Solitary pulmonary nodule CT scan

# Overview
CT scan is the method of choice for the diagnosis of solitary pulmonary nodule. On CT, characteristic findings of solitary pulmonary nodules include ground-glass opacity, rounded mass, and less than 30 mm in size. The evaluation of solitary pulmonary nodule will depend on the following characteristics: calcification pattern, size, location, growth, shape, margins, attenuation, and contrast enhancement.

# CT scan
- CT scan is the method of choice for the diagnosis of solitary pulmonary nodule.
- On CT, characteristic findings of solitary pulmonary nodules include:
- Single intraparenchymal lesion
- Less than 3 cm in size
- Rounded or spiculated lesion
- The evaluation of solitary pulmonary nodule will depend on the following characteristics:
Calcification
- Calcification patterns are commonly seen in granulomatous disease and hamartomas.
- Calcification patterns are normally a sign of benignancy
- Characteristic benign calcification patterns of pulmonary nodule include:
- Diffuse
- Central
- Laminated
- Popcorn
Size
- Different size ranges for pulmonary nodule include:
- Nodules less than 4 mm
- Nodules between 4 mm and 7 mm
- Nodules between 8 mm and 20 mm
- Nodules more than 20 mm
Location
- Common locations of pulmonary nodule are:
- Peri-lymphatic
- Peri-fissural
- Centrilobular
Growth
- The growth pattern of the pulmonary nodule plays an important role in the management strategy.
- A 4 times growth is associated with a 50% risk of malignancy
Shape
- Pulmonary nodule can occur in the following shapes:
- Polygonal
- Spherical
Margins
- Lobulated or scalloped margins
Associated with an intermediate malignancy risk
- Associated with an intermediate malignancy risk
- Smooth margins
Associated with nodule benignancy
- Associated with nodule benignancy
Attenuation
- Different types of pulmonary nodule attenuation are:
- Solid pulmonary nodules
- Malignancy rate of 7%
- Calcified pulmonary nodules
- Partly solid pulmonary nodules
- Malignancy rate of 63%
- Ground glass pulmonary nodules
- Malignancy rate of 18%
Contrast Enhancement
- Contrast enhancement of pulmonary nodules may be useful to determine benign or malignant features.
- Benign pulmonary nodules usually have < 15 Hounsfield units (HU) contrast enhancement.

## Other Radiological Signs of Pulmonary Nodule
- Corona radiata sign: Highly associated with malignancy
- Air bronchogram sign: Airway surrounded by fluid or inflammatory exudate filled alveolar spaces
- Halo sign: Zone of ground-glass attenuation surrounding a pulmonary nodule or mass on CT scan
- Tree-in-bud sign: CT scan appearance of multiple areas of centrilobular nodules with a linear branching pattern
- Cheerio sign: Pulmonary nodules with a central lucent cavity as seen on CT scan. It is due to the proliferation of (malignant or non-malignant) cells around the airway

# CT Surveillance
The American College of Chest Physicians (ACCP) recommends the following:
- If less than 8 mm in size, use guidelines by the Fleischner society (see table below).
- For nodules greater than 8 mm in diameter, assess the patient's risk of complications from thoracic surgery:
In low - moderate risk, assess the probability of cancer by a validated calculator and follow up with CT scan surveillance. A model developed at the Mayo Clinic has been the most extensively validated. An open-source version is available online.
In high risk, assess the probability of cancer by a validated calculator and obtain non-surgical biopsy.
- In low - moderate risk, assess the probability of cancer by a validated calculator and follow up with CT scan surveillance. A model developed at the Mayo Clinic has been the most extensively validated. An open-source version is available online.
- In high risk, assess the probability of cancer by a validated calculator and obtain non-surgical biopsy.

# Images