Necessity of adjuvant postoperative radiotherapy for diffuse pigmented villonodular synovitis of the knee

RATIONALE Pigmented villonodular synovitis (PVNS) is an idiopathic, proliferative disorder lesion of synovial tissue, which is regarded as a benign disease, but has a local invasion. Up to now, these are no consensus about the etiology and pathogenesis of PVNS. Because of the lack of typical clinical features, misdiagnosis and delayed diagnosis are not uncommon, magnetic resonance imaging (MRI) can assist diagnosis and histopathological examination is recognized as the gold standard for the final diagnosis. Because this disease is so rare, there is no standard treatment. Surgical resection of the lesion is considered the preferred treatment, but postoperative recurrence is a problem that cannot be ignored. Postoperative radiotherapy is necessary, especially for patients with diffuse PVNS of the knee. PATIENT CONCERNS A 27-year-old female teacher presented with 3 years chronic pain of the right knee, and progressive swelling aggravated for 1 week. The range of motion of the knee was limited. DIAGNOSES Clinical and laboratory examination failed to provide definitive diagnosis. Imaging can assist in diagnosis, and pathology is the gold standard. Erythrocyte sedimentation rate (ESR), antihemolytic streptococcus O (ASO), and rheumatoid factors (RF) were all negative. Joint puncture revealed giant cell tumor of the synovial membrane. PVNS was confirmed by postoperative pathology. The characteristic T2 weighted low signal of MRI suggests the recurrence of PVNS. INTERVENTIONS The patient underwent 2 stages of treatment: open synovectomy was performed in the first place and postoperative external radiotherapy was not considered. After 2 years of disease-free remission, she was diagnosed with a recurrence of the disease by MRI. Further, arthroscopic total synovectomy of the right knee was performed and external beam radiotherapy was carried out after the operation. OUTCOMES Up to now, the patient was followed up for 3 years without any sign of recurrence. LESSONS Adjuvant postoperative radiotherapy can improve the local control rate, it is a reliable treatment method for diffused PVNS.