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Synovial Sarcoma of the Foot and Ankle

Scully, Sean, P.*; Temple, H., T.**; Harrelson, John, M.*

Clinical Orthopaedics and Related Research: July 1999 - Volume 364 - Issue - p 220-226
Section II: Original Articles: Tumor

Synovial sarcoma of the foot and ankle frequently is misdiagnosed, which leads to delays in treatment. The clinical records of 14 patients with synovial sarcoma of the foot and ankle were reviewed. Common findings at presentation were an enlarging mass with a variable incidence of pain, tenderness, and edema. The patients tended to be younger than patients with other soft tissue sarcomas (30 years) and had a median duration of symptoms of 14 months. Of the 14 patients, 12 underwent an attempted curative surgical procedure. Ten patients had partial foot amputations or below knee amputations, whereas two had an attempted limb salvage by wide resection. Of the 14 patients, one experienced regionally recurrent disease and eight had pulmonary metastasis developed. All patients who had metastasis develop died of their disease. Tumor size was not observed to be a prognostic variable in this group of patients. Patients with biphasic histologic features had a better outcome than did those with a monophasic subtype. Patients with a prolonged duration of symptoms before diagnosis had a better outcome, presumably because these tumors biologically were less aggressive. Wide resection can be considered in a select group of patients.

From the *Section of Orthopaedic Oncology, Duke University Medical Center, Durham, NC; and **Walter Reed Army Medical Center, Bethesda, MD.

Reprint requests to Sean P. Scully, MD, PhD, Duke University Medical Center, Box 3312 Durham, NC 27710.

Received: March 26, 1998.

Revised: July 28, 1998; October 9, 1998; October 28, 1998; December 9, 1998.

Accepted: January 19, 1999.

Synovial sarcoma is a high grade, relatively rare neoplasm with an incidence of 2.57 per 100,000 population annually. In contrast to other soft tissue sarcomas, it has a tendency to arise in the extremities of young adults, between the ages of 15 and 40 years.19 There is a marked predilection for the lower extremity. Although synovial sarcoma comprises only 8% to 10% of all soft tissue sarcomas, it represents approximately 6% of all soft tissue tumors about the foot and ankle, and it is the most common sarcoma of the foot, comprising 45% to 56% of all such malignant lesions.6,7,9,12,15,18,20,26

Recognition of this disease requires a high index of suspicion to expedite staging and appropriate treatment. The current article highlights the clinical and pathologic features of this disease and presents the clinical outcome of treatment for 14 patients with synovial sarcoma of the foot and ankle who were treated at Duke University Medical Center (between 1970 and 1996) and Walter Reed Army Medical Center (between 1985 and 1995). The interval between symptom onset and diagnosis and histologic subtype were predictors of outcome, whereas tumor size was not. There was no difference in survival between groups of patients treated with limb salvage or amputation. This is despite a probable unintentional selection bias favoring limb salvage in that these lesions were smaller and more surgically accessible than those treated with amputation.

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PATIENTS AND METHODS

Fourteen cases of synovial sarcoma of the foot and ankle were evaluated and treated at the authors' institutions between 1970 and 1996. Minimum followup was 24 months, and average followup was 47 months (range, 24-134 months). The clinical records of each patient were analyzed retrospectively to determine age, race, gender, clinical presentation, radiographic features, pathologic findings, treatment modalities used, and disease outcome. Histologic evaluation confirmed the diagnosis of synovial sarcoma in all cases. The lesions were classified as either monophasic or biphasic subtypes. The biphasic histologic subtype was classified as such if present, even if it was not the predominant appearance. All lesions were interpreted as high grade sarcomas by experienced pathologists. A summary of this information is presented in Table 1.

TABLE 1

TABLE 1

Surveillance for recurrence of soft tissue sarcoma after local control measures consisted of chest radiographs and physical examinations every 3 months for 2 years, then every 6 months for 2 years, and annually thereafter. Time from biopsy to local or distant recurrence was calculated.

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Statistics

The parameters were grouped according to clinical outcome and the means compared for significance using the two-tailed Student's t-test. Kaplan-Meier survival curves were plotted to compare the ratios for patients with high latency by histologic subtypes and tumor size. Long latency was defined as more than 12 months, and large tumor size was defined as greater than 5 cm. Prognostic significance was determined by log rank analysis, and the null hypothesis was rejected with an alpha value of p = 0.05.

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RESULTS

Patient Demographics

The median age of the patients at the time of diagnosis of the primary tumor was 28 years (range, 8-53 years, Fig 1). Most patients (78%) presenting with synovial sarcoma were younger than 40 years. Eight patients were white, and six were African Americans; 10 patients were male and four were female. Three tumors occurred in the ankle, six were on the dorsum of the foot, and five were on the plantar surface of the foot.

