Retroperitoneal liposarcoma

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There is a large, heterogeneously enhancing necrotic mass centered within the left retroperitoneum measuring 16.2 x 8.4 x 14.9 cm (AP x W x CC). This mass is inseparable from the lateral border of the kidney and displaces the left kidney anteromedially and the spleen anterolaterally. The mass is separable from the left psoas muscle and appears to be predominately sited within the renal fascia (anterior and posterior).

There is no associated calcification but there is prominent vascularity inferior to the mass. The mass compresses the descending colon, however there is no bowel obstruction. There is no suspicious lymphadenopathy identified. There are no hepatic, lung parenchymal, or osseous metastases. The kidneys are otherwise normal bilaterally with simple Bosniak class I cysts and no renal tract obstruction. The left adrenal gland is normal.

There is an incidental type I hiatal hernia with a small fluid level.

(The staging CT chest has not been uploaded).

Image courtesy: Dr Y Ebrahim.

Gross pathology:

The specimen consists of a well-circumscribed and multilobulated tumor, measuring 195 x 175 x 90 mm and weighing 1718.08 g. On cut sectioning, areas of necrosis are identifiable. The tumor has a fibrous pseudo-capsule with no capsular breach.

Microscopy:

The sections are representative of a well-circumscribed and lobulated neoplasm with a thin fibrous capsule. Surrounding adipose tissue is noted in areas, infiltrated by the neoplasm. The neoplasm is composed of spindled cells, arranged haphazardly as well as in fascicles. The cells have scant cytoplasm and large, markedly pleomorphic, hyperchromatic nuclei. Multinucleation of the cells is identifiable and large bizarre nuclei are also seen. There are at least three mitotic figures per ten high power fields, and atypical mitotic figures are also present. A focus of homologous lipoblastic differentiation is noted, with lipoblasts identifiable. Myxoid areas are also identifiable.

Immunochemistry:

Desmin: positive, indicates myoid differentiation

SMA: positive within the vessels, negative within the tumor

MNF116: negative

S100: negative

HMB45: negative

Melan A: focal positive staining in the large pleomorphic cells

PXX8: negative

Myogenin: negative

MyoD1: negative

Vimentin: positive

H-caldesmon: negative

Final diagnosis: high-grade dedifferentiated liposarcoma with myoid and lipogenic differentiation.

Histopathology courtesy: DR MT Thobejane