Age / Sex : 51 / F

Age / Sex : 51/ female

Chief complaint : palpable mass on left knee from 1 year ago

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

* Send Application Answers to In Sook Lee, MD (lis@pusan.ac.kr)

Courtesy : Hyun-joo Kim, Soonchunhyang Seoul hospital

Localized pigmented villonodular synovitis

Discussion

Findings:

 Plain radiograph

There is a space occupying soft tissue density lesion in the Hoffa’s fat pad.

Left knee MRI

There is a 4.2x3.3x3.2 cm sized bilobulating contoured mass lesion in lateral aspect of Hoffa`s fat pad extending into anterior subcutaneous fat layer through the lateral aspect of the patellar tendon.

The lesion shows T1 slight low and T2 heterogenous iso SI with internal dark SI portions.

The lesion shows heterogenous enhancement with internal nonenhancing dark SI portions.

Differential Diagnosis:

}  Synovial hemangioma

Diagnosis:  

Pigmented villonodular synovitis, localized type.

Discussion:

 Pigmented Villonodular Synovitis

}  Benign proliferative disorder of synovium

}  3^rd or 4^th decade, M:F = 1: 2

}  5% of all primary soft tissue tumors

}  Monoarticular - knee (m/c), hip, ankle, shoulder, elbow

}  Hypertrophic synovial mass with hemosiderin laden macrophages

}  2 types

}  Diffuse form

}  Slowly progressive pain & swelling, more frequent recurrence

}  Aspiration - brown fluid d/t previous hemorrhage

}  Focal or localized form – nodular synovitis

}  Less common than diffuse form, adjacent to Hoffa’s fat pad

}  Variable hemosiderin deposition

}  Radiographic features

}  Soft tissue swelling or joint effusion

}  Preservation of joint space

}  ± bone erosion (hip, shoulder) and cysts

}  Absence of calcification

}  Normal bone mineralization

}  MR features

}  Well-defined mass localized to synovium

}  Diffuse nodular frond like proliferation of synovium

}  Low SI on both T1- & T2-WI, “blooming” artifact on GRE

}  Hemosiderin

Intense enhancement

References:

 Mark D. Murphey, John H. Rhee, Rachel B. Lewis, et al.  From the Archives of the AFIP

Pigmented Villonodular Synovitis: Radiologic-Pathologic Correlation. RadioGraphics 2008; 28:1493–1518