Vascular anomaly: Inclusive term comprising hemangioma, vascular malformation, & Kaposiform hemangioendothelioma
Vascular Malformation: Abnormal clusters of blood and/or lymph vessels that occur during fetal development. Veins usually display a relative lack of smooth muscle cells in their walls. Although these lesions are always present at birth, they may not be visible until weeks or even years after birth. These lesions will typically grow in proportion to the growth of the child. Will not spontaneously involute.
Categorized as either slow flow or fast flow. Arteriovenous malformations are fast-flow lesions. Capillary, lymphatic, and venous malformations are considered slow-flow lesions. Combined malformations may be either slow or fast flow.
Hemangioma: Benign tumors of vascular endothelium. Most common tumors of childhood. Characterized by a growth phase (plateau at 9 months) and involution phase (from 1 to 5-7 years of age).
Kaposiform hemangioendothelioma: Vascular tumor associated with the Kasabach-Merritt phenomenon (severe coagulopathy due to platelet trapping and spontaneous bleeding).
- Best diagnostic clue: ↑ Vascular channels ± discrete mass ± phleboliths
- Use ultrasound to make diagnosis & assess flow
- Use MR to define extent
- Head, including intracranial, & neck (40%)
- Trunk (20%) & extremities (40%)
- ± Multifocal, uni- or multi-compartmental
- Size: < 1 cm → > 100 cm
- Morphology: From single vessel ectasia ⇒ discrete well-defined mass ⇒ large ill-defined advancing collection of anomalous vessels
- Solid intensely hypervascular mass, usually lobulated
- ± Peripheral draining veins ± feeding arteries
- Venous malformation
- Slow-flow channels ± venous lakes ± cavernous veins
- Slow or no flow on color Doppler examination
- Moving echoes on real time imaging
- ± Thrombosed vessels
- ± Venous lakes = large, irregular spaces not conforming to vascular channel
- ± Cavernous veins = more tubular
- ± Phleboliths (very common); acoustic shadowing
- Supporting stroma
- Capillary malformation
- Thickening and increased echogenicity of dermis
- Ultrasound excludes underlying vascular anomaly
- Lymphatic malformation
- Microcystic: Multiple tiny cysts within matrix
- Cysts may be too small to resolve with ultrasound, appears as solid lesion
- Largely avascular
- Macrocystic; i.e., cystic hygroma: Thin-walled, septated, fluid-filled cystic spaces
- ± Internal echoes (hemorrhage or infection)
- Largely avascular
- Arteriovenous malformation
- High velocity flow and pulsatile ± mass
- Phleboliths uncommon
- T2WI FS
- Extent of involvement well demonstrated
- Skin, subcutaneous fat, muscle, neurovascular bundle, bone, synovium
- Focal, multifocal or diffuse
- Extent may be underestimated as vascular channels not distended or thrombosed
- Low-flow: No signal voids nor large feeding arteries
- High-flow: Signal voids ± large feeding arteries
- Connection with normal vasculature
- Hemangiomas- During proliferation MRI shows a focal, lobulated soft-tissue mass that is isointense relative to muscle on T1-weighted images and hyperintense on T2-weighted images. It has diffuse and homogeneous contrast enhancement and dilated feeding and draining vessels within and around the mass may be present. During the involutional phase, decreasing vascularity, decreasing enhancement, and progressive fibro-fatty replacement of the tumor is present. Lesions adjacent to bone may cause smoothly marginated erosion of the bone. Phleboliths and calcifications are not features of hemangiomas.
- Venous Malformations- VMs are high-signal-intensity lesions on T2-weighted images and low-signal-intensity lesions on T1-weighted MRIs; they have lobulated margins and may contain rounded signal voids that represent phleboliths. The contrast enhancement pattern allows the differentiation of VMs from hemangiomas and other low-flow anomalies, particularly lymphatic malformations (enhancement is more patchy and central in VMs, whereas no enhancement or minimal peripheral enhancement is seen in LMs).
- Kaposiform hemangioendothelioma- In contrast to common hemangioma, KHE characteristically involves multiple tissue planes, with cutaneous thickening, subcutaneous stranding, and edema. Superficial feeding and draining vessels are less frequent and less prominent than with common hemangioma. Destructive osseous changes in the adjacent bones are common in KHE, whereas only some remodeling occasionally occurs in infantile hemangiomas.
Angiography usually only performed prior to embolization or sclerotherapy.
Gross Pathologic & Surgical Features
- Maffucci syndrome
- Enchondromas + soft tissue venous malformations
- Osler-Weber-Rendu syndrome
- Arteriovenous malformations in skin, mucosa, lung and brain
- Klippel-Trenaunay-Weber syndrome
- Low-flow vascular malformations ± large aberrant lateral vein ± limb hypertrophy
- Gorham-Scott syndrome
- Intraosseous venous and lymphatic malformations
- Hemangioma: More lobulated, mass-like
- Vascular malformation: More ill-defined
- Hemangioma: Plump endothelial cells, especially during proliferative phase
- Extracellular matrix contains growth promoting proteins
- Vascular malformation: Flat endothelial cells
- Patchy deficiency of smooth muscle in wall → dilatation
- Extracellular matrix does not contain growth promoting proteins
- Arteries and arterioles (with elastic lamina in walls) integral part of arteriovenous malformations
- Even histologically, distinction between vascular anomalies can be difficult
- Hemangioma: Observation, Meds (steroids, propranolol, vincristine) laser therapy, or surgical resection.
- Venous Malformation: Observation, compression garments, sclerotherapy, laser therapy, surgical resection