Evaluation of solitary pulmonary nodule.GS Gaude, MJ Pinto
Department of Chest Diseases & TB, Goa Medical College, Panaji-Goa.
Keywords: Adult, Aged, Biopsy, Needle, Bronchoscopy, Coin Lesion, Pulmonary, diagnosis,therapy,Diagnosis, Differential, Female, Human, Lung Neoplasms, diagnosis,pathology,Male, Middle Age, Prognosis, Tomography, X-Ray Computed,
The finding of a solitary pulmonary nodule (SPN) on a chest radiograph in an asymptomatic individual remains an interesting challenge as the best approach to its management is still controversial.
By definition, a SPN is a fairly discrete pulmonary opacity completely surrounded by lung and not associated with atelectasis or adenopathy on the chest radiograph. Cummings et al has defined SPN as a spherical intrapulmonary roentgenographic density less than 6.0 cm in diameter with no calcium visible on roentgenograms, tomography, or computed tomography (CT). In published series, the size of the SPN has varied from 1 to 6 cm,. It is estimated that more than 150,000 new cases of SPN will be detected in the next year, 40% of which will be malignant with the majority being bronchogenic carcinoma.
SPNs are seen in about 1-2% per 1000 chest radiographs, most being detected on routine chest radiographs in asymptomatic individuals. Eighty different etiologies have been reported. The common causes of SPNs shown in [Table - 1].
Sixty percent are benign. granuloma accounting for a major portion (54%) bronchogenic carcinomas (35%), bronchial adenomas (2%) and metastatic lesions (3.5%) are amongst the other causes.
Prompt evaluation and management of an SPN are essential because of the significant number that are malignant. The goals of evaluation and management in the patient with an SPN are to minimise the number of thoracotomies for benign processes and expedite resection for malignant nodules there-by affording our patients the best chance of a potential surgical cure.
In the last two decades, flexible fibreoptic bronchoscopy, percutaneous transthoracic needle aspiration and CT of the chest have improved our ability to distinguish benign from malignant nodules. A complete history and physical examination should always be performed. Most patients are asymptomatic. Age, smoking history, exposure to potential carcinogens, residing or travelling to areas endemic for pulmonary mycoses, history of previous malignancy, and previous pulmonary disease should be ascertained'. In men over 50 years of age, 50% of non-calcified resected nodules are malignant. A history of a previous known malignancy in a patient with an SPN is important to rule out a metastatic lesion in the lung. Recent pulmonary symptoms such as hemoptysis or systemic symptoms such as weight loss, suggest malignancy, a careful and complete physical examination might yield valuable clues.
Both the standard PA and lateral chest films should detect the SPN if it arises from the lung parenchyma. Confirmation of SPN on plain chest X-ray is necessary as 10-20% of small lesions seen on chest X-ray are not actual pulmonary nodules. These spurious nodules can be caused by imaging arti-facts (ECG leads, buttons), pleural plaques, healed fracture of rib, skin lesions and nipple. These problems are eliminated by an oblique view, fluoroscopy and repeat X-ray chest with nipple markers. It the problem still remains unresolved, then CT scan may be used for confirmation.
After detection of an SPN, the need for further evaluation is usually determined by assessment of stability or the presence of calcification. The presence of calcium within a nodule in the following patterns is a reliable indicator of its benign nature. Laminated calcification is a characteristic sign of a granuloma "Popcorn" calcification typically occurs in hamartomas while a dense central nidus of calcification represents a benign process. Calcium may be present in a malignant lesion but is usually eccentrically located. An SPN with a speculated appearance accurately predicts malignancy in 88 to 94% of cases. If a nodule has a linear shape, with uniform width and without irregularity or nodularity, it is most likely to be benign. In general, irregular or ill-defined shaggy borders are more often associated with malignancy, whereas well-defined margins suggest a benign process. In the earlier studies, it was seen that in SPN less than 2 cm in diameter, the chances of malignancy was 10-25% but in a more recent study 42% of the nodules measuring less than 2 cm or less were malignant. The changing size of an SPN can help differentiate a benign from a malignant nodule. Growth of SPN suggests malignancy and is measured by the doubling time, which refers to the doubling of volume. Although there is an overlap at extremes, doubling times of 30 to 500 days suggest malignancy. Although doubling time is important to differentiate benign from malignant lesions, there are a few exceptions eg. choriocarcinoma and germ cell Tumour secondaries can grow very fast and may mimic benign lesion. In the evaluation of SPN, in young patients, though primary bronchogenic carcinoma is rare especially in non-smokers, isolated secondaries can occur from carcinoma of breast, kidney, testis or lymphoma. In India, hydatid cyst is quite common. Hence, abdominal sonography can help us in evaluating the above possibilities.
