Computed tomography of the retroperitoneal space

Aneurysms

Ectasia or aneurysms of the abdominal aorta usually develop as a result of atherosclerosis. They are often accompanied by mural thrombus formation. The abdominal aorta is considered aneurysmally altered when the expansion of the free lumen of the vessel reaches 3 cm or the external diameter exceeds 4 cm. In asymptomatic patients, surgical intervention is usually justified if the aneurysm diameter reaches 5 cm. The patient's general condition and the rate of expansion are assessed. The risk of aneurysm rupture with bleeding is reduced if the free lumen of the vessel is located centrally, and thrombotic masses surround it more or less evenly from all sides.

The risk of aneurysm rupture increases if the lumen is eccentric or the vessel contour in cross-section is very irregular. Lumen dilation of more than 6 cm in diameter also increases the risk of aneurysm rupture. When planning surgical treatment, it is important to know whether and to what extent the renal, mesenteric, and iliac arteries are involved. Sudden pain often accompanies aneurysm rupture or dissection. In this case, the process can extend from the thoracic to the abdominal aorta. Dynamic CT with enhancement allows visualization of the aneurysm dissection flap.

Phlebothrombosis

In the case of thrombosis of the veins of the lower extremities, phlebography does not always clearly determine whether the thrombus has spread to the pelvic veins. The contrast agent injected into the superficial vein of the foot is often so diluted by blood that it becomes difficult to assess the lumen of the femoral/iliac veins. In this case, it is necessary to conduct a CT study with intravenous administration of a contrast agent.

The lumen width of a freshly thrombosed vein is usually at least twice the normal width. The thrombosed segment is uniformly or partially hypodense compared with the adjacent artery. In a nonocclusive lesion, the thrombus is visualized as a filling defect within the lumen of the vein. In the case shown in the images on the right, the thrombus extends through the left common iliac vein into the caudal portion of the inferior vena cava, where it is seen as a hypodense zone surrounded by contrast-enhanced blood flow. CT images of the inferior vena cava should be continued cranially until the signs of thrombosis have resolved.

When contrast medium is injected into the superficial vein of the foot, satisfactory contrast quality is observed only in the veins of the corresponding lower limb. To assess the pelvic venous network, it is more appropriate to inject contrast medium into the veins of the upper limb. If one side is occluded, collateral circulation develops through the pubic venous network. If the thrombus in the deep veins does not dissolve, it can be created surgically. You must be careful not to confuse the inguinal lymph nodes with physiologically hypodense gates ("fatty gate symptom").

To avoid the development of pulmonary embolism in inferior vena cava thrombosis, the patient must remain motionless until the thrombus is covered by endothelium or dissolved by therapy. Sometimes significant collateral circulation through the lumbar veins develops.

Depending on the size of the thrombus and individual characteristics of the process, surgical intervention may be indicated - vessel probing with thrombectomy. If the process recurs, arteriovenous shunting is performed to exclude repeated thrombosis. During subsequent monitoring of the effectiveness of the therapy, color duplex ultrasound or phlebography is usually performed.

Enlarged lymph nodes

The density of lymph nodes is about 50 HU, which corresponds to the density of muscles. Lymph nodes up to 1.0 cm in diameter are usually considered unchanged, 1.0 - 1.5 cm - borderline, more than 1.5 cm - pathologically enlarged. Enlarged lymph nodes are usually located retrocrurally, in the mesentery, between the aorta and the inferior vena cava) and paraaortically).

It is very important to know the main lymphatic drainage pathways from the pelvic organs. For example, lymphatic drainage from the gonads is carried out directly to the lymph nodes at the level of the renal hilum. In case of testicular tumor, metastases are determined in the para-aortic lymph nodes around the renal vessels, and not in the iliac ones. Whereas in case of bladder, uterine or prostate cancer, the iliac lymph nodes should be examined especially carefully.

A conglomeration of lymph nodes around the aorta and its large branches, such as the celiac trunk, is a typical feature of non-Hodgkin's lymphoma.

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