Clinical Profile:

A 41year old man presented with the complaints of vague abdominal pain and distension since one month. He had low grade fever on and off since one month.  

Radiological findings:

Ultrasonogram [Fig1] :

There is a well defined lobulated heterogenously hypo to isoechoic lesion in the retroperitoneum on the right side. The lesion shows vascularity. The lesion is invading the inferior vena cava(IVC) with extension into the right atrium. There is mild hydronephrosis of the right kidney due to compression of the ureter by the lesion.

CT Abdomen(Plain)[Fig2]: 

Contrast was not given as the creatinine levels were raised at the time of the scan.

There is a large heterogenous soft tissue density lesion in the retroperitoneum in the right lumbar region, measuring 8.2x11.6x12cm(APxTRxCC).

The lesion is not arising from any of the retroperitoneal organs such as the kidneys, adrenals or the pancreas.

There is no calcification or macroscopic fat.

Superiorly it is extending till the subhepatic region and inferiorly till the right iliac fossa. Anteriorly the lesion is displacing the ascending colon anteriorly and to the left. The bowel loops are displaced to the left. Posteriorly it is in relation with the right kidney and the right psoas muscle. There is mass effect on the right ureter causing upstream hydronephrosis.

There is loss of fat planes with the infrarenal IVC with significant dilatation of the proximal segments of the IVC. Superiorly it is extending into the right atrium.

There is mild free fluid in the pelvis and minimal right pleural effusion.

There are no deposits in the lung parenchyma.

MRI abdomen[Fig3]:

There is a large well defined lobulated T2 heterogenously iso to hyperintense and T1 isointense soft tissue retroperitoneal lesion in the right anterior pararenal space. There are multiple peripheral areas of diffusion restriction with corresponding drop on ADC map. The lesion has heterogenous post contrast enhancement. There is loss of fat planes with the infrarenal segment of the IVC with intraluminal extension. The right renal artery is compressed by the lesion.

Radiological diagnosis:

Retroperitoneal leiomyosarcoma

Pathological diagnosis and treatment:

Retroperitoneal smooth muscle tumor

The patient is undergoing debulking chemo-radiotherapy and is symptomatically better.

Timeline

Discussion

Leiomyosarcoma is a malignant neoplasm that shows smooth muscle differentiation. It is the second most common sarcoma to affect the retroperitoneum and the most common to sarcoma to arise from large blood vessels in the retroperitoneum[1].

Epidemiology :

It occurs most commonly in the age group of 54 to 65 years[2]. Women are more commonly affected than men, with leiomyosarcomas with IVC involvement occuring five times more commonly than in men[3].

Clinical presentation :

Retroperitoneal leiomyosarcomas typically manifest as large soft tissue masses. Because of their retroperitoneal location and relative sparing of the visceral structures, these tumors may grow to large sizes before detection and are commonly incidental finding at imaging. When symptomatic they may cause compressive symptoms, including pain.

When they have an intraluminal component, they tend to present earlier[4]. Based on the segment of IVC involved, the presentation may vary from signs of Budd-Chiari syndrome like jaundice, hepatomegaly, ascites(suprahepatic IVC), renal dysfunction(mid IVC), limb edema(infrarenal IVC)

Histopathological features :

These tumors arise from smooth muscle tissue located in the retroperitoneum or the walls of the large retroperitoneal veins.

Key histological features used to diagnose leiomyosarcoma in the retroperitoneum includes at least one of the following : cellular pleomorphism or atypia, coagulative tumor cell necrosis and more than 10 mitotic figures per 50 high power fields(HPF) in women or more than one mitotic figure per 50HPFs in men [5]. 

The typical microscopic pattern seen is intersecting sharply marginated fascicles of spindle cells. Occasionally a focal storiform, palisaded or hemangiopericytoma like arrangement may be seen. They are usually compactly cellular, but fibrosis or myxoid change may be seen. In large masses, hyalinized hypocellular zones and coagulative tumor necrosis are common features. The tumor cell nuclei are typically centrally located, elongated, and blunt ended. Varying degrees of nuclear hyperchromasia and pleomorphism usually manifest. Mitotic figures and atypical mitoses are common.

IHC markers includes SMA, desmin, h-Caldesmon(smooth muscle markers). Two of these markers are more supportive of the diagnosis. Additionally focal positivity for keratin, epithelial membrane antigen, CD34 and S100 may be seen. CD117(KIT) is negative.

Genetic associations include defects in TP53(Li-Fraumeni syndrome) and RB1 gene(retinoblastoma cyclin D pathway).

Imaging features :

Retroperitoneal leiomyosarcomas classically appear as large soft-tissue masses, often with areas of necrosis, hemorrhage, or cystic change. The mean tumor size is approximately 11.3 cm for retroperitoneal leiomyosarcomas without vascular involvement. In cases with vascular involvement, mean tumor size is slightly smaller at 10.4 cm. Retroperitoneal leiomyosarcomas are usually located in the perirenal or posterior pararenal spaces. They exhibit three major patterns of growth. The most common is an entirely extravascular or extraluminal pattern, accounting for 62% of cases. In one-third of cases, the pattern of growth includes both extravascular and intravascular components . The least common pattern of growth, occurring in only 5% of cases, is an entirely intravascular or intraluminal mass. The most common sites of metastases are the lungs (65%), peritoneum (53%), liver (53%), muscle (41%), bones (35%), and lymph nodes (35%).

On ultrasound, leiomyosarcomas appear as lobulated solid masses with irregular cystic spaces secondary to hemorrhage and necrosis[6]. The solid components may be iso-hyperechoic compared to the liver. Intravascular growth pattern shows intraluminal solid mass with vascularity on Doppler. The IVC is often expanded.

On computed tomography, these tumors are hyperattenuating relative to muscle on post contrast images, The enhancement pattern is heterogenous. Necrosis appear as non enhancing hypoattenuating areas. Collateral vessels are a common finding[6]. Local invasion involving right kidney, liver, right adrenal, pancreas, stomach and spine is common. Intravascular component is seen as tumor thrombus.

Om magnetic resonance imaging, there is hypo to isointense T1 signal and high T2 signal in the solid components[6]. Areas of necrosis are typically T1 hypointense and T2 hyperintense compared with muscle. If hemorrhagic necrosis manifests, the T1 signal may be hyperintense relative to that of muscle. In cases with intravascular tumor, black blood imaging sequences nicely show the degree of intravascular tumor extension by highlighting the hyperintense tumor compared with the hypointense luminal blood. Multiplanar postcontrast imaging is also useful to evaluate the extent of vascular involvement and to differentiate tumor from bland thrombus.

Differentials include lymphoma, lymph nodal metastasis, other soft tissue sarcomas like liposarcoma, neurogenic tumors, germ cell tumors and tumors arising from reptroperitoenal organs. Non neoplastic differentials include hematoma, retroperitoneal fibrosis and Castleman disease.

Management:

First line treatment consists of surgical resection with the goal of negative margins[7]. For tumors with vascular involvement or of vascular origin, additional vessel reconstruction or ligation is done.

The use of chemoradiotherapy has been described in both neoadjuvant and adjuvant settings.

There is high risk of local recurrence and distal metastases. Overall 5-year survival is 39%-68%.

References:

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Acknowledgement :

We are grateful to the Department of Pathology  at our institution for providing us with an image from the histological findings as also its description.