The Use of Multislice Spiral CT to Predict the Re-sectability of Central Lung Cancer: Correlation with Pathologic and Surgical Findings

DISCUSSION

CT angiography has become an alternate angiographic technique in judging central pulmonary vascular involvement with central lung cancer. Advanced knowledge of the encasement of central pulmonary vessels is very important because it renders the prospect of resection difficult, requiring appropriate planning and mobilization of available resources. However, vascular encasement cannot be detected thoracoscopically or bronchoscopically. Dynamic CT scanning is accurate in predicting the unresectability of lung cancer. With recent advancements in CT scanning, detection and staging of lung cancer are improving.^[3-6]

In our study we explored the thesis that MSCT angiography with imaging reconstruction canimprove the prediction of tumor resectability by improving the detection of vascular invasion. Indeed, in our selected patients with lung cancer in the hilar area without distant metastasis, we found that CT-RI was more accurate than axial CT images alone in judging the relationship of central pulmonary vessels with the tumor both in the pathological group (78 vessels studied) and in the surgical group (186 vessels studied). The sensitivity and positive predictive value of unresectability of the vessels were all higher. Our results indicate that MSCT with imaging reconstruction can improve the accuracy in the detection of invasion of the central pulmonary vessels in patients undergoing pulmonary resection for central lung cancer and to predict the resectability.

Considering that the operative modality is affected by many factors, such as surgeons having different operative skills, whereas patients vary in general conditions. So in our series, we just evaluated the encasement and resectability of pulmonary vessels, but did not assume a particular operative modality. Nevertheless, after knowing the involvement of the related vessels, an experienced surgeon can easily establish an operative modality.

The inability of CT to accurately distinguish vascular encasement may be due to insufficient vascular en hancement or the relatively decreased resolution of cross-sectional imaging along the z-axis. Thus, subtle changes in the caliber of the central pulmonary vessels may be missed. Some of these problems may be reme died with the used of spiral CT and CT angiography, which both increases vascular opacification and, in ad dition to cross-sectional CT imaging, produces angio graphic images. However, spiral CT angiography does not improve resolution, and artifacts from image-pro cessing techniques and involuntary motion may further degrade the z-axis resolution.

MSCT has the capability of rapidly scanning a large longitudinal (z) volume with high z-axis resolution. A recent study indicated that 4-slice spiral CT can provide equivalent imagequality at 2 to 3 times the volume coverage speed of single slice spiral CT.^[7] At the same time, artifacts from image-processing techniques and involuntary motion are decreased.

In distinguishing vascular encasement, axial images alone often were insufficient becausemost vessels do not lie on the axial plane. MSCT with imaging reconstruction (2-dimensional, 3-dimensional models and CT virtual endoscopy) provided much more useful information (Figs. 1,2). Related vessels can be assessed by viewinguall aspects, especially multi-planar reformation (MPR) which overcame the visual limitation and thus improved the accuracy.

We conclude that MSCT with imaging reconstruction provides useful information about neoplastic invasion of the central pulmonary vessels. Compared with axial CT imaging alone, it improves staging for resectability and can be used to plan surgery and predict cases in which resection may prove to be difficult.

With the development of CT technology, more rapid scanning can be employed. MSCT will play more and more important roles in both diagnosis and in preoperative selection of patients for radical pulmonary resection.