Leiomyosarcomas are the second most common primary retroperitoneal tumor and the second most common sarcoma in adults. [2–3] They are the most common sarcomas arising from large retroperitoneal blood vessels, especially the inferior vena cava (IVC). The majority of cases are completely extravascular (or extraluminal), although retroperitoneal leiomyosarcomas can also present with both extravascular and intravascular components (Figs. 1 and 2), and rarely as completely intravascular (or intraluminal) masses. [2–3] Leiomyosarcomas arise from smooth muscle tissue within the retroperitoneum, from retroperitoneal venous walls, or from embryonic Wolffian remnants. [2] These tumors are most frequently diagnosed in patients between the ages of 54 and 65 years and occur more often in women than in men. [3]

Axial (a), coronal (b) and sagittal (c) contrast-enhanced CT images through the mid-abdomen show a heterogeneously enhancing right perirenal retroperitoneal mass with a large extravascular component (red arrows) and a small intravascular IVC component (blue arrows). Pathology confirmed leiomyosarcoma arising from the IVC

Axial T2-weighted image (a) without fat saturation and axial fat-saturated T1-weighted contrast enhanced image (b) demonstrate a heterogeneously enhancing right perirenal retroperitoneal mass with a large extravascular component (red arrows) and a small intravascular IVC component (blue arrows). Diffusion weighted image (c) shows high restriction diffusion within the mass (red arrows). Pathology confirmed leiomyosarcoma arising from the IVC

Retroperitoneal leiomyosarcomas are typically asymptomatic when small due to their relative sparing of adjacent visceral structures and are usually therefore detected incidentally. Symptoms may present when the tumor compresses adjacent organs, resulting in pain or they may present with nonspecific symptoms, such as malaise, weight loss, and nausea or vomiting. [3–4] Leiomyosarcomas with intravascular components tend to be symptomatic earlier. Specific symptoms depend on the tumor’s location. Involvement of the suprahepatic IVC may obstruct the hepatic veins and result in Budd-Chiari syndrome. On the other hand, involvement of the mid-IVC and/or renal veins may lead to renal dysfunction and/or right upper quadrant pain. [4] Involvement of the infrarenal IVC can result in lower extremity edema. [3]

The majority of retroperitoneal leiomyosarcomas are extravascular. These tumors initially displace adjacent organs, as they tend to expand along tissue planes of least resistance, allowing them to grow to potentially large sizes before detection. [2] Tumors can often grow to greater than 10 cm. [2] On computed tomography (CT) imaging, retroperitoneal leiomyosarcomas typically appear as large soft tissue masses and often demonstrate areas of necrosis, hemorrhage, and/or cystic change (Figure 3). Calcifications are uncommon. [2–3] These tumors almost always enhance heterogeneously, with hyperenhancement of the solid components of the tumor relative to muscle in 56-61% of cases. [3] Collateral vessels are also often seen. Although leiomyosarcomas tend to initially displace adjacent organs, subsequent invasion of adjacent structures is common. These may include the kidney, liver, adrenal gland, pancreas, stomach, and spine. [3] Hematogenous metastases to the lungs and liver are more common compared to lymphatic spread. [3]

Axial (a, b) and coronal (c) contrast-enhanced CT images show a large heterogeneously enhancing right retroperitoneal mass (red arrows). The lesion has low density components and exerts mass effect on the right kidney with hydronephrosis (blue arrow). The patient had biopsy proven leiomyosarcoma arising from the IVC

On ultrasound, these tumors usually appear as solid masses with lobulations. They often demonstrate irregular cystic spaces, which may be anechoic or may contain hypoechoic material, secondary to necrosis and/or hemorrhage. [3]

On magnetic resonance imaging (MRI), the solid components of the tumor typically demonstrate hypointensity to iso-intensity on T1-weighted images and hyperintensity on T2-weighted images. Areas of necrosis demonstrate T1 hypointensity and T2 hyperintensity compared to muscle. Hemorrhagic areas may demonstrate T1 hyperintensity. Contrast-enhanced images typically demonstrate heterogeneous enhancement, similar to CT (Figure 4). [3]

Axial and coronal T2-weighted images (a, b) without fat saturation and a coronal fat-saturated T1-weighted contrast-enhanced image (c) demonstrate a large heterogeneously enhancing right retroperitoneal mass (red arrows). The patient had biopsy proven leiomyosarcoma arising from the IVC

