Idiopathic portal hypertension (IPH) is a non-cirrhotic presinuosidal portal hypertension of unknown etiology. Stenosis of smaller portal veins with portal fibrosis is a pathologic hallmark of IPH. Association of systemic sclerosis (SSc) with IPH is recognized, and similar pathologic features are reported in small portal tracts and skin of IPH and SSc, respectively. In addition, levels of transforming growth factor-β (TGF-β) and connective tissue growth factor are elevated in serum and in affected skin and portal tracts of these two diseases, suggesting that IPH share fibrogenetic mechanisms with SSc. Endothelial to mesenchymal transition (EndMT) of microvasculatures of skin could be responsible for dermal fibrosis in SSc. In IPH, EndMT of portal vein endothelium via TGF-β/Smad activation may also be involved in small portal venpathy. In IPH, enhanced expression of pSmad2 in venous endothelium of smaller portal veins was associated with reduced CD34 expression. CD34 and S100A4, and CD34 and type I collagen were colocalized to portal vein endothelium in IPH. Such myofibroblastic phenotypes may be responsible for periportal-venous deposition of collagen and compressive portal venous obliteration. These small portal venous lesions may in turn lead to portal venous insufficiency followed by subcapsular atrophy in IPH.
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