Imaging of Vascular Malformations

Recent advances in imaging have allowed a better understanding of imaging features and classification of vascular anomalies. This article focuses on imaging of vascular malformations; describes the updated classification system and clinical and imaging characteristics of the different subtypes; and discusses the associated syndromes, differential diagnosis, and available treatment options, including the role of imaging in management.

Key points

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The latest classification from International Society for the Study of Vascular Anomalies (ISSVA) divides vascular malformations into simple, combined, vascular malformations of named major vessels and syndromic vascular malformations.
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Simple vascular malformations include high-flow and low-flow vascular malformations.
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Low-flow vascular malformations include venous malformations, capillary malformations, and lymphatic malformations.
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High-flow vascular malformations include arteriovenous malformations and arteriovenous fistulae.

Introduction

Vascular anomalies (VAs) are a group of lesions that result from errors of vascular embryogenesis. VAs include vascular tumors and vascular malformations, typically present during childhood, and may involve any part of the body. They often pose a diagnostic dilemma, because of the multiplicity of appearances, wide differential diagnosis, and the various classification systems that have been proposed over the years.

The International Society for the Study of Vascular Anomalies (ISSVA) provides the most standardized and accepted classification. The ISSVA classification was first introduced in 1997 and most recently updated in 2018. This classification divides VAs into 2 major categories: (1) vascular tumors, and (2) vascular malformations. ^, Vascular tumors are true neoplasms that show rapid postnatal growth and slow regression into late childhood; these include hemangiomata and kaposiform hemangioendothelioma. In contrast, congenital vascular malformations (CVMs) do not regress or enlarge; they grow at the same rate as the child and include arteriovenous malformations (AVMs), arteriovenous fistulae (AVFs), capillary malformations (CMs), venous malformations (VMs), and lymphatic malformations (LMs). In the current version of the ISSVA classification, CVMs are divided into 4 groups: simple malformations, combined malformations, malformations of major named vessels, and malformations associated with other anomalies (syndromic vascular malformation). Based on their flow characteristics, simple vascular malformations are further differentiated into high-flow lesions (AVM and AVF) and low-flow lesions (CM, VM, LM). The 2018 version of the ISSVA classification emphasizes the known genetic mutations associated with CVM, reflecting a growing interest in the genetic basis of vascular malformations ( Tables 1 and 2 ).

Table 1

The International Society for the Study of Vascular Anomalies vascular anomalies 2018 classification

VAs
Vascular Tumors	Vascular Malformations
Benign 1 Congenital hemangioma 2 Infantile hemangioma 3 Epithelioid hemangioma 4 Spindle cell hemangioma 5 Tufted angioma 6 Pyogenic granuloma 7 Others	Simple	Combined	CVMs of major named vessels	Syndromic CVMs
	High flow 1 AVM 2 AVF	1 CM-VM 2 CM-LM 3 LM-VM 4 CM-AVM 5 CM-LM-AVM 6 Others	Anomalies of 1 Origin 2 Course 3 Number 4 Length 5 Diameter 6 Valves 7 Connection 8 Persistence (of embryonal vessel)	See Table 2
Locally malignant 1 Kaposiform hemangioendothelioma 2 Retiform hemangioendothelioma 3 Others	Low flow 1 VM 2 LM 3 CM
Malignant 1 Angiosarcoma 2 Epithelioid hemangioendothelioma 3 Others	Low flow 1 VM 2 LM 3 CM

Table 2

Clinical syndromes associated with vascular malformations

Clinical Syndrome	Vascular Malformation	Other Manifestations	Mutation
Sturge-Weber	CM; face, trigeminal nerve distribution	Gyral atrophy, glaucoma	GNAQ
Klippel-Trénaunay	CM, LM, VM; cutaneous and soft tissue	Overgrowth of soft tissue and bone, usually limited to 1 limb	PIK3CA
Parkes Weber	CM, VM, AVM; cutaneous and soft tissue	Overgrowth of soft tissue and bone, usually limited to 1 limb	RASA1
Proteus syndrome	CM, VM, LM; soft tissue ± visceral	Disproportionate progressive overgrowth of hands or feet	AKT1
Maffucci syndrome	VM; soft tissue	Multiple enchondromas in the hands and feet, ±chondrosarcoma	IDHH1/IDH2
CLOVES syndrome	CM, VM, LM, AVM	Lipomatosis, nevi, scoliosis, skeletal anomalies hands and feet	PICK3CA

Abbreviation: CLOVES, congenital lipomatous overgrowth, vascular malformations, epidermal nevi, spinal/skeletal anomalies/scoliosis.

Imaging

Gray-scale ultrasonography coupled with color Doppler imaging and spectral analysis is the initial screening imaging modality at some centers for vascular malformation given the low cost, fast and real-time information, and lack of ionizing radiation. However, ultrasonography is limited in its ability to accurately assess large and deep lesions and to detect bone involvement. Contrast-enhanced ultrasonography has been suggested for evaluation of CVMs and has been used for monitoring response to therapy, including microcirculatory changes.

