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Pelvic Myxoid liposarcoma
S.A. Rooholamini, M.D.*, P.K. Chen, M.D.†,
A.H. Au, M.D.*, J. Rahimian, Ph.D.*,
From Departments of Radiological Sciences* and Pathology† Olive View-UCLA Medical Center, Sylmar, CA
CASE SUMMARY A 42-year-old man with mild right lower quadrant abdominal pain. On physical examination a firm mass was palpable in the right lower quadrant. The mass was mildly tender to palpation. Routine laboratory data were normal
FIGURE 1. (A and B) Axial CT images of the lower abdomen and pelvis with intravenous administration of contrast material demonstrate a large multilobulated space-occupying infiltrating lesion in the right lower quadrant. The mass shows a heterogeneous attenuation with fatty component.
FIGURE 2. (A and B) Axial delayed CT images of the upper and lower pelvis demonstrate a partially opacified urinary bladder (white arrow) which is displaced by the mass anteriorly and toward the left side of the pelvis. The right ureter is displaced anteromedially (black arrow). The right iliac vessels (arrowheads) are displaced by the mass anteriorly.
RADIOLOGIC FINDINGS Computed tomography of the abdomen and pelvis reveals a large multilobulated and infiltrating mass arising from the retroperitoneum on the right side and extending cephalad into the mid abdomen, caudad into the pelvis, and medially into the abdominal cavity and pelvis. The mass measures 11x6x17 cm, and it has compressed and displaced the psoas muscle anteriorly. It has also surrounded the right psoas and extends laterally to the right iliacus muscle. The inferior vena cava is flattened and pushed anteromedially. The distal abdominal aorta, including the bifurcation. is displaced anteriorly. There is displacement of the common iliac arteries with deviation to the left. The right iliac artery and vein are stretched, displaced anteromedially, and draped over the mass, but they are all patent. The mass crosses the midline, extends toward the left side of the pelvis, and displaces the urinary bladder toward the left side. The urinary bladder is positioned right behind the left rectus abdominis muscle. Likewise, the right ureter is markedly displaced anteromedially, but it is patent, and there is no ureteral dilatation. Displacement of the colon and small bowel loops is also seen. The mass is heterogeneous in density, containing areas of fat and soft tissue densities. No calcifications are visible within the mass or in the wall. No other abnormalities are encountered in the abdomen and pelvis. No lymphadenopathy is present. Following intravenous administration of contrast material, heterogeneous enhancement of the mass is seen. The degree of enhancement is moderate.
DIAGNOSIS Myxoid liposarcoma, diagnosed by biopsy.
DISCUSSION Liposarcoma accounts for less than 20% of all soft tissue tumors occurring in the adult population, and less than 5% among the pediatric age group. There are nearly 5,000 new patients with soft tissue tumor seen in the United States annually (1). Liposarcoma is considered a lipogenic tumor, arising from the deeply-seated connective tissues, and it arises from the primitive mesenchymal cells, rather than from mature fat cells. The most common location of liposarcomas is the lower extremity, and then in the order of frequency are retroperitoneum, shoulder area, neck and face. In children, there is a higher incidence of lower extremity involvement. The average age of the patients at presentation is 50 years among adults. A bimodal incidence exists among the pediatric age group with the mean ages of 14 months and 13.5 years. The presenting symptoms may be a painless or painful slow growing or rapidly growing mass. A fairly well circumscribed palpable mass may be felt on examination. Diffuse abdominal enlargement may occur in retroperitoneal liposarcomas. Histologically, there are four subtypes of liposarcomas. These include well-differentiated, myxoid, pleomorphic and round cell liposarcomas. The pleomorphic and round cell subtypes are considered highly malignant with a tendency for local recurrence and metastasis. Metastases are to the lungs. The myxoid subtype is regarded as intermediate, and the well-differentiated subtype is considered as a low-grade malignancy. The prognosis of the disease depends on the histologic subtype. Factors that influence the prognosis and behavior of the disease are histologic features, site of occurrence, and size of the tumor. The 5-year survival rate ranges from 15-80%. Myxoid liposarcoma accounts for 30-40% of all liposarcomas occurring in the extremities (2). Myxoid liposarcoma is histologically a subtype of liposarcoma, and most commonly occurs in the lower extremity, especially in the thigh. Other sites of occurrence in decreasing order are retroperitoneum, trunk, ankle, shoulder region, head and neck, and wrist. The patients’ age varies from 18 to 67 years, with a mean of 42 years. These tumors may present as large, slow growing, soft, painless masses. The histology of myxoid liposarcoma consists of myxoid matrix, lipoblasts, and vascular structures. Since only 10-25% of the content of the tumors are fat, they are not totally of low attenuation on computed tomography and may show a mixed density on a non-enhanced CT. However, because of the delicate vascular network, these neoplasms demonstrate heterogeneous enhancement after contrast material injection. The same principle holds true with magnetic resonance studies in which typical features of a lipomatous tumor may not be seen on non-enhanced images. However, enhancement is visible after gadolinium injection. The presence of myxoid matrix with abundant water mimics a cystic lesion. Necrosis also contributes to the areas of low attenuation on CT. Percutaneous CT-guided core biopsy of the tumor demonstrates proliferating lipoblasts, a plexiform capillary network, and abundant myxoid material (figures 3 and 4). The plan of treatment for this patient is chemotherapy to shrink the tumor, followed by surgical excision.
CONCLUSION Myxoid liposarcoma is a subtype of liposarcoma. Because of the myxoid and the delicate vascular components, the tumor is heterogeneous on unenhanced and enhanced CT images. This is also true on MR images.
REFERENCES 1. Konstantakos A, Dudgeon DL. Liposarcoma. www.emedicine.com/PED/topic 1317.htm 2. Sung M-S, Kang HS, Suh JS, Le JH, Park JM, Kim JY, Lee HG. Myxoid liposarcoma: Appearance at MR imaging with histologic correlation. Radiographics 2000; 20:1007-1019
ACKNOWLEDGMENT The authors express their thanks to Paul Beers, René Retana and Shervin Ghamghamy for their valuable technical and secretarial work in the preparation of this manuscript.
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