Primary lymphedema may occur as an isolated congenital defect (simple congenital lymphedema) or as the familial Milroy disease (heredofamilial congenital lymphedema), resulting from agenesis or hypoplasia of lymphatics. Secondary or obstructive lymphedema stems from the accumulation of interstitial fluid behind an obstructed, previously normal lymphatic; such obstruction can result from the following disorders or conditions:
Tumors involving either the lymphatic channels or the regional lymph nodes
Surgical procedures that sever lymphatic connections (e.g., axillary lymph nodes in radical mastectomy)
Regardless of the cause, lymphedema increases the hydrostatic pressure in the lymphatics distal to the obstruction and causes edema. Chronic edema in turn may lead to deposition of ECM and fibrosis, producing brawny induration or a peau d’orange appearance of the overlying skin (as may occur in the skin overlying a breast carcinoma). Eventually, inadequate tissue perfusion may lead to skin ulceration. Rupture of dilated lymphatics, typically following obstruction by an infiltrating tumor mass, can lead to milky accumulations of lymph in various spaces designated chylous ascites (abdomen), chylothorax, and chylopericardium.
Tumors of blood vessels and lymphatics include benign hemangiomas (extremely common), locally aggressive http://ebooksmedicine.net
Table 10.5 Classification of Vascular Tumors and Tumor-Like Conditions neoplasms that metastasize infrequently, and rare, highly malignant angiosarcomas (
Table 10.5
Vascular neoplasms arise either from endothelium (e.g., hemangioma, lymphangioma, angiosarcoma) or cells that support or surround blood vessels (e.g., glomus tumor). Primary tumors of large vessels (aorta, pulmonary artery, and vena cava) occur infrequently and are mostly sarcomas. Although a benign hemangioma cannot by confused with an anaplastic angiosarcoma, “gray-zone” lesions of uncertain malignancy are sometimes observed. Congenital or developmental malformations and non-neoplastic reactive vascular proliferations (e.g., bacillary angiomatosis) can also manifest as tumor-like lesions that may present diagnostic challenges. In general, benign and malignant vascular neoplasms are distinguished by the following features:
Benign tumors usually are composed of vascular channels filled with blood cells or lymph that are lined by a monolayer of normal-appearing ECs.
Malignant tumors are more cellular, show cytologic atypia, are proliferative, and usually do not form well-organized vessels; confirmation of the endothelial derivation of such proliferations may require immunohistochemical detection of EC-specific markers.
Ectasia is a generic term for any local dilation of a structure, while telangiectasia is used to describe a permanent dilation of preexisting small vessels (capillaries, venules, and arterioles, usually in the skin or mucous membranes) that forms a discrete red lesion. These lesions can be congenital or acquired and are not true neoplasms.
• Nevus flammeus (a “birthmark”), the most common form of vascular ectasia, is a light pink to deep purple flat lesion on the head or neck composed of dilated vessels. Most ultimately regress spontaneously.