Magnetic resonance (MR) imaging is the most valuable modality for imaging vascular malformation because of its high temporal and contrast resolution, which allows accurate assessment of CVMs and their relation to the surrounding structures. The ability to characterize flow dynamics by MR imaging permits differentiation of high-flow and low-flow CVMs and enables discrimination between CVMs and other vascular lesions. MR imaging has also been used for treatment planning and assessment of treatment success. A comprehensive MR imaging examination should include contrast-enhanced conventional MR imaging and dynamic contrast-enhanced MR angiography (MRA), such as time-resolved imaging of contrast kinetics (TRICKS) or time-resolved angiography with interleaved stochastic trajectories (TWIST). The protocol for vascular malformations at our institution includes triplanar T2-weighted images with fat saturation, precontrast axial T1-weighted images, and postcontrast triplanar T1-weighted images with fat saturation. Because flow characteristics (arterial, venous, both arterial and venous, none) are essential to the classification of vascular malformations, we obtain our dynamic contrast-enhanced images with a temporal resolution of 1 to 1.5 seconds to allow separation of arterial and venous phases. Other investigators have recommended optional three-dimensional arterial spin labeling sequences for hemangiomas and arteriovenous shunting as well, and diffusion-weighted imaging to rule out other lesions and tumors when the diagnosis is uncertain ( Table 3 ).

Table 3

Magnetic resonance imaging and ultrasonography findings for simple vascular malformation

	Venous	Lymphatic	Capillary	AVM	AVF
Appearance	Serpentine tubular structures or dilated channels	Septated lobulated mass, microcytic or microcytic	Skin-thickness lesion	No well-defined mass Enlarged feeding arteries and draining vein + nidus	No well-defined mass Enlarged draining vein, no nidus
T1WI	Intermediate	Low	Low	Intermediate	Intermediate
T2WI	High	High	Slight high	High	High
GRE	Intermediate	Low, intermediate, high	—	High	High
Flow voids on SE	No	No	No	Yes	Yes
Fluid-fluid levels	Uncommon	Common	No	No	No
Enhancement	No arterial or early venous enhancement, slow gradual diffuse enhancement on delayed images	Rim and septal enhancement if macrocystic; no significant or slight diffuse enhancement if microcystic	Faint subcutaneous enhancement	Early enhancement of enlarged feeding arteries and nidus with shunting to draining veins	Early enhancement of enlarged feeding arteries with shunting to draining veins, no nidus
Ultrasonography	Heterogeneous, compressible	Variable echogenicity, noncompressible	Subtle low echogenicity	Low echogenicity	Low echogenicity
Color Doppler 1 Vascular density 2 Spectral Analysis	Low Venous flow, or sometimes no flow	No or low flow in the septa Both arterial and venous flow in the septa	Low to moderate	High Arteries: high velocity, low resistance, spectral broadening Veins: pulsatile venous flow Nidus: turbulent flow	High Arteries: high velocity, low resistance, spectral broadening Veins: pulsatile venous flow
Others	Phleboliths	—	—	Calcifications	—

Abbreviations: GRE, gradient recalled echo; SE, spin echo; T1WI, T1-weighted imaging; T2WI, T2-weighted imaging.

Radiography and contrast-enhanced computed tomography (CT) are not routinely used for the diagnosis of a vascular malformation owing to the use of ionizing radiation and the lower temporal resolution compared with MR imaging; however, radiographs and CT may detect phleboliths, calcification, and bone involvement. CT may be used as an alternative imaging for patients who cannot undergo MR imaging.

Simple vascular malformations

Low-Flow Malformations

Capillary malformation

CMs, usually referred to as port-wine stain, are found in 0.5% of the population and affect the skin capillaries. They commonly present at birth as pink or red macules that do not involute. Most of these lesions involve the face and tend to be in the trigeminal nerve distribution. The lesion enlarges and darkens as a child grows older, resulting in a cobblestone appearance. Central nervous system (CNS) involvement can occur, particularly in association with lesions in the V1 or midline distribution. The risk of having Sturge-Weber syndrome increases to 25% when half of the face, including the ophthalmic division of the trigeminal nerve, is involved, and increases to 33% when both sides of the face are involved.

Most CMs can be diagnosed by a physical examination. With high-frequency ultrasonography transducers, CMs can appear as superficial hypoechoic areas that vary in depth from 0.2 mm to 3.7 mm, with increased vascularity on color Doppler imaging. ^, If MR imaging is performed, the lesion may appear as subtle signal abnormality within the subcutaneous fat with skin thickening. MR imaging and CT are helpful in evaluation for CNS involvement and may detect progressive gyral atrophy, gyral enhancement, enhancement of ipsilateral choroid plexus, and cortical calcification ( Fig. 1 ). Abnormal cortical veins and contrast stasis can be seen on cerebral angiography.