Skeletal Radiol (1992) 21:393-395
Skeletal Radiology
Case report 745 D. Martinez, F.R.C.R. ~, P.A. Millner, F.R.C.S. 2 A. Coral, F.R.C.R. 1, R.J. Newman, F.R.C.S. 2, G.J. Hardy, F.R.C. Path 3, and W.P. Butt, F.R.C.R. 1 Departments of 1 Radiology, 2 Orthopaedics, and 3 Pathology, St. James's University Hospital, Leeds, UK
Imaging studies
Clinical information
Fig. 1. A lateral projection of a single con-
A 62-year-old m a n presented with a 1-day history o f a painful left calf. The past history included adult onset diabetes mellitus, angina and calf claudication. O n examination, the calf was w a r m and tender. A n effusion o f the knee was present, but a full range o f m o v e m e n t was noted. Plain radiog r a p h and v e n o g r a m results were normal. Aspirated synovial fluid showed i n f l a m m a t o r y cells but no crystals or m i c r o o r g a n i s m s and no g r o w t h on culture. A n a r t h r o g r a m (Fig. 1) d e m o n s t r a t e d a leak o f contrast m e d i u m projecting f r o m the
trast arthrogram shows filling defects lying posteriorly within the suprapatellar bursa Fig. 2. Sagittal scan of the knee using a 5MHz linear array transducer demonstrates a villous lesion surrounded by fluid in the suprapatellar bursa; b, bursal fluid; F, femur; black arrowhead, quadriceps tendon; white arrow, lesion Fig. 3. An axial CT scan shows the lesion (arrowhead) projecting subsynovially into the bursa, surrounded by enhancing synovial membrane Address reprint requests to: D. Martinez,
F.R.C.R., Department of Radiology, St. James's University Hospital, Beckett St, Leeds LS9 7TF, UK
posterior p o r t i o n o f the joint into the popliteal fossa, but no filling o f a Baker's cyst. In addition, irregular filling defects in the suprapatcllar bursa were present. U l t r a s o u n d studies (Fig. 2) showed a collapsed Baker's cyst and encysted fluid tracking along the medial side o f the gastrocnemius; the lesions were shown to arise f r o m the posterior wall o f the suprapatellar bursa. C o m p u t e d t o m o g r a p h y (CT) (Fig. 3) confirmed a synovial lesion which contained tissue with measurements o f - 4 0 to - 6 0 Hounsfield units. The knee was explored surgically. 9 1992 International Skeletal Society
394
D. Martinez et al. : Case report 745
Diagnosis: Synovial lipoma arborescens
Operative and pathological studies Fig. 4. Operative appearance showing a fronded fatty lesion in the supratellar bursa
Macroscopically, a fronded, fatty lesion was present, producing villous projections arising subsynovially from the posterior aspect of the joint (Fig. 4). The histological appearances were typical (Fig. 5). The subsynovial tissue was completely replaced by mature adipose cells, and the synovium was chronically inflamed.
