Fig. 2: Infantile capillary hemangiomas on contrast enhanced MR in two patients. (a) Hemangioma of the left shoulder (arrow) and (b) the right shoulder (arrow).
80% of patients have a solitary cutaneous lesion, with the remaining 20% having multiple cutaneous lesions. A patient with multiple lesions (eg >= 5) is at higher risk of having visceral hemangiomatous involvement, with the most common visceral sites involved being the liver, lungs and gastrointestinal tract, in that order. Appearance on MR varies depending on stage of growth of the hemangioma. In all instances, these mass lesions are uniformly and markedly hyperintense on T2WI, they have numerous large-caliber flow voids, and are high-flow lesions on time-resolved imaging. Post-contrast sequences demonstrate uniform contrast enhancement (Fig. 2, 3). During the involution phase, these lesions shrink in size, and linear regions of T1 hyperintensity are identified on non-fat suppressed T1WI due to fibrofatty tissue proliferation. Progressive loss of lesion vascularity is also noted.
Arteriovenous Malformations
Arterial malformations, arteriovenous malformations, and arteriovenous fistulas make up the high-flow vascular malformations. Arterial malformations include congenital arterial ectasias, atresias, aneurysms, or coarctations. An arteriovenous malformations (AVM) is a diffuse or localized collection of abnormal arteries and veins with multiple microscopic vascular fistulas and absence of the normal intervening capillary bed. An arteriovenous fistula is comprised of a localized shunt from large arterial branches to nearby veins and may be related to prior venipuncture/arterial puncture or trauma.
Fig. 3: Congenital hemangioma of the thigh, hyperintense on axial T2WI (a) and isointense to muscle on axial T1WI TSE (b). Note large flow void (arrow), with numerous additional smaller flow voids. Nearly uniform enhancement on CE T1 FS GRE (c). Consecutive coronal MIPs of time resolved MRA (TA=7 sec) demonstrating preferential arterial flow to left lower extremity with tortuous enlarged left iliac/femoral arteries (d); early lesion and dilated tortuous draining vein enhancement on subsequent series (e).
Like other malformations, these high-flow malformations can be either focal or diffuse, though they often are diffuse when involving the extremities. As a result of high flow, they can result in tissue overgrowth and associated limb length discrepancies, a finding which can occasionally be seen with high-flow hemangiomas. However, unlike hemangiomas, there is no associated soft tissue mass, though surrounding small enhancing vessels within arteriovenous malformations may rarely simulate a true mass. Clinically, a palpable thrill or audible bruit may be appreciated, and the overlying skin may be warm to the touch.
MR imaging will reveal a tangle of numerous, and dilated flow-voids, with preferential flow to the involved region. This high-flow state can lead to marked supplying arterial tortuousity and kinking (Fig. 4). Early venous enhancement can always be appreciated on time-resolved imaging. While diffuse enhancement may be present owing to enhancing small vessels within the AVM nidus, a true focal soft tissue mass is usually not present.
Fig. 4: Arteriovenous malformation. Warm, enlarged extremity with palpable thrill (a). SSFSE demonstrating multiple flow voids (b). Coronal MIPs of time-resolved 3D CE MRA delineating high-flow diffuse AVM with enlarged and tortuous feeding arteries and draining veins (c, d).
Venous Malformations
Venous malformations are the most common symptomatic vascular malformation of the extremities. They tend to be identified at or near birth, though they may present later; all vascular malformations will grow proportionally with the child, though infection, hormonal changes and hemorrhage can result in temporary increases in lesion size, thus bringing them to clinical attention. Complications not only include hemorrhage but also thrombosis and thrombophlebitis. Venous malformations, which have in the past been called cavernous hemangiomas, may also be associated with either a localized or generalized consumptive coagulopathy. They have many presentations, from isolated congenital venous varicosities and dilatations to localized spongy masses; they may be localized or diffusely infiltrating in nature. Unlike hemangiomas, superficial venous malformations are usually soft and easily compressible bluish-hued lesions that can blanch with manual compression. Thrombi and phleboliths can occasionally be physically palpated.
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