Vascular Malformations

Abstract

Vascular malformations (VM) are anomalies in the morphological development of the vascular system. Vascular malformations differ from hemangiomas and benign vascular tumors because a lack of endothelial cell proliferation is present at birth, are often diagnosed due to their exacerbation, and do not regress spontaneously (Table 15.1).

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Diagnosis and Clinical Findings

Vascular malformations (VM) are anomalies in the morphological development of the vascular system. Vascular malformations differ from hemangiomas and benign vascular tumors because a lack of endothelial cell proliferation is present at birth, are often diagnosed due to their exacerbation, and do not regress spontaneously (Table 15.1).

Table 15.1 Difference between hemangioma and vascular malformation

Classification

Vascular malformations are classified according to the predominant vessel abnormality: capillaries, veins, arteries, lymphatic system, or a combination of the above. Moreover, they could be classified according to their hemodynamic characteristics as high-flow or low-flow malformations. The former corresponds to arterial malformations (macrofistulas or microfistulas via the nidus); the latter includes the veins, lymphatic system and capillaries.

Classification according to hemodynamic characteristics makes it possible to plan the best treatment options (Table 15.2).

Table 15.2 Classification and treatment of vascular malformation

Clinical Findings

The main clinical findings of arteriovenous malformations are: esthetic impairment, compression of vascular and nervous structures, pain, ulceration, decreased function of the affected extremity, venous stasis, ischemia, skeletal abnormalities, localized consumptive coagulopathy and risks of bleeding during surgery. These clinical findings are due to the enlargement of the arteriovenous malformation, and exacerbation can follow trauma, sepsis or hormonal changes.

Diagnosis

Non-invasive imaging modalities, such as Color Doppler UltraSound (CDUS), CT-angiography (CTA), and Magnetic Resonance (MRA), are mainstays in treatment planning. In fact, treatment is planned according to the classification of each patient’s conditions as high-flow or low-flow lesions basing on imaging findings.

High-flow lesions could be treated either with transarterial embolization or surgical excision or a combination of these; low-flow lesions are treated with percutaneous sclerotization or laser therapy.

CDUS is a first-line imaging technique for arteriovenous malformation followed by CTA and/or MRA. Digital subtraction angiography (DSA), due to its invasiveness, is mainly performed to guide treatment.

Imaging and Reporting

Patient Preparation

• Patient in a prone or supine position depending on the location of the lesion;

• Peripheral venous access (22–20 G), positioned in the contralateral upper arm with respect to the lesion location in order to avoid artifacts;

• Removal of movable dental prostheses and all metallic objects;

• Surface coil.

Technical Aspects of CTA

Arteriovenous malformations are typical at CTA, being inhomogeneous and hypodense in non-enhanced scans, with typical enhancement after contrast media injection depending on the type of malformation (early, delayed).

CTA enables the evaluation of the extent of the vascular malformation, but with a lower contrast resolution and radiation exposure in comparison with MRA (Fig. 15.1).

Fig. 15.1

38-year-old male patient complaining of palpable swelling of the left latero-cervical region. a CTA in the coronal plane depicts an intramuscular arteriovenous malformation involving the left sternocleidomastoideus muscle (arrow). b T2 FSE sequence in the coronal plane shows the anatomical relation of the lesion with the surrounding structures (arrow). c MRA demonstrates both the arterial feeders and venous drainage of the lesions (arrow)

Technical Aspects of MRA

MRA is an excellent imaging method for the evaluation of vascular malformations for its capability to define the anatomical relationship between the lesion and surrounding structures (muscles, bones, tendons, nerves, airways).

The examination protocol involves: T1 and T2 weighted Fast Spin-Echo (FSE) sequences with and without fat suppression for anatomical evaluation and 3D T1 weighted time-resolved sequences before and after contrast medium administration (Fig. 15.2).

Fig. 15.2

13-year-old female patient with a vascular malformation involving the left parotid space; a T2 FSE weighted sequence with fat suppression depicts hypointense areas inside the lesion suggestive of intralesional thrombosis (arrow). b T1 weighted GRE sequence acquired in the delayed phase shows how the lesion is only partially enhanceing, and thus classified as low-flow

Arteriovenous malformations are usually hypointense or isointense in T1 weighted sequences (with a heterogeneous signal in the case of thrombosis or bleeding), and hyperintense in T2 weighted sequences with hypointense areas usually related to thrombus, internal septa or phlebitis. (Tables 15.3, 15.4). In case of bleeding, the signal in both T1 and T2 weighted sequences changes in relation to the state of hemoglobin degradation (Table 4.7 in chapter 4).

