Differential Diagnosis: Tender Superolateral Patellar Bulge
A tender, small, rubbery bulge just superior and lateral to the right patella is most likely a ganglion cyst, though bursitis in an atypical location remains a consideration.
Primary Diagnosis: Ganglion Cyst
The superolateral location is not a typical site for a named bursa 1, making ganglion cyst the leading diagnosis. Ganglion cysts commonly occur around the knee joint and present as smooth, well-circumscribed masses 2.
Key Diagnostic Features Supporting Ganglion:
- Location specificity: The anatomic location of a cystic lesion often permits correct diagnosis, and the superolateral patellar region is more consistent with ganglion than typical bursae 3
- Physical characteristics: Ganglion cysts typically present as rubbery, mobile masses that may be tender 4, 2
- Communication with joint: Ganglion cysts frequently have an identifiable thin stalk communicating to the joint space 2
Alternative Consideration: Atypical Bursitis
While less likely, bursitis in an atypical location cannot be entirely excluded 4. The lateral superior knee region lacks a typical named bursa 1, but fluid collections can develop in response to trauma or repetitive stress 5.
Recommended Diagnostic Approach
High-frequency ultrasound (≥10 MHz) is the first-line imaging modality to definitively characterize this lesion 6, 7, 1:
- Ganglion appearance: Smooth, well-circumscribed, anechoic or hypoechoic mass with possible connection to joint 2
- Bursal fluid: Would show fluid collection with possible synovial thickening and hyperemia if inflamed 8
- Real-time assessment: Dynamic scanning during knee movement helps differentiate pathologies 8
If Ultrasound is Inconclusive:
MRI without contrast is appropriate for further characterization 6:
- Ganglion cysts appear as homogeneously T2-hyperintense, thin-walled, unilocular lesions 2
- Can identify associated joint disorders and evaluate relationship to surrounding structures 4
- Critical pitfall: Internal solid contrast enhancement should raise concern for neoplasm requiring biopsy 3
Important Clinical Caveats
- History of trauma: Consider epidermal inclusion cyst if there is history of penetrating trauma to the area, though this typically occurs prepatellar 9
- Atypical features: Septations, internal debris, or thick walls may indicate hemorrhage, infection, or neoplasm requiring further evaluation 3, 2
- Associated joint pathology: Evaluate for underlying osteoarthritis or meniscal pathology, as ganglion and synovial cysts often occur in association with these conditions 2