Pathologic findings:
 

Gross appearance external

Gross appearance cut surface

Consists of a multilobulated mass weighing 60 gm and measuring 7.0x4.5x4.0 cm in dimension. Although much of the mass is well encapsulated, the capsule is absent near one pole and the tumour at this area appears incompletely excised. Small amounts of adherent fat, a grossly normal ovary and tube are also present on its surface. Cut surfaces show solid whitish tumour tissues.
 

Low power capsule	Low power	Low power	Medium power
High power	High power necrosis	High power mitosis	High power mitosis

Sections show a circumscribed tumour which appears to be enveloped by a discontinuous layer of smooth muscles and thick walls vessels. The tumour septae also contain bundles of smooth muscles suggestive of an origin from a large vessel or smooth muscle layer of an organ. The tumour is more cellular and pleomorphic than the tissues seen in the recent needle biopsy. It is also more organised consisting of fascicles and groups of malignant cells in a focally myxoid stroma. This degree of organization is not suggestive of a nerve sheath tumour. An interlacing pattern like those of smooth muscle tumour is seen. Focally, a storiform pattern is also seen but foamy cells and histiocytic features are not found. The tumour cells are mostly spindle shaped but occasional giant pleomorphic nuclei could be seen. The mitotic rate is estimated to be about 4 per 10 hpf. Focal necrosis and infaction changes could be seen. At the area where the tumour capsule is absent, the tumour appears to be incompletely excised. The ovarian stroma and fallopian tube show no significant pathology.

Pathologic Diagnosis:

Tumour left retroperitoneum - Low grade sarcoma, consistent with a leiomyosarcoma arising from the IVC.

Pathologist Comments:

Most  soft tissues leiomyosarcomas are located in the extremities, many arising from the walls of arteries and veins of widely differing caliber. The is an inverse relationship between the incidence and the intraluminal pressure within the vascular bed. Most common in large veins such as vena cave, far less common in pulmonary artery and excessively rare in systemic arteries.

Between 80 to 90% of inferior vena cava tumours occur in women. Clinical symptoms and surgical resectability are dependent on level at which tumour arises. Suprahepatic tumours causes the Budd-Chiari syndrome and are unresectable. Mid level tumours may mimic biliary tract disease or cause renal impairment. Some of these cases are resectable. Tumours below renal veins cause lower leg oedema and are often amendable to surgical excision. A few cases of  vena cava tumours are associated with RBC abnormalities and consumptive coagulopathy. Leiomyosarcoms arising from other veins affect the sexes equally.

Most tumours are well circumscribed. Microscopically, merging of tumour cells with blood vessel walls is an important diagnostic clue to leiomyosarcomas of vascular origin. Some tumours may resemble peripheral nerve sheath tumour and fibrohistiocytic tumours histologically. Epithelioid features may also be present.

Distinction between leiomyoma and leiomyosarcoma may be difficult. The histologic criteria are different from those of uterine leiomyosarcomas. Tumours with high mitotic rate (5 or more per 10 hpf) are considered malignant. If the mitotic rate is lower, necrosis, overly large tumours (more than 10 cm), haemorrhages and nuclear pleomorphism are also indicators of malignant behaviour. This patient has a mitotic rate of 4 per hpf but there is also nuclear pleomorphism and necrosis. Hence a diagnosis of malignancy is justified.

Prognosis correlates with tumour size, mitotic rate and depth. Tumour location will also affect surgical resectability. About half the patient have metastases at diagnosis, mainly to liver and lung. Stuart and Baker analyzed 10 cases and of 5 followed up for longer than 1 year, all died.

Reference:

Ackerman's Surgical Pathology, Eight Edition 1996, vol2, p2076
Soft Tissues Tumours, Enzinger & Weiss, Second Edition 1988, p417