Pulmonary nodule CT

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]Associate Editor(s)-in-Chief: Maria Fernanda Villarreal, M.D. [2]

Overview

Computed tomography 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 30mm. The evaluation of solitary pulmonary nodule will depend on 7 characteristics: calcification patterns, size, location, size, growth, shape, margins, attenuation, and contrast enhancement.

CT

• Computed tomography 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 spicluated 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 types of size ranges for pulmonary nodule, include:

• Nodules less than 4mm
• Nodules between 4mm and 7mm
• Nodules between 8mm and 20mm
• Nodules more than 20mm

Location

• Locations of pulmonary nodule, include:

• Perilymphatic
• Perifissural
• Centrilobular

Growth

• The growth pattern of the pulmonary nodule plays an important role in the management strategy.
• Nodule growth should be evaluated on a individual basis and based on the risk assessment score
• A 4x growth is associated with a 50% risk of malignancy

Shape

• Different types of shape for pulmonary nodule, include:

• Polygonal
• Spherical

Margins

• Different types of margins for pulmonary nodule, include:

• Lobulated or scalloped margins

• Intermediate malignancy probability

• Smooth margins

  Associated with nodule benignancy

Attenuation

• Different types of attenuation for pulmonary nodule, include:
• Solid pulmonary nodules

• Malignancy rate of only 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 a contrast enhancement less than 15 HU

On CT, radiological signs of pulmonary nodule, include:

• Corona radiata sign: highly associated with malignancy
• Air bronchogram sign: airway surrounded by collection in alveolar spaces, non-specific sign
• Halo sign: zone of ground-glass attenuation surrounding a pulmonary nodule or mass on CT images
• Tree-in-bud sign: CT 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. It is due to proliferation of (malignant or non-malignant) cells around an airway

CT Surveillance

According to the American College of Chest Physicians (ACCP) for the CT surveillance of pulmonary nodules, recommends the following:

• If less than 8 mm, use guidelines by the Fleischner society (see table below).
• For nodules greater than 8 mm in diameter, assess the patients risk of complications from thoracic surgery:
  • If low to moderate risk for complications of surgery, assess probability of cancer by a validated calculation. The model developed at the Mayo Clinic has been the most extensively validated. An open-source version is available online.
  • If high risk for complications of surgery, assess probability of cancer by a validated calculation. If low to moderate risk of cancer follow up with CT scan surveillance. If moderate to high risk of cancer obtain non-surgical biopsy.

Fleischner Society guidelines for follow-up and management of nodules <8 mm
Detected incidentally at non-screening CT

Nodule Size (mm)	Low risk patients†	High risk patients‡
<= 4	No follow-up needed	Follow-up at 12 months. If no change, no further imaging needed
> 4 - 6	Follow-up at 12 months. If no change, no further imaging needed	Initial follow-up CT at 6 -12 months If no change follow-up CT at 18 - 24 months
> 6 - 8	Initial follow-up CT at 6 -12 months If no change follow-up CT at 18 - 24 months	Initial follow-up CT at 3 - 6 months >If no change follow-up CT at 9 -12 and 24 months
> 8	Follow-up CT at around 3, 9, and 24 months Dynamic contrast enhanced CT, PET, and/or biopsy	Same at for low risk patients
† Low risk patients: Minimal or absent history of smoking and of other known risk factors. ‡ High risk patients: History of smoking or of other known risk factors

Gallery

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  Halo sign: Ground glass opacity surrounding a pulmonary nodule

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  Thorax CT

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  Thorax CT