Extending the Diagnostic Frontier: Slim Endobronchial Ultrasound in Navigation Bronchoscopy: A Case Series

Conventional convex endobronchial ultrasound (EBUS) is limited to the central airways, whereas radial EBUS lacks real-time guidance. As navigation bronchoscopy expands into the peripheral lung, a gap persists in the (sub)segmental "mid-zone," where visualization, tool alignment, and vascular anatomy challenge diagnostic sampling.

Seven patients with suspected lung cancer in the mid-zone underwent slim EBUS (s-EBUS) with or without cone-beam CT-guided navigation bronchoscopy. Anatomical access, sampling strategy, diagnostic contribution, and safety were evaluated. s-EBUS allowed precise real-time visualization and needle placement in mid-zone targets, including stations 12L and peribronchial lung nodules beyond (sub)segmental bronchi. In two cases, a pulmonary artery branch separated airway and lesion; under ultrasound control, transvascular needle access was feasible without adverse events. In a single case, s-EBUS-guided cryobiopsy was successfully performed using a 1.1-mm probe and yielded diagnostic tissue for histology and molecular analysis. s-EBUS provided clinically relevant diagnosis or staging information in all cases.

s-EBUS extends ultrasound-guided bronchoscopy beyond the central airways and may close an important anatomical diagnostic gap in navigation bronchoscopy. Advantages include mid-zone access, vascular mapping, selective transvascular sampling, and targeted cryobiopsy. Further studies should assess performance, safety, and clinical impact.