Most soft tissue lesions are benign. The important key is identifying features that make a lump more likely malignant.

EVALUATION

History

• Length of time the mass has been present
  -a new mass rapidly increasing in size suggests malignancy
• Is the mass causing pain
  -Larger lesions cause aching pain. Small very tender lesions suggest neural lesion
  (compression, neurofibroma, neuroma) or Glomus tumour.
• History of trauma
  -Heterotopic ossification can be caused by trauma, as can false aneurysms and haematoma. Foreign bodies can cause granulomas.
• History of cancer
  -Suggests metastatic disease. Carcinoma of the lung, pancreas as well as lymphomas can metastasize to the skin. 
• History of fever
  -Infection, Ewings.

Haemangiomas present as a mass that aches on prolonged standing, but disappears on lying.

Examination

Involves evaluating the usual size, character and mobility of the mass. Regionallymph nodes are also felt.

Firm, deep, immobile and >5cm masses suggests malignancy. Some malignant tumours can be small, such as epitheloid sarcoma and tendon clear cell sarcoma. Extra-abdominal desmoid tumuors are rock-hard.

Imaging

First step involves plane X-rays. You look for mineralization and changes in the underlying bone. Benign soft tissue lesions which may contain mineralization include: Heterotopic ossification, lipomas, chondromas and haemangiomas. In heterotopic ossification the mineralization begins peripherally and the centre of the lesion remains lucent. Lipomas have islands of bone, chondromas have calcification, and haemangiomas have small phleboliths. The principle malignant lesions which may have ossification include; synovial sarcoma (usually peripheral), liposarcoma and soft tissue osteosarcoma.

MRI is the main modality to help in diagnosis. Lipomas can be readily seen and shown as well demarcated. Haemangiomas may contain flow voids that represent vessels. Ganglions are bright on T2.

Biopsy

Biopsy can be by needle, trucut (core), open incisional or excisional.

Two types of needle biopsy exist, fine needle and core. The former easy, but limited tissue can be obtained. Core biopsy with a 14-gauge needle can give enough information in most settings. If inadequate, open biopsy is needed.

BENIGN TUMORS

These are classified according to the direction of differentiation of the cells.

Fibrous tissue                              Fibroma, Nodular fasciitis, proliferative fasciitis

                                                       Fibromatoses (superficial, palmer and plantar)

Fibrohistiocytic                            Fibrous histiocytoma, atypical fibroxanthoma

Adipose                                         Lipoma and all it’s variants

Muscle                                           Smooth (Leiomyoma, angiomyoma)

                                                       Striated (rhabdomyoma)

Blood vessels                               Haemangioma, Glomus tumor

Lymph vessels                              Lymphangioma, cystic hygroma

Synovial tissue                             Giant cell tumor of tendon sheath (localized, diffuse)

Peripheral nerves                         Neuroma, Morton neuroma, neurolemoma, neurofibromas

Cartilage/bone tissues                 Myositis ossificans, extraskeletal chondroma, osteoma

Pluripotential mesenchyme         Mesenchyoma

Unknown                                       Myxoma, tumoral calcinosis.

Staging

Lipomas

Most common tumor. Five categories are described.

These usually occur in adults, more common with increasing age. Usually over the back, neck, shoulder, proximal arm or thigh. They grow slowly, cause few symptoms, doughy consistency. Deeper lipomas feel more firm. MRI allows easy diagnosis, histology shows them to contain mature fat. Marginal excision is all that is needed.

Angiolipomas are painful subcutaneous nodules, often on the forearm in young adults. These may be multiple 

A spindle cell lipoma presents as a painless firm nodule, often in the neck and shoulder in men between 45 and 60. Histologically there is fat and spindle cells, and excision is easily performed. A pleomorphic lipoma is similar to the spindle cell, but also with giant cells. 

Intramuscular lipomas can attain a large size before detection, and often grow around peripheral nerves. 

Intramuscular and intermuscular lipomas become large, and produce few symptoms. An adequate sample is needed to exclude low-grade liposarcoma. These do not have a capsule, and tend to infiltrate the surrounding muscle.

Ganglion cysts

Usually arise from the wrist, but can arise from the superior tibiofibular joint, ankle joint and knee. These represent myxoid degeneration. They arise in dense ligamentous tissue and contain a translucent material. The walls consist of dense paucicellular fibrocartilagenous tissue, lacking a synovial lining. In excision, the stalk must be removed from the origin.

Haemangiomas

Haemangiomas are vascular abnormalities that show endothelial hyperplasia and increased numbers of mast cells. All other vascular abnormalities with increased flow are termed arteriovenous malformations. Haemangiomas may be superficial (cutaneous or subcutaneous) or deep. The superficial present with a visible and palpable mass, increased on standing (red-purple), whilst the deep present as a deep ache on prolonged standing. X-rays may show phleboliths or periosteal thickening of adjacent bone. MRI is characteristic, showing the vessels. Histologically, these may be small-vessel, cavernous or mixed. In general, the small vessel capillary type occur in childhood, and the venous type in adulthood.

