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Superior mediastinal shift in right-lower-lobe collapse: the "upper triangle sign".

In some patients with right-lower-lobe collapse a triangular shadow was seen in the right upper lung field, continuous with the mediastinum and with its apex pointing toward the right hilus. This represents a shift of the upper anterior mediastinum to the right and may be mistaken for right-upper-lobe collapse or an infiltrate by the unwary observer. This finding, which the authors call the "upper triangle sign," occurs frequently enough in cases of significant right-lower-lobe collapse to be a useful diagnostic sign.