Leiomyosarcoma of veins is a rare malignant tumour arising from the smooth muscle cells of the vessel wall. The IVC being the most common site of origin, followed by the pulmonary artery, and the thoracic aorta. Leiomyosarcoma of the IVC generally occurs in middle-aged women (approximately 80% of reported cases).
The clinical symptoms and metastatic potential of these tumours are related to their position in the vessel wall and to the portion of the IVC involved. Those arising in the intima, metastasize early, frequently, and have a poor prognosis. The cases arising in the media have a far better prognosis. They may remain hidden for a long time, they have much lower metastatic potential until tumorous protrusion into the lumen has occurred. Therefore, early diagnosis is essential.
Imaging plays an important role in the detection of such retroperitoneal tumours. In addition to detection of disease, CT and MRI are vital in determining surgical resectability. The CT and MRI findings depend on whether there is intra- or extraluminal growth.
In patients with extraluminal growth (62%), CT reveals a large, lobulated, heterogeneously enhancing, retroperitoneal mass with low density regions of necrosis. On MRI, an extraluminal mass is seen. It is of homogeneous intermediate signal intensity on T1-weighted images, and heterogeneous intermediate to high signal intensity on T2-weighted images.
In cases with intraluminal growth (5%), contrast-enhanced CT shows filling defects within a markedly dilated IVC. On MRI, a tumour mass with homogeneous intermediate signal intensity is seen on T1-weighted images. The tumour mass is seen to obstruct and dilate the IVC. T1-hyperintensities corresponding to thrombi may also be present. On T2-weighted images, the tumour appears hyperintense, and thrombus formation is associated with markedly high T2-hyperintensity. In 33% the disease presents with both extra- and intraluminal components, as in this case. In our patient, CT was useful in detecting the vascular obstructive process and the CT findings were suggestive that the tumour was arising from the IVC wall.
Though less useful, ultrasound and cavography are other means of imaging IVC leiomyosarcomas. On sonography, the tumour appears as a hypoechoic, soft tissue mass, and Doppler examination may be utilized to detect IVC thrombosis. Cavography shows either an intraluminal filling defect or compression and deviation of the IVC, depending on whether there is intra- or extraluminal tumour growth. Cavography is important for evaluation of collateral venous circulation and planning of venous reconstruction.
IVC leiomyosarcomas respond only minimally to chemotherapy or radiation, and surgical resection is the only potentially curative treatment. The prognosis is poor: the mean survival time is 1 month in inoperable patients and 34 months in those who undergo surgery. Mean 5-year postresection survival rate is 28%. Prognosis is poor because of haematogenous metastases and high local recurrence rate after surgical resection, reported to be approximately 36%.
We think that radiologists should be aware of the existence of malignant tumours arising in the great vessels: they should keep in mind, that behind a threatening aortic dissection there might exist a primary malignant tumour of the aorta, and particularly behind a huge retroperitoneal mass, there might be a hidden tumour of the IVC.