Benign vs malignant pulmonary nodule

Differentiating benign from malignant pulmonary nodules is of great importance as it determines the further course of management of the patient.

Benign pulmonary nodule

• size: the smaller the size the more likely to be benign

  • ~80% of benign nodules are <2 cm in size.

• margin: smooth, regular; however, ~ 20% of malignant nodules have smooth margins

• internal characteristics: homogenous attenuation on thin-section CT is seen in ~ 55% of benign nodules vs 20% of malignant nodules

• smooth, thin-walled cavitary nodules (wall thickness usually <4mm)

• presence of intranodular fat reliably indicates a benign hamartoma

• calcification

  • central, diffuse solid and laminated type of calcification are usually seen in prior granulomatosus infections

  • "pop-corn" like calcification is usually seen in hamartoma

• growth rate

  • doubling time >450 days indicates a benign nodule

  • doubling time <30 days usually represents an acute infection

• contrast enhancement <15 HU

• low FDG uptake on PET; however, false negative results can be seen in primary pulmonary malignancies (e.g. adenocarcinoma in situ, carcinoid tumors, other cancers <1 cm)

Malignant pulmonary nodule

• size: the larger the size the more likely to be malignant, however, ~55% are <2 cm in diameter

• margin: lobulated, irregular or spiculated margins; however, lobulated margins in ~ 25% of benign nodules

  internal characteristics: pseudocavitation is usually seen in adenocarcinoma in situ, while presence of air-bronchogram is suggestive of lymphoma

• irregular, thick walled cavitary nodules (wall thickness usually >16 mm)

• calcification: diffuse and amorphous or punctate calcification can be seen in lung cancers or metastases

• growth rate: doubling time is usually between 30 and 400 days

• contrast enhancement of >20 HU.

• increased FDG uptake on PET; however, false positive results can be seen in infectious and inflammatory processes (e.g. active tuberculosis, histoplasmosis, rheumatoid nodules)

Practical points

• doubling time refers to the time duration required for doubling of the volume of pulmonary nodul; it results in 26% increase in the diameter of the nodule

See also

• solitary pulmonary nodule

• Fleischner Society pulmonary nodule recommendations