Fig 1

Fig 1

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Clinical Findings

Like soft tissue sarcomas in general, and in other sites, there is no specific clinical feature or combination of clinical characteristics specific for synovial sarcoma of the foot and ankle. The most common clinical signs and symptoms were pain, tenderness, edema, and an enlarging mass. Three patients presenting with synovial sarcoma had neither pain nor local tenderness; aside from a soft tissue mass, they had no symptoms. Only one patient presented with constitutional symptoms reporting weakness and a 20-lb weight loss. None of the patients had skin involvement, inguinal adenopathy, vascular impairment, or neurologic symptoms at presentation.

The median duration of symptoms before presentation was 14 months (range, 1-48 months, Table 1). Six patients were referred after initial diagnoses of benign entities. Two lesions were thought to be ganglia, one was thought to be plantar fasciitis, two others were thought to be nonspecific synovitis, and another was thought to be a plantar fibroma. Conservative treatment of these patients resulted in a delay of diagnosis. All lesions were confirmed to be synovial sarcoma after biopsy. Ten patients presented with a history of antecedent trauma, which frequently was a misleading part of the history. Injuries included torsional injuries and blunt trauma. The time from injury to tumor diagnosis was between 3 and 9 months. When the duration of symptoms was evaluated as a prognostic factor for patient outcome, it was observed that patients with longer delays in diagnosis had a better disease outcome (Fig 2). This observation approached, but did not reach, significance (p = 0.158).

Fig 2

Fig 2

Two patients presented with radiographically evident pulmonary metastases. Twelve patients presented with nonmetastatic disease, but six of these patients subsequently had pulmonary metastases develop. The disease free interval for patients who had pulmonary metastases develop was 28 months (range, 2-98 months). No patients had regional lymphatic metastasis or bone metastasis. All patients who presented with metastasis or had metastasis develop died of disease.

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Radiographic Findings

Intralesional mineralization was seen on plain radiographs in three patients. Technetium99 pyrophosphate scans were performed in all patients and revealed increased radiotracer uptake in the soft tissue lesions in all patients. There was increased osseous uptake in five of 14 patients. Computed tomography (CT) of the extremities was done in seven patients, and was helpful in delineating the extent of the mass, the presence of soft tissue calcification, and osseous involvement. Computed tomography also showed areas of hemorrhage, necrosis, and cyst formation, which are not uncommon appearances of synovial sarcoma.

Magnetic resonance (MR) imaging was performed on 10 patients. This modality most accurately characterized the extent of the soft tissue extent of the tumor (Fig 3). Like most soft tissue sarcomas, synovial sarcoma typically is hypointense with respect to muscle on T1 weighted imaging. The signal intensity on T2 weighted imaging is heterogeneous because of hemorrhage and necrosis,11,14,17 and frequently a surrounding halo of increased signal on T2 imaging was observed, suggesting reactive edema. These data were used in planning the surgical procedure and determining the extent of the resection necessary. When the necessary resection could be performed and the residual foot was plantigrade and sensate, limb salvage options were considered.

Fig 3

Fig 3

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Pathologic Findings

The average tumor size was 5 cm, with a range from 1 to 9.5 cm in greatest dimension. There were eight patients with tumors smaller than or equal to 5 cm; of these eight patients, three experienced recurrences. In the group of six patients with tumors larger than 5 cm, five patients experienced recurrences. When this was evaluated with survival analysis and a log rank test, there was no statistically significant difference between the two groups (p = 0.881).

Histologically all tumors were high grade sarcomas2; eight lesions were biphasic and six were monophasic subtypes. The biphasic lesions had areas of pseudoglandular, plump epithelioid cells forming papillary projections within a spindle cell stroma. Mineralization was seen in four specimens, each of which was of the biphasic subtype. Two specimens had calcification evident on plain radiographs, and two specimens had calcification evident microscopically. The histologic subtype of the lesion was examined for prognostic significance (Fig 4). It was observed that patients with monophasic synovial sarcoma had a reduced survival, with 50% of the patients surviving less than 500 days, in contrast to patients with the biphasic subtype, of whom 50% survived longer than 3500 days. This difference approaches, but did not reach, statistical significance (p = 0.098).

Fig 4

Fig 4

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Treatment

In general, synovial sarcoma is treated surgically with or without adjuvant radiation. The goal of resection is to obtain wide surgical margins and maintain a sensate plantigrade foot. Depending on the size and location of the tumor within the foot, these clinical goals may not be achieved practically, and amputation becomes necessary. Of the 14 patients in this series, 12 underwent definitive surgery. Eight had below knee amputations, two had Chopart amputations, and two had wide resections with neoadjuvant radiation therapy. Two patients who had radiation therapy and a wide local excision also had a vascularized soft tissue transfer for wound closure.1 Two patients declined surgical intervention and were treated with a combination of radiation and chemotherapy. Radiation and chemotherapy also were used for palliation in cases of metastatic disease. Although multiple systemic agents were used, none of the patients had a significant reduction in tumor volume as a result of treatment. In the absence of response to systemic therapy, none of the patients underwent metastectomy.

