9 Vascular Malformations

With an incidence of 1.5% in the general population,⁷ vascular malformations (VMs) should not be among the “zebra diseases” that are missed because the initial impression favors a less exotic diagnosis. Potentially serious conditions can develop in young adults due to ignorance of the natural history of VMs, causing possible interventions to be postponed to adulthood or even withheld. This is due partly to a past philosophy of therapeutic nihilism, frequent confusion with hemangiomas, and the bewildering variety of eponymous syndromes named for the authors who first described them.

For years now, color duplex sonography (CDS) has been widely available for the investigation of arterial, venous, and lymphatic diseases and has greatly influenced the diagnosis and management of complex vascular disorders. This particularly applies to VMs for which CDS has become the first-line imaging study at centers experienced in the treatment of VMs.^{3 ,​ 10 ,​ 19 – 21}

9.2 Etiology and Pathogenesis

VMs are always congenital. They are vascular anomalies, present at birth, that may present initially with subtle clinical manifestations. Patients may show a steady progression of pathologic changes, or there may be a variable latent period before the VM manifests in later life. Precipitating factors, called triggers, may consist of local trauma, surgery in the affected area, or hormonal changes related to puberty or pregnancy. No instances of spontaneous regression are known.

Circumscribed VMs may be mistaken for hemangiomas, especially in infants and small children, as their clinical features are sometimes similar.⁹ Hemangiomas, however, are always benign tumors that result from endothelial proliferation; hence, they are not vascular malformations, but vascular neoplasms based on the primary sprouting of blood vessels or elements of the vessel walls.¹⁷

9.3 Differential Diagnosis

The most common vascular tumor is infantile hemangioma, which occurs after birth, usually goes through a proliferative stage lasting several months, then undergoes a gradual regression or involution that is usually complete by 5 years of age (Fig. 9.1).¹ The involution stage of hemangioma may be followed by variable but persistent residual changes.¹² The need to differentiate VMs from hemangiomas (Table 9.1) is based on differences regarding the best treatment option and the timing of treatment. Note that while infantile hemangioma is not congenital, there are two congenital forms of hemangioma that are present and fully developed at birth. One form, called rapidly involuting congenital hemangioma (RICH), undergoes a rapid regression during the first year of life. The other form, called noninvoluting congenital hemangioma (NICH), does not regress and grows in proportion to the body growth of the child.²³ Details on the pathogenesis and treatment of hemangiomas are beyond our present scope.

Table 9.1 Main differentiating criteria between vascular tumors (infantile hemangioma) and vascular malformations

Interdisciplinary communication about these potentially complex disorders is made difficult by the variety of synonymous terms, differences in their historical evolution, and the continued use of eponymous syndrome names despite recent diagnostic discoveries. These traditional eponyms convey no information on the etiology, anatomy, or pathophysiology of the complex disorders, and currently they are no longer used except for certain combined VMs such as Klippel-Trenaunay syndrome or Parkes-Weber syndrome.⁴

The Hamburg classification was developed in 1988 to address this issue.² It has proven successful in practical use² and has gained general acceptance.^{5 ,​ 12} This system divides VMs into six main groups (Table 9.2).

Table 9.2 Modified Hamburg classification of vascular malformations (Based on Lee and Villavicencio¹²)

The Mulliken classification provides an important adjunct to the Hamburg classification by differentiating the hemodynamic characteristics of VMs¹⁶ (Table 9.3).

Table 9.3 Low-flow versus high-flow malformations: the Mulliken system (Based on Mulliken²⁸)

McCuaig summarized the advanced classification of vascular anomalies for the International Society for the Study of Vascular Anomalies (ISSVA) since 2014.²⁸

9.5 Pathophysiology

Our understanding of the pathophysiology of VMs is based on the development of the human vascular system, which starts as an undifferentiated capillary plexus that assumes a reticular structure during the initial weeks of development. As embryogenesis proceeds, it develops to a final truncular stage with differentiation into arterial, venous, and lymphatic vessels. According to their appearance, venous malformations are the most common representative of vascular anomalies (70 %), followed by lymphatic malformations (12 %), arteriovenous (AV) malformations (8 %), combined malformation syndromes (6 %), and capillary malformations (4 %).²⁷

The development of extratruncular malformations is characterized by the persistence of mesenchymal reticular cells, which are angioblasts with the capacity for growth and proliferation. After birth, any of the trigger events noted above can induce the spread of mesenchymal feeder vessels past organ boundaries into muscle tissue or bone, for example.

