Abstract
The etiologies of pediatric solid intra-articular soft-tissue masses are not well described and can present diagnostic dilemmas. Our hypothesis was that these entities have a limited differential diagnosis and are mostly benign. We reviewed knee magnetic resonance imaging (MRI) scans performed at our tertiary care institution between 2001 and 2019 (n=3,915). Our inclusion criterion was knee MRI with a solid intra-articular soft-tissue mass. Our exclusion criteria were cases with no masses or non-solid intra-articular lesions with clear radiologic diagnoses. Multiple radiologic characteristics were evaluated. Radiologic and histological diagnoses were collected when available. Cases without histology were assigned a suspected diagnosis. Twenty-five out of 3,915 (<1%) cases met the inclusion exclusion criteria. twenty patients underwent biopsy. patient age ranged from 1 to 19 years with a mean age of 12 years. lesion size ranged from 1 to 7 cm with a mean of 3.3 cm. the top three histological diagnoses were pigmented villonodular synovitis (pvns) (7 20, 35%), vascular malformations (2 20, 10%) and inflammatory arthritis (2 20, 10%). there was one malignant case of synovial sarcoma (1 20, 5%). of the five cases without biopsies, pvns was the most common diagnosis (3 5, 60%). five out of 10 (50%) pvns cases were focal and 5 10 (50%) were multifocal. all pvns cases (10 10, 100%) had hypointense signal on t2. solid intra-articular soft-tissue masses of the knee in children are rare, with a prevalence of><1% in our study. the vast majority are benign with pvns being the most common diagnosis. the etiologies of pediatric solid intra-articular soft-tissue masses are not well described and can present diagnostic dilemmas. our hypothesis was that these entities have a limited differential diagnosis and are mostly benign. we reviewed knee magnetic resonance imaging (mri) scans performed at our tertiary care institution between 2001 and 2019 (n="3,915)." our inclusion criterion was knee mri with a solid intra-articular soft-tissue mass. our exclusion criteria were cases with no masses or non-solid intra-articular lesions with clear radiologic diagnoses. multiple radiologic characteristics were evaluated. radiologic and histological diagnoses were collected when available. cases without histology were assigned a suspected diagnosis. twenty-five out of 3,915 (><1%) cases met the inclusion exclusion criteria. twenty patients underwent biopsy. patient age ranged from 1 to 19 years with a mean age of 12 years. lesion size ranged from 1 to 7 cm with a mean of 3.3 cm. the top three histological diagnoses were pigmented villonodular synovitis (pvns) (7 20, 35%), vascular malformations (2 20, 10%) and inflammatory arthritis (2 20, 10%). there was one malignant case of synovial sarcoma (1 20, 5%). of the five cases without biopsies, pvns was the most common diagnosis (3 5, 60%). five out of 10 (50%) pvns cases were focal and 5 10 (50%) were multifocal. all pvns cases (10 10, 100%) had hypointense signal on t2. solid intra-articular soft-tissue masses of the knee in children are rare, with a prevalence of><1% in our study. the vast majority are benign with pvns being the most common diagnosis.>
