Alveolar soft part sarcoma.
Subject: Sarcoma
Authors: Dickerson, Tina D.
Owen, John A.
Pub Date: 11/01/2008
Publication: Name: Applied Radiology Publisher: Anderson Publishing Ltd. Audience: Academic Format: Magazine/Journal Subject: Health Copyright: COPYRIGHT 2008 Anderson Publishing Ltd. ISSN: 0160-9963
Issue: Date: Nov, 2008 Source Volume: 37 Source Issue: 11
Accession Number: 209239244
Full Text: CASE SUMMARY

A 22-year-old woman presented with a palpable left thigh mass that had recently become tender. Her medical history was otherwise unremarkable.

IMAGING FINDINGS

Ultrasound images revealed a 7 x 5 x 3-cm vascular mass lying adjacent but not fixed to the anterior femur. Magnetic resonance imaging (MRI) of the left thigh with and without contrast was performed. MRI revealed a 6.5 x 6.0 x 4.5-cm mass. The mass originated 12.5 cm above the knee joint situated between the anterior medial left femur and vastus medialis muscle. There was smooth displacement of the vastus medialis muscle without obvious invasion of either the femur or musculature. This mass was isointense to muscle on T1-weighted (T1W) images (Figure 1), was heterogeneously bright on T2-weighted (T2W) images (Figure 2), and enhanced rather homogenously on postcontrast images (Figure 3). There was no evidence of hemorrhage or mass. Flow voids were appreciated within the proximal portion. At least 3 enlarged vessels acting as a vascular pedicle for the tumor were seen on the source images. A left-lower-extremity arteriogram (Figure 4) revealed a hypervascular tumor that received the majority of its blood supply from the profunda femoral artery.

During the arteriogram, the neoplastic vessels were embolized using polyvinyl alcohol, Embosphere Microspheres (BioSphere Medical, Rockland, MA), and microcoils. Surgical excision of the mass was then performed. The patient subsequently underwent a whole-body bone scintigraphy (Figure 5) and computed tomography (CT) scan of the chest (Figure 6). Both showed probable metastatic disease.

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DIAGNOSIS

Alveolar soft part sarcoma (ASPS)

DISCUSSION

Alveolar soft part sarcoma was first described in 1952 by Christopherson, Foote, and Stewart as a soft tissue sarcoma with unique clinical and pathological features. (1) The name was derived from its microscopic appearance. Alveolar soft part sarcoma is a high-grade malignant tumor comprising 0.5% to 1% of all soft tissue sarcomas in adults and 0.8% to 1.8% of those in children. (2,3)

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Alveolar soft part sarcoma most commonly presents between the ages of 10 and 35 years, with women being diagnosed on the average at 20 to 22 years and men at 27 to 30 years. It has been documented in children as young as 2 years of age. (4) Alveolar soft part sarcoma is overall more common in females; however, after the age of 30, men are more frequently diagnosed. The most common site of origin is within the lower extremity, particularly the fascial planes or skeletal muscle of the anterior thigh. In children, the head and neck region is a more common site of origin, with the orbit and tongue as predominant locations.1 The usual presentation is that of a slow-growing, painless mass within the lower extremity without other symptoms. Possibly because of this insidious onset, the tumor size is usually quite large and metastasis is detected in approximately 20% to 33% of patients at the time of initial diagnosis. (2,4) The most common locations of metastasis are lungs, bone, and brain, in that order. Therefore, whole-body bone scintigraphy and chest CT are required for staging. Bones may be affected by direct or metastatic spread; however, distant bony metastasis is much more common, and local bony extension is reported as relatively rare. (5) Many cases of metastasis may be detected as late as 10 years after the initial diagnosis.

