(iii) Evaluation and treatment of benign soft tissue tumors

(iii) Evaluation and treatment of benign soft tissue tumors

Current Orthopaedics (1997) 11, 98-104 © 1997Pearson ProfessionalLtd Mini-symposium: Soft tissue tumors of the musculoskeletal system (iii) Evaluati...

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Current Orthopaedics (1997) 11, 98-104 © 1997Pearson ProfessionalLtd

Mini-symposium: Soft tissue tumors of the musculoskeletal system

(iii) Evaluation and treatment of benign soft tissue tumors

R. Vlasak, M. G. Rock

INTRODUCTION

This paper reviews the diagnosis and treatment of the more common benign soft tissue tumors and specifically discusses lipomas, myositis ossificans, extra-abdominal desmoid tumors, peripheral nerve sheath tumors, hemangiomas and vascular malformations, and ganglions.

The majority of soft tissue tumors are benign. The incidence of soft tissue tumors is difficult to determine since many of these are not reported. In a hospital-based population, benign soft tissue tumors out-number malignant tumors by a margin of approximately 100 to 1.1 During the investigation and treatment of benign soft tissue tumors, the potential of a mass being malignant needs to be kept in mind. In general, there are no completely reliable physical signs that can distinguish between a benign-and malignant mass. The only definitive test is a biopsy. Although malignant soft tissue tumors tend to be deep-seated, approximately one-third of soft tissue sarcomas of the extremities are subcutaneous? In developing a differential diagnosis of a soft tissue mass, size larger than 5 cm or a deeply seated mass should make one suspicious of a sarcoma? After a careful history and physical examination, magnetic resonance imaging (MRI) can be very helpful in characterization of a soft tissue mass. In the majority of the cases, MRI can help classify a soft tissue tumor as benign or malignant with 90% accuracy. 4 In a review of over one hundred cases of soft tissue masses, MRI was able to make a specific diagnosis in 24%. 5 A differential diagnosis of a soft tissue mass is based on a thorough history and physical examination with a knowledge of the diagnostic possibilities.

LIPOMAS Lipoma is one of the most common and widely disseminated mesenchymal neoplasms. It is usually solitary, but may be multiple in approximately 1% of cases. Microscopically, a lipoma is composed of mature fat cells and is usually thinly encapsulated. Patients usually present with a painless, slowly growing mass which is mobile and has a soft consistency. Superficial lipomas are much more common than deep-seated lipomas and their diagnosis can generally be made by physical examination. Fewer than 1% of all lipomas occur in deep soft tissue sites. Deep-seated or subfascial lipomas tend to present at a larger size than the superficial lipomas due to the lack of symptoms. MRI can usually confirm the diagnosis because the signal of a deep-seated lipoma is the same as subcutaneous fat on all pulse sequences (Fig. 1). 4,5 Treatment of simple lipomas is local excision with the recurrence rate expected to be less than 5%; however, the recurrence rate can increase substantially with large deep-seated lipomas that infiltrate muscle. ~ A higher recurrence rate with deep-seated intramuscular lipomas is most likely associated with the greater difficulty in obtaining a true marginal excision. Well-differentiated adipose tissue tumors with atypical cells are classified as atypical lipomas or welldifferentiated liposarcomas. 6,7 Both of these terms most likely represent the same tumor which has a

R.Vlasak MD, Consultant, Department of OrthopedicSurgery, Watson Clinic LLP, 1600Lakeland Hills Blvd., Lakeland, Florida 33804, 941-680-7000,941-680-7935,M. G. Rock MD, Consultant and Professor,Department of Orthopedics,Mayo Clinic, 200 First Street Southwest, Rochester,Minnesota 55905, USA. Address correspondence to: M. G. Rock 98

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Fig. 1 (A) Axial T-l-weighted MR image of an intramuscular lipoma in the posterior compartment of the arm. A fifty-year-old man presented with a painless mass which was treated by marginal excision. The tumor is iso-intense with subcutaneous fat on MRI pulse sequences. (B) T-2-weighted coronal MR image shows the intramuscular lipoma is iso-intense to subcutaneous fat. (C) Histology shows mature fat cells with slight variation in size (hematoxylin and eosin; x 120).