Truncular malformations, on the other hand, result from a developmental disturbance that occurs after vascular differentiation is complete. It may involve the persistence of embryonic vessels such as a marginal vein (Fig. 9.14) or may take the form of stenosis, aplasia, hyperplasia, or aneurysmal malformations of vessels with an anatomically normal position.

The subdivision into truncular and extratruncular malformations applies to the predominant types listed in Table 9.2, each of which may occur as local or diffuse variants.^{7 ,​ 12}

9.5.1 Truncular Malformations

Truncular malformations without shunts may occur in several forms:

•Aplasia, hypoplasia, or obstruction: The vessel proximal and/or distal to the stenosis may show aneurysmal dilatation. The collateral vessels are dilated and tortuous. Histologic examination shows hypoplasia or hyperplasia of the vessel walls.

•Dilatation: It may be localized (aneurysm) or diffuse (megadolichoartery, phlebectasia, lymphectasia). The vessel wall may be thinned or thickened. Long venous segments are often avalvular.

Truncular AV malformations may include the presence of deep AV shunts (direct communication of arterial and venous trunks) or superficial AV shunts (connections between arterial branches and superficial venous trunks). Combined truncular malformations display all possible combinations of arterial and venous changes or combinations of dysplastic blood vessels and lymphatics.

9.5.2 Extratruncular Malformations

These malformations may occur with or without shunts and may show an infiltrative or expansile type of growth.

•Infiltrative form: Most infiltrative lesions are AV; purely venous malformations are less common. The changes may be localized or diffuse. Histology shows severely altered dysplastic vessels within the infiltrated tissue, often with subtle AV communications (nidus theory).

•Localized form: This form may consist of ectatic and tortuous vessels with AV connections. Others consist of cavernous or spongy spaces that do not have AV shunts, but which may show expansile growth. Combined malformations contain dysplastic blood vessels and lymphatics.¹⁸

9.6 Examination Technique

9.6.1 Goals

An effective diagnostic workup of congenital VMs should address four main points²²:

•Type of malformation: Determination of the type of malformation is important for making a prognosis and for planning further diagnosis and treatment.

•Anatomic location: Localization should include determining whether the malformation is single or multiple and defining its relationship to neighboring organs. Also, a working diagnosis is essential for communicating and consulting with other colleagues.

•Qualitative and quantitative hemodynamic changes: These include the shunt volume, steal effects, and changes in peripheral resistance (AV connections).

•Secondary effects of the malformation: It is common to find infiltration of organs, joints, and soft tissues with associated functional disturbances. Secondary effects may also be important in disability evaluations, for example.²¹

9.6.2 Necessary Equipment

▶ Transducer. We routinely use a 7.5-MHz linear array transducer. It provides high spatial resolution, has sufficient penetration depth for most examinations, and is particularly useful for the detection of smaller vessels. Certain portions of the thigh, calf, and groin require a 5-MHz linear array transducer, or a 3.5-MHz sector transducer may be needed for a larger field of view. A 3.5-MHz sector transducer is recommended for deep lesions in the gluteal region and for abdominal vessels. A 17-MHz linear array transducer provides excellent near-field resolution for superficial imaging and can display even the finest blood vessels with very low flows.

▶ Coupling medium. We apply a thick layer of ultrasound gel to minimize probe pressure. This provides good acoustic coupling without having to press the probe against the skin. With this technique, we can trace even superficial vessels that would otherwise be easily compressed. Malformations in the hands or fingers can be imaged without any pressure in a warm-water bath (Fig. 9.2).

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