Treatment involves NSAID’s and stockings. Embolization is an option if there is a large feeder vessel. To remove these, a soft tissue expander is needed, as extra skin will be needed to cover the defect. Small deep lesions can be removed, however some large haemangiomas in the muscle can only be excised if the muscle can be sacrificed.

Angiomatosis is a condition of multiple vascular lesions, involving the skin, fat, muscle and bone. Hypertrophy of the limb can occur.

Nodular and proliferative fasciitis

Both present as firm enlarging soft tissue masses.

Nodular fasciits is a non-neoplastic proliferation of fibroblasts, which may be subcutaneous, intramuscular or fascial. Margin excision is all that is needed.

Proliferative fasciitis also non- neoplastic, and contains immature fibroblast-like spindle cells, giant cells and occasional mitotic figures. These occur in older patients, usually subcutaneous on the forearm and thigh.

Aggressive Fibromatoses

This is the most serious of the benign soft tissue tumours. It does not have a capsule and infiltrates beyond its clinical boundaries. Found on the neck, shoulder and pelvis areas. Intrathoracic or intraperitoneal extension can result in death. Wide excision is needed, due to the high recurrence.

The fibromatoses can be split into two subtypes. The superficial, encompass Dupuytrens and plantar types. The deep (desmoids) include the abdominal and extraabdominal varieties. These deep types present as multinodular masses that arise from fascial planes and infiltrate to some extent into the surrounding skeletal muscle, and can envelop vessels and nerves.

The hallmark of these is the uniformity of the spindle cells and the regularity of the pattern. Mitoses are rare. The matrix consists of dense collagen bundles.

Heterotopic Ossification

This commonly occurs following trauma to the musculoskeletal system. Patients present with swelling, pain and decreased range of joint motion. The most common areas are the quadriceps, brachialis, deltoid and hand. Initially X-ray shows the dotted-veil pattern, (faint, floccular radiodensities). Later, bone formation is shown, beginning at the periphery, radiolucent in the centre. Generally it is not attached to the bone, unless the initial trauma encited a periosteal reaction. Over time the bone decreases gradually. Treatment involves rest, NSAID’s and physio.

Neurolemoma (Schwannoma)

This is a common nerve sheath tumor in adults 20-50. It usually involves the flexor surfaces of the upper and lower extremities, painless and grows slowly. Neurological symptoms are uncommon. Clinically it is mobile in all planes except the longitudinal direction of the nerve. MRI will allow diagnosis, and it can be dissected free of the nerve surgically. Histologically there is two components, a highly ordered cellular component (Antoni A – plump spindle cells in fascicles, whorls or palisades) and a loose myxoid component (Antoni B). The parallel alignment of two rows of nuclei has been called a Verocay body. These are not associated with Von-Recklinghausen’s disease (neurofibromatosis type I). These lesions are surrounded by a true capsule, composed of epineurium.

Neurofibromas

These are not encapsulated, often enlarge the nerves and may undergo malignant degeneration (20-65%). Histologically they consist of Schwan cells associated with collagen fibrils and myxoid material. These cannot be surgically detached from the nerve. Surgery is only needed if malignant degeneration is suspected. Associated with Von- Recklinghausen’s disease. Histologically there are slender bundles of elongated wavy spindle cells closely opposed to dense fibers of mature collagen.

Pigmented Villonodular synovitis

This is a rare primary disease of the synovium, with exuberant proliferation of synovium with formation of villi and nodules. It presents with pain, joint swelling, thickened synovium and a brownish effusion. Occurs between 20-50 years, knee> hip> ankle. Synovial biopsy allows definitive diagnosis. X-rays show juxtacortical erosions on both side of the joint and marked joint/and or bone destruction. Arthroscopy shows brownish synovium with large flattened nodules and villous proliferation. Nodular and diffuse types.

Microscopically the villi are lined by several layers of plump synovial cells, beneath these are histiocytes, Xanthoma cells, hemosiderin-laden macrophages and mulinucleated giant cells. Treatment involves excision, which may mean synovectomy.

SOFT TISSUE SARCOMAS

Most of these occur in adulthood, except rhabdomyosarcoma, and most are found in the lower extremities. Soft tissue sarcomas tend to remain intracompartmental. Grading is done according to the degree of malignancy, and staging depending on location, grade and metstases. Classification is dependent on the main dircetion of tissue differentiation.

Fibrous tissue                                    Adult and post-radiation fibrosarcoma

Fibrohistiocytic                                  Malignant fibrous histiocytoma

Adipose                                               Liposarcoma and its variants.

