What is the recommended workup for a suspected thymoma?

Workup for Suspected Thymoma

The recommended workup for a suspected thymoma includes chest CT with contrast, evaluation for myasthenia gravis and other paraneoplastic syndromes, and appropriate laboratory tests including CBC and tumor markers to rule out other diagnoses. 1

Initial Imaging

• Contrast-enhanced CT scan of the thorax is the standard initial imaging modality for suspected thymic tumors, allowing complete exploration of the mediastinum and pleura 1
• Chest MRI with and without contrast is recommended when CT findings are inconclusive or to better differentiate thymic malignancy from thymic cyst or hyperplasia 1
• FDG-PET/CT scan (skull base to mid-thigh) should be considered as clinically indicated, particularly for tumors with aggressive histology or advanced stage 1

Laboratory Evaluation

• Complete blood count with platelets to assess for possible paraneoplastic syndromes 1
• Serum beta-human chorionic gonadotropin (beta-hCG) and alpha-fetoprotein (AFP) to rule out germ cell tumors 1
• Systematic immunological assessment including 1:
  • Complete blood count with reticulocytes
  • Serum protein electrophoresis
  • Anti-acetylcholine receptor antibodies
  • Anti-nuclear antibodies

Clinical Evaluation for Associated Conditions

• Thorough neurological examination for signs of myasthenia gravis, which is present in approximately 30-50% of patients with thymoma 1
• Assessment for other paraneoplastic syndromes such as pure red cell aplasia (5% of cases) and hypogammaglobulinemia (Good syndrome: 5% of cases) 1
• Pulmonary function tests as clinically indicated, especially if surgery is being considered 1

Need for Biopsy

• Pretreatment biopsy is not required if the diagnosis of thymic tumor is highly probable and upfront surgical resection is achievable 1
• Biopsy is required in all other clinical situations, particularly when the diagnosis is uncertain or if the tumor is deemed unresectable 1
• Biopsy approaches may include 1:
  • Percutaneous core-needle biopsy
  • Incisional surgical biopsy through mediastinotomy or mini-thoracotomy
  • Fine-needle aspiration is generally not recommended 1

Diagnostic Criteria

Thymic epithelial tumors are likely if 1:

1. A well-defined mediastinal mass is present in the thymic bed
2. The mass is not continuous with the thyroid gland
3. Tumor markers (AFP, beta-hCG) are negative
4. No other adenopathy is present

Special Considerations

• Chemical-shift MRI may be particularly useful in equivocal cases to detect microscopic fatty infiltration, which is seen in thymic hyperplasia but not in thymoma 1
• Therapeutic intervention is usually not required if the lesion is <30mm, given a low risk of progression or malignancy 1, 2
• In patients with myasthenia gravis, additional preoperative assessment should include respiratory function testing with negative inspiratory force and vital capacity measurements 3

Common Pitfalls to Avoid

• Failing to evaluate for myasthenia gravis and other paraneoplastic syndromes, which may significantly impact treatment planning and perioperative management 1, 4
• Relying solely on CT without considering MRI in equivocal cases, potentially leading to unnecessary thymectomy for benign conditions 1
• Using fine-needle aspiration instead of core biopsy, which has lower diagnostic accuracy for thymic lesions 1
• Not considering the possibility of ectopic thymoma outside the typical location in the anterior mediastinum 5

By following this systematic approach to the workup of suspected thymoma, clinicians can ensure accurate diagnosis and appropriate staging to guide subsequent treatment decisions.