What is the initial workup for a patient presenting with a retroperitoneal mass?

Workup for Retroperitoneal Mass

Initial Imaging

CT of the abdomen and pelvis with IV contrast is the preferred initial imaging modality for evaluating a retroperitoneal mass. 1

• CT with IV contrast provides optimal tissue differentiation to distinguish the mass from normal anatomic structures including blood vessels and the duodenum 2
• MRI can be used as an alternative when CT is contraindicated or when distinguishing active inflammation from chronic fibrosis is critical 2
• CT is superior to MRI for rapid diagnosis, particularly in unstable or uncooperative patients 2

Imaging Pitfalls to Avoid

• Do not rely on ultrasound for diagnosis or characterization of retroperitoneal masses, as it has severe limitations in visualizing retroperitoneal structures and frequently misses the extent of disease 2
• Plain radiography is highly nonspecific with low sensitivity and should not be used for initial evaluation 1

Additional Imaging Studies

Obtain chest imaging for histologic subtypes with potential for lung metastases. 1

• Chest CT is preferred over plain radiography to detect pulmonary metastases in sarcomas and other malignancies with metastatic potential 1

Clinical Evaluation

Perform a thorough history and physical examination focusing on:

• Abdominal pain or discomfort (the predominant presenting symptom in retroperitoneal masses) 3
• Palpable abdominal mass 4
• Constitutional symptoms suggesting malignancy 3

Tissue Diagnosis Strategy

The decision to perform biopsy depends on whether neoadjuvant therapy is being considered and the differential diagnosis. 1

When Biopsy is Required

• Preresection biopsy is mandatory if neoadjuvant therapy is being considered, as confirmation of sarcoma diagnosis including histologic subtype is required 1
• Biopsy is essential when suspicion exists for malignancy other than sarcoma (lymphoma, germ cell tumor, GIST) to avoid inappropriate major resection 1, 3

Biopsy Technique

• Image-guided core needle biopsy (CT or ultrasound-guided) is strongly preferred over open surgical biopsy 1
• Core needle biopsy coupled with immunophenotyping and flow cytometry is a practical and reliable method, with more than half of cases successfully diagnosed this way 3

When Biopsy May Not Be Necessary

• Preresection biopsy is not required for all patients, particularly when the clinical and imaging features strongly suggest a resectable sarcoma and neoadjuvant therapy is not planned 1

Differential Diagnosis Considerations

The differential diagnosis of retroperitoneal masses includes: 1

• Malignant lesions: Soft tissue sarcomas (most common), GISTs, lymphomas (particularly diffuse large B-cell lymphoma), germ cell tumors 1, 3
• Benign lesions: Desmoid tumors (aggressive fibromatosis), retroperitoneal fibrosis 1, 5
• Cystic lesions: Primary retroperitoneal mucinous tumors 4

Multidisciplinary Review

All patients should be reviewed by a multidisciplinary sarcoma panel before treatment initiation whenever possible. 1

• This is particularly important given the rarity and complexity of retroperitoneal masses 1
• Adherence to evidence-based guidelines is associated with improved survival outcomes 1

Special Scenario: Incidental Discovery

If a retroperitoneal sarcoma is encountered unexpectedly during laparotomy:

• Perform core needle biopsy to establish diagnosis, histopathologic type, and tumor grade 1
• Refer to a center with sarcoma expertise for optimal subsequent resection 1
• Do not attempt definitive resection without proper staging and multidisciplinary planning 1