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Fig. 2 (A) Axial T-l-weighted MR image with well-differentiated liposarcoma from the anterior compartment of the thigh. This seventyyear-old woman presented with a large painless mass in her right thigh. The center of the tumor contains conglomerate areas of tissue which does not image like subcutaneous fat. There is low single intensity on the T-l-weighted image which becomes hyper-intense on the T-2-weighted image. (B) Axial T-2-weighted MR image shows the hyper-intense area of non-lipomatous tissue. This area differentiates this tumor as a well-differentiated liposarcoma rather than a lipoma. (C) Grossly well-differentiated liposarcoma composed predominantly of loose fibrous tissue with atypical cells in scattered clusters of adipose sites (hematoxylin and eosin; x 120).

p r o p e n s i t y for recurrence with i n a d e q u a t e excision a n d can u n d e r g o de-differentiation into a higher g r a d e l i p o s a r c o m a . These t u m o r s have a recurrence rate o f a p p r o x i m a t e l y 60% if r e m o v e d with only m a r g i n a l excision. 7 W i d e local excision is r e c o m m e n d e d if feasible w i t h o u t excessive m o r b i d i t y . L o c a l recurrences after m a r g i n a l excision are n o t u n u s u a l even m o r e t h a n ten years following the initial o p e r a tion a n d d e - d i f f e r e n t i a t i o n can occur in u p to 17% o f the cases. 7 These lesions a p p e a r largely l i p o m a t o u s on MR1. However, t h e y have areas o f heterogeneity which d o n o t i m a g e like s u b c u t a n e o u s fat a n d are n o t seen in classic l i p o m a s (Fig. 2). These areas o f atypical cells which a r e a s s o c i a t e d with well-differentiated l i p o s a r c o m a s o r a t y p i c a l l i p o m a s are h y p o - i n t e n s e on T1 w e i g h t e d M R images a n d hyper-intense o n T2 weighted M R images. 6

MYOSITIS OSSIFICANS Myositis ossificans is a benign c o n d i t i o n o f heterot o p i c n o n - n e o p l a s t i c b o n e f o r m a t i o n . It is e s t i m a t e d t h a t over h a l f the cases develop after a t r a u m a t i c episode, a l t h o u g h patients m a y n o t r e m e m b e r such an event. M y o s i t i s ossificans occurs m o s t c o m m o n l y in the s e c o n d a n d third decades o f life with the m a j o r i t y o f cases o c c u r r i n g in the q u a d r i c e p s a n d brachialis muscles. 8,9 Clinically, patients present with p a i n in the affected muscle, a p a l p a b l e mass, a n d a decreased r a n g e o f m o t i o n . H e t e r o t o p i c b o n e c a n be seen o n X - r a y s as early as two to three weeks after i n j u r y a n d can be a s s o c i a t e d with p e r i o s t e a l r e a c t i o n (Fig. 3A). Myositis ossificans m u s t be differentiated f r o m o t h e r c o n d i t i o n s which can have soft tissue ossification o r calcification such as o s t e o s a r c o m a , mesenchyreal c h o n d r o s a r c o m a , synovial s a r c o m a , o r even a

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G D Fig. 3 (A) Lateral radiograph of a twenty-two-year-oldman who was admitted with a painful swelling in the anterior compartment of the thigh. This is a case of myositisossificans. (B) Axial T-2-weightedMRI shows an infiltrativeprocess of the anterior compartment of the thigh. This could be mistaken for a sarcoma. (C) CT scan shows the characteristic zoning phenomenon of myositisossificans. The peripheral zone consists of mature ossifiedbone. The interior area consists of radiolucent immature mesenchymaltissue. (D) A low power photomicrograph shows the mature peripheral zone on the left and the inner immature zone on the right. The peripheral zone consists of trabecular bone while the immature zone is made up of undifferentiated proliferatingmesenchymalcells. The key to making the diagnosis of myositisossificanslies in the recognition of this classic zoning phenomenon.

