Uroradiology & genital male imagingCase Type
Elena Zabía Galíndez, Marisol Fernández López-Peláez, Millán García-Isidro, Elena Ayerbe UnzurrunzagaPatient
54 years, male
A 54-year-old man presented with progressive abdominal distension without bowel or genitourinary complaints. Physical examination revealed a large mass in the right side of the abdomen. Laboratory findings were normal.
Abdominal computed tomography (CT) scan was performed with and without IV contrast media.
CT images showed a large partially calcified mass in the right retroperitoneal space bounded by a thin-rime and with fatty, cystic and solid components, the latter with subtle enhancement after contrast administration.
The mass crossed over the median line and causes lateral displacement of the kidney and medial displacement of the duodenum and the pancreas.
The diagnosis of liposarcoma was suggested by the moderate amount of fat -mostly located in the periphery of the lesion- with thin septa and poorly defined solid-appearing areas with no clear demarcation between them and fat.
Dedifferentiation was suspected by the large calcifications and the well-demarcated solid components with distinct planes between fat and solid tumour.
Due to the close relationship between the tumour and the renal sinus and capsule, renal liposarcoma was considered before surgery, even despite its rareness.
MRI could have better depicted purely fatty components, solid components and possible associated myxoid components, but patient refused it.
Surgery confirmed the infiltration of both anterior and posterior perirenal fascias and the mass and the kidney were removed.
Liposarcoma is the most common malignant retroperitoneal soft-tissue tumour in adult patients (35%) followed by leiomyosarcoma and malignant fibrous histiocytoma .
It mostly affects 50-70 years old patients with no gender predilection.
Unlike liposarcomas in the extremities, retroperitoneal tumours can remain unnoticed and have more time to grow and undergo dedifferentiation. Symptoms depend on its mass effect on adjacent structures.
Liposarcomas are subclassified into five groups : well-differentiated liposarcoma (WDL), dedifferentiated liposarcoma (DL), myxoid liposarcoma (ML), round cell liposarcoma (RCL) and pleomorphic liposarcoma (PL) with different genetic, clinical, radiologic and pathologic characteristics:
- WDL: The most common subtype. It appears as a well-defined predominantly fat-containing lesion with thin septa and minimal poorly defined soft-tissue components.
Any retroperitoneal purely fatty lesion (indistinguishable from lipomas) should be considered a WDL and undergo biopsy [3, 4]
They have good prognosis if they can be completely resected, which is often not possible due to the large proportions the tumour can reach before being symptomatic.
- DL: Dedifferentiation has been reported to occur in 15% of the cases with an average latency period of 7-8 years  and has a worse prognosis due to more aggressive behaviour and its ability to metastatise.  75% of these tumours occur in the retroperitoneum. 
It is suggested by focal well-demarcated nodular non-lipomatous regions larger than 1cm  within a lesion consistent with WDL.
Ossification or calcification often indicate dedifferentiation and are a sign of poor prognosis. 
- ML: They occur in younger patients, typically in extremities and rarely in the retroperitoneum, most of them with enough fat to suggest the diagnosis. Non-lipomatous components include the myxoid component (resembling cysts but with higher attenuation than simple fluid), focal nodules and thick septa.
- RCL: A high-grade liposarcoma described as a subtype of ML with minimum amount of fat and higher amount of round stromal cells that coalesce to form sheets. 
ML and RCL have a 5-year survival rate of 60-90%.
- PL: It is the less common subtype, affects the retroperitoneum and the extremities with equal frequency, shows little if any visible fat and has bad prognosis with a local recurrence rate of 30-40% and a 5-year survival rate of 30%. 
Surgery is the treatment of choice but complete resection is not always possible. Resection of lung and liver metastases is reasonable in selected cases. Radiation therapy and chemotherapy remain controversial .
Written informed patient consent for publication has been obtained.
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