ARRS 2022 Abstracts

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E1274. Lipoma Arborescens: Imaging of Typical and Atypical Disease and Differentiation From Other Intraarticular Pathology
Authors
  1. David Kephart; San Antonio Uniformed Services Health Education Consortium
  2. David Oettel; San Antonio Uniformed Services Health Education Consortium
  3. Liem Bui-Mansfield; Uniformed Services University of Health Sciences
Background
Lipoma arborescens is a benign intra-articular lesion characterized by villous lipomatous proliferation of the synovium, most commonly found in the knee joint. The purpose of this educational exhibit is to review typical and atypical cases.

Educational Goals / Teaching Points
In this presentation, we will review the clinical features and imaging characteristics of lipoma arborescens. Histologic findings are examined to explain its imaging appearance. Differential diagnosis is discussed.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
72% of patients with lipoma arborescens had a typical presentation, elderly with chronic painless joint swelling. Half of these patients had diffuse involvement of the knee; the other half had focal disease. Other symptoms include pain, limited range of motion, crepitus, locking, and mass. Its etiology is unknown, but 92% of patients have osteoarthritis (OA), 18% inflammatory arthritis, 15% diabetes, or 5% steroid therapy, suggestive of secondary reactive process associated with chronic joint inflammation. 28% of patients had atypical disease presentation: multifocal lipoma arborescens, joints other than the knee, or extra-articular disease involving bursa or tendon sheath. There was no significant difference in age at presentation, presence of OA or known inflammatory arthritis between the typical and atypical disease. 87% of the patients had involvement of only one joint. Synovectomy is the recommended treatment due to absence of complete regression with conservative therapy. Total knee arthroplasty is reserved for advanced OA. The imaging findings reflect the underlying histology. On radiography, large suprapatellar effusion and osteoarthritis are the main findings. Sonography reveals a uniformly echogenic frond-like mass in the suprapatellar bursa with a large effusion and popliteal cyst. Under real-time evaluation, the synovial mass bends and waves with dynamic compression and manipulation. On CT, the villous synovial proliferative mass has low attenuation isodense to subcutaneous fat. MR reveals multiple finger-like and globular synovial masses that are isointense to fat on all MR sequences. Post-contrast, there is frond-like synovial enhancement. Arthroscopy shows frond-like fatty synovial proliferation. Photomicrograph reveals papillary synovial proliferation, demonstrating mature adipocytes in a myxoid stroma beneath synovial epithelium. Multiple dilated vessels within the papillary fronds are consistent with chronic synovitis. Differential diagnoses include synovial osteochondromatosis, localized nodular synovitis or pigmented nodular synovitis (PVNS), intra-articular lipoma, Morel-Lavallee lesion, rice bodies, and myxoid liposarcoma. Review of clinical history and careful interpretation of imaging findings lead to correct diagnosis.

Conclusion
Lipoma arborescens is a monoarticular non-neoplastic reactive process typically involving the synovial membrane of the knee joint; however, it may involve other joints, bursae, or tendon sheaths and can be multifocal. It has characteristic imaging findings that can be diagnosed definitively on cross-sectional imaging by the presence of frond-like fatty masses.