Fig. 5. Microscopic appearance showing chronically inflamed synovium with underlying lipomatous tissue ( x 80)
Discussion The synovium is the specialised lining of diarthrodial joints. It consists of an inner layer of synovial cells closely related to underlying fibroblasts. Beneath the synovial cells is the subsynovial layer which consists of fibroalveolar tissue with collagen, fat, lymph channels, nerves and blood vessels; it is here that neoplasms arise [4]. A synovial tumour should be considered if there is a history of swelling with intermittent pain. The differential diagnosis of a benign synovial tumour includes osteochondromatosis, pigmented villonodular synovitis, xanthoma, haemangioma, lipoma, lipoma arborescens, plexiform neuroma and vascular malformations. Lipoma arborescens is rare. It should be differentiated from a small lipoma in the prefemoral fat pad and fibrolipoma arising from a ligament [13]. Hallel has suggested renaming the condition "villous lipomatous proliferation of the synovial membrane" in order to avoid neoplastic connotations [5]. The lesion is a benign hyperplastic process in which diffuse subsynovial infiltration by mature adipose cells causes proliferative villous projections [12]. Confusion in the literature about the nature of the condition exists. Descriptions by Placeo and Tassi [11] and Hoffa [6] suggest a traumatic aetiology. However, the 67 cases Placeo and Tassi collected are not true lipoma arborescens but are synovial proliferation replacing fat normally present in and around the patella. Such proliferation is common following chronic irritation of the syno-
vium. The cases were associated with meniscal tears. However, Stout (quoted by Weitzman and Hallel et al. [5, 13]) showed that the lesion in lipoma arborescens is a replacement of the subsynovial tissue by mature fat cells, producing villous projections particularly in the suprapatellar region. Lipoma arborescens occurs in association with degenerative joint disease, chronic rheumatoid arthritis and diabetes mellitus [1]. Our patient had diabetes mellitus, and at arthrotomy minor degenerative changes were found. The condition commonly affects men, and the knee is the usual site of involvement, although it has been described in the wrist and hips [10]. Bilateral involvement of
the knee has also been recorded [2,
131. Investigations usually reveal serosanguinous aspirate with no crystals or microorganisms. The erythrocyte sedimentation rate and uric acid level are normal, and the rheumatoid factor result is negative [3, 8]. Plain films may show a soft-tissue mass. At arthrography, irregular, nonspecific filling defects are noted, usually in the posteromedial aspect of the suprapatellar pouch [3]. Although ultrasound has been used to assess the synovium in many other conditions (including rheumatoid arthritis, haemophilia, pigmented villonodular synovitis and synovial osteochrondromatosis) [7, 9, 14] its use has not been previously
D. Martinez et al. : Case report 745 r e p o r t e d in l i p o m a a r b o r e s c e n s . In this case r e p o r t , u l t r a s o u n d c o n f i r m e d a nonspecific, s y n o v i a l l y b a s e d lesion. C T defines the f a t t y n a ture, size a n d e x t e n t o f the lesion [6]. Its low a t t e n u a t i o n a n d l a c k o f cont r a s t e n h a n c e m e n t d i f f e r e n t i a t e d it f r o m p i g m e n t e d v i l l o n o d u l a r synovitis, w h i c h p r o d u c e s a high a t t e n u a t i o n a n d a n e n h a n c i n g lesion [1]. S y n o v i a l h a e m a n g i o m a shows striking c o n t r a s t e n h a n c e m e n t o n C T a n d angiography. Synovial chondromatosis is t y p i f i e d b y discrete, o f t e n calcified lesions w h i c h m a y be visible o n plain radiographs. In summary, a case is p r e s e n t e d o f l i p o m a a r b o r e s c e n s o f the knee with a n a t y p i c a l , s u d d e n onset. A r thrography and ultrasound conf i r m e d a s y n o v i a l l y b a s e d lesion in the s u p r a p a t e l l a r p o u c h . C T e n a b l e d a preoperative diagnosis of lipoma a r b o r e s c e n s to be m a d e , w h i c h was c o n f i r m e d b y surgical excision o f a f r o n d e d f a t t y mass. H i s t o l o g i c a l studies s h o w e d h y p e r p l a s t i c villi with m a t u r e a d i p o s e cells in the s u b s y n o vial layer. R e s e c t i o n o f the s y n o v i u m
395 is c o n s i d e r e d curative, with o n l y one case o f r e c u r r e n c e after s y n o v e c t o m y h a v i n g been r e p o r t e d [4].
