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Thoracic Surgery, Massachusetts General Hospital, Blake 1570, 55 Fruit St, Boston, MA 02114
(Email: wright.cameron{at}mgh.harvard.edu).
This article by Parsons and colleagues [1] addresses an important clinical problem in thoracic surgery, which is the accuracy in detecting pulmonary metastases [1]. Although resection of pulmonary metastases has never been proven to improve survival in a randomized clinical trial, complete resection has been a consistent prognostic factor in many phase 2 trials, suggesting the efficacy of resection and the importance of detecting and removing all metastatic disease. Modern computed tomographic (CT) scanning has greatly improved our preoperative detection of suspected metastatic disease with a single breath hold and fine slice thickness (2.5 to 5 mm).
Resection of peripheral small pulmonary metastases would seem an ideal indication for a video-assisted thoracic surgical approach (VATS). Indeed many surgeons have used a VATS approach to pulmonary metastatectomy, relying on preoperative CT imaging for localization of metastases. Additional lesions can be picked up by inspection of the visceral pleural surface and by limited palpation of the superficial lung through the port sites. Nonetheless, many surgeons believe this is a suboptimal approach, as lesions will be missed. Indeed a well-known trial performed at the Sloan Kettering Cancer Center in 1996 was stopped due to a very high incidence of missed lesions [2]. Several studies as noted by the authors have been reported since that time, which have confirmed the inaccuracy of CT scans in detecting all pulmonary metastases.
The current study is limited by the modest number of patients, the use of old "thick" slice (8 to 10 mm) scans in 68% of the patients, and its retrospective design. Subgroup analysis however suggested that slice thickness did not correlate with missed metastases. Metastases were missed in a surprising number of patients by both radiologists (ie, 46% and 47%). We are not told the size or location of these missed lesions. From my own experience, it is guessed that these were small and immediately subpleural. Importantly, the surgeon also missed many metastases with 26% and 34% of lesions missed based on the readings of the two radiologists. Another important finding was that unilateral disease by CT was bilateral in 23% of patients, suggesting that bilateral exploration would usually be prudent. Clearly these data suggest the need for close continued CT follow-up of these patients to detect disease missed by the radiologist, the surgeon, or both.
The authors correctly point out in their discussion the uncertainty of the importance in removing all metastatic disease in this small subgroup of patients who have metastatectomies. Approximately two thirds of the patients will die of progressive metastatic disease and thus would presumably not benefit from removal of additional small lesions. This leaves a small number of patients at risk who might benefit from repeat resections if recurrent or persistent disease, or a combination thereof, is identified. A randomized trial would need to be done to answer the question of limited removal of lesions based on imaging versus bilateral palpation and resection. This trial would need a very large number of patients because most will die of progressive metastatic disease and the expected difference between the 2 groups would be rather modest. In addition, the enthusiasm and potential for funding such a trial would be problematic at best. So what is a surgeon to do? As always, weigh all the unique patient factors and make a thoughtful decision with an informed patient. Ideally the preoperative CT should be a 2.5-mm slice helical CT to maximize the opportunity for detection of nodules. Factors that might weigh in for bilateral exploration include young age, favorable histology (ie, sarcoma, testicular, or cancer), and more than one nodule detected. Comorbid disease, previous chest surgery, and patient desire (with informed consent) for a VATS approach favor unilateral resection. Indeed the authors follow a similar approach for selective exploration as 20 of their 60 resections were unilateral.
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