We introduce a concept of topological disorder line for systems with ordered internal surfaces. At one side of the line the ordered structure exhibits strong topological fluctuations, accompanied by changes in the Euler characteristics. At the other side topological fluctuations are rare. In a system of oil-water-surfactant, in the lamellar phase, the crossover between two regimes is marked by the appearance-of thin wormhole passages and their further proliferation. Close to the lamellar-microemulsion phase boundary thin wormhole passages merge leading to the formation of large channels between lamellas pierced with holes. The lamellar phase with many large "torus-like" passages strongly resembles the microemulsion phase. In order to illustrate these concepts we perform Monte Carlo simulations of the one scalar order parameter Landau-Ginzburg model of microemulsions. We show how the Euler characteristics can be effectively used in such simulations to identify different ordered phases and count the number of wormhole passages.