Variability in lesion depth on prone and supine CT scans of the chest: implications for the accuracy of transthoracic needle aspiration biopsy.

Transthoracic needle biopsy of the lung is often performed fluoroscopically in the prone position; nodule depth measurements are made from accompanying computed tomographic (CT) scans performed supine. We evaluated the effect of prone and supine positioning on the effect of nodule depth as measured from the skin surface. Twenty consecutive patients having CT-guided biopsy performed in the prone position were assessed. Nodule depth from posterior skin surface to nodule was compared with prebiopsy supine CT scan. Nodules above the carina showed minimal change in depth. Those below the carina showed considerable variability, with depth changes < or = 4.0 cm. Awareness of the magnitude of the potential effect of patient position on lesion depth should be helpful in reducing the likelihood of false negative results in fluoroscopically guided biopsy.