By Dr Alex AL Tang, Consultant Clinical Radiologist (Interventional & Vascular), MBBS(Mal), MMed Radiology (UKM), FRCR (UK), AM (Mal).

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Systemic vascular malformation is an inborn error of vascular morphogenesis of unknown aetiology. It is believed to be the result of the arrest or misdirection of normal development of the vascular tree during vasculogenesis. There is a great deal of confusion with regard to the correct classification of this disease. Many authors showed their conceptions at a given moment in the development of angiology and hence a large number of classifications exist.
 

In general, the biological classification by Mulliken J.B¹ had been accepted as the official nomenclature used by the International Workshop of Vascular Anomalies. It is divided into two major types of vascular birthmarks based on the cellular kinetics:

1. Hemangioma, which demonstrates evidence of endothelial hyperplasia

2. Vascular malformations, with normal endothelial turnover. The vascular malformation is further subclassified into:

1. High-flow types, i.e., with the presence of arteriovenous shunting

2. Low-flow types, i.e., the capillary, venous, lymphatic and mixed varieties.

In interventional radiology, for the ease of the management and planning strategy, the high flow types are further subdivided (Houdart² et al, Neuroradiology 1993) into:

1. Arterio-venous malformation - those with less than 3 separate feeding arteries supplying a single initial venous compartment (see Figure 1a, 1b)

2. Arteriolo-venous malformation-multiple arteries shunt into a single central dilated venous compartment (see Figure 2a, 2b)

3. Arteriolo-venular malformation - multiple shunts between arterioles and venules, and the 1st identifiable normal venous compartment is separated from the shunts. (see Figure 3a, 3b)

In the management of vascular malformation, Colour Doppler ultrasound (CDU), MRI and catheter angiogram are the most useful modalities. CDU differentiates the high-flow from low-flow lesions, assess the extent of lesion and evaluate associated deep venous anomalies, e.g., venous aplasia or hypoplasia. It is a cheap and good non-invasive tool for follow up.

MRI is the most useful investigation in both initial evaluation and follow up. A fat-suppressed sequence provides the best contrast for the lesion’s extent and is able to identify a high- from the low-flow lesions (see Figure 4). It can beautifully delineate the soft tissue and bony involvement.

Categorization of the high-flow malformation (see Figure 5) is best done with catheter angiography, in order to determine the treatment strategy and best approach for the embolisation. The usefulness of MR and CT angiogram is hence debatable. Catheter angiography is not useful in pure low-flow lesions, except in venous malformation and with the intention to treat.
 

Management of vascular malformation should be done in a specialised centre with multi-disciplinary involvement. In general, the treatment option includes conservative management with a carefully supervised regime, surgical resection/reconstruction, percutaneous embolisation, laser therapy, or a combination of surgical intervention with pre-operative percutaneous embolisation.

Percutaneous embolisation (PE) is applicable in both high- and low-flow malformations. In the high-flow types, PE is the mainstay management of the deep seated lesions; especially those with multi-compartmental involvement. It is also useful in the superficial lesions for down sizing, controlling or in pre-operative purposes. The aims of PE are targeted at providing symptomatic improvement or control (e.g., pain, bleeding, size and hyperhydrosis), cosmetic improvement and in the control of high output failure. It is also aimed to prevent future complications; if possible, knowing the cure of this disease is rare.

The treatment should be a targeted approach based on the patients’ symptomatology and presentations. Many techniques can be utilized, i.e., the transarterial approach, direct sclerotherapy and transvenous embolisation. A wide range of embolic agents is utilized, namely Histoacryl (glue), Onyx, coils, silk thread, absolute alcohol, 3% sodium tetradecryl and there are others. Polyvinyl alcohol (PVA) particle has recently been found to have the property of transarterial migration through the embolised arteries after 2 weeks, resulting in recanalisation and revascularization of the AVM. It is hence, not recommended to be used as the primary embolic agent in treatment of this condition.

The primary target in embolisation is in treating the nidus, i.e., the core of the communication or at the level of the venous sac. These nidus or the venous sac should be carefully looked for and ablated with various superselective means during the PE. Proximal trunk occlusion or surgical ligation is to be avoided at all cost as distal reconstitution via collateral channels will invariably occur instantaneously. It will also narrow the margin of safety for the PE. Similarly, surgical denuding exercise of the overlying skin (of huge AVM with deep compartmental involvement) is discouraged.

PE should be a staged procedure. An interventional radiologist should avoid excessive or overzealous devascularisation and angiographic perfection at all cost in order to minimize complications. Complications of PE include post embolic syndromes, paradoxical embolisation (e.g., pulmonary embolism), neural paralysis, skin burn, infection, pain, etc. PE is a high risk procedure and should not to be tried by untrained hands.
 

1. Mulliken JB, Classification of Vascular Birthmarks. In Mulliken JB, Young AE (eds), Vascular birthmarks. Hemangioma and malformations. Philadelphia: WB Saunder, 1988.

2. Houdart et al, Neuroradiology 1993.