It should be noted that the most common presentation of asymptomatic lung cancer is indeed a
solitary pulmonary nodule (SPN), but for most symptomatic lung cancers the nodule is at least 3 cm in diameter at the time of initial diagnosis. The author does a good job of providing documentation to refute one of his critical hypotheses, which indicates that "neoplasm can often be strongly suspected or excluded based on the radiologic characteristics of the single pulmonary nodule."
Only Three Clinically Useful Criteria
In our experience, there are only three criteria that give one a sense of relief in pronouncing a nodule to be more likely benign than malignant. A lesion that is either unchanged over at least 2 years or has doubled in size in less than 1 month is not likely to represent a malignancy. The only other criterion of importance on conventional radiography is the presence of the characteristic "popcorn" calcification. Any other radiographic description or criteria provide little comfort for the referring clinician or the patient, and therefore, the decision to resect or follow the lesion is a clinical one.
The decision to do percutaneous aspiration or biopsy depends on the availability of exquisite cytopathology and the comfort zone that may be provided by a negative result.
The advantage of the CT contrast enhancement technique described by
Swenson et al has validity. It would be particularly effective for patients
who may be at high risk for surgical in-
tervention or where needle aspiration and/or biopsy has led to equivocal results. Even with this technique, there will be a few patients with a definite malignancy who show little contrast
It should be noted that FDG-PET scanning is more commonly used for staging a malignancy or for following a patient with suspected disease recurrence than for differentiating between benign and malignant SPNs. FDG imaging clearly can produce false-positive studies. This has been reported in aspergillomas, abscesses, and tuberculosis. However, as a relatively new technology, FDG-PET may ultimately become the most cost-effective way to evaluate suspicious pulmonary opacities. More clinical studies are needed to assess its overall accuracy.
The discussion of the radiographic manifestations of the four primary
cell types of lung cancer is, by and large, excellent, but the radiographic
distinction of cell types is so imprecise that it has very little clinical
Also, many of these primary cancers are actually of a mixed cell type with either a squamous or adenocarcinoma component dominating. With most large series, squamous cell carcinomas, rather than adenocarcinomas (the most common cell type), produce the Pancoast syndrome.
Radiologic Assessment of Disease Extent
The radiologic assessment of the anatomical extent of lung cancer is essential for determining treatment options, particularly the extent of surgery. Peripheral tumor spread will define the area of extrapleural dissection or en-bloc resection of the lung and chest wall. The author accurately defines the role of CT in confirming invasion of the chest wall, but the failure to mention the role of MRI in evaluating the extrapleural surface wall is an unfortunate limitation of this area of discussion. Magnetic resonance imaging produces superior soft tissue contrast resolution and has multiplanar capability which gives it an advantage in evaluating pleural and extrapleural extension. It is particularly useful in the evaluation of superior sulcus tumors.
CT and MRI studies have been reported to have similar accuracies in diagnosing mediastinal involvement, but the Radiologic Diagnostic Oncology group has recently proven MRI to be slightly more accurate than CT in assessing the mediastinum. Scans with CT and MRI assess distant metastases equally, particularly adrenal and hepatic metastases. As mentioned previously, initial studies suggest that FDG-PET imaging shows great promise for more accurately indicating the presence or absence of local or distant metastases, but larger and better controlled clinical trials are needed.
In summary, the author wisely points out that the most reliable and important study in the assessment of a single pulmonary nodule is comparison with prior radiographs. Unfortunately, for too many individuals, finding prior films is difficult mostly because old films are frequently destroyed. The advent of digital technologies and the ability to store these images in a more cost-effective way provides a more favorable outlook for nodule evaluation. At present, many resources are being expended in an effort to determine the benign or malignant nature of such lesions, with variable quantifiable results. The specificity and sensitivity of current imaging staging techniques show great promise for the elimination of unnecessary surgery in patients with either benign or malignant diseasewhether intra- or extrathoracic in origin.