Abstract:

Low grade fibromyxoid sarcoma (LGFMS) is a rare soft tissue tumor typically arising in the extremities of young adults, with a benign looking morphology often consisting of spindle cells. It is well known that this nonthreatening appearance may disguise the potentially aggressive and recurring nature of these tumors, making them a formidable histological diagnostic challenge. We present the case of a 33-year-old Caucasian female who presented with symptoms of acute cholecystitis, and a left lower quadrant retroperitoneal mass with focal calcifications was incidentally noted on computed tomography (CT). The mass was resected and appeared to involve the left psoas muscle. Grossly, the specimen consisted of lobulated, rubbery, tan-yellow soft tissue measuring 8.7 cm. Serial sectioning revealed a well-circumscribed white-tan solid mass with a thin capsule, whorled cut surface, pink-tan fleshy areas, and possible spicules. No areas of hemorrhage or necrosis were identified. Histologically, the neoplasm was composed of bland spindle cells with an alternating pattern of fibrous and myxoid regions. Mitotic activity was not significant, though mild hyperchromasia was apparent. Unusually prominent calcifications were identified throughout the neoplasm. Ultrastructural analysis agreed with the light microscopy. Based on the morphology, a diagnosis of LGFMS with prominent calcifications was rendered. Beyond the idea that this entity is uncommon in and of itself, retroperitoneal locations are rare. The presence of unusual prominent calcifications provides additional uniqueness. The significance of this is that identification of calcification in such a mass on imaging can help guide the differential diagnosis. While not present in all cases, prominent calcifications may alert the pathologist to consider LGFMS. Our case demonstrates the importance of a broad differential diagnosis in dealing with soft tissue tumors despite atypical locations or non-classic morphologic features.

Financial Disclosure:
No current or relevant financial relationships exist.

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Katherine Jerew, MD