What is the best immediate diagnostic workup for a patient with a history of thymoma (thymic tumor) and chronic lymphadenopathy (enlarged lymph nodes) who presents with new onset groin pain radiating to the abdomen?

Immediate Diagnostic Workup for Thymoma with New Groin Pain

This patient requires urgent CT abdomen/pelvis with IV contrast to evaluate the new groin pain, as the combination of known thymoma, chronic lymphadenopathy, and new radiating pain mandates immediate exclusion of disease progression, lymph node involvement, or complications such as vascular compression or metastatic spread. 1

Primary Imaging Approach

Obtain CT abdomen/pelvis with IV contrast immediately to evaluate:

• Abdominal and pelvic lymphadenopathy progression 2
• Potential vascular compression or thrombosis causing referred pain 1
• Distant metastatic disease (thymomas can metastasize to distant sites including abdomen) 3, 4
• Complications from locally invasive disease 1

The standard imaging for thymic tumors is IV contrast-enhanced CT, which is the imaging modality of choice for characterizing the primary tumor and staging disease 1, 5, 6. While chest CT is standard for thymic masses, the new groin pain radiating to the abdomen necessitates extending imaging to the abdomen and pelvis 1.

Additional Staging Considerations

Consider FDG-PET/CT from skull base to mid-thigh if:

• The thymoma is aggressive histology (type B3 or thymic carcinoma) 1
• Advanced stage disease is suspected 1
• Characterization of indeterminate lesions is needed 7, 8

However, recognize that PET scan is generally not recommended for routine assessment of thymic masses, as thymic hyperplasia can also show hypermetabolism 1. PET is optional for completing staging workup in aggressive tumors or characterizing suspicious recurrences 1.

Critical Laboratory Workup

Obtain immediately:

• Complete blood count with reticulocytes 1
• Serum protein electrophoresis 1
• Lactate dehydrogenase (LDH) - elevated LDH suggests lymphoma rather than thymoma progression 1, 2
• Anti-acetylcholine receptor antibodies 1
• Anti-nuclear antibodies 1

These tests are essential because thymomas are associated with autoimmune syndromes and immune disorders that may impact treatment 1, 9.

Tissue Diagnosis Strategy

Biopsy is required if imaging suggests disease progression or new lesions 1:

• Percutaneous core-needle biopsy (preferred for accessibility) with sensitivity 40-93% 1
• Request routine histology, flow cytometry, and immunohistochemistry 2
• Avoid fine-needle aspiration (not recommended for thymic tumors) 1

For abdominal/pelvic lymphadenopathy specifically, excisional or core needle biopsy of the most abnormal/accessible node provides best architectural assessment 2.

Differential Diagnosis to Exclude

The chronic lymphadenopathy with new symptoms requires distinguishing:

• Lymphoma - suggested by rapid onset, elevated LDH, and coexistent lymphadenopathy 1, 2
• Tuberculous lymphadenitis - obtain tuberculin skin test or interferon-gamma release assay if clinically suspected 2
• Metastatic thymoma - thymomas can rarely metastasize to distant sites 3, 4, 9

Common Pitfalls to Avoid

• Do not use corticosteroids before obtaining tissue diagnosis, as they can mask histologic features of lymphoma or malignancy 2
• Do not rely on PET/CT alone for thymic mass assessment, as it has limited specificity 1
• Do not delay imaging - thymomas can be locally invasive and the combination of chronic lymphadenopathy with worsening symptoms warrants urgent evaluation 1, 3, 4
• Respect pleural spaces during biopsy to avoid tumor cell seeding 1

Staging and Prognosis Implications

If disease progression is confirmed, staging according to Masaoka-Koga system is essential, as prognosis closely parallels disease stage 1, 4. Invasive thymomas have worse prognosis but may respond to radical resection combined with radiation and chemotherapy 3, 4, 9.