To assess the role of IVUS in

1. Providing diagnostic important data as: luminal diameters, cross-sectional area, assessment of potential thrombus volume which enables optimal choice of appropriate angioplasty technique, endovascular device guidance, and their impact on procedural technical success and patency rates.
2. comparing diagnostic accuracy of intravascular ultrasound (IVUS) with multiplanar venography and CT venography for iliocaval obstruction.

Acute and chronic venous disorders of the lower extremities affect millions of people and cause substantial disability. Surgeons and pathologists identified the presence of 'spur-like' abnormalities of the left common iliac vein, these abnormalities were hypothesized to result from compression and/or irritation from the adjacent crossing right common iliac artery. In the 1990s, physicians, starting to perform catheter-directed thrombolysis to treat extensive deep vein thrombosis (DVT), observed that about 50% of patients had an iliac vein stenosis.Treatment is aimed at ameliorating the symptoms and, whenever possible, at correcting the underlying abnormality. Graduated compression is the cornerstone of modern therapy. Deep system disease is often refractory to treatment, but superficial system disease can usually be treated by ablating the refluxing vessels. Effective venous return from the lower extremities requires the interaction of the heart, a pressure gradient, the peripheral muscle pumps of the leg, and competent venous valves. In the absence of pathology, this system functions to reduce venous pressure from approximately 100 mm Hg to a mean of 22 mm Hg within a few steps.

Nonthrombotic venous compression patients with left common iliac vein compression can present in the 2nd or 3rd decade of life and are more common in women. Patients can have limb pain, limb swelling, ipsilateral chronic venous insufficiency, lipodermatosclerosis, recurrent superficial venous thrombophlebitis, and venous claudication.

Thrombotic iliofemoral venous compression with a predisposing anatomic configuration with a prothrombotic physiological state can present with acute pain and swelling of the left lower extremity consistent with an acute iliofemoral DVT mostly phlegmasia cerulea dolens . In the acute phase, patients with a patent foramen ovale can also present with a pulmonary embolism, cryptogenic stroke, with or without pulmonary embolism, or systemic arterial embolism.

The abnormalities in venous physiology associated with chronic venous disease, and their quantification by diagnostic tests, are also considerably more complex than for PAD. With CVD one must gauge the effects of obstruction and/or reflux in a vascular bed uniquely designed to return venous blood to the heart against gravity with the aid of a peripheral muscle pump and in phase with respiratory mechanics.

Duplex ultrasound (DUS) is initial diagnostic test. The criteria include: poststenotic turbulence, as indicated by a mosaic velocity profile, abnormal Doppler signal at the area of stenosis, continuous flow with the Valsalva maneuver, and sluggish with no spontaneous flow and poor augmentation and no respiratory phasicity. But there is limitations as obesity ,casts, dressings, open wounds, Patients with severe edema/swelling and limited patient mobility.

Cross-sectional imaging includes computed tomographic venography (CTV) with venous phase contrast or magnetic resonance venography (MRV).

Catheter-based phlebography traditionally is considered to be the most definitive technique for the evaluation of venous obstruction, supplemented with direct pressure measurements across an area of perceived stenosis in order to determine whether a pressure gradient exists.

Intravascular ultrasound (IVUS) uses a catheter-based ultrasound probe that enables high-resolution evaluation of the vein wall and internal venous architecture in 360. IVUS is more sensitive than phlebography for the detection and characterization of iliac vein pathology. This would be expected since IVUS gives a 360 image versus a single plane image shown by standard phlebograms. Intravascular ultrasound also identifies intraluminal trabeculations, septations, webs, and wall thickening, which can be minimized or missed on standard phlebography, plus reduced radiation exposure in contrast to other modalities.

IVUS is better in evaluating lesion morphology, accurate assessment of luminal dimensions, transmural lesion characteristics. Delineation by IVUS of the spatial distribution of the lesion in a concentric or eccentric pattern and the presence of a soft (fibrous) or hard (calcified) plaque may influence the choice of endovascular therapy as well as predict the risk of immediate or late complications (ie, perforation, thrombosis, restenosis). Evaluation of lesion volume before and after the procedure by IVUS provides a quantitative method to estimate the amount of lesion debulking or displacement and a reference point from which to assess the lesion recurrence/restenosis. IVUS also fulfills many of the necessary requirements of a guidance system for endovascular procedures, namely precise delivery and positioning of stents within target lesions. IVUS is particularly helpful in assessing the relationship of the ostia of branch vessels to the lesion that can be used as landmarks during procedures.

Inclusion Criteria:

• 1-acute iliocaval obstruction 2-chronic iliocaval obstruction with CEAP clinical class 3-6 3- acute on top of chronic iliocaval obstruction with CEAP clinical class 3-6 4-symptomatic acute femoro-iliocaval occlusion who underwent successful thrombolysis

Exclusion Criteria:

1 - concomitant peripheral arterial disease in the affected limb. 2-life expectancy less than 5 years. 3- pregnancy 4- malignancy 5-raised renal chemistry 6-pelvic fibrosis 7- contraindication to anti-coagulation therapy. 8-congenital venous malformations 9-Not providing informed consent 10-Any concurrent disease as heart failure

subjects with with acute or chronic iliocaval obstruction CEAP classification 3-6.