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Pediatric solid intra-articular masses of the knee: prevalence, imaging features and etiologies



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.

Materials and methods

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.

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Correspondence to Bardia Nadim.

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Nadim, B., Samet, J.D. Pediatric solid intra-articular masses of the knee: prevalence, imaging features and etiologies. Pediatr Radiol 51, 1412–1420 (2021).

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  • Children
  • Intra-articular
  • Knee
  • Magnetic resonance imaging
  • Mass
  • Pigmented villonodular synovitis
  • Soft tissue