References 1. Armstrong SJ, Watt I (1989) Lipoma arborescens of the knee. Br J Radiol 62:178 2. Arzimanoglu A (1957) Bilateral arborescent lipoma of the knee. A case report. J Bone Joint Surg [Am] 39 : 976 3. Burgan DW (1971) Lipoma arborescens of the knee: another cause of filling defects on a knee arthrogram. Radiology 101 : 583 4. Coventry MB, Harrison EG, Martin JF (1966) Benign synovial tumors of the knee: a diagnostic problem. J Bone Joint Surg [Am] 48:1350 5. Hallel T, Lew S, Bansal M (1988) Villous lipomatous proliferation of the synovial membrane (lipoma arborescens). J Bone Joint Surg [Am] 70:264 6. Hoffa A (1904) The influences of the adipose tissue with regard to the pathology of the knee joint. JAMA 43:795 7. Holsbeeck van M, Hoisbeeck van K, Gevers G, Marchal G, Steen van A, Favril A, Gielen J, Dequeker J, Baert A (1988) Staging and follow-up of rheumatoid arthritis of the knee. Comparison
of sonography, thermography, and clinical assessment. J Ultrasound Med 7 : 561 8. Kaufman RA, Towbin RB, Babcock DS, Crawford AH (1982) Arthrosonography in the diagnosis of pigmented villonodular synovitis. A JR 139 : 396 9. Moss GD, Dishuk W (1984) Ultrasound diagnosis of osteochondromatosis of the popliteal fossa. J Clin Ultrasound 12:232 10. Noel ER, Tebib JG, Dimontet C, Colson F, Carrett JP, Vauzelle JL, Bouvier M (1987) Synovial lipoma arborescens of the hip. Clin Rheumatol 6:92 11. Placeo F, Tassi D (1953) Considerazioni cliniche su 62 osservazioni di lipoma arborescente postraumatico del ginocchio come entita patologica a se stante associata a lesione meniscale. Minerva Chirurgica 8:316 12. Schajowitz F (1981) Tumour and turnout-like lesions of bone and joint. Springer, Berlin Heidelberg New York, p 545 13. Weitzman G (1965) Lipoma arborescens of the knee. J Bone Joint Surg [Am] 47:1030 14. Wyld P J, Dawson KP, Chisholm RJ (1984) Ultrasound in the assessment of synovial thickening in the haemophilic knee. Aust NZ J Med 14:678
Skeletal Radiology
Case report 745 D. Martinez, F.R.C.R. ~, P.A. Millner, F.R.C.S. 2 A. Coral, F.R.C.R. 1, R.J. Newman, F.R.C.S. 2, G.J. Hardy, F.R.C. Path 3, and W.P. Butt, F.R.C.R. 1 Departments of 1 Radiology, 2 Orthopaedics, and 3 Pathology, St. James's University Hospital, Leeds, UK
Imaging studies
Clinical information
Fig. 1. A lateral projection of a single con-
A 62-year-old m a n presented with a 1-day history o f a painful left calf. The past history included adult onset diabetes mellitus, angina and calf claudication. O n examination, the calf was w a r m and tender. A n effusion o f the knee was present, but a full range o f m o v e m e n t was noted. Plain radiog r a p h and v e n o g r a m results were normal. Aspirated synovial fluid showed i n f l a m m a t o r y cells but no crystals or m i c r o o r g a n i s m s and no g r o w t h on culture. A n a r t h r o g r a m (Fig. 1) d e m o n s t r a t e d a leak o f contrast m e d i u m projecting f r o m the
trast arthrogram shows filling defects lying posteriorly within the suprapatellar bursa Fig. 2. Sagittal scan of the knee using a 5MHz linear array transducer demonstrates a villous lesion surrounded by fluid in the suprapatellar bursa; b, bursal fluid; F, femur; black arrowhead, quadriceps tendon; white arrow, lesion Fig. 3. An axial CT scan shows the lesion (arrowhead) projecting subsynovially into the bursa, surrounded by enhancing synovial membrane Address reprint requests to: D. Martinez,
F.R.C.R., Department of Radiology, St. James's University Hospital, Beckett St, Leeds LS9 7TF, UK
posterior p o r t i o n o f the joint into the popliteal fossa, but no filling o f a Baker's cyst. In addition, irregular filling defects in the suprapatcllar bursa were present. U l t r a s o u n d studies (Fig. 2) showed a collapsed Baker's cyst and encysted fluid tracking along the medial side o f the gastrocnemius; the lesions were shown to arise f r o m the posterior wall o f the suprapatellar bursa. C o m p u t e d t o m o g r a p h y (CT) (Fig. 3) confirmed a synovial lesion which contained tissue with measurements o f - 4 0 to - 6 0 Hounsfield units. The knee was explored surgically. 9 1992 International Skeletal Society
394
D. Martinez et al. : Case report 745
Diagnosis: Synovial lipoma arborescens
Operative and pathological studies Fig. 4. Operative appearance showing a fronded fatty lesion in the supratellar bursa
Macroscopically, a fronded, fatty lesion was present, producing villous projections arising subsynovially from the posterior aspect of the joint (Fig. 4). The histological appearances were typical (Fig. 5). The subsynovial tissue was completely replaced by mature adipose cells, and the synovium was chronically inflamed.
