Best Initial Test for Left Leg Groin Mass
For a suspected mass in the left leg groin, ultrasound is the best initial diagnostic test, as it provides high sensitivity (94.1%) and specificity (99.7%) for superficial soft tissue masses while allowing differentiation between solid and cystic lesions. 1
Initial Diagnostic Approach
Start with Radiographs (X-rays)
- Plain radiographs should be obtained first for any suspected soft tissue mass in the groin region, despite being often considered "unrewarding" 1
- Radiographs demonstrate positive findings in 62% of soft tissue masses, including:
- X-rays can identify phleboliths within hemangiomas or rule out skeletal abnormalities masquerading as soft tissue masses 1
Follow with Ultrasound as Primary Imaging
Ultrasound is the most appropriate next step and often the definitive initial imaging study for groin masses 1, 2
Advantages of Ultrasound:
- Sensitivity of 94.1% and specificity of 99.7% for superficial soft tissue masses 1, 3
- Differentiates solid from cystic lesions with high accuracy 1
- Confirms fluid content in suspected ganglion cysts 1
- Demonstrates relationship between mass and adjacent neurovascular structures 1
- Can identify hernias (the most common groin abnormality) during dynamic Valsalva maneuver 2, 4
- Evaluates for lipomas (most common benign tumor), hematomas, lymph nodes, and inflammatory processes 4
Protocol-Driven Ultrasound Evaluation:
A comprehensive groin ultrasound should include 2:
- Hip joint evaluation for effusion or synovitis 2
- Anterior hip musculature assessment 2
- Iliopsoas bursa examination 2
- Inguinal lymph node evaluation 2
- Pubic symphyseal region 2
- Dynamic evaluation with Valsalva maneuver to assess for hernias 2
When to Proceed to MRI
MRI without and with IV contrast is indicated when: 1, 3
- Ultrasound findings are atypical or inconclusive 1
- The mass is deep-seated or in complex anatomy 1, 3
- There are concerning features suggesting malignancy 1
- Preoperative planning is needed 3
Why Not MRI First?
The literature does not support MRI as the initial examination for soft tissue masses due to inherent limitations and cost-effectiveness considerations 1
Common Groin Mass Differentials
The most common groin abnormalities identified on ultrasound include 4:
- Hernias (most common) - containing bowel loops, omental fat, or peritoneal fluid 4
- Lipomas (most common benign tumor) 4
- Lymphadenopathy (metastatic or inflammatory) 4
- Hematomas 4
- Cystic lesions (ganglion cysts, canal of Nuck cysts in females) 5, 6
- Vascular abnormalities (femoral aneurysms or pseudoaneurysms) 7
Critical Pitfalls to Avoid
- Never perform biopsy before ultrasound or advanced imaging, as the biopsy tract must be planned for potential removal during definitive surgery 1
- Physical examination alone correctly identifies only 85% of soft tissue tumors 1, 3
- Radiographs may be unrewarding for small, deep-seated, or non-mineralized masses 1
- Always perform dynamic evaluation with Valsalva maneuver when evaluating for hernias to avoid false negatives 2
- Document findings in two orthogonal planes 2