DIFFERENTIAL DIAGNOSIS 1. Lipoma Arborescens 2. Pigmented Villonodular Synovitis (PVNS) 3. Synovial Chondromatosis 4. Rheumatoid Arthritis 5. Intra-articular Synovial Liipoma FINAL DIAGNOSIS Lipoma Arborescens of the Peroneal Sheath
intensity on T1 weighted images and varying signal intensity on T2 weighted images, depending on the extent of ossification. Intermediate T1 and T2 signal intensity noted with rheumatoid arthritis due to areas of fibrosis. Additionally specific laboratory values are noted with rheumatoid arthritis. REFERENCES 1. Sanamandra SK, Ong KO. Lipoma arborescens. Singapore Med J. 2014;55(1):5-11. doi:10.11622/smedj.2014003 2. Babar SA, Sandison A, Mitchell AW. Synovial and tenosynovial lipoma arborescens of the ankle in an adult: a case report. Skeletal Radiol. 2008Jan;37(1):75-7 3. A. Hoffa, “The influence of the adipose tissue with regard to the pathology of the knee joint,” The Journal of the American Medical Association, vol. 43, no. 12, pp. 795–796, 1904. 4. Meyers SP. MRI of bone and soft tissue tumors and tumorlike lesions, differential diagnosis and atlas. Thieme Publishing Group. (2008) ISBN:3131354216. 5. Y. Dogramaci, A. Kalaci, T. T. Sevinç, E. Atik, E. Esen, and A. N. Yanat, “Lipoma arborescens of the peroneus longus and peroneus brevis tendon sheath: case report,” Journal of the American Podiatric Medical Association, vol. 99, no. 2, pp. 153–156, 2009. 6. Vilanova JC, Barceló J, Villalón M, Aldomà J, Delgado E, Zapater I. MR imaging of lipoma arborescens and the associated lesions. Skeletal Radiol. 2003 Sep;32(9):504-9. doi: 10.1007/s00256-003-0654-9. Epub 2003 Jun 17. PMID: 12811424. 7. Patil PB, Kamalapur MG, Joshi SK, Dasar SK, Rao RV. Lipoma arborescens of knee joint: role of imaging. J Radiol Case Rep. 2011;5(11):17-25. doi: 10.3941/jrcr.v5i11.783. Epub 2011 Nov 1. PMID: 22470770; PMCID: PMC3303421.
DISCUSSION Lipoma arborescens, also known as synovial lipomatosis, is a rare, benign lesion characterized by diffuse proliferation and infiltration of sub-synovial connective tissue by mature adipose cells forming hypertrophic synovial villi 1 . Lipoma arborescens was first described in 1904 by Hoffa 3 and named for its macroscopic treelike morphology. Typically unilateral, it most often involves the suprapatellar pouch and presents between the 5th to 7th decades as an insidious onset of intermittent exacerbation of pain and swelling. Isolated involvement of the tenosynovial sheath is exceedingly rare – in such cases, there is often preferential involvement around the ankle joint 2,5 . While most often occurring without any antecedents, lipoma arborescens is often associated with inflammation, joint disease and trauma 4 . Although typically monoarticular, bilateral involvement has been reported in approximately 20% of patients with lipoma arborescens 6 . Rare cases of lipoma arborescens of the synovial joints presents with intermittent insidious swelling, followed by pain caused by trapping of the frond-like projections within the joint space 5 . As the clinical presentation of lipoma arborescens is often nonspecific, other pathologies must be ruled out through evaluation of laboratory values as well as sampling of synovial fluid through joint aspiration. MRI often is sufficient to make the diagnosis, given its pathognomonic appearance of an ill-defined, nonencapsulated synovial mass with frond-like configuration and concurrent joint effusion 6 . Both T1 and T2-weighted sequences demonstrate high signal intensity frond-like tissue, with saturation on fat suppressed sequences noted. Lipoma arborescens is characterized by soft tissue prominence, as demonstrated by radiographs of the ankle in our case. Histopathological analysis demonstrates villous papillary proliferation with replacement of subsynovial tissue by mature adipocytes 7 . Imaging differential diagnosis includes pigmented villonodular synovitis (PVNS), synovial chondromatosis, rheumatoid arthritis, and intra-articular synovial lipoma. While PVNS manifests as joint swelling in a similar age group, on MRI PVNS is characterized by low signal intensity on all sequences due to hemosiderin deposition (characteristic blooming on gradient echo) 8 . Synovial chondromatosis demonstrates intermediate to low signal
8. Garner H, Ortiguera C, Nakhleh R. Pigmented Villonodular Synovitis. RadioGraphics. 2008;28(5):1519-23.
ACKNOWLEDGEMENTS Mitchell Ta is a 4th year Medical Student at Tulane University School of Medicine in New Orleans, La. Ahmed T. Rashad MD is a PGYIV Resident in the Department of Radiology at Tulane University School of Medicine in New Orleans, La. Neel Dewan Gupta, MD is a clinical and academic musculoskeletal radiologist in New Orleans and serves as a clinical assistant professor within the Department of Radiology at the Tulane University Medical Center. Jeremy Nguyen MD, FACR is clinical radiology professor within the Department of Radiology at the Tulane University Medical Center. Donald Olivares, Digital Imaging Specialist and Graphic Designer. ■
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J LA MED SOC | VOL 174 | FALL 2022
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