Fig. 5. Microscopic appearance showing chronically inflamed synovium with underlying lipomatous tissue ( x 80)
Discussion The synovium is the specialised lining of diarthrodial joints. It consists of an inner layer of synovial cells closely related to underlying fibroblasts. Beneath the synovial cells is the subsynovial layer which consists of fibroalveolar tissue with collagen, fat, lymph channels, nerves and blood vessels; it is here that neoplasms arise [4]. A synovial tumour should be considered if there is a history of swelling with intermittent pain. The differential diagnosis of a benign synovial tumour includes osteochondromatosis, pigmented villonodular synovitis, xanthoma, haemangioma, lipoma, lipoma arborescens, plexiform neuroma and vascular malformations. Lipoma arborescens is rare. It should be differentiated from a small lipoma in the prefemoral fat pad and fibrolipoma arising from a ligament [13]. Hallel has suggested renaming the condition "villous lipomatous proliferation of the synovial membrane" in order to avoid neoplastic connotations [5]. The lesion is a benign hyperplastic process in which diffuse subsynovial infiltration by mature adipose cells causes proliferative villous projections [12]. Confusion in the literature about the nature of the condition exists. Descriptions by Placeo and Tassi [11] and Hoffa [6] suggest a traumatic aetiology. However, the 67 cases Placeo and Tassi collected are not true lipoma arborescens but are synovial proliferation replacing fat normally present in and around the patella. Such proliferation is common following chronic irritation of the syno-
vium. The cases were associated with meniscal tears. However, Stout (quoted by Weitzman and Hallel et al. [5, 13]) showed that the lesion in lipoma arborescens is a replacement of the subsynovial tissue by mature fat cells, producing villous projections particularly in the suprapatellar region. Lipoma arborescens occurs in association with degenerative joint disease, chronic rheumatoid arthritis and diabetes mellitus [1]. Our patient had diabetes mellitus, and at arthrotomy minor degenerative changes were found. The condition commonly affects men, and the knee is the usual site of involvement, although it has been described in the wrist and hips [10]. Bilateral involvement of
the knee has also been recorded [2,
131. Investigations usually reveal serosanguinous aspirate with no crystals or microorganisms. The erythrocyte sedimentation rate and uric acid level are normal, and the rheumatoid factor result is negative [3, 8]. Plain films may show a soft-tissue mass. At arthrography, irregular, nonspecific filling defects are noted, usually in the posteromedial aspect of the suprapatellar pouch [3]. Although ultrasound has been used to assess the synovium in many other conditions (including rheumatoid arthritis, haemophilia, pigmented villonodular synovitis and synovial osteochrondromatosis) [7, 9, 14] its use has not been previously
