Post-thrombotic aneurysmal dilatation of the hypogastric vein

Clinical History

Young male active drug intravenous user, currently on maintenance therapy with methadone, with chronic hepatitis C virus liver disease treated with interferon plus ribavirin, and long-standing history of lower limb thrombophlebitis.
Currently hospitalized because of fever, superinfected skin ulcer at his right calf. Elevated C-reactive protein and plasma D-Dimer assays.

Imaging Findings

Five years earlier ultrasound (Fig. 1) diagnosed chronic venous thrombosis of the right lower limb from the popliteal to the common femoral vein.
Currently, multidetector CT (Fig. 2) requested to investigate sepsis and suspected deep venous thrombosis showed a well-demarcated ovoid mass lesion with 30-35 Hounsfield units attenuation abutting the right obturator muscle. The lesion compressed the urinary bladder, did not infiltrate adjacent structures, and enhanced homogeneously and synchronously with venous vessels. Multiplanar reconstructions (Fig. 2f-h) confirmed the lesion to be consistent with aneurysmal dilatation of the right hypogastric vein, measuring 5.5x3x3 cm, probably secondary to recurrent thrombophlebitis. The inferior cava, common and external iliac veins did not show abnormal dilatation nor thrombosis. Arteriovenous communications and compressing masses were excluded.
The patient improved with antibiotics and wound care. Surgical repair was excluded considering absence of symptoms and complications.
Ultrasound follow-up (Fig. 3) showed unchanged shape and size and absent thrombosis of the venous aneurysm.

Discussion

Very uncommon compared to their arterial counterparts, venous aneurysms (VA) may be developmental (perhaps related to weakness of elastic fibers in the vein wall) or acquired in origin, and mostly occur in the extremities (particularly at the popliteal site), the neck and central thoracic veins, and the splenic-portal-mesenteric system in descending order of frequency [1] .
In the iliac system VAs have been sporadically reported, often in association with congenital or post-traumatic arteriovenous malformations (AVM, approximately 50% of cases), proximal flow obstruction (17%), pregnancy or cardiovascular anomalies which increase flow and/or pressure within the venous system. Primary VAs without AVM, prior trauma or inflammatory disease are extremely rare. The hypogastric artery is the least frequently reported site [2-8].
Iliac VAs ma be asymptomatic and detected incidentally, or manifest with venous thrombosis, chronic venous insufficiency, abdominal pain or mass. Although the natural history and clinical significance of iliac VAs remain unclear, these rare abnormalities may occasionally present or be complicated by potentially life threatening events such as thrombosis, embolism, or rupture [2-8].
As exemplified by this occurrence in a patient with long-standing history of lower limbs thrombophlebitis and infections, multidetector CT represents the most reliable modality to detect and correctly characterize VAs as venous structures. The cross-sectional imaging appearance of these rare abnormalities is segmental venous dilatation with enhancement paralleling that of the other veins in the same system, sometimes with intraluminal opacification defects consistent with partial thrombosis. Use of intravenous contrast and awareness of this entity are necessary to avoid misinterpretation as lymphadenopathy, retroperitoneal or adnexal cystic tumours, lymphoceles, urinomas, or arterial aneurysms, which may result in dangerous procedures such as biopsy [5,6, 8,9].
Due to the rareness, therapeutic guidelines and indications for surgery have not been established. Low-risk cases are treated with anticoagulation and elastic compression measures. Surgical treatment should be considered given the potential risk for developing thromboembolic complications or compression on adjacent structures. Repair is mandatory following rupture or thrombosis. Surgery generally involves tangential aneurysmectomy plus lateral venorraphy or venous patch, since re-establishing the venous continuity is required to prevent post-phlebitic syndrome. Histology of some operated VAs described preservation of all three mural layers with medial thinning and thickened fibrotic intima, without inflammation [1, 4, 5].

Differential Diagnosis List

Final Diagnosis

Uncomplicated post-thrombotic aneurysm of the right hypogastric vein.

URL:	https://eurorad.org/case/13432
DOI:	10.1594/EURORAD/CASE.13432
ISSN:	1563-4086