Lymphadenopathy, retroperitoneal

CT is the best modality for imaging retroperitoneal lymphadenopathy (Fig.1). Abnormal nodes must be distinguished from bowel loops, left-sided inferior vena cava, retroaortic or circumaortic renal vein, dilated normal veins, diaphragmatic crus, retroperitoneal haemorrhage and retroperitoneal fibrosis. Oral and intravenous contrast agents are extremely helpful and sometimes vital in diagnosing lymphadenopathy. In areas difficult to image by CT, such as the diaphragmatic region, MRI with its multi-planar capability is often of value.

Abnormal nodes may occur singly or in clusters. An abnormal number of normal-sized nodes are seen in patients with lymphoproliferative disease. Lymphadenopathy is usually of soft tissue density. However, attenuation values are variable, including negative values in lipoplastic lymphadenopathy, near fluid density in necrotic lymphadenopathy, or high attenuation (up to 120 Hounsfield units (HU) in patients with Hodgkins disease or metastases from breast or ovarian carcinoma. Calcification occurs following chemotherapy and in nodal metastases from testicular carcinoma.

A normal CT scan does not exclude the possibility of lymphadenopathy, as foci of metastatic disease may be present in a normal-sized node. MRI may provide additional information. Nodes harbouring fibrotic tissue after chemotherapy or radiation are hypointense on T2-weighted images, while those bearing tumour are hyperintense. MRI is excellent for distinguishing vessels from nodes, as flow voids are seen in vascular structures. Lymphangiography is more sensitive at depicting abnormalities in internal architecture, but it is performed with decreasing frequency given the patient discomfort it causes. Lymphangiography is also limited in the evaluation of pelvic lymphadenopathy, given the deep drainage patterns of the pelvic nodes. Also, image-guided fine-needle aspiration has partially replaced the diagnostic role of imaging.

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