Accurate characterization of vascular anomalies is important in predicting clinical course and guiding treatment. This article provides an imaging review of vascular anomalies, highlighting the particular imaging characteristics of hemangiomas and malformations. Discussed are the appropriate imaging modalities for the evaluation of the anomalies and the associated abnormalities that require further investigation.
Key points
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Vascular anomalies can be divided into two groups, tumors and malformations, on the basis of biologic behavior.
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Types of vascular tumors include infantile hemangioma and kaposiform hemangioendothelioma. Infantile hemangioma is seen as a well-defined mass with fast flow, whereas kaposiform hemangioendothelioma has poorly defined, infiltrative margins and is strongly associated with Kasabach-Merritt phenomenon.
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Low-flow malformations include venous and lymphatic malformations. LM can be subdivided into macrocystic, which demonstrate peripheral and septal enhancement, and microcystic, which appear more solid.
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Fast-flow vascular malformations include arteriovenous fistula and arteriovenous malformation. In arteriovenous fistula, there is a direct connection between the artery and vein, whereas in arteriovenous malformation, an intervening nidus is seen. Neither has an associated mass.
Introduction
Vascular anomalies comprise a diverse group of conditions in the pediatric and adult age group. The subject is often complicated by the use of improper descriptive terminology. Although the biologic classification proposed by Mulliken and Glowacki in 1982 and later adopted by the International Society for the Study of Vascular Anomalies substantially helped to resolve this dilemma, vague terminology continues to be used in the clinical setting and medical literature. Accurate characterization of vascular anomalies is crucial in predicting the clinical course, prognosis, and need for intervention. It is therefore important to adhere to a standard classification system in clinical assessment and radiologic characterization.
Mulliken and Glowacki divided vascular anomalies into two groups: hemangiomas and malformations, with the first category later expanded to include multiple vascular tumors in addition to hemangiomas. This distinction is based on endothelial cell characteristics. Vascular tumors consist of proliferating cells with increased mitotic activity. Malformations arise from abnormal vascular channels in the absence of abnormally proliferating endothelium.
Infantile hemangiomas (IH) are the most common type of vascular tumor; however, they must be distinguished from other vascular tumors including rapidly involuting congenital hemangiomas (RICH), noninvoluting congenital hemangiomas (NICH), kaposiform hemangioendothelioma (KHE), and tufted angioma.
Vascular malformations can be further divided into slow-flow, fast-flow, and mixed lesions. Slow-flow lesions include capillary, venous, and lymphatic malformations (LM). Fast-flow lesions are arteriovenous malformations (AVM) and arteriovenous fistulas (AVF).
Introduction
Vascular anomalies comprise a diverse group of conditions in the pediatric and adult age group. The subject is often complicated by the use of improper descriptive terminology. Although the biologic classification proposed by Mulliken and Glowacki in 1982 and later adopted by the International Society for the Study of Vascular Anomalies substantially helped to resolve this dilemma, vague terminology continues to be used in the clinical setting and medical literature. Accurate characterization of vascular anomalies is crucial in predicting the clinical course, prognosis, and need for intervention. It is therefore important to adhere to a standard classification system in clinical assessment and radiologic characterization.
Mulliken and Glowacki divided vascular anomalies into two groups: hemangiomas and malformations, with the first category later expanded to include multiple vascular tumors in addition to hemangiomas. This distinction is based on endothelial cell characteristics. Vascular tumors consist of proliferating cells with increased mitotic activity. Malformations arise from abnormal vascular channels in the absence of abnormally proliferating endothelium.
Infantile hemangiomas (IH) are the most common type of vascular tumor; however, they must be distinguished from other vascular tumors including rapidly involuting congenital hemangiomas (RICH), noninvoluting congenital hemangiomas (NICH), kaposiform hemangioendothelioma (KHE), and tufted angioma.
Vascular malformations can be further divided into slow-flow, fast-flow, and mixed lesions. Slow-flow lesions include capillary, venous, and lymphatic malformations (LM). Fast-flow lesions are arteriovenous malformations (AVM) and arteriovenous fistulas (AVF).
