown. A 75-year-old man with a 30-pack-year smoking history presented with 2 months of progressive confusion, headaches, and diplopia. Examination revealed bilateral abducens nerve palsies and bitemporal hemianopia. Laboratory evaluation demonstrated central hypothyroidism and secondary hypogonadism. Brain magnetic resonance imaging showed a 1.7 cm contrast-enhancing sellar mass with pituitary stalk thickening, features highly suggestive of metastatic disease. Chest and abdominal computed tomography revealed right middle lobe collapse, subcarinal lymphadenopathy, and hepatic metastases. Rather than pursuing high-risk transsphenoidal pituitary biopsy, endobronchial ultrasound-guided transbronchial needle aspiration (EBUS-TBNA) of the subcarinal lymph node was performed, confirming extensive-stage SCLC (thyroid transcription factor-1+, synaptophysin+, chromogranin A+, insulinoma-associated protein 1+, marker of cellular proliferation > 80%). The pituitary lesion was presumed metastatic based on characteristic clinical and radiological features. Hormone replacement and platinum-etoposide chemotherapy with durvalumab were initiated. At 3-month follow-up, the patient demonstrated partial hepatic response, stable pituitary disease, resolution of diplopia, and improvement in functional status from Eastern Cooperative Oncology Group (ECOG) 2 to ECOG 1. This case highlights the pivotal role of EBUS-TBNA in establishing a definitive diagnosis from an accessible extracranial site, avoiding unnecessary neurosurgical intervention and enabling prompt initiation of guideline-directed therapy.