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It is the most common soft tissue tumor seen in histiocytoma dog the extremity (1). Lipoma can be classified as cutaneous and deep seated, based on its location. Intra muscular lipoma is a rare deep seated lipoma (2). It can be classified as well circumscribed type and infiltrating histiocytoma dog type, on histology (3). Intra muscular lipomas may compress the adjacent neurovascular bundle causing histiocytoma dog symptoms. Lipoma and well-differentiated liposarcoma are difficult to distinguish on imaging. Radiological evaluation is mainly aimed at differentiating lipoma from well-differentiated liposarcoma and also to look for fat plane between histiocytoma dog it and surrounding structures in cases of compression.

On CT, lipoma appears as fat density lesion compressing and displacing adjacent histiocytoma dog structures (figure 1A-C) (1). On MRI, lipoma displays hyperintense signal on T1 and T2W images and histiocytoma dog are suppressed on STIR images. Presence of thick septa and solid component which show enhancement histiocytoma dog on post contrast T1 W images goes on favor of histiocytoma dog well-differentiated liposarcoma rather than lipoma (4).

Hemangioma: hemangioma is the most frequently encountered vascular soft tissue tumor histiocytoma dog (5). Soft tissue hemangioma can be classified as cutaneous, subcutaneous, intra muscular and synovial based on the site of origin histiocytoma dog (6). Based on the size type of predominant vessel; hemangioma can be classified as cavernous, capillary, venous and arteriovenous (7). Further based on the anatomical relationship to a joint it histiocytoma dog can be classified as juxtra-articular, intra-articular and intermediate types. Synovial hemangioma is usually seen in early adolescents. Knee is the most common site. It is also reported in elbow, wrist ankle (8).

Hemangioma may be well-circumscribed or have poorly defined margins, with varying amounts of hyperintense T1 signal owing to either histiocytoma dog reactive fat overgrowth or haemorrhage (5). Hemangioma appears as a bunch of grapes on T2W images histiocytoma dog (figure 2A, B). This appearance is due to cavernous vascular spaces containing stagnant histiocytoma dog blood. Some hemangiomas demonstrate fluid-fluid levels (figure 2C, D) (8). Areas of signal void correspond to phleboliths. Post contrast T1 W images demonstrate extra-articular involvement (9). Open or arthroscopic surgical excision is the treatment of choice.

Synovial chondromatosis: synovial chondromatosis is a benign mono-articular neoplastic process of the synovium. Pathologically, it is characterized by chondroid metaplasia of synovium with formation histiocytoma dog of multiple cartilaginous nodules (10). It can be primary or secondary. Secondary synovial chondromatosis is seen in patients with arthritis or histiocytoma dog other mechanical joint conditions (9). Primary synovial chondromatosis is usually seen adults of 3 rd histiocytoma dog to 5 th decade. It is more common in men. Knee is the most common joint involved followed by elbow, hip shoulder (11). Clinically patient presents with pain, swelling and restriction of motion of the affected joint.

Radiological diagnosis is usually straight forward on plain radiographs with histiocytoma dog presence of multiple loose bodies in the affected joint showing histiocytoma dog ring and arc type of matrix mineralization (figure 3A,B) (10). Cross sectional imaging is required in patients where there is histiocytoma dog no mineralization of loose bodies (figure 3). In addition we can also demonstrate the bony erosions and histiocytoma dog extent of the disease process. MR is indicated to look for extent of lesion and histiocytoma dog also follow-up of patients with suspected recurrence (12). On MRI, multiple loose bodies are seen in the affected joint which histiocytoma dog display variable signal depending on the amount of mineralization (figure 3D,E). Well mineralized lesions display hypointense signal on T1 W and histiocytoma dog T2W images. Surgical resection is the treatment of choice. Synovial chondromatosis is known to reccur after treatment and recurrence histiocytoma dog rate is between 3- 23% (10).