calcified lipoma. Myositis ossificans can be mistaken for extraosseous osteosarcoma or a periosteal osteosarcoma. M R I can frequently lead to more confusion because it shows widespread infiltrative changes throughout the muscle (Fig. 3B). The diagnosis rests on identifying the zoning phenomenon first described by A c k e r m a n ? The central zone consists of immature mesenchymal cells with mitotic figures occasionally present. This zone can be mistaken for a sarcoma. The peripheral zone shows mature trabecular bone and fibrous tissue in distinction to a sarcoma, in which the most aggressive and malignant cells are in the periphery (Fig. 3C & D). CT is the best way to image the mature ossified peripheral zone (Fig. 3C). Myositis ossificans tends to evolve more rapidly than any sarcoma. Within two to three weeks, the acute pseudo-inflammatory phase evolves into the subacute pseudo-tumoral phase which is characterized by a painless hard mass. The process tends to mature in growth by three to six months and thereafter enters the chronic phase of gradual resolution. Treatment of myositis ossificans consists mostly of prevention and recognition. 9 In the first twenty-four to forty-eight hours following a thigh contusion, a patient is treated by limitation of range of motion along with rest and ice. Following this early period of rest, function is gradually restored. Myositis ossificans

can frequently reabsorb spontaneously and excision should only be carried out when serial bone scans indicate maturation of the lesion in a patient with significant symptoms.

EXTRA-ABDOMINAL DESMOID TUMORS Desmoid tumors which are also known as aggressive fibromatosis most frequently present between puberty and age forty. Patients generally present with a painless, firm, fixed, deeply seated mass. The most comm o n site is the shoulder followed by the chest wall, back and thigh. 1°,11 The lesions tend to be infiltrative and it is very difficult to distinguish the lesion from normal tissue and especially scar tissue associated with recurrences. In addition, the natural history of this lesion is difficult to predict. Desmoid tumors can occur in surgical scars or in areas of previous trauma many years following the original insult. Occasionally spontaneous regression of recurrent desmoids has been reported. M R I is the best way to stage the lesion and plan operative treatment (Fig. 4). The M R I picture can be quite variable. Frequently the t u m o r may show a hypo-intense signal on T2-weighted images similar to adjacent fascial structures or scars seen in recurrent cases. Histologically, desmoids are composed of

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Fig. 4 (A) Sagittal T-l-weighted MR image of a desmoid tumor involvingthe left flank and posterior ilium. This seventeen-year-oldwoman presented with an enlarging, firm, fixed, and painless mass. (B) Axial T-2-weightedMR image. Differentiationof this desmoid from a soft tissue sarcoma could not be made without biopsy. The patient was treated with a wide excision and has not had a recurrence in three years. (C) High power photomicrograph shows denselycollagenized mature fibrous connectivetissue with relativelysparse number of cells and absent mitotic figures (hematoxylinand eosin).

densely collagenized mature fibrous connective tissue with a relatively sparse number of cells (Fig. 4). Mitoses are rare to absent and generally these tumors are avascular and provoke very little reaction from adjacent tissues. The extent of local invasion can be very difficult to determine, both on preoperative M R I and at the time of excision. Recommended treatment of desmoid tumors is wide excision. ~°,H Recurrence rates can range from 20% to 100% with complete local excision being difficult despite gross surgical margins appearing to be free of tumor. This is related to the fact that satellite foci of tumor without continuity to the main lesion are found in up to 15% of the cases. Desmoids do not metastasize, but malignant transformation following radiation has been observed and is extremely rare. Pain often escalates with each recurrence making management more difficult. Both chemotherapy I2 and radiation therapy 13can be used as adjuvant treatment. Doxorubicin, dacarbazine, along with hormonal agents such as tamoxifen have been used with some success. 12 Local control substantially improves with postoperative radiation therapy when operative margins are less than wide. ~3 Radiation therapy also is effective when resection is not possible. Benign neglect with close follow-up may be reasonable in selected cases of recurrence or in situations where function is not impaired. Despite the high local recurrence, the prognosis of survival is excellent with less than 1% mortality due to erosion of vital structures.

BENIGN PERIPHERAL NERVE SHEATH TUMORS Benign nerve sheath tumors can be divided into two broad categories consisting of benign schwannomas (also known as neurilemmomas) and neurofibromas.

