Chest Radiology > Pathology > Solitary Pulmonary Nodule


Solitary Pulmonary Nodule

A solitary pulmonary nodule is not an uncommon finding on a chest x-ray.   A solitary pulmonary nodule can result from a wide range of causes.   Most nodules are benign but some can be malignant.

Nodules are diagnosed as benign if they:
  • Show little or no growth for 2 years
  • Calcification
    • Central, laminated or diffuse pattern indicates a granuloma
    • Eccentric calcification can be seen in a carcinoma or in a cancer that has engulfed a granuloma

 

The CT image above shows a right lower lobe centrally calcified nodule, consistent with a benign granuloma.

 

 

A differential of possible etiologies is as follows:
  • Granuloma - usually caused by fungal infections like histoplasmosis or tuberculosis
  • Lung Carcinoma
  • Solitary metastasis - usually from colon, breast, kidney, ovary, or testis
  • Round pneumonia
  • Abscess
  • Round atelectasis
  • Hamartoma - popcorn calcification is sometimes seen
  • Sequestration
  • Arteriovenous malformation
Granulomas and lung cancer are by far the two most common causes for a pulmonary nodule.

 

Other things can cause an apparent nodule but are actually outside the lung including:
  • Fluid in an interlobar fissure
  • Pleural plaques - small, often calcified, plate-like surfaces on the pleura often caused by asbestos fibers that invade the pleura from the lungs
  • Skin lesions - nipple shadow, mole, lipoma, etc.
Incidental small pulmonary nodules, especially less than 5 mm, are an extremely common finding on chest CT in the population over age 50.  The current recommended follow-up of incidental solid pulmonary nodules per the Fleischner Society 2017 is given below.  In a patient with a prior history of malignancy, a difference in intervals can be based on additional considerations of the likelihood of pulmonary metastases given the specific primary.

 

Low Risk Patient
≤ 6mm No follow-up needed
6-8mm CT at 6-12 mo
>8mm CT at 3 mo, PET CT or biopsy

 

High Risk Patient (eg. smoking history or history of malignancy)
≤ 6mm Optional CT at 12 mo
6-8mm CT at 6-12mo; consider- follow-up at 18-24 mo
>8mm Consider CT at 3 mo, PET CT or biopsy

 

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