Preliminary Diagnosis: Thymoma

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

CT of the chest with IV contrast

II. Describe the advantages and disadvantages of this technique for diagnosis of thymoma.

Advantages

  • Can help distinguish thymomas from other anterior mediastinal abnormalities.

  • Can help determine extent of involvement including invasion into surrounding vasculature, pleural involvement, or pericardial dissemination.

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  • Can often identify patients with more advanced disease, who may benefit from neoadjuvant therapy prior to surgery (Stage III and IV disease), vs patients with earlier stage, who should go directly to surgery.

  • Accessible within most medical centers.

Disadvantages

  • Sometimes has difficulty in determining local disease accurately (i.e., pericardial invasion vs. abutment; thymic capsular vs. pericapsular involvement)

  • Requires the use of IV contrast.

  • May have limited correlation between radiographic appearance and histologic subtype of thymoma.

  • Expensive and exposes patient to ionizing radiation.

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

Contraindicated in pregnant patients, those with iodine allergies, and patients with renal insufficiency.

IV. What alternative imaging techniques are available?

  • MRI of the chest

  • CXR

  • FDG-PET (thaliium-201 PET or indium-111 octreotide PET)

V. Describe the advantages and disadvantages of the alternative techniques for diagnosis of thymoma.

MRI of the chest
Advantages

  • Can be used to determine vascular invasion without the need for IV contrast, useful in patients with allergies to iodinated contrast.

  • Because of better contrast resolution, MRI, in certain cases, may be able to more effectively distinguish cystic thymomas from congenital cysts.

  • Does not require the use of ionizing radiation.

Disadvantages

  • MRI features of thymoma are often non-specific.

  • May be difficult to differentiate thymoma from surrounding fat.

  • Poor visualization of the lung parenchyma.

  • Time-consuming exam with limitations in obese and claustrophobic patients.

  • Expensive and not as easily accessible.

CXR
Advantages

  • Low radiation dose

  • Easily accessible

  • Inexpensive

Disadvantages

  • Limited assessment of tumor invasiveness.

  • Low sensitivity in diagnosing smaller thymomas.

  • Low specificity in differentiating thymomas from other anterior mediastinal masses.

FDG-PET (thaliium-201 PET or indium-111 octreotide PET)
Advantages

  • May be able to identify patients who could potentially respond to octreotide therapy by determining thymic tumor uptake.

  • May be of some use in assessing metastatic disease.

Disadvantages

  • Expensive and often inaccessible.

  • PET diagnostic criteria for thymomas often overlap with other thymic conditions.

  • Low resolution and visualization of thymoma.

  • Unable to differentiate between low-grade and high-grade thymomas; thus, is limited in affecting decision for surgery or neoadjuvant therapy.

  • Thymoma blood flow may be difficult to differentiate from the normal blood flow of the mediastinum.

  • Lacks large studies investigating its use and cost-effectiveness.

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

MRI of the chest

  • Contraindicated in patients with pacemakers, patients with implantable devices not compatible with MRI, or patients with chronic renal insufficiency (if contrast used).

CXR

  • There are no major contraindications to the use of this imaging modality.

FDG-PET (thaliium-201 PET or indium-111 octreotide PET)

  • There are no major contraindications to the use of this imaging modality.

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