Imaging
Although the diagnosis can sometimes be made clinically, radiologic assessment is often helpful in the management of vascular anomalies, particularly for atypical or deep lesions, and is important for treatment planning. Ultrasound (US) and magnetic resonance imaging (MRI) are the mainstay of imaging vascular anomalies, with limited roles for radiography and computed tomography (CT).
US is a relatively accessible, noninvasive modality that can be performed in the often young patient population without sedation or ionizing radiation. With gray-scale imaging, the vascular anomaly can be characterized as cystic, composed of channels, or as a solid mass with well or poorly defined margins. Calcifications can be identified as echogenic foci with posterior shadowing. With Doppler imaging, one can assess for the presence and distribution of blood flow to the lesion. Spectral waveforms can determine if the flow is arterial or venous, and assess for the presence of shunting. Skin lesions should be imaged with a high-frequency linear transducer, although deeper lesions necessitate lower-frequency transducers.
MRI is superior to US in evaluating the extent of the lesion, including the tissue planes and adjacent structures involved. Routine sequences include short time inversion recovery (STIR)/T2-weighted images with fat saturation (FS), which for most vascular anomalies provide sharp contrast between the lesion and normal tissue. Depending on the appearance of these fluid-sensitive sequences, T1-weighted FS postcontrast images may be useful to assess perfusion to the anomaly. MR angiography (MRA) is sometimes helpful in the assessment of fast-flow vascular anomalies. Techniques include noncontrast imaging angiography using two-dimensional time-of-flight or phase-contrast imaging, or dynamic imaging with gadolinium-enhanced time resolved MRA, which allows the arterial and venous phases to be imaged separately, demonstrating feeding arteries, draining veins, and location of shunts. Large vessels can be imaged using spin echo (SE) sequences, where they appear as signal voids, or gradient recall echo (GRE) sequences, where vessels are bright. GRE images also demonstrate calcification and blood products, either from bleeding of the anomaly or from thrombus.
Radiographs may be used to assess the bony changes associated with vascular anomalies. These are almost always related to malformations rather than hemangiomas and include periosteal reaction, well-defined lucent lesions in the bone, leg length discrepancy, and overgrowth of the affected side. CT is largely reserved for accurate evaluation of bone destruction.
Vascular tumors
Infantile Hemangiomas
Background and clinical presentation
IH are the most common tumors of infancy, with risk factors including fair skin, prematurity, and female gender. They are most commonly found in the head and neck region, followed by the trunk, then the extremities. Subtle skin findings are sometimes present at birth, although in most cases the diagnosis is made at 2 to 4 weeks of age. IH then typically undergo a 6- to 8-month period of rapid growth in neonatal life, plateauing at 10 to 12 months, followed by a period of involution lasting 1 to 7 years.
The cutaneous manifestation depends on the depth of the tumor, with superficial lesions appearing raised and red (“strawberry appearance”), whereas the overlying skin can be normal with deeper lesions.
Radiologic imaging
Ultrasound
The US appearance of IH depends on whether it is in the proliferating to plateau phase or the involuting phase. In the earlier phases, it appears as an echogenic, well-circumscribed soft tissue mass. Gray-scale imaging can occasionally demonstrate anechoic channels, corresponding to the high-flow vessels. Color Doppler imaging is better at demonstrating the vascularity, with high vessel density seen (five or more vessels in a square centimeter), and arterial and venous waveforms obtained ( Fig. 1 A, B). Involuting IH are rarely imaged because they are unlikely to present a diagnostic dilemma at that stage, but have been described as isoechoic, difficult to differentiate from adjacent soft tissues, and with no demonstrable blood flow.
Magnetic resonance imaging
The MRI appearance of IH also depends on its stage of growth. During the proliferative and plateau phase, they are seen as focal, lobulated soft tissue masses that are isointense to muscle on T1-weighted images, hyperintense on T2-weighted images, and demonstrate homogeneous enhancement (see Fig. 1 C–F). SE and GRE sequences demonstrate enlarged high-flow vessels within the mass, although intralesional flow voids may be difficult to discern in early infancy. These features can help to distinguish IH from other tumors, such as sarcomas, which tend to enhance heterogeneously, and have a more random distribution of vessels.