Table 15.3 Signal characteristics of vascular malformations at MRI

Table 15.4 CEMRA protocol and technical parameters

To adequately classify hemodynamic characteristics of vascular malformations, time-resolved 3D T1 weighted sequences are needed. The use of monophasic or biphasic vascular imaging, or non-enhanced vascular sequences (Time of Flight and Phase Contrast) is not indicated, because only time-resolved sequences enable evaluation of the physiology of the flow.

Key Points for Reporting

• 1) Identify the nidus of the malformation, describing its extent, localization and dimensions;

• 2) Evaluate its relationship with surrounding structures (muscles, bones, tendons, nerves, airways) in order to clarify a possible clinical manifestation and guide eventual surgical excision;

• 3) Identify the origin, morphology and caliber of arterial feeders (Fig. 15.3);

• 4) Identify the venous drainage of the nidus and its pathways, and evaluate the presence of venous spaces and flow voids in non-enhanced sequences;

• 5) Classify the arteriovenous malformation as high-flow or low-flow in order to schedule the patient for a transarterial embolization session or in combination with percutaneous sclerotization;

• 6) Evaluate the presence of thrombosis.

Fig. 15.3

32-year-old female patient complaining pain in the left forearm. a-c Time-resolved MRA shows a huge vascular malformation involving the left shoulder and forearm (arrow). Arterial feeders originate in the subclavian and forearm arteries. d-f High resolution T1 weighted sequences show the whole extent of the vascular malformation (star)

Differential Diagnosis

The differential diagnosis between arteriovenous malformations and arteriovenous fistulas is fundamental. The main difference is that, in the first case, communication between the arterial feeders and venous drainage is via a nidus, while in the second case, the arterial and venous beds are directly connected.

Moreover, arteriovenous fistulas are often traumatic or iatrogenic (biopsy, surgical intervention) and have larger dimensions (Fig. 15.4, Fig. 15.5).

Fig. 15.4

35-year-old male patient. a-c Time-resolved MRA demonstrates the presence of an arteriovenous fistula between the right renal artery and vein. The latter is markedly dilated and associated with an enlarged inferior vena cava. d CTA obtained in the arterial phase confirmed the presence of the fistula. e VR view gives a better evaluation of the fistula dimensions. f DSA confirms arteriovenous fistula (arrow) and consequent venous dilation. Due to the high flow of the fistula and its large size, endovascular treatment was not possible and the patient underwent nephrectomy

Fig. 15.5

45-year-old female patient. CTA obtained in the arterial phase demonstrates an arteriovenous fistula between the celiac trunk and the spleno-mesenteric confluence that appears markedly dilated

Treatment

Treatment of arteriovenous malformations may be surgical, endovascular and/or percutaneous.

Quite often the surgical approach, although it enables radical excision, must be avoided due to the localization of the lesion and the high risk of bleeding.

Interventional procedures alone or in association with surgery are planned based on the hemodynamic characteristics of the lesions. A percutaneous approach is preferred for low-flow arteriovenous malformation; whereas in cases of high-flow arteriovenous malformations, an endovascular approach, sometimes combined with a percutaneous approach, is preferred. Usually more treatment steps are needed because during follow-up the recruitment of new feeders (neoangiogenesis) from the nidus is often demonstrated.

Percutaneous treatment involves direct puncture of the lesion’s nidus and subsequent injection of 95% ethyl alcohol or 2% aetoxisclerol (either foam or liquid); treatment is performed with needles of differing calibers (18–25 G). Prior to sclerotization, digital subtraction venography must be performed in order to study the possibility of venous drainage of the nidus; treatment must be performed only when direct injection into the nidus is possible, avoiding systemic spreading of embolization agent.

Endovascular treatment, usually via the common femoral artery, is performed with selective or even superselective embolization of the nidus feeders by using Onyx®, Polyvinyl alcohol particles or cyanoacrylate (Figs. 15.6, 15.7).

Fig. 15.6

39-year-old male patient with swelling of the left suprascapular region. a DSA confirms the presence of a voluminous high-flow vascular malformation fed by the superior thyroid artery (yellow arrow). The venous drainage nidus is a tributary of the internal jugular vein (red arrow). b Embolization of all feeder branches (yellow arrow) was performed with 4 mL of Onyx®-34 (Micro Therapeutics, Irvine, CA, USA)

Fig. 15.7

19-year-old male patient with a low-flow vascular malformation involving the right lips. Percutaneous sclerotization is carried out with a 21 G needle by injecting 95% ethyl alcohol (arrow)

Post-procedural complications include pain, edema, swelling, skin ulceration, and non-target vessel embolization.

