Solitary Pulmonary Nodule

Solitary Pulmonary Nodule is a topic covered in the Washington Manual of Medical Therapeutics.

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General Principles

  • The goal of a careful evaluation of the solitary pulmonary nodule (SPN) is to determine if the lesion is more likely malignant or benign.
  • A lesion >3 cm has a high likelihood of malignancy and should be treated as such, whereas lesions <3 cm need more careful assessment.
  • Nodules with benign characteristics should be closely followed so that invasive procedures with associated risks can be avoided.
  • Identifying early lung cancer is of the utmost importance because there is a >60% survival rate of patients who have a malignant SPN removed.1

Definition

An SPN is defined as a rounded lesion <3 cm in diameter. It is completely surrounded by lung parenchyma, unaccompanied by atelectasis, intrathoracic adenopathy, or pleural effusion. Pulmonary nodules <8 mm remain within this definition; however, there is evidence to suggest that these nodules have a lower overall malignancy risk.1

Epidemiology

Historically the incidence of SPN has been cited to be 150,000 in the United States. A 2015, California based, integrated health care system’s review extrapolated this value to be over 1.5 million. This value is susceptible to errors associated with this form of methodology. However, it does highlight that the incidence of SPN has increased with changes in clinical practice post National Lung Screening Trial.2

Etiology

  • Although underlying etiologies for pulmonary nodules are varied, the most important designation clinically is deciphering between a malignant and a nonmalignant process.
  • Malignancy accounts for approximately 40% of SPNs, although this may vary geographically depending on the prevalence of nonmalignant processes such as histoplasmosis.
  • Granulomas (both infectious and noninfectious) may account for 50% of undiagnosed SPNs, depending on the prevalence of cancer in the particular population.
  • The remaining 10% are composed of benign neoplasms, such as hamartomas (5%) and a multitude of other causes.

Risk Factors

  • Smoking is the most important associated risk factor for almost all malignant SPNs.
  • For infectious etiologies, an immunocompromised state promotes an increased risk.

Lung Cancer Screening

Screening high-risk patients using low-dose chest CT resulted in a 20% relative reduction in mortality from lung cancer compared with screening with CXR.3

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