This is one of the numerous hospital admissions for this 34-year-old AIDS patient with known cutaneous Kaposi's sarcoma (KS), who presented with a history of one episode of hemoptysis, fever, and decreasing exercise tolerance. On admission his CD 4 count measured 10 cells/mm3. His initial chest radiograph showed non-specific bilateral interstitial and air-space opacities in both mid and lower lung fields.

Protocol
The patient was scanned on a GE HiSpeed Advantage system using a protocol specifically developed for airway evaluation, particularly for patients presenting with hemoptysis - a protocol that combines three-phase and helical/axial techniques.

For phase 1, we perform an initial helical acquisition using 7-mm sections and a 1:1 pitch from C5 (the level of the cords) to the carina. These data are reconstructed at 7 mms.

For phase 2, a second helical acquisition is performed, using 5-mm sections from the carina to the level of the inferior pulmonary veins. A pitch of 1:1 or greater is used as needed, depending on the individual patient's size. These data are then reconstructed at 3 mms.

For phase 3, 1-mm HRCT images are obtained @ 10 mm from the level of the inferior pulmonary veins through the lung bases, and are reconstructed with an edge-enhancing (bone vs. lung) algorithm.

Contrast is optional, although it is preferred in patients with a questionably abnormal mediastinal and/or hilar contour on routine chest radiographs. When used, 60% contrast is administered at a rate of 2 cc/second with a 30-second delay. Administration may begin at the outset of the study or be withheld to the second phase, reflecting the likely presence of either mediastinal and /or hilar pathology.

This approach allows optimal identification of both potential focal central-airway pathology and peripheral bronchiectasis - the two most likely causes of hemoptysis in patients with non-localizing chest radiographs.

The findings
The axial CT sections through the mid and lower trachea (Fig.1,2) reveal subtle areas of focal asymmetry of the tracheal lumen, with minimal irregularity and thickening of the tracheal wall. A 3-D surface rendering of the trachea (Fig.3) clearly shows the presence of two well-defined focal abnormalities involving both the anterosuperior and right inferolateral tracheal walls. These findings were also apparent with virtual bronchoscopy (a Works-in-Progress).

Fig. 1 & 2	Fig. 3	Fig. 4

Evaluation with fiberoptic bronchoscopy (Fig.4) confirmed the presence of focal tracheal abnormalities corresponding precisely to the CT findings; these subsequently proved to be due to invasive Aspergillus fumigatus.

Clinical advantages
The clinical advantage of accurate, non-invasive localization of abnormalities within and/or adjacent to the tracheobronchial tree is apparent. Although the case presented here involves an HIV (+) patient, all patients with suspected focal abnormalities within the tracheobronchial tree may be studied to advantage with CT.

To date, CT has proved of greatest clinical relevance in the work-up of patients with known or suspected lung cancer. In this setting, determining the true extent of disease both within and outside the bronchial lumen is critical to appropriate clinical management. CT is of particular value in identifying those patients for whom pre-operative staging is indicated, with mediastinoscopy, transbronchial needle aspiration and/or surgery - and in determining which of these staging alternatives is most likely optimal.

In select cases, CT findings of extensive invasion of mediastinal structures may obviate invasive staging altogether.

Patient advantages
For patients, the major benefit of CT is its ability to non-invasively identify and characterize both bronchial and parenchymal abnormalities. When findings are present, CT allows the appropriate selection of patients for whom invasive procedures are needed.

Equally important, in select cases CT may obviate invasive procedures altogether, either by disclosing no significant findings, or by identifying otherwise unsuspected pathology to account for the patient's symptomatology.

To date, these advantages have proved of greatest value in patients presenting with hemoptysis and a non-localizing chest radiograph in whom there is a low index of suspicion for cancer.