D. Martinez et al. : Case report 745 r e p o r t e d in l i p o m a a r b o r e s c e n s . In this case r e p o r t , u l t r a s o u n d c o n f i r m e d a nonspecific, s y n o v i a l l y b a s e d lesion. C T defines the f a t t y n a ture, size a n d e x t e n t o f the lesion [6]. Its low a t t e n u a t i o n a n d l a c k o f cont r a s t e n h a n c e m e n t d i f f e r e n t i a t e d it f r o m p i g m e n t e d v i l l o n o d u l a r synovitis, w h i c h p r o d u c e s a high a t t e n u a t i o n a n d a n e n h a n c i n g lesion [1]. S y n o v i a l h a e m a n g i o m a shows striking c o n t r a s t e n h a n c e m e n t o n C T a n d angiography. Synovial chondromatosis is t y p i f i e d b y discrete, o f t e n calcified lesions w h i c h m a y be visible o n plain radiographs. In summary, a case is p r e s e n t e d o f l i p o m a a r b o r e s c e n s o f the knee with a n a t y p i c a l , s u d d e n onset. A r thrography and ultrasound conf i r m e d a s y n o v i a l l y b a s e d lesion in the s u p r a p a t e l l a r p o u c h . C T e n a b l e d a preoperative diagnosis of lipoma a r b o r e s c e n s to be m a d e , w h i c h was c o n f i r m e d b y surgical excision o f a f r o n d e d f a t t y mass. H i s t o l o g i c a l studies s h o w e d h y p e r p l a s t i c villi with m a t u r e a d i p o s e cells in the s u b s y n o vial layer. R e s e c t i o n o f the s y n o v i u m
395 is c o n s i d e r e d curative, with o n l y one case o f r e c u r r e n c e after s y n o v e c t o m y h a v i n g been r e p o r t e d [4].
References 1. Armstrong SJ, Watt I (1989) Lipoma arborescens of the knee. Br J Radiol 62:178 2. Arzimanoglu A (1957) Bilateral arborescent lipoma of the knee. A case report. J Bone Joint Surg [Am] 39 : 976 3. Burgan DW (1971) Lipoma arborescens of the knee: another cause of filling defects on a knee arthrogram. Radiology 101 : 583 4. Coventry MB, Harrison EG, Martin JF (1966) Benign synovial tumors of the knee: a diagnostic problem. J Bone Joint Surg [Am] 48:1350 5. Hallel T, Lew S, Bansal M (1988) Villous lipomatous proliferation of the synovial membrane (lipoma arborescens). J Bone Joint Surg [Am] 70:264 6. Hoffa A (1904) The influences of the adipose tissue with regard to the pathology of the knee joint. JAMA 43:795 7. Holsbeeck van M, Hoisbeeck van K, Gevers G, Marchal G, Steen van A, Favril A, Gielen J, Dequeker J, Baert A (1988) Staging and follow-up of rheumatoid arthritis of the knee. Comparison
of sonography, thermography, and clinical assessment. J Ultrasound Med 7 : 561 8. Kaufman RA, Towbin RB, Babcock DS, Crawford AH (1982) Arthrosonography in the diagnosis of pigmented villonodular synovitis. A JR 139 : 396 9. Moss GD, Dishuk W (1984) Ultrasound diagnosis of osteochondromatosis of the popliteal fossa. J Clin Ultrasound 12:232 10. Noel ER, Tebib JG, Dimontet C, Colson F, Carrett JP, Vauzelle JL, Bouvier M (1987) Synovial lipoma arborescens of the hip. Clin Rheumatol 6:92 11. Placeo F, Tassi D (1953) Considerazioni cliniche su 62 osservazioni di lipoma arborescente postraumatico del ginocchio come entita patologica a se stante associata a lesione meniscale. Minerva Chirurgica 8:316 12. Schajowitz F (1981) Tumour and turnout-like lesions of bone and joint. Springer, Berlin Heidelberg New York, p 545 13. Weitzman G (1965) Lipoma arborescens of the knee. J Bone Joint Surg [Am] 47:1030 14. Wyld P J, Dawson KP, Chisholm RJ (1984) Ultrasound in the assessment of synovial thickening in the haemophilic knee. Aust NZ J Med 14:678
