Initial Imaging for a Solid Mass in the Left Hip
Radiographs (X-rays) should be the first imaging test ordered for evaluation of a solid mass in the left hip 1, 2.
Diagnostic Algorithm for Hip Mass Evaluation
Step 1: Initial Radiographic Assessment
- Begin with standard radiographs including:
- AP (anteroposterior) pelvis view
- Lateral hip view
- Frog-leg lateral view if tolerated
Radiographs provide critical initial information about:
- Bone involvement or destruction
- Presence of calcifications
- Matrix characteristics of the mass
- Periosteal reaction patterns
- Joint space abnormalities
- Soft tissue extension
Step 2: Advanced Imaging Based on Radiographic Findings
If radiographs are normal, equivocal, or non-diagnostic:
- MRI without contrast is the preferred next step 1, 2
- Superior soft tissue contrast
- Excellent for characterizing mass composition
- Can detect marrow abnormalities
- Helps determine relationship to adjacent structures
If radiographs show osseous involvement:
- MRI remains the preferred advanced imaging modality
- Consider contrast enhancement if:
- Infection is suspected
- Need to differentiate solid from cystic components
- Evaluation of tumor vascularity is needed
Rationale for Radiographs as Initial Test
Radiographs are recommended as the first imaging test for several reasons:
- Cost-effective screening tool
- Widely available
- Provides essential baseline information
- Guides selection of subsequent imaging modalities 1
- Excellent for detecting bone involvement and calcifications
The American College of Radiology states that "radiographs should be obtained first in most, if not all, cases" 1 when evaluating hip pain, including masses. This is considered standard practice despite limited scientific evidence supporting this approach 1.
MRI Advantages for Hip Mass Evaluation
After initial radiographs, MRI is the preferred advanced imaging modality because:
- Excellent soft tissue contrast for characterizing masses 3
- Can differentiate between benign and malignant features in many cases
- Provides information for both diagnosis and staging 3
- Helps determine extent of disease and relationship to critical structures
- Can detect marrow abnormalities not visible on radiographs
Important Considerations and Pitfalls
- Do not skip radiographs: MRI should not be interpreted without recent radiographs available for comparison 4
- Avoid unnecessary CT: There is insufficient evidence to support CT as the initial imaging procedure for hip masses 1
- Communication is crucial: Provide relevant clinical information to the radiologist to optimize protocol selection 2
- Consider specialized views: For certain conditions, specialized radiographic views may provide additional diagnostic information 5, 6
Special Situations
- If prosthetic hip is present: Radiographs remain first-line, but subsequent MRI should use metal artifact reduction sequences (MARS) 1, 2
- For suspected pseudotumor: MRI can classify these into thin-walled cystic (Type I), thick-walled cystic (Type II), or predominantly solid masses (Type III) 7
- For suspected infection: Consider contrast-enhanced MRI after initial radiographs 2
By following this evidence-based approach of starting with radiographs followed by appropriate advanced imaging (typically MRI), you can ensure optimal diagnostic accuracy while minimizing unnecessary testing for a solid mass in the left hip.