Pigmented villonodular synovitis[PVNS]: it is a benign neoplastic process of the synovium. It may also involve the bursa, joint and the tendon sheath (13). Synovial involvement can be diffuse or focal. Pigmented villonodular synovitis of tendon sheath is also called giant histiocytoma dog cell tumor of tendon sheath (14). Pathologically PVNS is characterized by villous, nodular villonodular proliferation of synovium with hemosiderin pigmentation (15). Hemosiderin pigmentation is detected very well on MRI which makes histiocytoma dog it imaging modality of choice. PVNS is usually seen in middle age adults. Knee is the most common joint involved followed by hips. Clinically it presents as pain and swelling in the affected histiocytoma dog joint. Unlike other soft tissue tumors, imaging in PVNS is done to look for specific diagnosis, apart from specific diagnosis we can also evaluate whether the histiocytoma dog disease is diffuse or localized and its extent and also histiocytoma dog post surgical follow-up to look for recurrence.

On MR imaging localized PVNS is seen as asymmetric nodular histiocytoma dog thickening of the synovium with lobulated contours. These lesions display characteristic low signal on all sequences (figure 4A, B) and blooming on gradient images (figure 4C) due to presence of hemosiderin pigmentation (13). On post contrast T1W images there is enhancement of the histiocytoma dog abnormal synovium (figure 4D). Surgical excision is the treatment of choice. Localized disease could be excised on arthroscopy. PVNS has a high recurrence post surgery recurrence rate is histiocytoma dog between 8- 56% (16).

Synovial sarcoma:synovial sarcoma is a primary malignant mesenchymal tumor found most histiocytoma dog commonly in the lower extremities (17). It is a misnomer as it does not arise from histiocytoma dog the synovium, but form primitive mesenchymal cells in the extra articular soft histiocytoma dog tissue close to the synovium. Pathologically synovial sarcoma display dual epithelial and mesenchymal differentiation (18). It has three main histological sub types namely; biphasic, monophasic and poorly differentiated (19). It usually affects adolescent and young adults between 5 – 40 yrs. Knee is the most common site followed by foot and histiocytoma dog ankle (20). Clinically the patient presents with slowly growing palpable mass. Radiological evaluation is mainly aimed at evaluating the extent and histiocytoma dog staging of tumor besides suggesting a specific diagnosis. MRI is the imaging modality of choice.

On T1-weighted MR images, synovial sarcoma typically appear as a prominently heterogeneous multilobulated soft histiocytoma dog tissue mass (figure 5A, B) (21). On T2-weighted MR images it appears heterogeneous with calcification, haemorrhage or necrosis and a solid component (figure 5 C). This finding is characteristically called as triple sign (22). The solid component show homogenous enhancement on post contrast T1 histiocytoma dog W images. Synovial sarcomas are known to invade into the adjacent bone histiocytoma dog and joint (18). Synovial sarcoma shows high uptake of radio tracer on PET-CT (figure 5D) (23). Wide local surgical excision with removal of normal cuff of histiocytoma dog surrounding tissue is the treatment of choice.

Soft tissue sarcoma: these are a histological diverse group of malignant tumors which histiocytoma dog predominantly arise from soft tissue. There are more than 50 various sub types described in histiocytoma dog literature (24). Most common of them are liposarcoma, leiomyosarcoma, malignant fibrous histiocytoma [MFH], fibrosarcoma and synovial sarcoma (25). Synovial sarcoma has been described earlier. Thigh is most common site for soft tissue tumors followed histiocytoma dog by pelvis, arm or trunk (26). These tumors are usually seen in adults (27). Imaging in these tumors is mainly indicated to evaluate the histiocytoma dog extent, staging; morphological characterization and post operative post chemo- radiotherapy follow up. Specific diagnosis is arrived mostly after histopathology.

MRI is the imaging modality of choice. Most tumors have non-specific features in the form of hypointense signal on T1W histiocytoma dog images (figure 6A) and hyperintense signal on T2W images. Hyperintense signal on T1W images points to fatty component; in this case diagnosis goes in favor of liposarcoma (4). In addition look for encasement of vessels (figure 6B), inter compartmental extension (figure 6), extension into joint skin (figure 6D), multifocal lesions and marrow infiltration. Wide surgical excision is the treatment of choice. Entire muscle could be excised if the functional loss is histiocytoma dog not too great (28). Encased vessels are bypassed and then resected along with the histiocytoma dog tumor tissue. If the fat plane between the lesion and the neurovascular histiocytoma dog structures is ill defined, then patient is subjected to pre and post operative radiotherapy histiocytoma dog (28). These tumors are known to have high recurrence rate depending histiocytoma dog on the histological type and grade.

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