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Macroscopically, the tumor is well circumscribed and usually measures 3 to 6 cm. Tumors up to 20 cm have been reported. (6) The larger tumors often exhibit hemorrhage and necrosis. Alveolar soft part sarcoma has a characteristic microscopic appearance. Nests of large granular cells surrounded by capillaries are seen in a pattern resembling alveoli. These cells contain periodic acid-Schiff (PAS)-positive and diastase-resistant crystals, which helps make the diagnosis a certainty. (2) The histogenesis of ASPS is still unclear. Muscle-associated proteins are often found in immunohistochemical studies, suggesting a myogenic origin; however, there is conflicting data regarding these studies. This remains an area of continued research.

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Radiographic findings, though not specific, can, when combined with an adequate history, usually lead to the correct diagnosis. Ultrasound will typically show a hypoechoic, hypervascular mass. CT may reveal a well-circumscribed mass with marked contrast enhancement. MRI is the most sensitive and specific imaging modality. Typical findings include isointensity to a slight increase in intensity on T1W images, increased signal with T2W sequences, and strong enhancement. Multiple large flow voids consistent with peritumoral vessels may also be appreciated. (2) Angiography shows a highly vascular lesion with enlarged feeding arteries, arteriovenous shunts, and delayed washout. As mentioned previously, a CT chest and whole-body bone scan are performed for staging. These studies will show a typical appearance for metastatic disease if present.

Despite its slow growth, ASPS has a grave prognosis. Several studies report a 5-year survival rate of approximately 60% with a range of 45% to 88% depending on the selection of the patients. Two of these studies reported a median survival time of only 6 to 7 years. (2,6) The size of the tumor and the presence of metastasis have been implicated as the main prognostic factors. There is some evidence to suggest that age is also a significant prognostic factor, with children exhibiting a much longer survival time than those diagnosed at an older age. (7) The initial treatment of ASPS is radical excision with negative surgical margins. Local recurrence is uncommon if complete excision is performed. The metastatic disease is the most difficult aspect of treatment. If it is possible, the resection of pulmonary metastatic lesions can significantly increase survival time. Chemotherapy and radiation have shown inconsistent results and may be used successfully with individual patients.

CONCLUSION

Alveolar soft part sarcoma is a rare soft tissue sarcoma that presents most commonly within the lower extremity fascial planes or skeletal muscle of young females. Lung, bone, and brain metastasis are common. Median survival time is 6 to 7 years, depending upon the age of the patient, the size of the tumor, and the extent of metastasis. Imaging is nonspecific. Isointensity on T1W images, hyperintensity on T2W images, enhancement, and multiple flow voids are common MRI findings.

REFERENCES

(1.) Pang LM, Roebuck DJ, Griffith JF, et al. Alveolar soft part sarcoma: A rare soft-tissue malignancy with distinctive clinical and radiological features. Pediatr Radiol. 2001;31:196-199.

(2.) van Ruth S, van Coevorden F, Peterse JL, Kroon BB. Alveolar soft part sarcoma. A report of 15 cases. Eur J Cancer. 2002;38:1324-1328.

(3.) Suh JS, Cho J, Lee SH, et al. Alveolar soft part sarcoma: MR and angiographic findings. Skeletal Radiology. 2000;29:680-689.

(4.) Ordonez NG. Alveolar soft part sarcoma: A review and update. Adv Anat Pathol. 1999;6:125-139.

(5.) Durkin RC, Johnston JO. Alveolar soft part sarcoma involving the ilium. A case report. Clin Orthop Relat Res. 1999;359:197-202.

(6.) Ordonez NG, Mackay B. Alveolar soft-part sarcoma: A review of the pathology and histogenesis. Ultrastruct Pathol. 1998;22:275-292.

(7.) Pappo AS, Parham DM, Cain A, et al. Alveolar soft part sarcoma in children and adolescents: Clinical features and outcome of 11 patients. Med Pediatr Oncol. 1996;26:81-84.

Tina D. Dickerson, DO, and John A. Owen, MD

Prepared by Tina D. Dickerson, DO, and John A. Owen, MD, Department of Radiology, Baptist Integris Medical Center, Oklahoma City, OK.
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