Muscle                                                 Smooth (Leiomysarcoma)

                                                             Striated (rhabdomyosarcoma)

Blood vessels                                     Haemangiosarcoma, Haemangiopericytoma

Lymph vessels                                    Lymphangiosarcoma

Synovial tissue                                   Malignant Giant cell tumor of tendon sheath 

                                                             Synovial sarcoma

Peripheral nerves                              Malignant schwannoma

Cartilage/bone tissues                      Extraskeletal chondrosarcoma, osteosarcoma

Pluripotential mesenchyme             Malignant Mesenchyoma

Unknown                                            Extraskeletal Ewings, clear cell sarcoma of tendons

Combination chemotherapy has been shown to be more effective in preventing pulmonary dissemination from high-grade lesions than single agent therapy. Adriamycin, Methotrexate, Cisplatin and Ifosfamide are the agents often used. Radiation of 50 to 65 Gy can help reduce local recurrence.

Surgically Enneking has shown that a radical resection alone has a 5% local recurrence rate. Wide excision alone has a 50% local recurrence rate, however this decreases to 5% when combined with chemotherapy and radiotherapy.

Malignant fibrous histiocytoma

Most common STS (soft tissue sarcoma) in older adults. Usually in the lower extremity. The histologic grade is usually medium to high, although the myxoid variant is low.

The lesion may be solitary of multinodular, with either clear of infiltrative boarders. It may undergo hemorrhagic cystification, thus be mistaken for a haematoma.

There is a broad histologic spectrum, depending on the dominant cell type. These include fibroXanthosarcoma (Xanthoma cells), malignant fibroxanthoma, storiform (most common), spindle, inflammatory (contains many acute and chronic inflammatory cells) and histiocytic cells (with a cartwheel pattern), myxoid and malignant giant cell tumor of soft parts. The basic cellular constituent of all fibrohistiocytic tumors includes fibroblasts, hisitocyte-like cells and mesenchyme cells.

Fibrosarcoma

Usually a neoplasm of adulthood, affecting the lower extremity.

Arises from the fascial and aponeurotic structures of the deep soft tissues, superficial variants are rare. The small lesions are well circumscribed, becoming more infiltrative as they enlarge.

The abundant cell is the fibroblast, a spindle cell capable of producing collagen. Collagen is detected with Masson’s stain. The well-differentiated form has fascicles intersecting at acute angles, forming the Herringbone pattern. Poorly differentiated form does not have fascicles, with increased pleomorphism, cellular atypia and increased mitoses.

Liposarcoma

This is common, with a wide range of malignant potential, depending on the grade. Multiple masses can occur in the one patient. Occasionally can occur in children.

Can present large, especially in the retroperitoneum. Tend to be well circumscribed and multilocular.

Four histological types exist:

• Well differentiated (Spindle, lipoma-like, sclerosing, inflammatory, dedifferentiated).
• Myxoid
• Round cell
• Pleomorphic

Regardless of the type, the identification of lipoblasts is mandatory to establish the liposarcoma diagnosis. The lipoblast has one or more round fat droplets indenting the nucleus. The dedifferentiated form has both well differentiated areas and some elements of undifferentiated spindle cell sarcoma.

Synovial sarcoma

These have a biphasic pattern that gives the impression of gland formation, thus originally thought to be indicative of synovial origin. However, they rarely arise in a joint, but have a distribution similar to other STS. Many patients are below 40 years, with the hand, ankle and foot affected. X-ray can show some calcification.

Usually it is a deep-seated well-circumscribed mass. Histologically there are two distinct cell populations, spindle cells and epitheloid cells. The more prominent spindle cells form an interlacing fascicular pattern, epitheloid cells form glands.

Epitheloid sarcoma

This is a small tumor, often misdiagnosed as benign. It is common in the wrist and hand, and occurs often in young adults.

It arises in deep soft tissues, in relation to tendons, fascia and aponeuroses. It is firm and nodular, central necrosis can occur.

Microscopically, there are nodules of epitheloid cells, like granulomas, with eosinophilic cytoplasm and hyperchromatic nuclei. Tendon/fascial invasion by tumor cells can be seen, and may metastasize to lymph nodes.

Clear cell sarcoma

Thought to be related to melanoma, as 50% have melanin. Found around the foot and ankle in those 20-40. Lymphatic spread is common.

Usually a solitary or mulitnodular mass adherent to tendons, often large. It forms distinct fascicles and nests of spindle cells, separated by trabeculae. PAS stain shows that the cells contain glycogen.

Malignant Schwannoma

Commonly found in Neurofibromatosis. Present with a mass associated with neurological symptoms. It appears as a bulbous enlargement of a large nerve, within the deep soft tissues. In Neurofibromatosis it often arises in an existing neurofibroma. It infiltrates the soft tissues as it enlarges.

Intersecting spindle cell fascicles are seen, and the nuclei are characteristically wavy. Various whorled, tactoid or plexiform patterns are seen.