Solitary Pulmonary Nodule
A solitary pulmonary nodule (SPN) is defined as a single discrete pulmonary opacity that is surrounded by normal lung tissue and is not associated with adenopathy or atelectasis. The finding of an SPN on a chest radiograph is a diagnostic dilemma often faced by many clinicians. The differential diagnosis may be broad but implications rest on whether the lesion is benign or malignant.
Radiographically, a nodule is defined as a lesion smaller than 3 cm. Anything larger than 3 cm is termed a mass
Frequency
SPNs are fairly common. Screening studies in adults reveal SPNs in 1-2 per 1000 chest radiographs
Clinical Details
Most SPNs are asymptomatic.
Important features in the patient history include the following:
-Age - Risk of malignancy increases with age
-Age - Risk of malignancy increases with age
- Smoking history
- Prior history of malignancy
- Travel history - Travel to areas with endemic mycosis (eg, histoplasmosis, coccidioidomycosis, blastomycosis) or a high prevalence of tuberculosis
- Occupational risk factors for malignancy - Exposure to asbestos, radon, nickel, chromium, vinyl chloride, and polycyclic hydrocarbons
- Previous history of tuberculosis or pulmonary mycosis
RADIOGRAPH:
Often, SPNs are discovered first as incidental findings on chest radiographs. The first step is to determine whether the nodule is pulmonary or extrapulmonary.
- Nodule size: Nodules greater than 3 cm in diameter are more likely to be malignant, while those less than 2 cm are more likely to be benign.
Growth rate - Comparison of previous chest radiographs of the patient allows assessment of the growth rate. The growth rate refers to the doubling time of a nodule, ie, doubling in volume.
- Bronchogenic carcinomas usually have a doubling time of 20-400 days.
- Doubling times shorter than 20-30 days are seen in infections, infarction, lymphoma, or fast-growing metastases.
- Doubling times greater than 400 days are typically benign.
Margin characteristics: Benign lesions tend to have well-circumscribed smooth borders. Malignant nodules typically have irregular, lobulated, or spiculated (corona radiata) borders.
Calcification: Calcification within a nodule is more likely to be seen in a benign nodule; however, approximately 10% of malignant nodules demonstrate calcification. In benign lesions, 5 patterns of calcification are seen commonly, including diffuse, central, laminar, concentric, and popcorn (chondroid) calcifications. The popcorn pattern typically is described in hamartomas. A stippled or eccentric pattern is seen most commonly in malignant lesions
CT SCAN :
In addition to the features seen also on plain film , CT of the chest allows better assessment of nodules. The advantages of CT over plain film include the following:
- Better resolution: Nodules as small as 3-4 mm are detectable. Morphologic features of specific diagnosis are better visualized (eg, rounded atelectasis, arteriovenous malformations).
- Areas that are difficult to assess on plain radiography are visualized better on CT, such as the lung apices, perihilar regions, and costophrenic angles.
- Multiple nodules can be detected on CT scans.
- Malignancy can be staged using CT.
- CT can help guide needle biopsy.
Other features of CT include the following:
- Contrast enhancement: Malignant nodules tend to have greater vascularity than benign nodules. Assessment of enhancement involves repeated measurement of attenuation of a nodule over a 5-minute period. Nodular enhancement of less than 15 HU suggests that a lesion is benign, and enhancement of greater than 20 HU is more likely associated with malignancy.
- Feeding vessel sign: This sign may be seen in hematogenous or vascular causes of pulmonary nodules such as metastatic deposits or septic emboli.
- Cavity wall thickness: Cavitation can be seen in both malignant and benign nodules. While a thin-walled cavity is highly suggestive of a benign lesion (£1 mm), a thick-walled cavity usually is indeterminate and is present in both benign and malignant lesions.
MRI:
MRI provides better imaging for pleural, diaphragm, and chest wall disease than CT when staging lung cancer. MRI is comparable to CT in assessing mediastinal involvement and is less useful in assessing the lung parenchyma (especially assessing pulmonary nodules) because of poorer spatial resolution. Since MRI costs more and is less available, MRI use is reserved for tumors that are difficult to assess on CT (eg, Pancoast tumors).
PET& SPECT imaging:
They are promising noninvasive techniques for differentiating malignant lesions from benign lesions and aiding in the assessment of indeterminate lesions