Pathological Conditions

A variety of tumours, both benign and malignant, may arise within the retroperitoneum. The commoner lesions are discussed here.

Liposarcoma: arising within the retroperitoneal fat, well-differentiated liposarcoma, particularly the sclerosing subtype, represents one of the commonest histological subtypes. There is a very low risk of metastasis with this type of lesion, which indeed has been described as an atypical lipoma at other sites. However, such lesions can be difficult to excise from the retroperi-toneum and may prove lethal because of pressure effects on adjacent organs or local recurrence if incompletely excised. These tumours may also contain or develop a dedifferentiated spindle cell component, resembling a high-grade spindle cell sarcoma. Careful macroscopic examination and adequate sampling are important. Lipomas also arise at this site; careful evaluation is necessary to distinguish from well-differentiated liposarcoma as described above.

Other sarcomas: these include malignant fibrous histiocytoma and leiomyosarcoma. Careful consideration must be given before rendering a diagnosis of malignant fibrous histiocytoma as it is increasingly recognised that a proportion of such lesions represent anaplastic forms of other malignant tumours. At this site lesions such as sarcomatoid renal cell carcinoma should also be excluded. Both benign and malignant smooth muscle tumours may occur. Leiomyoma is reported as very rare and is to be distinguished from leiomyosarcoma and renal angiomyolipoma. Leiomyosarcoma may arise from the wall of the inferior vena cava or its tributaries.

Peripheral nerve tumours: relatively common at this site, although not as frequent as in the mediastinum. Schwannomas may be quite large and show cystic degeneration; neurofibromas and malignant peripheral nerve sheath tumours are also described. Rarer tumours include lesions such as paraganglioma (chemodectoma/aortic body tumour), ganglioneuroma, neuroblastoma and other small, round, blue cell tumours such as Ewing's sarcoma/PNET and intra-abdominal desmoplastic small cell tumour.

Solitary fibrous tumour, haemangiopericytoma and carcinoid tumours: although haeman-giopericytoma-like areas may be seen in various soft tissue tumours, the retroperitoneum remains a typical site for true haemangiopericytomas in middle-aged female patients. The histogenesis of retroperitoneal carcinoid tumours is uncertain. Some may represent a form of germ cell tumour, which also occur at this site either as primary tumours or more commonly as lymph node metastases from a testicular or ovarian primary.

Malignant lymphoma and metastatic disease: lymphoma may involve the retroperitoneal lymph nodes and lead to massive enlargement. Diffuse large B cell lymphoma (and variants such as T-cell-rich B cell) and follicle centre cell lymphomas are among the commonest. Pelvic and retroperitoneal nodes are a common site for metastatic disease from malignant germ cell tumours of the testis, prostatic carcinoma or gynaecological malignancy.

Miscellaneous: abdominal aortic aneurysms are only rarely biopsied. Idiopathic retroperitoneal fibrosis is an uncommon reactive, inflammatory condition that may simulate a tumour at laparotomy - it strictures and distorts the ureters resulting in hydronephrosis. Most cases are of unknown aetiology, a minority being drug related or associated with inflammatory type aortic aneurysms.

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