What is the initial workup for a suspected lymphoma presenting as a retroperitoneal mass at the aortoiliac region?

Initial Workup for Suspected Retroperitoneal Lymphoma at the Aortoiliac Region

For a retroperitoneal mass at the aortoiliac region with suspected lymphoma, obtain tissue diagnosis via core needle biopsy (avoiding transperitoneal approach) combined with CT imaging of chest/abdomen/pelvis with IV contrast, complete blood work including LDH and β2-microglobulin, and PET-CT for staging once diagnosis is confirmed. 1, 2

Tissue Diagnosis - The Critical First Step

Core needle biopsy is the practical and reliable method for retroperitoneal masses when surgical excisional biopsy is not feasible due to anatomical location. 1, 2, 3

• Core needle biopsy coupled with immunophenotyping and flow cytometry successfully diagnoses more than half of primary retroperitoneal lymphomas (17/32 cases in one series) 3
• The biopsy should NOT be performed through the peritoneum to avoid contamination 1
• Fine-needle aspiration is insufficient and should never be used as the sole diagnostic method 1, 2
• Surgical excisional biopsy remains the gold standard when accessible lymph nodes are present, but retroperitoneal location makes core biopsy the practical choice 1, 2

Common pitfall: Starting treatment without definitive histological diagnosis and proper lymphoma subtype classification is a critical error to avoid 2

Essential Imaging Studies

CT Abdomen and Pelvis with IV Contrast

CT is the reference standard for assessing retroperitoneal masses and detecting lymphadenopathy. 1

• CT provides rapid, reproducible assessment of the para-aortic and paracaval regions 1
• Lymph nodes >1 cm in short axis are highly suspicious for metastatic disease, particularly in para-aortic or caval areas 1
• CT accuracy for detecting metastatic retroperitoneal lymph nodes ranges from 73-97%, with sensitivity 65-96% and specificity 81-100% 1
• Use IV contrast to enhance detection and characterization of masses 1

CT Chest

Obtain chest CT to assess for thoracic lymphadenopathy and pulmonary involvement. 1

• Mediastinal and hilar lymph node assessment is aided by IV contrast 1
• Essential for complete staging as lymphoma frequently involves multiple nodal sites 1

PET-CT for Staging

PET-CT should be performed after histological confirmation to complete staging. 1, 2

• PET-CT improves accuracy of staging for both nodal and extranodal sites 1
• Mandatory to confirm true extent of disease before treatment planning 1
• A separate diagnostic CT is not required if PET-CT is performed 1

Important nuance: While PET-CT is valuable for staging, tissue diagnosis must come first - never rely on imaging alone 2

Laboratory Workup

Obtain comprehensive baseline blood work before initiating any treatment. 1, 2

Essential laboratory tests include:

• Complete blood count 1, 2
• Lactate dehydrogenase (LDH) - prognostic marker 1, 2
• β2-microglobulin - incorporated in revised prognostic indices 1
• Uric acid 1, 2
• Routine chemistry including liver and renal function 1
• Immunoglobulin levels 1
• Hepatitis B, Hepatitis C, and HIV screening 1

Bone Marrow Assessment

Perform bone marrow aspirate and biopsy of sufficient size (at least 20 mm) as part of initial staging. 1

• Bone marrow involvement affects staging and prognosis 1
• Required for complete staging workup in follicular and other indolent lymphomas 1

Specialized Pathology Studies

After obtaining tissue, ensure comprehensive pathological assessment including immunophenotyping and molecular studies. 2

• Immunophenotypic investigations are mandatory 2
• Assessment of MYC and BCL2 rearrangements using FISH for aggressive lymphomas 2
• Classification according to WHO criteria 1, 3
• Expert hematopathology review is advised, particularly for grade 3 follicular lymphomas 1

Clinical Assessment Priorities

Document specific symptoms and perform focused physical examination. 4

• Presence of symptoms correlates significantly with malignancy (P < 0.01) 4
• Abdominal pain or discomfort is the predominant presenting symptom in primary retroperitoneal lymphomas 3
• Assess for B symptoms (fever, night sweats, weight loss) which affect staging 1

Imaging Characteristics That Suggest Lymphoma

On dynamic MRI, 90% of malignant retroperitoneal tumors show early enhancement with either quick or slow washout. 4

• Irregularity of tumor margins correlates significantly with malignancy (P < 0.01) 4
• However, imaging alone cannot definitively distinguish lymphoma from other retroperitoneal malignancies 4

Critical caveat: Malignant lymphoma can show various enhancement patterns, making histological diagnosis essential 4

What NOT to Do

• Do not use ultrasound as primary imaging - it is less accurate and reproducible than CT for retroperitoneal assessment 1
• Do not perform transperitoneal biopsy - use retroperitoneal approach 1
• Do not rely on fine-needle aspiration alone 1, 2
• Do not delay tissue diagnosis in favor of additional imaging studies 2
• Do not start treatment without definitive histological diagnosis and lymphoma subtype classification 2

Differential Diagnosis Considerations

Retroperitoneal masses at the aortoiliac region have a broad differential beyond lymphoma. 5, 6

• Approximately 70-80% of primary retroperitoneal soft-tissue tumors are malignant 5
• Differential includes sarcomas (most common), metastatic disease, and benign tumors 6
• Diffuse large B-cell lymphoma is the most common lymphoma subtype in this location (12/32 cases in one series) 3
• This underscores why tissue diagnosis is non-negotiable 3, 6