When dealing with nerve sheath tumors one should always keep in mind that the difference between benign and malignant is not always absolutely clear. Both atypical and low grade malignant nerve sheath neoplasms exist. Tumors may have both benign and malignant elements present and an adequate biopsy is very important, to prevent limited sampling which could lead to an erroneous diagnosis. 14 M R I may be used to direct the biopsy of different areas within a tumor.

Benign schwannomas A benign schwannoma is an encapsulated tumor of the nerve sheath often referred to as a neurilemmoma. This is a c o m m o n solitary neoplasm which most commonly presents itself in early adulthood and is frequently found in the head, neck and flexor surfaces of the extremities (Fig. 5). Benign schwannomas can range in size from less than one inch to several inches and typically present as a painless, enlarging, solitary mass. A Tinel's sign is often present at the level of the lesion. Benign schwannomas are treated best by marginal excision when they become symptomatic. These encapsulated neoplasms are eccentrically located within the nerve and do not invade the nerve fibers. This allows marginal excision to be performed without sacrificing the involved nerve. The excised t u m o r should be sampled generously to rule out subtle foci of malignant transformation.14 Histologically, benign schwannoma frequently consists of two distinct alternating groups of cells within the tumor. Antoni A areas are highly cellular and consist of benign spindle cells (Fig. 5C). Antoni B areas are much less cellular and contain myxomatous appearing tissue. Recently, a variety of schwannoma called cellular schwannoma has been described. ~5 Cellular schwannomas may be mistaken for sarcomas because they

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C Fig. 5 (A) Axial T-2-weightedMR image of a benign schwannoma originating from the median nerve in the forearm. The forty-fiveyear-oldman had an enlargingpainless mass with occasional dysesthesias in the median nerve distribution. (B) SagittalT-2weighted MR image shows the schwannomain continuitywith the median nerve.This was helpfulin making the differential diagnosis. The patient was treated with a marginal excision followingan incisionalbiopsy.(C) Low powerphotomicrograph shows compact spindle cells arranged in short bundles and interlacingfascicles(hematoxylinand eosin; x 160)These cellular areas of schwannomasare called Antoni A.

are composed predominantly of highly cellular Antoni A areas with frequently hyperchromatic nuclei. These tumors have a predilection for the paravertebral region of the retroperitoneum and the pelvis. The schwann-cell nature of this tumor can be easily seen under electron microscopy and with immunohistochemical reactions. 15 Malignant transformation of benign schwannomas is extremely rare but can occur? 4 Neurofibroma

Neurofibroma may occur as solitary lesions or as multiple lesions in neurofibromatosis Type I (von Recklinghausen's disease). 14 The majority of neurofibromas are solitary, and are not associated with neurofibromatosis. They present as a painful mass with burning dysesthesias and occasional loss of nerve function. Neurofibromas are non-encapsulated and permeate the nerve of origin. Unlike benign schwannomas which have an eccentric appearance on the nerve of origin, neurofibromas are centrally located. In large neurofibromas, gross evidence of nerve origin may not be apparent, especially if the original nerve is small. The diagnosis therefore depends on

recognition of the characteristic light microscopic neurofibromatous histology as well as immunohistochemical or electron microscopy demonstration of schwannian, perineurial, or fibroblastic cellular elements? 4 Unlike benign schwannomas, which are composed almost exclusively of Schwann cells, neurofibromas have a heterogenous population of cells. Malignant transformation in solitary neurofibromas is rare. Three to six percent of von Recklinghausen's patients develop malignant transformation by the fourth decade. This incidence of malignant transformation increases with age as well as with radiation exposure. 14 In addition to transformation of neurofibromas into malignant nerve sheath tumors, patients with yon Recklinghausen's disease have a much higher incidence of other malignancies than the general population. They can develop neuroblastoma, ganglioneuroma, nephroblastoma, urogenital rhabdomyosarcoma, and non-lymphocytic leukemias. Surgical treatment for neurofibroma is recommended only for symptomatic lesions involving a peripheral nerve or in situations where the clinical behavior of the lesion is suspicious for a malignant transformation. Since the neurofibroma is not encapsulated and infiltrates the peripheral nerve, it is impossible to perform an en-bloc excision without sacrificing the nerve.

