Vascular malformations of the orbit: hemodynamic concepts.

Vascular malformations of the orbit can best be understood within the context of their hemodynamics, of which there are three types. Type 1 (no flow) lesions have essentially little connection to the vascular system and include lymphangiomas or combined venous lymphatic malformations. Type 2 (venous flow) lesions appear as either distensible lesions with a direct and rich communication with the venous system or nondistensible anomalies that have minimal communication with the venous system. Types 1 and 2 can be combined with both features of distensible and nondistensible hemodynamics. Arterial flow lesions, type 3, include arteriovenous malformations characterized by direct antigrade high flow through the lesion to the venous side. Cavernous hemangiomas are also malformations that demonstrate direct low flow through the lesion.