CT scan has replaced conventional tomography in the initial evaluation of SPN. In early studies, density of SPN was considered as important parameter as less dense lesions were more often malignant. But Goldwin et al concluded with this respect that CT was not more useful than conventional radiography. The density and CT number of SPN depends on many factors like anatomic difference in patients size, location of nodule, respiratory variation and slice thickness. It can also vary among scanners and time spent as well as kilo-electron voltage X-ray beam and reconstruction rhythm. In an attempt to overcome this lack of standardisation among scanners, the CT reference phantom has been developed which can reduce the sources of densitometric error and provide a standard for comparison.
This phantom is an antyropomorphic model made of tissue equivalent resins and density rods that can be arranged to simulate the shape, dimensions, location and density of a SPN. Nodules demonstrating higher areas of attenuation than that of the phantom higher areas of attenuation than that of the phantom are considered benign. Using this phantom model, one co-operative study, found that more than half of benign lesions were shown to contain calcification not identified with conventional technique and CT densitometry is most effective in nodules with smooth or lobulated borders measuring less than 3 cm in diameter.
CT scan besides calcification can show presence of fat and vascular connection. CT scan is more useful in nodules less than 2-3 cm in diameter, since larger nodules are more commonly malignant. Irregular or speculated lesions are usually malignant and less after calcified. So conventional 10 mm sections are adequate in evaluation by CT scan. Current studies employ a thin slice CT (HRCT) approach to evaluate calcium in pulmonary nodules as it is more sensitive. HRCT with 1.0-5.0 mm thin slices create smaller voxels and decrease tissue averaging. which allows better density determination. In most cases, the presence or absence of calcification becomes readily apparent. It allows a better assessment to type, distribution and severity of parenchymal abnormalities than is possible on conventional CT. But sometimes it is difficult to differentiate between vascular structures and SPN and thus HRCT can increase false positive results due to the vascular shadows.
HRCT is recommended for all indeterminate nodules 2 cm or less in diameter with smooth or lobulated borders. It can also allow a definite diagnosis of an AV fistula, fungal ball mucus plugs, rounded atelectasis and pleural plaques. When biopsy of SPN is planned, CT scanning is helpful in guiding the physician to the optimal biopsy site.
Flexible fibreoptic bronchoscopy with washings brushings, and biopsy has a 110%-28% yield for malignant nodules less than 2 cm in diameter. For those with diameter more than 2 cm, trans-bronchial biopsy under fluoroscopic guidance is successful in 40%-69% of cases. Percutaneous fine needle aspiration biopsy is very useful in the diagnosis of malignancy with a sensitivity ranging from 64%-97% with very few false positive results. In benign disease the accuracy varies between 50% to 88%. Complications from aspiration biopsy include pneumothorax from aspiration biopsy include pneumothorax in 20% to 34% of cases, with 5% to 14% requiring chest tube drainage. [Table - 2] gives important features of benign and malignant nodules.
Decision about managing SPNs may be influenced by numerous factors including the probability that the nodule is malignant, risks or surgery accuracy of biopsy techniques, fear that delay in surgical resection may forfeit the possibility of cure and the patients attitudes toward alternative approaches. The management options for SPN are either observation i.e. the "Wait and Watch" strategy or immediate thoracotomy or biopsy of the nodule based on which decision is taken. If biopsy findings are not specifically diagnostic of either malignant or benign disease then either surgery is carried out immediately or the patient is followed up conducting serial chest films to determine rate of growth of nodule.
The proponents of immediate surgery argue that if surgery is delayed, it allows time for growth of SPN and therapy reduces the chances of a 5 year survival. However, there are no studies demonstrating a decrease in survival when a patient is kept under observation for few months to assess the growth of nodule. Observation is advisable when the risk of malignancy is low, the risk of thoracotomy is high, or when the patient refuses further invasive procedures.
Cummings et al proposed the use of decision analysis based on the probability that the nodule is malignant. Using Bayes Theorem and four variables i.e. age, history of cigarette smoking, diameter of nodule, and prevalence of malignancy is SPNs, an estimation of malignancy was calculated. The average life expectancy in years of various strategies was then compared. In patients with a calculated probability of malignancy greater than 75% to 80% early thoracotomy appeared slightly superior to the needle biopsy. In patients with probability of malignancy less than 75% to 80%, needle biopsy was slightly superior to immediate thoracotomy. Observation was suggested when the likelihood of malignancy was less than 5% or the risk of surgery was high. In most of the circumstances, the differences between strategies were so small that it was a "close call".
If surgery is contraindicated because of poor lung functions, age or coexistent cardiovascular disease or results of CT scan, further management is influenced by symptoms and probability of malignant disease. Management of SPN is complex and should be individualised. The basic guidelines to be followed are presented as algorithm for management of SPN in [Table - 3].
Finally, the role of the physician is crucial in the management of an SPN. Informing the patient and family about each option and their uncertainties as well as about the immediate and long term risks and benefits of each step is extremely important. It is also important to assess and respect the patientís anxiety, fears and attitude. Active patient participation in decision making allows these factors to be incorporated into the patients decision. Each patient must be dealt with on an individual basis. In short, we must treat the patient and not the SPN.
[Table - 1], [Table - 2], [Table - 3], [Table - 4]