Histologically, involuting IH are replaced by fibrofatty tissue. This is reflected in their MRI appearance, where they follow the signal intensity of the surrounding fat. There is also a decrease in enhancement and visualized vessels.
Angiography
Angiographically, IH appear as well-circumscribed masses, with a lobular pattern of intense tissue staining. They are supplied by slightly enlarged but otherwise normal branches of systemic arteries, demonstrate a distinct tumor blush, and are drained by small veins that communicate with dilated but otherwise normal local veins. Typically, no direct AV shunting is seen within the mass.
Imaging associations
In certain cases, additional imaging is required to screen for other potential anomalies. The presence of five or more cutaneous hemangiomas raises suspicion for the presence of visceral, particularly liver, hemangiomas. These infants should be screened by US or MRI. Large cervicofacial hemangiomas in a “beard” distribution are associated with subglottic airway hemangiomas, which in addition to direct imaging by endoscopy can be imaged MRI, CT, and high-resolution US. Large facial hemangiomas are associated with PHACE syndrome. Those in the lumbosacral region are associated with spinal anomalies including tethered cord, spinal lipoma, and intraspinal hemangioma, and with SACRAL and LUMBAR syndromes ( Table 1 ).
| Syndrome | IH Distribution | |
|---|---|---|
| PHACE | Posterior fossa brain malformation Hemangiomas Arterial anomalies Coarctation of the aorta and cardiac defects Eye abnormalities | Large, facial |
| LUMBAR | Lower body IH and other skin defects Urogenital anomalies and ulceration Myelopathy Bony deformities Anoretal malformations, Arterial anomalies Renal anomalies | Extensive of lower half of body, often involving entire limb |
| SACRAL | Spinal dysraphism Anogenital Cutaneous Renal and urologic anomalies, associated with an angioma of lumbosacral localization | Perineal |
Treatment and complications
Because IH spontaneously involute, most do not require treatment. However, medical therapy may be indicated if the location of the hemangioma compromises vision or the airway. Currently, the first line of treatment is oral administration of propranolol or steroids. In addition, if multifocal hepatic hemangiomas are identified, thyroid-function testing should be performed as soon as possible. The triiodothyronine deiodinase produced by these tumors peripherally deactivates T3 and these infants often require large doses of thyroid hormone replacement for correction. Intralesional injections, embolization, and resection are generally reserved for a small minority of hemangiomas causing significant cosmetic deformity or cardiac failure.
Congenital Hemangiomas
Clinical presentation
In contrast to IH, CH reach their maximum size at the time of birth and can sometimes be diagnosed prenatally. Unlike IH, there is no gender predilection and the tumors do not test positive for glucose transported protein 1. CH demonstrate two patterns of clinical progression. Most undergo rapid postnatal involution, resolving by 14 months of age, as a RICH. Alternatively, the CH never regresses and continues to grow proportionately with the child, and is called NICH. Some of the lesions demonstrate initial rapid decrease in size and then plateau and remain unchanged. Therefore, it is possible that NICH represents a later stage of RICH in some patients.
CH are usually solitary and often involve the head or the limbs near a joint. The involved skin is usually blue or violaceous, with telengiectasias; a pale peripheral halo is more characteristic of NICH than RICH.
Radiologic imaging
Ultrasound
The sonographic findings in CH are often similar to IH, with a fast-flow soft tissue mass seen in both cases ( Fig. 2 ). Features more suggestive of CH are heterogeneity, calcifications, and increased conspicuity of intralesional vessels.
RICH and NICH cannot initially be easily distinguished from each other by US. However, as they involute, RICH are characterized by tortuous compressible channels demonstrating venous flow. These correspond to the histologic finding of thin-walled drainage channels separated by fibrous tissue. NICH are more likely to demonstrate microshunting, manifested as increased turbulence or pulsatility in the venous waveforms.
Magnetic resonance imaging
CH are isointense on T1- and hyperintense on T2-weighted images, with intense enhancement after contrast administration. They are more likely to have heterogeneous enhancement and poorly defined borders than IH, although they still lack surrounding edema, which can be seen in more aggressive lesions ( Fig. 3 ). On SE and GRE sequences, feeding and draining vessels can be seen.
