Imaging

Solitary Pulmonary Nodule

Preliminary Diagnosis: Solitary Pulmonary Nodule

I. What imaging technique is first-line for this diagnosis?

CT of the chest with IV contrast (preferably with thin sections through nodule) is the first-line imaging technique when a solitary pulmonary nodule is identified on CXR.

II. Describe the advantages and disadvantages of this technique for diagnosing solitary pulmonary nodule.

Advantages

  • Provides more information on the density, location, and edge characteristics of the nodule.

  • Can identify lymphadenopathy, other parenchymal lesions/nodules, or invasion of the chest wall or mediastinum.

  • Can provide morphologic clues to help distinguish benign from malignant nodules.

  • Low-dose chest CT has been shown in the National Lung Cancer Screening Trial (NEJM, 2011) to provide a 20% relative reduction in mortality versus chest x-ray in a high-risk population.

  • Better tolerated in obese patients, claustrophobic patients, or patients with SOB/those unable to hold breath.

Disadvantages

  • Low sensitivity (40-84%) and specificity (57-94%) for identifying mediastinal and lymph node involvement.

  • Limited in detecting chest wall or parietal pleural invasion.

  • Requires the use of IV contrast.

  • Exposure to ionizing radiation.

III. What are the contraindications for the first-line imaging technique?

  • May be contraindicated in pregnant patients.

  • Relative contraindication for contrast use in patients with renal failure.

  • Relative contraindication for contrast use in patients with contrast allergy.

IV. What alternative imaging techniques are available?

  • Chest X-ray

  • FDG-PET

  • MRI of the chest with IV contrast

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of Solitary Pulmonary Nodule.

Chest X-ray

Advantages

  • Can sometimes determine areas of benign calcifications (diffuse, central, laminated, or popcorn), which would not require further diagnostic workup.

  • Cheap, easily accessible, and easy to administer.

  • Requires low dose of radiation exposure.

  • Helpful to compare with previous films in order to determine if further workup is necessary.

Disadvantages

  • Shadowing of the nipple or ribs can mimic pulmonary nodules.

  • Nodules can often be obscured by surrounding bony structures and superimposed lung disease/changes.

  • Insufficient to assess mediastinal and lymph node metastases.

  • Low-dose chest CT has been shown in the National Lung Cancer Screening Trial (NEJM, 2011) to provide a 20% relative reduction in mortality versus chest x-ray in a high-risk population.

  • Cannot determine extrathoracic metastases.

FDG-PET

Advantages

  • Delineates anatomy and also determines metabolic activity of nodules.

  • Improved sensitivity versus CT alone at identifying mediastinal invasion and lymph node metastases.

  • Improved sensitivity and specificity versus CT alone for detecting extrathoracic metastatic disease.

  • Can be helpful in guiding a biopsy of the most metabolically active portion of a nodule, thus improving diagnostic yield.

  • Most useful in patients with a low pre-test probability and indeterminate CT findings.

Disadvantages

  • Less sensitive for nodules measuring less than 8-10 mm with a high number of false negatives and occasional false positives.

  • May provide false positive results in patients with infectious or inflammatory lung disease.

  • Should not be performed in patients with a high pre-test probability of malignancy (>60%) or lesions less than 8-10 mm.

  • Expensive and sometimes inaccessible at medical facilities.

MRI of chest with IV contrast

Advantages

  • Can help assess extrathoracic and chest wall invasion.

  • Does not expose patients to ionizing radiation.

  • Can help delineate brain, adrenal, or spinal metastases.

Disadvantages

  • Largely experimental, with no consensus regarding standardization and use in solitary pulmonary nodules.

  • Loss of signal from physiologic lung movement.

  • Not as well tolerated in obese, claustrophobic, or patients with SOB/those not able to hold breath.

  • More time consuming than CT.

  • Expensive.

  • Requires significant patient cooperation to minimize motion artifact.

VI. What are the contraindications for the alternative imaging techniques?

Chest X-ray

  • There are no major contraindications for this imaging modality. Some institutions may require consent for pregnant patients.

FDG-PET

  • There are no major contraindications to the use of FDG-PET because of low doses of radiation exposure.

MRI with contrast

  • Contraindicated in patients with pacemakers and other implantable, MRI-incompatible devices.

  • As contrast is administered, caution should be used in patients with renal insufficiency.

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