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Outcome

One patient who had a below knee amputation had regionally recurrent disease develop that was treated with an above knee amputation. The rate of lymph node metastasis in soft tissue sarcomas is 10% but may be higher in synovial sarcoma.16 No patients had lymph node metastasis in the current study. Both patients presenting with pulmonary metastatic disease died within 2 years of diagnosis. Six additional patients had metastatic disease develop after initial staging, with a median time from diagnosis to pulmonary metastases of 22 months (range, 2-97 months). These patients had a median overall survival of 33 months (range, 13-135 months). Six surviving patients have been followed up for 24 months to 136 months without disease recurrence.

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DISCUSSION

Synovial sarcoma can occur at any age but is most common in patients younger than 40 years; in the current study the median age at diagnosis was 28 years, and 78% of patients were younger than under 40 years. Symptoms often are indolent, leading to long delays in seeking treatment and frequently missed diagnoses. The average delay of 21 months between the onset of symptoms and subsequent histopathologic diagnosis is similar to reported delays in other studies.12,13,25 In addition to the more common mistaken diagnosis of ganglion for lesions on the dorsum of the foot and fibromatosis for plantar lesions, synovial sarcomas of the foot and ankle have been confused with Morton's neuroma and tarsal tunnel syndrome.21,22

Three patients had lesions that were not painful or tender at presentation. Two of these were masses on the dorsum of the foot, where space occupying lesions are less likely to cause discomfort than on the plantar surface. A painless mass is the most common presentation in several series.8,13 In many cases the lesions were present for several years before presentation and aroused little suspicion because of their insidious growth pattern. These lesions are locally invasive and may involve underlying bone or the adjacent joint. Patients who had a longer duration of symptoms before presentation had a better outcome. This most likely can be explained on the basis of the biologic activity of the underlying lesion. Lesions that are more aggressive increase more rapidly in size and are more likely to cause symptoms, thus leading to earlier recognition. Despite early recognition, lesions with an aggressive biologic phenotype are more likely to metastasize. The malignancy of a foot and ankle mass cannot be ruled out from chronicity or a lack of symptoms. Most patients gave a history of antecedent trauma preceding the diagnosis of synovial sarcoma. Antecedent trauma has been reported in a significant number of cases in several series, but no correlation between trauma and tumorigenesis has been proven.5

The definitive diagnosis of synovial sarcoma is based on histologic findings, but radiographically calcification may be seen in soft tissue in as many as 40% of cases.5 The significance of this finding is uncertain, but Varela-Duran and Enzinger23 observed 26 of 32 patients with extensively calcified synovial sarcoma lesions with an average size of 4.6 cm. Their 5-year survival rate of 82.6% seemingly is higher than other 5-year survival rates reported in the literature.3,5,13,25 However, all of the lesions that were heavily calcified were of the biphasic histologic subgroup, which has been shown to have a better prognosis in most series.3,10 In the current series, an improved disease outcome was observed for event free and overall survival for patients with biphasic lesions in contrast to patients with monophasic lesions.

Tumor size has served as a prognostic factor in many series of soft tissue sarcomas. Hajdu et al,10 in a review of 126 cases, concluded that the size of the tumor and exposed areas, such as the foot, ankle, hand, and wrist, probably are more important to prognosis than are anatomic site, histologic subtype, or type of treatment. Patients with tumors smaller than 5 cm in these areas had a 5-year survival rate of 79%, as opposed to 33% for patients with tumors larger than 5 cm. In the current study, size was not a prognostically significant factor, but the number of patients in this series was small relative to the studies that included many anatomic locations.

Treatment of synovial sarcoma primarily is surgical. Most cases present as Stage 2B lesions and require wide surgical margins for local disease control. In the foot and ankle, anatomic considerations and the inability to maintain a plantigrade and sensate foot in whole or part necessitates amputation to optimize function. If a plantigrade and sensate foot cannot be achieved, below knee amputation should be done. In patients with limited disease, excellent functional and oncologic results can be obtained with limb sparing surgery and adjunct radiation, as proved by the four patients who underwent foot preserving procedures in this series and remain free of disease.

Despite successful local disease control, synovial sarcoma can metastasize months to years after initial treatment. For most other soft tissue sarcomas, metastases often occur within 18 months of initial treatment and most occur within 3 years. Recurrences in this group of patients were seen as long as 8 years after initial treatment. Overall, synovial sarcoma has been found to metastasize or recur locally in as many as 80% of cases.4,19,24,25 Lymph node metastases, although uncommon, can occur with this disease, although none was observed in this series.16

Mortality in this series was 57% (eight of 14 patients) and is similar to mortality described in other reported series of patients with synovial sarcoma overall. There seems to be little, if any, survival benefit in patients with distal appendicular lesions compared with patients with synovial sarcoma and more proximal tumors. The course of this disease in the foot and ankle is insidious, and the signs and symptoms are nonspecific and confused with other more common neoplastic and nonneoplastic conditions. The current study emphasizes the need for early diagnosis, staging, and treatment of synovial sarcoma of the foot and ankle because local disease control rates are high with current treatment modalities. Metastatic disease most frequently occurred in the lungs and was uniformly fatal in this series of patients. Metastasis and local recurrences can occur early and late, so continued vigilance is necessary during a patient's lifetime to monitor this disease.

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