Multifocal pigmented villonodular synovitis coexisting in both the knee joint and the patella: a case report and literature review

Abstract

Backgroud: Pigmented villonodular synovitis (PVNS) is an uncommon entity of proliferative lesion of the synovium, presenting with different clinical signs and symptoms. PVNS rarely forms an osteolytic lesion in a bone. Here we report a unique case of PVNS with a nodular lesion in the left patella.

Case presentation: A 37-year-old female was referred to our hospital with complaints of ongoing left knee pain and a painful and palpable mass in her left popliteal fossa. MRI demonstrated a nodular lesion in the left patella, diffuse affected synovial tissue in the left knee and an extra-articular mass in the left popliteal fossa. After a primary diagnosis of PVNS had been established, combined arthroscopic synovectomy and open resection were performed. The postoperative pathological diagnoses of the resected mass from the popliteal fossa, the affected synovial tissue and the lesion in the patella were consistent with PVNS. At 1-year follow-up, no evidence of recurrence was noted.

Conclusions: Based on brief literature review of PNVS, we presented a very rare case of PVNS with a nodular lesion in the left patella, diffuse affected synovial tissue in the left knee and an extra-articular mass in the left popliteal fossa.

Keywords: Case report; Giant cell tumor of tendon sheath; Localized form; Multifocal lesions; Patella; Pigmented villonodular synovitis; Popliteal fossa.

Fig. 1

Frontal (a), lateral (b) and the axial (c) views of the patella show a well-defined lytic lesion in the left patella, which has eroded almost all the medial half of the patella. Small degenerative osteophyte formation and slight knee joint effusion is also presented

Fig. 2

Magnetic resonance imaging (MRI) reveals extensive nodular synovial proliferation in the knee, a well-defined lesion confined to the patella and a lobulated mass-like lesion in the poplitea. Sagittal T1-weighted scans (a1, a2) show inhomogeneous low signal foci and depict a clear border of the foci. Axial T2-weighted scans (b1, b2) exhibits long T2 signal of joint effusion and tissue edema. Proton density-weighted imaging (c1, c2) shows lobulated, heterogeneous lesions with high intensity of PDWI signals are in patella, the suprapatellar bursa and the posterior region of knee. Focal hypointense areas represent the hemosiderin. No destructive lighment changes and cartilage damage is detected. After the administration of gadolinium-DTPA fat suppressed T1-weighted imaging (d1, d2) illustrates a distinct enhancement of the foci. The MRI appearance of is suggestive of the PVNS diagnosis

Fig. 3

A short S-shaped incision was mad over the posterior knee joint. The posterior mass in poplitea was exposed, dissected and marginally resected

Fig. 4

Arthroscopic images (a, b) of the left knee indicating prolific synovium with coarse villi, heavily pigmented diffuse pigmented villonodular synovitis. No communicating link was found under arthroscopic observation (c). Although the chondromalacia changes are visible on the articular surface of patella, it seems exactly intact without any eroded hole (d)

Fig. 5

A cortical window of 1.5 × 1.5 cm was made over the anteromedial aspect of the patella (a). The tumor was brownish (a) and was scooped out. On the inner side of the cavity there is a sclerotic margin (b). Bone defect in the patella was filled with iliac crest bone graft (c)

Fig. 6

Photomicrographs of H&E stain samples, which were taken from the resected mass in poplitea (a1–3), the proliferated synovial tissue in the knee (b1–3) and the lesion in the patella (c1–3), respectively. Low power views (a1, b1, c1; ×40) are characterized by a prominent number of epithelioid cells with fibrous stroma. Medium power (a2, b2, c2; ×100) views demonstrates numerous mononuclear cells, scattered multinucleated giant cells and occasional cytoplasmic hemosiderin. Under higher magnification (a3, b3, c3; ×200), the mononuclear cells are round or spindled and they have minimal cytoplasm and eccentric nuclei. There are some foam cells. Some cells typically contain cytoplasmic hemosiderin granules. No mitotic figures and atypia were found. The pathological features of the lesions from different locations are very similar to one another. Histologically, all findings consistently confirmed the original diagnosis of PVNS