Retroperitoneal leiomyosarcomas growing in an entirely intravascular or intraluminal pattern are rare. The most common vessel involved in the retroperitoneum is the IVC, with the most common segment being the portion between the hepatic veins and renal veins. [3] Leiomyosarcomas with intravascular components are more commonly metastatic at the time of diagnosis compared to extravascular leiomyosarcomas. [3]

The imaging findings are similar to those of other tumor thrombi, including heterogeneous enhancement of the intraluminal tumor and dilatation of the IVC, if involved. [3] Obstruction of the vessel lumen may occur, with resultant development of extensive collateral vasculature. One useful finding described for intravascular leiomyosarcoma is an imperceptible IVC at the level of its contact with the mass. [4–5] (Figs. 5, 6, and 7). A tumor of extravascular origin would tend to compress the IVC instead. [4]

Intravascular Leiomyosarcoma. Axial contrast-enhanced CT images through the upper abdomen in arterial (a) and portal venous (b) phases demonstrate a large heterogeneously enhancing mass expanding and obliterating the lumen of the suprarenal IVC (red arrows). This is the imperceptible IVC sign, indicating an intravascular tumor

Axial contrast-enhanced CT images one level below that of Fig. 5 in arterial (a) and portal venous phases (b) demonstrate a large contiguous extravascular tumor component with similar enhancement characteristics (red arrows)

Coronal contrast-enhanced CT image in the arterial phase demonstrates a large bilobed heterogeneously enhancing suprarenal IVC mass with both intravascular (red arrow) and extravascular components (blue arrow). The patient has a IVC filter. Pathology confirmed leiomyosarcoma arising from the IVC

MRI may be helpful to further demonstrate the degree of tumor extension and differentiate tumor from bland thrombus. Black-blood sequences in particular delineate the degree of intraluminal tumor extension well, given the contrast between the hypointense intravascular blood and the hyperintense tumor. [3] Gradient-echo images may alternatively demonstrate hypointense tumor relative to high intraluminal signal within the vessels. [2] An enlarged IVC, increased T2 signal within the mass, and internal enhancement are more suggestive of IVC leiomyosarcoma as opposed to bland thrombus. [3–4] MRI may also help detect extensive collateral vessels which may develop due to slow growth of the tumor. [4] The tumor typically demonstrates similar signal characteristics as extravascular leiomyosarcoma: hypointense on T1-weighted sequences and hyperintense on T2-weighted sequences. [4] Metastases often occur via hematogenous spread and tumor may also subsequently metastasize lymphatically. Common sites of metastases include the liver, lungs, and lymph nodes. Metastatic lesions usually demonstrate similar MRI signal characteristics as the primary tumor. [4]

Ultrasound imaging typically shows an intraluminal solid mass with internal Doppler flow. [3] Large tumors tend to be heterogeneous, while smaller tumors demonstrate homogeneity. [3] Abnormal or even absent Doppler flow within the involved vessel may be seen. [4] 18 F-fluorodeoxyglucose positron emission tomography (FDG PET) can potentially be helpful to evaluate the extent of disease, although its true role in diagnosis and management of IVC leiomyosarcoma has not been established. [4]

Leiomyosarcomas involving the gonadal veins have been reported in the literature, but are extremely rare. [6] Gonadal vein leiomyosarcoma most commonly presents as a large heterogeneous enhancing mass replacing the normal gonadal vein and often in a longitudinal orientation. [7] (Figs. 8 and 9). As with IVC leiomyosarcomas, cystic, necrotic, and hemorrhagic areas may be seen. [7]

Leiomyosarcoma of the left gonadal vein. Axial (a) and coronal (b, c) contrast-enhanced CT images show an ovoid heterogeneously enhancing left retroperitoneal mass (red arrows) along the course of the left ovarian vein (blue arrows)

Axial T1 and T2-weighted images (a, b) without fat saturation demonstrate the mass to be T1 hypointense and moderately T2 hyperintense (red arrows). A coronal fat-saturated T1-weighted contrast enhanced image (c) demonstrates the mass (red arrow) to be avidly enhancing and contiguous with the left ovarian vein (blue arrow)