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Microlymphatics of human skin form two superposed networks. The superficial one located at the level of dermal papillae may be visualized by fluorescence microlymphography. Microlymphatics fill from a subepidermal depot of minute amounts of FITC-dextran 150,000. In primary lymphedema with late onset the depicted network with vessels of normal size is significantly larger than in healthy controls, whereas in congenital lymphedema (Milroy's disease) microlymphatics are aplastic or ectatic (diameter > 90 microns). Lymphatic microangiopathy with obliterations of microvessels develops in chronic venous insufficiency, in lipedema (preliminary results) and after recurrent erysipelata. In healthy controls microlymphatics are permeable to FITC-dextran 40,000 and impermeable to the larger molecule 150,000. Preserved fragments of the network in chronic venous insufficiency exhibit increased permeability to FITC-dextran 150,000. After visualization of the vessels by the fluorescent dye microlymphatic pressure may be measured by the servo-nulling technique. First results indicate that microlymphatic hypertension contributes to edema formation in patients with primary lymphedema.
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Fluorescence microlymphography (FML) is an almost atraumatic technique used to visualize the superficial skin network of initial lymphatics through the intact skin of man. Visualization was performed with an incident light fluorescence microscope following subepidermal injection of minute amounts of FITC-dextran 150,000 using microneedles. Emanating from the bright dye depot, the surrounding network of microvessels is filled, documentation performed by photography or video film. In congenital Milroy lymphedema, a lack of microlymphatics (aplasia) is typical while in other primary lymphedemas and in secondary lymphedema after mastectomy or irradiation of proximal lymph nodes, the network remains intact but the depicted area is enlarged. Lymphatic microangiopathy characterized by obliterations of capillary meshes or mesh segments develops in phleboedema with trophic skin changes, progressive systemic sclerosis and Fabry's disease. In lipedema, lymphatic microaneurysms are stained. Microlymphatic pressure may also be measured using FML. For this purpose, glass micropipettes are inserted into the capillaries by means of a micromanipulator and pressure is determined by the servo-nulling technique. Normal subjects produced significantly lower pressure (7.9 +/- 3.4 mmHg) compared to patients with primary lymphedema (15.0 +/- 5.1 mmHg, p<0.001). This characteristic lymphatic hypertension may be improved by complex physiotherapy or local application of prostaglandins. Additionally, a modification of the FML procedure can be used to measure lymphatic capillary flow velocity in controls and patients. FML is suited to confirm the clinical diagnosis of lymphedema, contributes to distinguish among various forms of edema, and is useful in clinical research. In addition, FML has also become a tool for experimental animal studies including the depiction of gastric microlymphatics, the measurement of flow velocity in the naked mouse tail, and in evaluation of lymphangiogenesis in a model of Milroy disease.
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"Lipedema," a special form of obesity syndrome, represents swelling of the legs due to an increase of subcutaneous adipose tissue. In 12 patients with lipedema of the legs and in 12 healthy subjects (controls), fluorescence microlymphography was performed to visualize the lymphatic capillary network at the dorsum of the foot, at the medial ankle, and at the thigh. Microaneurysm of a lymphatic capillary was defined as a segment exceeding at least twice the minimal individual diameter of the lymphatic vessel. In patients with lipedema, the propagation of the fluorescent dye into the superficial lymphatic network of the skin was not different from the control group (p > 0.05). In all 8 patients with lipedema of the thigh, microaneurysms were found at this site (7.9 +/- 4.7 aneurysms per depicted network) and in 10 of the 11 patients with excessive fat involvement of the lower leg, multiple microlymphatic aneurysms were found at the ankle region. Two obese patients showed lymphatic microaneurysms in the unaffected thigh and in only 4 patients were microaneurysms found at the foot. None of the healthy controls exhibited microlymphatic aneurysms at the foot and ankle, but in one control subject a single microaneurysm was detected in the thigh. Multiple microlymphatic aneurysms of lymphatic capillaries are a consistent finding in the affected skin regions of patients with lipedema. Its significance remains to be elucidated although its occurrence appears to be unique to these patients.
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The authors assessed the use of magnetic resonance imaging in differentiating lymphedema, phlebedema, and lipedema of the lower limb. They examined 14 patients: five with lipedema, five with lymphedema, and four with phlebedema. T1- and T2-weighted transaxial sequences were performed before administration of gadolinium tetraazacyclododecane-tetraacetic acid (DOTA) and T1-weighted spin-echo sequences were performed after administration of Gd-DOTA in each patient. Images of patients with lipedema showed homogeneously enlarged subcutaneous layers, with no increase in signal intensity at T2-weighted imaging or after Gd-DOTA administration. Patients with phlebedema had areas containing increased amounts of fluid within muscle and subcutaneous fat. In lymphedema, a honeycomb pattern above the fascia between muscle and subcutis was observed, with a marked increase in signal intensity at T2-weighted imaging. After Gd-DOTA administration, there was only a slight increase in signal intensity in the subcutis in lymphedema and phlebedema and a moderate increase in signal intensity in muscle in phlebedema.
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