9 Radiologic Evaluation of Vascular Malformations
Vascular malformations of the head and neck included in the International Society for the Study of Vascular Anomalies (ISSVA) classification are categorized into four major types: capillary malformation (CM), venous malformation (VM), lymphatic malformation (LM), and arteriovenous malformation (AVM). This system is based on the work published by Mulliken and Glowacki in 1982 and adopted by the ISSVA during its 1996 workshop. 1 The CMs, VMs, and LMs are considered slow-flow malformations, whereas AVMs are high-flow malformations. Combined malformations such as mixed venous LMs also occur and can be identified by the presence of multiple malformation elements.
Magnetic resonance imaging (MRI) is the mainstay for the imaging of VMs of the head and neck. The vast array of imaging sequences available with MRI, along with the multiplanar capability of MRI and the ability to assess contrast enhancement with gadolinium contrast agents, are ideal for differentiating the tissue characteristics unique to each of the vascular malformations. Computed tomography (CT) is a useful adjunct imaging technique for assessment of the adjacent osseous structures and for the identification of phleboliths.
The first goal of imaging is to determine whether the lesion is a VM as opposed to a hemangioma, congenital cyst, or other vascular tumor and to categorize the lesion into one of the four major types. This is accomplished by assessing the anatomical location and extent of the lesion, the presence or absence of prominent internal blood vessels, the presence or absence of phleboliths, the presence or absence of bone involvement with abnormal lysis or sclerosis, the enhancement characteristics, and the solid versus cystic nature of the lesion. Also important is defining the extent of the lesion, with particular emphasis on proximity to the airway, orbital contents, and major nerves such as the facial nerve. Involvement of the mandible or maxilla can also be crucial with respect to dental disease and potentially life-threatening hemorrhage, complicating dental extraction.
Additional roles for radiologic imaging include identifying other occult lesions, assessing for potential complications such as lesional hemorrhage or thrombosis, establishing a baseline examination, and assessing responses to therapy.
9.2 Capillary Malformations
The CMs include port-wine stains and telangiectasias; CMs typically affect the skin and subcutaneous tissues. The port-wine stain or nevus flammeus, is a slow-flow lesion characterized by a clinically apparent, well-circumscribed region of purplish skin discoloration and thickening. On radiologic imaging, these CMs may be occult or appear as an asymmetric region of enhancing cutaneous and subcutaneous soft tissue thickening ( Fig. 9.1 ).
A small percentage of patients with port-wine stains have Sturge-Weber syndrome (encephalotrigeminal angiomatosis). This syndrome is characterized by the presence of a CM in the distribution of one or more dermatomes of the trigeminal nerve in association with a pial angioma. The cerebral cortical tissue affected by the pial angioma will often develop typical tram-track calcification over time. Aberrant deep cortical venous drainage toward the ipsilateral lateral ventricle may also be present, with associated engorgement of the lateral ventricular choroids plexus. In addition, patients with Sturge-Weber syndrome who have an upper eyelid nevus flammeus typically have retinal choroidal angiomas ( Fig. 9.2 ). 2
9.3 Venous Malformations
The VMs are slow-flow vascular malformations that are present from birth but may enlarge over time, often becoming clinically apparent in later years. 3 These malformations consist of endothelial-lined venous lakes lacking a smooth muscle layer. On MRI, VMs are well-defined lesions that are usually of intermediate signal on T1-weighted imaging and increased signal on T2-weighted imaging. These lesions enhance after intravenous gadolinium administration with a variable pattern, which can fill in over time ( Fig. 9.3 ). The enhancement is the imaging feature that most distinguishes VMs from LMs, as well as from other congenital cystic masses of the head and neck.
Although VMs can occur anywhere in the head and neck, there is a propensity for facial involvement, and these lesions may be found in the lips, masticator space, parapharyngeal space, buccal space, tongue, or intramuscularly. 4 There is a propensity for involvement of the masseter muscle. VMs can also be multispatial, tracking along normal vascular pathways ( Fig. 9.4 ). Intraosseous involvement, although not a typical feature, can occur. 5
Phleboliths are present in almost 50% of VM’s and when present are pathognomonic. 6 Although these can be seen with MRI as focal signal voids, they are best visualized with CT, where they appear as lamellated calcifications ( Fig. 9.5 ). 7 It is important to distinguish between focal signal voids on MRI representing phleboliths in a VM and prominent vascular flow voids, which are typically absent in VMs. The presence of prominent vascular flow voids would be indicative of a high-flow lesion, such as an AVM or hemangioma ( Table 9.1 ).
Cutaneous and subcutaneous
Enhances, may fill in over time
Only periphery or septations enhance
Patchy ill-defined enhancement
Skin and subcutaneous
Well-defined lesion, cystic, may have fluid levels
No well-defined lesion, soft tissue swelling
Well-defined lesion, solid
Adjacent bone may be hypertrophic
May occur with hypertrophy of bone
May be involved with lytic lesions
High unless there is internal hemorrhage
Usually low but may be high from blood or lipids
Abbreviations: CM, capillary malformation; VM, venous malformation; LM, lymphatic malformation; AVM, arteriovenous malformation.