The imaging methods employed during follow-up do not differ in terms of technical aspects from preoperative methods.

Reporting must focus on the dimensions and extent, by identifying:

• shrinkage of the nidus as a technical success;

• possible changes in the hemodynamic characteristics (new feeders);

• the presence of thrombosis inside the nidus, which is a direct consequence of treatment (Fig. 15.8).

Fig. 15.8

32-year-old female patient; MRA follow-up 1 month after endovascular treatment. a-c Time-resolved MRA shows delayed filling of the vascular malformation. (arrow) d T2 weighted sequences demonstrate a shrinkage in the size of the vascular malformation. e,f High-resolution T1 weighted sequences show treatment-related focal thrombosis (large arrow); a portion of the vascular malformation is slightly augmented (asterisk) and the intracortical vessel is hypertrophic (arrow head)

Clinical Cases

• Figs. 15.9–15.11 show vascular malformation of the right maxillary and mandibular region.

• Figs. 15.12–15.14 describe a high-flow vascular malformation involving the left forearm and wrist.

• Figs. 15.15–15.17 demonstrate a high-flow vascular malformation of the right hemi-face with associated ectasia corresponding to the right mandibular arch.

Fig. 15.9

21-year-old male patient with a vascular malformation involving the right maxillary and mandibular regions. a-d Time-resolved MRA shows the nidus to be fed by both the internal maxillary and facial artery and their branches (arrow). e Involvement of the mandibular region (arrow head). f,g Delayed phase high-resolution T1 weighted sequences show the enhancement of the venous component of the nidus (asterisk)

Fig. 15.10

a,b DSA of the right carotid artery that confirms no significant arterial feeders to the vascular malformation, thus classifying it as low-flow. (arrow) c Percutaneous sclerotization was then performed (arrow head)

Fig. 15.11

Post-operative time-resolved MRA (a-d) and T2 weighted (e asterisk) sequences demonstrate volumetric shrinkage of the vascular malformation. High-resolution T1 weighted sequences (f,g) depict the presence of multiple intralesional thrombi due to treatment (arrow head)

Fig. 15.12

18-year-old female patient. a-c Time-resolved MRA shows a high-flow vascular malformation involving the left forearm, fed by all three forearm vessels. d,e Flow to the nidus is very high, recruting blood from the contralateral arm and from the last two fingers (arrow head); highresolution T1 weighted sequences demonstrate the involvement of intraosseous branches in the radius (f) (large arrow)

Fig. 15.13

DSA confirms the presence of a high-flow vascular malformation involving the left forearm and wrist. a,c The nidus is fed by the interosseous artery that appears hypertrophic and tortuous. b,d After superselective catheterization of the interosseous artery, embolization is performed by injecting 3 mL of Onyx®-34 (Micro Therapeutics, Irvine, CA, USA). Completion angiography demonstrates complete exclusion of the principal feeder of the nidus (arrow head)

Fig. 15.14

Six-month CEMRA follow-up: the vascular malformation appears unchanged. a-c Time-resolved MRA clearly shows the presence of other arterial feeders and dilated venous drainage (arrow). d,e highresolution T1 weighted sequences confirm the involvement of the radius (arrow head and arrow). e,f No evidence of intralesional thrombosis (large arrow)

Fig. 15.15

12-year-old female patient. (a,c) Time-resolved MRA shows a high-flow vascular malformation involving the right face with associated venous ectasia at the level of the right mandibular arch. Arterial feeders originate in the lingual and mandibular arteries. Venous drainage is flows into the internal jugular vein

Fig. 15.16

DSA confirms the origin of the arterial feeder (lingual and mandibular arteries) and the pathway of venous drainage (internal jugular vein). a Digital subtraction angiography. b Angiography without digital subtraction. Nidus embolization is performed with a combined trans-arterial and transvenous approach, using coils and Onyx®-34 (Micro Therapeutics, Irvine, CA, USA). c Completion angiography demonstrates the complete exclusion of the nidus

Fig. 15.17

Six-month follow-up: time-resolved MRA obtained in the sagittal phase and contrast-enhanced T1 weighted images obtained in the axial plane confirm the complete exclusion of the nidus of the vascular malformation