HEMANGIOMAS Hemangiomas are the most common tumors of infancy and childhood. By age one year, approximately 10 to 12% of white children have a hemangioma, with the majority being cutaneous hemangiomas. Intramuscular hemangiomas are a less common variant which are often seen initially by orthopedic surgeons (Fig. 6). The lower extremity is the most common location for intramuscular hemangiomas. 16 They constitute the most common benign tumor of the skeletal muscles. Children and adolescents present with sharp pain and swelling around the muscle which is involved. Patients may develop a contracture of the ankle or knee since pain is accentuated by tension of the muscle involved. X-rays are frequently negative, but may show localized periosteal reaction (Fig. 6A) or the diagnostic phlebolites. Histologically, proliferating endothelial cells infiltrate between muscle fibers and within nerve sheaths. Variable amounts of adipose tissue are a common finding within the tumor vascular matrix. Histologically, some intramuscular hemangiomas exhibit characteristics that may be worrisome for malignancy and can occasionally lead to the erroneous diagnosis of angiosarcoma. The majority of small vessel hemangiomas contain a variable number of mitotic figures and frequently contain immature appearing

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Fig. 6 (A) Lateral radiograph of a six-year-old child with a painful posterior compartment Ieg mass. There is some remodeling of the distal diaphysis of the fibula. (B) Axial T-2-weighted MR image shows distinctive high-signal striated-septated configuration which correlates with the endotheliaMined vascular channels separated by fibrous and fatty linear strands. This is quite characteristic of an intramuscular hemangioma. (C) Incisional biopsy confirmed an intramuscular hemangioma. Histology shows large vascular channels filled with blood and separated by septae composed of fibrous tissue and mature fat cells (hematoxylin and eosin; x 120).

nuclei. 16 Intramuscular hemangiomas are non-encapsulated and frequently are found to invade perineural structures and muscle fibers. Recently, MRI has been found to be very helpful in the diagnosis of intramuscular hemangiomas as well as vascular malformations. ~7 T2-weighted images show distinctive high signal striated-septated configuration which correlates with the fibrous and fatty septa between endothelial-lined vascular channels (Fig. 6). Spontaneous regression is very common for both superficial and deep hemangiomas. Hemangiomas have three histologic phases - proliferation, early involution, and late involution. ~8 Every hemangioma has an initial proliferating phase followed by a prolonged involuting phase. The rapid growth period generally occurs in infancy or early childhood and is characterized by hypercellularity and endothelial multiplication. Involution and regression frequently occurs later in childhood. Most lesions do not require any treatment once the diagnosis is made. Surgical excision is difficult due to the infiltrative nature of intramuscular hemangiomas. Complete surgical resection requires wide local excision. This morbidity must be weighed against the natural history of these lesions to frequently spontaneously resolve. Other modalities such as embolic therapy, radiotherapy, laser treatment and medical management with steroids have been tried for difficult painful lesions.

originate, from tlae capsule of a joint or a tendon sheath and are filled with myxoid tissue and surrounded by a thickened fibrous capsule. Unlike synovial cysts, ganglions are not lined by synovium. The true pathogenesis of ganglia is obscure and they frequently fluctuate in size. Ganglia typically measure approximately 1-3 cm. Many ganglions present as painless superficial masses. They can, however, be tender and interfere with function and occasionally can present as a more deep-seated mass (Fig. 7). A diagnosis is generally established by the characteristic appearance and location. In superficial lesions, transillumination may help make the diagnosis. When they are deep-seated such as the case in Figure 7, then MRI can be helpful in making the diagnosis since it gives a characteristic homogenous hyper-intense signal on T2 weighted images and homogenous hypo-intense signal on T1 weighted images. Treatment is indicated only for symptomatic lesions and can vary from aspiration and injection of steroids to simple surgical excision. 19All methods can be associated with a significant recurrence rate. If surgical treatment is performed, the excision must be complete and should include part of the capsule or tendon sheath where the ganglion originates in order to prevent a recurrence.

GANGLION

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A ganglion is a cystic lesion generally found near or attached to tendon sheaths especially along the dorsum of the wrist, hands, and feet but also occasionally found within tendons or muscles. Ganglia usually

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