Imaging diagnosis
Case 203
【Progress】
She was transported to medical university hospital
【Discussion】
Retroperitoneal space is the space between transverse fascia and parietal peritoneum. It is subdivided into five compartments by fascia: anterior pararenal space, perirenal space, posterior pararenal space, peri-great vessel space and peri-psoas muscle space (1-4). In the upper abdomen, renal fascia contributes to create perirenal space by enclosing kidneys, and subdividing anterior pararenal space and posterior pararenal space. These three compartments converge to two compartments in the lower abdomen or pelvis: peri-great vessel space and peri-psoas muscle space. Peri-renal space communicate with peri-great vessel space and peri-psoas muscle space.
There is a Winslow foramen (epiploic foramen) between IVC and main portal vein. Peritoneal space is divided into two compartment: main peritoneal space and omental bursa. Omental bursa is a lumen formed by both of lesser omentum and greater omentum. Winslow foramen is communication route between main peritoneal space and omental bursa. It exists behind the hepato-gastroduodenal ligament. CT shows Winslow foramen exists in a space between main portal vein and inferior vena cava. This space is known as the space where aberrant right hepatic artery passes through.
In our case, abdomen CT showed a fat containing mass expanding the space between IVC and main portal vein which was interpreted the mass invades to Winslow foramen to omental bursa. This mass also occupies the right perirenal space and rotates right kidney, implying the mass arises from right retroperitoneal space. Is there any communication route from retroperitoneal space to peritoneal space (Winslow foramen and omental bursa of lesser omentum) ? Based on the previous literatures, there is no possible route of the large mass entering peritoneal space from retroperitoneal space except fascia spread theory. Fascia spread theory originates from fluid spread. It is hard to believe that tumor extends and grows massively along with the fascia from retroperitoneal tumor to peritoneal tumor. We believe that the tumor in the perirenal space grows massively and extends rapidly to peri-great vessel space, shifting inferior vena cava anteriorly, and separating the distance between IVC and abdominal aorta and the distance between main portal vein and IVC, collapsing Winslow foramen and omental bursa.
Liposarcoma is categorized into well-differentiated liposarcoma, myxoid liposarcoma and dedifferentiated liposarcoma. Well-differentiated liposarcoma belonging to low grade was seen in 55%, myxoid liposarcoma belonging to low-intermediate grade in 30% and dedifferentiated liposarcoma belonging to high grade in less than 15% (5, 6). Intermediate type implies high incidence of local recurrence but not of distant metastasis. High grade implies to proliferate like cancer. In our case, CT showed not only lipid component but also myxoid component, indicating to be suspicious of myxoid liposarcoma.
【Summary】
We present a seventy two-year-old female with retroperitoneal liposarcoma. Abdomen CT showed the liposarcoma which looked like to occupy perirenal space, Winslow foramen and omental bursa in the lesser omentum, expanding the space between inferior vena cava (IVC) and main portal vein which implies the existence of Winslow foramen, and expanding the space between IVC and abdominal aorta. We speculate this tumor arise from perirenal space and grow to the great-vessel compartment and to extend the space between IVC and main portal vein, leading to compress Winslow foramen and omental bursa in the lesser omentum. It is borne in mind that retroperitoneal space is subdivided into anterior pararenal space, perirenal space, posterior pararenal space, great-vessel space and peri-psoas muscle space. Peritoneal space is subdivided into main space and omental bursa. Winslow foramen is a route between main peritoneal space and omental bursa. Winslow foramen exists between IVC and main portal vein on abdomen CT. Liposarcoma is subcategorized into well differentiated liposarcoma, myxoid liposarcoma and dedifferentiated liposarcoma.
【References】
1.Nishino M, et al. Primary retroperitoneal neoplasms: CT and MR imaging findings with anatomic and pathologic diagnostic clues. Radiographics. 2003; 23 : 45-57.
2.Craig WD, et al. Fat-containing lesions of the retroperitoneum: radiologic-pathologic correlation. Radiographics. 2009;29: 261-90.
3.Ellingson JJ, et al. Computed tomographic distinction of perirenal liposarcoma from exophytic angiomyolipoma: a feature analysis study. J Comput Assist Tomogr. 2008;32: 548-52.
4.William D. et al. Fat-containing Lesions of the Retroperitoneum: Radiologic-Pathologic Correlation1. RadioGraphics. 2009; 29 : 261-90
5.Akshay D, et al. Soft-Tissue Sarcomas: An Update for Radiologists Based on the Revised 2013 World Health Organization Classification. American Journal of Roentgenology. 2016;206: 924-932.
6.Thomas JM. Retroperitoneal sarcoma. Br J Surg 2007; 94:1057–810.
2020.9.2