Osteochondroma

The most commonly encountered benign tumor of bone is osteochondroma, which typically arises near the long ends of bones. Osteochondromas are often painful because of formation of bursae (small fluid-filled sac) overlying the lesion and/or tenting and irritation of overlying soft tissues. They can cause interference with neurovascular function due to tenting of such structures over the osteochondroma surface, and they have the potential for causing growth deformity in the involved and adjacent bones. Long-term complications are uncommon except for rare cases of dedifferentiation into chondrosarcoma. There is no estimate of the number of patients seen with nonoperatively managed osteochondromas due to lack of records. An annual US prevalence of >1,500 surgical cases is based on records kept by Dr. Ward; this is believed to be clearly underestimated. This estimate would not include cases treated by general orthopedic surgeons and pediatric orthopedic surgeons, who, in addition to orthopedic oncologists, provide medical and surgical treatment of many osteochondromas.

Unicameral Bone Cysts

Unicameral bone cysts (simple bone cysts) are the second most commonly encountered benign bone lesions, with an estimated annual prevalence of more than 1,250 surgical cases. The etiology of these fluid-filled bone cysts, usually found in the growing ends of children’s long bones such as the proximal humerus or femur, is unclear. Because they never metastasize and are usually quite characteristic on radiographs, many of these are treated by other orthopedic surgeons, especially pediatric orthopedic surgeons. The true incidence, therefore, is probably significantly higher than that estimated by extrapolation from Dr. Ward's practice experience. These cystic lesions cause weakening of the bone and the patients may require multiple surgeries to rebuild the bone with bone grafts, injections, and other techniques. They occur in children, and typically recur multiple times until skeletal maturity is achieved.

Giant Cell Tumor of Bone

Giant cell tumor of bone, with an estimated annual prevalence of more than 750 cases, is the third most commonly encountered benign bone neoplasm and accounts for significant disability and dysfunction. This typically occurs near the end of the long bones, most commonly the lower femur or upper tibia, and causes destruction of the bone. The tumor may extend through the cortex of the bone into the soft tissues and, if large enough prior to treatment, can be associated with pathologic fracture of the involved bone. Smaller tumors can be treated with bone resection and reconstruction with bone grafts or cement filler. Cases that are more complicated require sophisticated reconstruction with massive joint replacements and/or massive allografts which can cause severe long-term disability. On rare occasions, giant cell tumors metastasize to the lungs. In such cases, they typically respond poorly to chemotherapy and may cause death. These tumors are rarely treated by general orthopedic surgeons. Although currently not considered the standard of care, many patients' tumors have had excellent responses to denosumab treatment, a monoclonal antibody directed against RANK ligand, the activator of osteoclasts (giant cells). This is very similar to the mechanism of action of bisphosphonates. Initial studies with denosumab have shown a very favorable response in many tumors so treated but presently, even with denosumab pretreatment, surgical resection appears to be ultimately required. Current research continues and with enhanced understanding of the underlying pathogenic mechanisms, nonsurgical management may become possible in the future.

Enchondroma

A fourth commonly encountered tumor that may require surgery is enchondroma, estimated at more than 725 annual surgical cases. Bones typically form as cartilage during the embryo stage of human development, and this cartilage model ultimately converts into bone structure. The cartilage-based growth plates add length to the bones from bone growth. Enchondromas are tumors derived from remnants of these cartilaginous tissues that abnormally remain in the skeleton as remnants or nodules from the normal pattern of maturation and development. If these achieve sufficient size, they can cause cortical bone erosion and pain or fracture and may present diagnostic challenges requiring biopsy. They often require treatment by curettage and bone grafting. These lesions can dedifferentiate into malignant cartilage tumors called chondrosarcomas. Many small enchondromas are seen incidentally, cause no symptoms, and are treated with simple observation, thus, total incidence of enchondromas is much higher than calculated from extrapolation of the surgical data. In addition, the burden of enchondromas requiring surgical treatment is very conservatively estimated, as many are treated by general orthopedic surgeons, pediatric orthopedic surgeons, and hand surgeons.

Other Benign Bone Tumors

Multiple other benign tumors are commonly encountered.

