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A soft tisue mass with a bony lesion should prompt thequestion of which is the origin. Although not absolutely certain, there aresome helpful clues to help the differentiation between soft tissue tumor withbone invasion and bone tumor with soft tissue invasion. A large soft tissue mass with smaller bone lesion generallyindicates secondary bone invasion (exception: malignant lymphoma, Ewingsarcoma, etc.). the center position of the mass is also useful fordetermination of the primary site. The tip of the destroyed bony cortex may also help thedifferentiation. Periosteal side tends to indicate bone tumor, and bone marrowside for soft tissue tumor. Periostealreaction is another clue to determine the primary site. Bone tumor typicallyelicits a periosteal reaction when extending into adjacent soft tissues. Softtissue tumor usually destroys the periosteum and the bony cortex withouteliciting a periosteal reaction(exception: myositis ossificans etc.)
Representative lesions by compartment Subcutaneous
Intermuscular
Intramuscular
Intra-articular
Juxta-articular
Tendinous/musculoaponeurotic
Identification of intramuscular mass/intermuscular mass Fat is sometimes detectable at the periphery of deeply located soft tissue tumor on MRI. Split fat sign represents fine fat deposition around the lesion and is usually seenas a tapered rim of fat signal adjacent to the proximal and distal ends of thelesion. Split fat is produced as a intermuscular mass grows, and normal fat isdisplaced and effaced around the lesion (fig.9). This sign is commonly seen in benign soft tissue tumors that originate from the intermuscular space (eg. Benign nerve sheath tumor)(4). Intramuscular slow growing tumors, such as intramuscular myxoma, lead to atrophy of the surrounding muscle. Circumferential fat, named as fat rind, is therefore sometimes detectable at the periphery of this tumor type on MRI(fig.10)(5). Careful assessment is important to avoid confusing these tumors with a fat containing tumor (eg. liposarcoma).
Relationshipto the peripheral nerve An entering and exiting nerve is often seen on MR images in benigh peripheral nerve sheath tumor (6). The “target sign”, characterized by low to intermediate signal intensity centrally and high signal intensity peripherally, may appear on T2-weighted MR images, and lesions that demonstrate a target sign typically show more prominent enhancement in their centers on postcontrast images (7,8). In the case of schwannoma the mass is usually encapsulated and nerve is splayed by the mass. In contrast with schwannoma, neurofibroma is rarely encapsulated, and the parent nerve is central to or obliterated by the mass (fig. 12). Traumatic neuromas also demonstrate continuity with the parent nerve proximally (9). The history of antecedent trauma/surgery with the lack of a garget sign is a useful clue for the appropriate diagnosis (fig.13). MR imaging appearance of lipomatosis of nerve, called cable-like/spaghetti-like appearance, isusually pathognomonic, with longitudinally oriented cylindrical areas of low signal intensity (nerve fascicles) surrounded by adipose tissue in a diffusely thickened nerve (fig.14)(10,11)
Relationshipto the fascia/aponeurosis Superficial fibromatos is (palmar/plantar fibromatosis) usually arises from fascia oraponeurosis. MR imaging findings of predominantly low to intermediate signal intensity, nonenhancing bands of low signal intensity on long repetition time MR images that represent collagenized bands, and extension along fascialplanes (“fascial tail” sign) add specificity for diagnosis (fig.15)(12). These MR findings are occasionally observed in deep fibromatosis (desmoids-typefibromatosis). Myxofibrosarcoma is considered one of the most common sarcomas to occur in the extremities of elderly people, and is characterized by a high frequency of local recurrence because of extension into surrounding tissues for substantial distances along normal anatomical planes, particularly fascia (expecially in the case of subcutaneous lesions). This infiltrative spread may appear as “fascial tail” sign extending from the mass-like portion of the tumor (fig.16) (13,14).
Bursal lesion mimicking soft tissue tumor Anatomical knowledge of bursal distribution is indispensable in the diagnosis of bursal disease(figs.17-20). Subcutaneous bursae are found between skin and underlying bony prominences, such as olecranon and patella. Subfascial bursae exist between deep fascia and bone,and subtendinous bursae occur where one tendon overlies another tendon. Interligamentous bursae separate ligaments, and submucosal bursae are located between muscle and bone, tendon, or ligament. When a bursa exists near a joint, the synovial membrane of the bursa may becontinuous with that of the joint cavity, producing communicating bursae(fig.21)(15) Many bursal lesions(eg. Lipoma arborescens, pigmented villonodular synovitis, etc.) have specific MR characteristics and an awareness of these characteristics along with their pathological and anatomical features can allow for an accurate diagnosis(fig.22)(16,17).
Lymph node lesion mimicking soft tissue tumor In daily clinical practice, normal lymph nodes in the extremities are too small to be identified by imaging assessment (fig.23). MRI examination is only evaluated when suspicion has arisen for metastasis from various dermatological malignancies( eg. Popliteal lymph node for clear cell sarcoma of the ankle tendon). However, these lymph nodes are enlarged due to various diseases( infection, metastasis, lymphoma/ leukemia, collagen tissue disease,sarcoidosis, toxicities, etc.) and sometimes masquerade as primary soft tissuetumor. Cat-scratch disease is one of the benign regional lymphadenitis caused by infection from bartonello henselae. Epitrochlear region, neck, and groin are common sites, and MR imaging shows a regional lymphadenopathy with surrounding edema(fig.24) (18). Familiarity with the MR findings of the various lymph node lesions, along with their anatomical features and clinical information, could be helpful in ensuring accurate diagnosis and proper patient management(fig.25).
《每天朗读一段医学影像学英语文章》先睹为快：蜡泪样骨病（melorheostosis）
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来自： 昵称42715024 > 《胸部~华夏》