Angiography
NICH demonstrate arterial feeding vessels, with tumor-like capillary blush. They have dilated draining veins as can be seen with AVF or AVM ( Fig. 3 ). However, unlike these entities, NICH do not demonstrate early venous drainage.
Because of their natural history, RICH are less likely to be assessed angiographically, but do demonstrate inhomogenous parenchymal staining; large, irregular, and disorganized feeding arteries; direct AV shunts; and intravascular thrombi.
Complications and treatment
Because of the rapid involution in most RICH cases, no treatment is required. In a few cases, there is redundant skin after involution with central fissuring and ulceration, which necessitates surgical resection. NICH are surgically resected.
Kaposiform Hemangioendothelioma
Background and clinical presentation
KHE is a rare vascular lesion that can be congenital, with 50% presenting at birth in one series, but can also present later in childhood. They grow rapidly, and are locally aggressive, but have been seen to spontaneously regress. There is no gender preference. They often involve the trunk, extremities, retroperitoneum, and rarely the cervical/facial region. The overlying skin is red to purple in color with a rim of ecchymosis, and is warm and edematous to palpation. Importantly, there is a frequent association with Kasabach Merritt phenomenon (KMP), a consumptive coagulopathy, with 90% of cases of KMP occurring secondary to KHE.
Ultrasound
On US, KHE has variable echogenicity. The margins are ill defined, a major distinguishing characteristic from IH ( Fig. 4 A, B). They may also contain foci of calcification, a feature not seen in IH. Although there have been reports of decreased vessel density compared with IH, color Doppler imaging characteristics cannot reliably differentiate the two lesions.
On MRI, KHE are seen as soft tissue masses that are hypointense to isointense to muscle on T1-weighted images, and heterogeneously hyperintense on T2-weighted images. They are infiltrative, extending to involve multiple tissue planes, with ill-defined borders, stranding in the subcutaneous tissues, and overlying skin thickening. On postgadolinium T1-weighted images, the tumor demonstrates a strong reticular enhancement pattern, corresponding to the same pattern seen on T2-weighted images ( Fig. 4 C–E). Associated prominent vascular channels are seen either on postcontrast images or as flow voids on SE sequences. Compared with IH where the size of the feeding and draining vessels is proportional to the size of the tumor, the vessels of KHE are small relative to tumor size. KHE may contain hemosiderin, blood products, or fibrosis, which are best demonstrated on GRE images.
Complications and treatment
There is significant mortality associated with KHE, ranging from 10% to 30%, with the rate higher for retroperitoneal tumors. This is caused by the sequela of local invasion and the high association with KMP. The mainstay of treatment is medical therapy with agents including vincristine, corticosteroids, ticlopindine, interferon-α, and propranolol. Surgical resection may be possible in localized cases.
Slow-flow vascular malformations
Venous Malformation
Background and clinical presentation
VM are congenital malformations characterized by dilated venous channels deficient in smooth muscle. These channels also lack normal valves and have stagnant flow. VM may take many different forms, ranging from varicosities and ectasias to complex channels and localized spongiform masses.
Like all vascular malformations, they are present at birth. VM do not regress and grow proportionately with the patient, with periods of enlargement during puberty and pregnancy because of hormonal influence. On physical examination, VM are soft, compressible, and nonpulsatile. The overlying skin may be normal or have a bluish tinge. Maneuvers that increase venous pressure (dependant position, crying, Valsalva) cause them to increase in size. VM most commonly involve the head and neck, followed by the extremities, with truncal involvement less frequently seen. Although skin involvement is common, VM can extend to or have isolated involvement of muscle, bone, and abdominal organs.
Radiographic imaging
Ultrasound
There is a varied US appearance of VM that reflects the different morphologies of this entity, ranging from the hypoechoic or heterogeneous spongiform appearance of localized cavernous spaces, to anechoic vascular channels of dysplastic veins ( Fig. 5 ). When Doppler flow is present, it is monophasic, low-velocity flow. Twenty percent of VM show no flow on Doppler imaging because of either undetectably slow flow or true lack of flow secondary to thrombosis. In this case, the lack of cystic cavities can help distinguish them from LM. Phleboliths can be seen as hyperechoic, shadowing foci.