• Aneurysmal/ bone cysts (ABCs) are aggressive cystic lesions similar to unicameral bone cysts. However, ABCs are more destructive, expanding and weakening the bone and causing greater bone destruction. They tend to fill with blood and tissue, not simple fluid. Usually, ABCs respond favorably to curettage and bone grafting, but recur in at least 20% of cases. Some ABCs arise secondarily in other bone lesions and conditions such as fibrous dysplasia.
• Metaphyseal fibrous defects (non-ossifying fibromas) are focal defects in normal bone that are filled with soft tissue. These occur in 2% to 3% of children. Most resolve without ever causing symptoms and may never be detected unless the child receives an X-ray or MRI scan for another problem. Large ones may require surgery, such as bone grafting to prevent fracture and for surgery to treat completed fractures that have already occurred.
• Osteoid osteoma is a small tumor typically occurring in children that is associated with severe, unrelenting night pain. It usually requires resection or radio frequency ablation and occasionally may require bone grafting. When located in the spine, it can cause a painful scoliosis. Recently, successful treatment with radio frequency ablation under radiographic guidance has become the treatment of choice for accessible lesions.
• Chondroblastoma is an unusual neoplasm that occurs in the ends of growing bones in teenagers and young adults. This requires resection of the lesion and bone grafting. If untreated, it can cause collapse and degenerative arthritis in the associated joint and, on rare occasion, can metastasize to the lung. Chondroblastomas are usually referred to orthopedic oncologists.
• Numerous other less common benign bone tumors often are treated similarly to giant cell tumors, ABCs, or chondroblastomas with curettage, resection, and bone grafting. Most cause some degree of disability and dysfunction of the involved extremity.

As with the benign bone tumors, there is no national registry of benign soft tissue tumors. By comparing Dr. Ward's 13 years of practice history from 1991 to 2004 and computing an incidence index relative to that of osteosarcoma, some estimate of the minimal prevalence of surgically treated lesions may be obtained.

From this index estimate, a baseline estimated extrapolation of the national incidence can be calculated. However, benign soft tissue tumors are the most likely category of tumors to be treated by other surgeons, such as general orthopedic surgeons, plastic surgeons, and general surgeons; therefore, this national estimate is extremely conservative. The prevalence and burden In the United States from benign soft tissue tumors is significantly higher than estimated herein. (Reference Table 6A.C.1 PDF [1] CSV [2])

Benign soft tissue tumors are usually detected as asymptomatic masses. Treatment typically requires resection. Benign lesions rarely cause death, and it is rare that an amputation is necessary. However, depending on the site of involvement and size of the lesion, significant disability of the involved extremity and/or joint can occur. The true cost of these otherwise benign neoplasms can be high for healthcare costs, lost worktime, morbidity, emotional cost, and disability expenses.

Tumors of Fat Tissue

Lipomas: Benign tumors of fat tissue

Lipomas are the most common benign soft tissue tumor. Most are found under the skin, but they can develop anywhere in the body. Many lipomas are present for years and inactive, but those that are growing lesions are probably the most commonly resected soft tissue benign tumor. Resection of small growing lesions is usually performed in local community settings by multiple surgical specialists and even by primary care practitioners. Only patients with larger, more concerning lesions are typically referred to surgeons with a focus in surgical oncology. Not infrequently, a slow-growing sarcoma is mistakenly diagnosed as a lipoma, leading to a delay in the diagnosis of soft tissue sarcoma. This misdiagnosis can lead to an original suboptimal resection of the unappreciated sarcoma by the unsuspecting community surgeon.

Lipoblastomas

Lipoblastomas are benign fat tumors that occur in infants and young children.

Hibernomas

Hibernomas are benign fat tissue tumors that behave similarly to lipomas. They are so named because of their brownish coloration that resembles the appearance of the fatty tissue of bears, hence the name hibernomas. They are much less common than lipomas.

Tumors of Muscle Tissue

Leiomyomas (Smooth Muscle Benign Tumors)

Smooth muscle is found in internal organs such as stomach, intestines, blood vessels, or uterus. Unlike skeletal muscle that contracts voluntarily, smooth muscle contracts involuntarily. Leiomyomas are benign tumors of smooth, or involuntary muscle. Leiomyomas can arise almost anywhere in the body in either men or women because they start in widespread tissues such as blood vessels or intestine. The most common leiomyomas is the fibroid tumor that often develops in the uterus.

Rhabdomyomas (Skeletal Muscle Benign Tumors)

Skeletal muscle is the muscle that allows movement of arms and legs and other body parts. These are voluntary muscles. Rhabdomyomas are benign tumors of skeletal muscle and are very rare.

Benign Tumors of Peripheral Nerve Tissue (Benign Peripheral Nerve Sheath Tumors)

Neurofibromas, schwannomas (neurilemmomas), and neuromas are benign tumors of nerves. These tumors can occur almost anywhere in the body. An Inherited condition called neurofibromatosis, or Von Recklinghausen disease, causes people to develop many neurofibromas throughout their body. Some of these may dedifferentiate and become malignant. These dedifferentiated malignant tumors usually form from large neurofibromas in the upper arms, neck, pelvis, or thigh. Patients with the dedifferentiated neural sarcomas have a very poor prognosis and most ultimately succumb to the cancer.

Tumors of Joint Tissue

Joints are surrounded by tough tissue called synovium, which produces fluid that lubricates joint surfaces allowing them to move smoothly. Joint tissue tumors typically arise from the synovium.

