What is the recommended approach for evaluating thymoma?

Thymoma Evaluation

The evaluation of thymoma begins with contrast-enhanced chest CT as the primary imaging modality, followed by assessment for paraneoplastic syndromes (particularly myasthenia gravis), serum tumor markers to exclude germ cell tumors, and multidisciplinary review to determine resectability before any tissue sampling. 1

Initial Imaging Studies

• Chest CT with contrast is the standard first-line imaging study for evaluating suspected thymoma, typically revealing a well-defined round or oval mass in the anterior mediastinum without lymph node enlargement 1
• Chest MRI with and without contrast should be considered when CT findings are equivocal, as MRI better discriminates thymic malignancy from benign conditions like thymic cysts or thymic hyperplasia, potentially avoiding unnecessary surgery 1
• FDG-PET/CT from skull base to mid-thigh is recommended as clinically indicated to assess for distant metastases and help determine disease extent 1
• MRI is the preferred alternative imaging modality in patients who cannot tolerate iodinated contrast 1

Laboratory and Serologic Testing

• Serum beta-hCG and AFP levels must be measured to exclude germ cell tumors, which can present as anterior mediastinal masses 1
• Anti-acetylcholine receptor antibody testing is mandatory when thymoma is suspected, as approximately 30-50% of patients have myasthenia gravis, which may be subclinical 2, 3
• Complete blood count with reticulocytes should be obtained to screen for pure red cell aplasia, a paraneoplastic syndrome occurring in less than 10% of thymoma patients 3
• Serum protein electrophoresis is recommended to evaluate for hypogammaglobulinemia, another associated paraneoplastic condition 3
• Thyroid function tests (TSH, T3, T4) should be measured as clinically indicated to rule out mediastinal goiter 1

Clinical Assessment for Paraneoplastic Syndromes

• All patients must be evaluated clinically for signs and symptoms of myasthenia gravis including ptosis, diplopia, dysphagia, muscle weakness, and respiratory symptoms before any intervention 1, 2
• Myasthenia gravis should be medically controlled prior to surgical resection if present 1
• Assessment for other autoimmune and paraneoplastic syndromes should be performed, as thymomas are frequently associated with immune-mediated conditions 3

Pulmonary Function Assessment

• Pulmonary function tests should be performed as clinically appropriate as part of the initial evaluation, particularly when surgical resection is being considered 1

Tissue Diagnosis Strategy

• Surgical biopsy should be avoided if a resectable thymoma is strongly suspected based on clinical and radiologic features, as patients should proceed directly to complete surgical resection 1
• Core-needle biopsy or open biopsy is recommended only for locally advanced unresectable thymic masses to confirm diagnosis before initiating neoadjuvant therapy 1
• Biopsy of a possible thymoma should avoid a transpleural approach to prevent potential tumor seeding 1
• The diagnosis is ultimately made by histological examination, with anterior mediastinotomy being the standard approach when biopsy is necessary for unresectable disease 1

Differential Diagnosis Considerations

• A thymic tumor is likely when: (1) a well-defined anterior mediastinal mass in the thymic bed is present, (2) tumor markers (AFP, beta-hCG) are negative, and (3) no other adenopathy exists 1
• For undifferentiated or lymphocyte-predominant forms, Hodgkin lymphoma, non-Hodgkin lymphoma, and germ cell tumors must be excluded 1
• Other differential diagnoses include lung metastases (the most common mediastinal mass overall), lymphoma, thymic carcinoma, thymic carcinoid, thymolipoma, intrathoracic goiter, and thymic cysts 1

Staging and Classification

• The Masaoka-Koga staging system should be used as it is the most widely accepted system for management and prognosis determination 1
• The WHO histologic classification system distinguishes thymomas (types A, AB, B1, B2, B3) from thymic carcinomas and thymic carcinoids 1
• Central review of histological slides by experienced pathologists is recommended, with routine documentation of cellular atypia 1

Multidisciplinary Evaluation

• All patients with thymic malignancies should be evaluated by a multidisciplinary team including radiation oncologists, thoracic surgeons, medical oncologists, pathologists, and diagnostic imaging specialists before treatment 1
• A board-certified thoracic surgeon must determine whether the mass is surgically resectable, as this is the critical decision point that determines the treatment pathway 1

Critical Pitfalls to Avoid

• Do not perform biopsy on apparently resectable thymomas, as this delays definitive treatment and risks tumor seeding without changing management 1
• Do not proceed with minimally invasive surgical approaches outside specialized centers, as long-term data on recurrence and survival are lacking 1
• Ensure myasthenia gravis is medically optimized before surgery to prevent perioperative myasthenic crisis 1