Tumors and tumor-like lesions of blood vessels

Abstract

Tumors and tumor-like conditions of the vascular system are divided into three categories according to their degree of malignancy: benign vascular lesions, lesions of intermediate malignancy, and malignant vascular tumors. The vast majority of the lesions belong to the benign group. These are found predominantly in younger children and adolescents. They may involve either the skin and subcutis or the deep soft tissues. Classification of these lesions is still the source of much controversy and is based on clinical appearance, pathology, embryology, and endothelial growth characteristics [12, 41, 42]. There are two major classification schemes for vascular tumors. That of Enzinger et al. [12] relies on pathological criteria and includes clinical and radiological features when appropriate. On the other hand, the classification of Mulliken and Glowacki [42] is based on endothelial growth characteristics and distinguishes hemangiomas from vascular malformations. The latter classification shows good correlation with the clinical picture and imaging findings. Hemangiomas are characterized by a phase of proliferation and a stationary period, followed by involution. Vascular malformations are no real tumors and can be divided into low- or high-flow lesions [65]. Cutaneous and subcutaneous lesions are usually easily diagnosed and present no significant diagnostic problems. On the other hand, hemangiomas or vascular malformations that arise in deep soft tissue must be differentiated from malignant neoplasms. Detailed assessment by medical imaging is necessary for adequate planning of surgery. On magnetic resonance imaging (MRI) benign vascular lesions have a characteristic configuration, generally allowing a correct diagnosis. MRI is superior to other imaging techniques in defining the extent of these lesions, which is important since some types may involve large segments of the body. Generally the classification of soft tissue vascular anomalies based on endothelial growth characteristics [66] shows good correlation with MRI appearance of these lesions [37]. Since this classification has been useful clinically [54], recognition of these characteristic MRI features is essential for improving therapeutic outcome in these patients. Vascular lesions of intermediate malignancy and malignant vascular tumors are far more rare. Hemangioendothelioma is a neoplasm of endothelial cells that can be benign or malignant. Angiosarcoma is an aggressive tumor with high local recurrence rate and risk of distant metastases. Imaging findings have only been sparse, probably due to the tendency of these lesions to involve skin and superficial tissue, in contrast to other soft tissue sarcomas. MRI is used for staging rather than for characterization of these lesions.