Pigmented villonodular synovitis (PVNS) is a benign tumor of joint tissue. It is most common in its nodular form in the hands, and more common in women than in men. The nodular form rarely recurs following adequate and complete excision. PVNS also occurs in a diffuse form that typically will involve the entire joint lining and has a high recurrence rate after attempted resections. PVNS in its diffuse form is most commonly encountered in the knee joint, where it often causes recurrent bloody effusions (swollen knees filled with bloody fluid). It does not spread to other joints, but when recurrent or persistent, can destroy the involved joint.

Tumors of Blood Vessels and Lymph Vessels

Hemangiomas are benign tumors of blood vessels. They are rather common, are often present at birth, and can affect the skin or internal organs. They sometimes disappear without treatment, but when located in muscles and other deep tissues, can be quite problematic and may require surgical treatment.

Glomus tumors are benign perivascular (surrounding blood vessels) tumors. They usually are found under the skin and often under fingernails. They are usually small (<1 cm), but are exquisitely tender and painful. They may make the overlying skin sensitive to even light touch from clothing.

Hemangiopericytoma is a tumor of perivascular tissue. It most often develops in the legs, pelvis, and retroperitoneum (the back of the abdominal cavity) and is most common in adults. These can be either benign or malignant. They rarely spread to distant sites but tend to recur locally following surgical resection unless very widely excised. They may be multifocal.

Lymphangiomas are benign lymph vessel tumors that are usually present at birth. Lymph is a type of fluid that circulates in every tissue of the body. Lymph fluid is collected and routed back into the venous system by the lymphatic system. It contains waste products from tissues and immune system cells. Lymphangiosarcomas are the malignant lymph vessel equivalents of angiosarcomas.

Tumors of Fibrous Tissue

Fibrous tissue forms tendons and ligaments and covers bones as well as other organs in the body.

Fibromas, elastofibromas, extra-abdominal fibromatosis, and fibrous histiocytomas are all benign soft tissue tumors. Fibromatosis is the most problematic of these tumors. They frequently recur following resection, and may require additional treatment with repeat surgery, radiation therapy, chemotherapy, or other therapies. Although these tumors do not metastasize, they can be challenging. Fibromatoses (desmoid tumors) were discussed at length under the malignant soft tissue section above where they are often grouped due to their locally aggressive nature.

Tumors of Uncertain Tissue Type

Through microscopic examination and other laboratory tests, doctors can usually find similarities between most soft tissue tumors and certain types of normal soft tissues. This is how soft tissue tumors are classified. However, some soft tissue tumors have not been linked to a specific type of normal soft tissue.

Myxoma is a benign tumor that is usually located in muscles but does not develop from muscle cells. The cells of a myxoma produce mucus-like material in and around the cells, a distinguishing feature of this tumor. They are usually found in adults, and rarely recur after treatment. Myxoma must be differentiated from myxofibrosarcoma, a malignant neoplasm that can appear very similar under the microscope as well as in gross appearance. The challenge for the treating physician is to avoid overtreating myxomas and to avoid undertreating myxofibrosarcomas, in terms of the extent of normal tissue margin around the tumor to be resected with the tumor to minimize the risk of recurrence.

Granular cell tumors are very uncommon and are usually benign tumors of adults that can be found almost anywhere in the body. They are frequently multifocal.

Tumor-like Conditions of Soft Tissue

Some conditions of soft tissues are caused by inflammation or injury that forms a mass similar to a soft tissue tumor. Unlike a true tumor, they do not come from a single abnormal cell; they have limited capacity to grow or spread to nearby tissues, and never spread through the bloodstream or lymph system. Examples include nodular fasciitis and myositis ossificans, which involve tissues under the skin and muscle tissues, respectively.

There are also deposition diseases that are often grouped with tumors. The most commonly encountered ones are tophi, often seen in cases of poorly controlled gout. These tophi can achieve massive size and may be mistaken for true tumors. They can erode through the skin, causing skin breakdown and infection that may require surgical treatment and antibiotics. Calcium deposits are often seen in renal failure and poorly managed dialysis patients. They may be painful and may require difficult resection of deposits infiltrated into normal tissue. When not associated with diseases of abnormal calcium metabolism, such as renal failure and dialysis, the disease is termed tumoral calcinosis. It behaves essentially the same as the calcium deposition mentioned in association with renal disease. Amyloid deposition can rarely cause a soft tissue (or bony) mass. These are most often seen in poorly controlled dialysis patients. Rheumatoid nodules are soft tissue deposits of antibody-laden, inflammatory soft tissue masses that can be quite painful and may require resection for symptomatic relief. Adequate treatment of the underlying rheumatoid arthritis with current disease-modifying medications usually prevents the occurrence of such lesions.