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Retroperitoneal Liposarcoma

Howard T Heller, MD
Julia R Fielding, MD

December 2, 1996

Presentation

A 36-year-old man presented with gradually increasing abdominal discomfort. Physical examination suggested a mass in the pelvis.

Imaging Findings

CT of the lower abdomen and pelvis

Computed tomographs (CT) of the lower abdomen and pelvis with oral and intravenous contrast demonstrate a 12 x 11 x 11 cm mass centered anterior to the sacral promontory (white arrow), displacing the left psoas muscle posterolaterally and the bladder dome posteriorly and to the right (arrows). The mass has well-defined margins without apparent invasion of surrounding structures. Its attenuation is heterogeneous with predominantly muscle-density material, but fatty components are also present (black arrow). From its location within the pelvis and its relation to adjacent retroperitoneal structures, the mass appears to be retroperitoneal in origin.

Differential Diagnosis

This mass is most likely liposarcoma. Teratomas contain fat, but also calcification (not present here), and would most likely have arisen from the testis in this patient. No evidence from the images suggests testicular origin.

Other mesenchymal tumors (engulfing adjacent fat), such as malignant fibrous histiocytoma, desmoid, and leiomyosarcoma, are less plausible. Lymphoma should also be considered. If the mass were more intimately related to the anterior bladder wall and if calcification were present, a urachal adenocarcinoma could be considered.

Diagnosis

Well-differentiated liposarcoma

Discussion

Retroperitoneal liposarcoma is among the most common primary retroperitoneal tumors, along with malignant fibrous histiocytoma and leiomyosarcoma. It is slow-growing and has a propensity to displace rather than invade adjacent structures. Histiologic subtypes include well-differentiated, myxoid (the most common form) and pleomorphic. Liposarcoma is most often seen in the fifth to seventh decades and is more common in men. The appearance of fat in a retroperitoneal tumor can aid in diagnosis. Fat is invariably present in liposarcoma and notably absent in less well-differentiated masses. Calcifications occasionally are visible. The overall 5-year survival rate is about 30%.

References

1. DeVita VT, Hellman S, Rosenberg SA. Cancer: principles and practice of oncology. 3rd edition. Philadelphia: Lippincott, 1989.

2. Cohan RH, Dunnick NR. The retroperitoneum. In: Haaga JR, Zerhouni E, Lanzieri C. Computed tomography and magnetic resonance imaging of the whole body. 3rd edition. St Louis: Mosby, 1994.

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