The purpose of this study is to determine the exact position of a mesh which is placed in underlay position in umbilical hernia in vitro. The investigators want to gain information if the mesh lays directly next to the abdominal wall fascia or if there´s fat tissue between mesh and fascia. Furthermore they hope to get some information about the tissue incorporation.

The literature tells to supply umbilical hernia with a mesh, that overlaps 5-6 cm in each direction. To achieve this overlap an extensive taxidermy is necessary, which causes a big operation trauma. An umbilical hernia is an extended physiological stoma and compared to an incisional hernia has no risk to rip further. Therefore the researchers act on the assumption that this generous overlap is not necessary. For a short time there is a new mesh available, which combines all the necessary requirements as elasticity, effective porousness and a structure of monofilaments with MRI visibility. In a randomised clinical trial two sorts of meshes, a conventional PVDF(polyvinylidene fluoride) mesh (DynaMesh-CICAT) and a MRI visible PVDF(polyvinylidene fluoride) mesh (DynaMeshVisible) shall be compared.The investigators postulate that there is no difference between the two groups concerning complications, relapse and life quality after 4 weeks and 12 months. Altogether the goal of the study is to determine the exact position of the mesh in vitro.

The study design is a double-blinded, multicentric randomised controlled study. The radiologist and the examiner are blinded. It will be reported according to the CONSORT Statements.

The eligibility criteria is written anywhere else. The operation results after an single shot antibiotics in open method. The access happens via a semicircular infraumbilical cut. There will be prepared until the linea alba and the umbilical hernia orifice to display the hernia gap and the hernia sac. If there´s only a fat prolapse, it will be removed by ligation. If there´s an peritoneal hernia sac, the content will be repositioned and the hernia sac will be removed. The preperitoneal space will be prepared bluntly and the peritoneum will be released from the rectus sheath. A 4-6 cm trimmed mesh with a central thread will be inserted in underlay position. The central thread is used for orientation. The hernial gap will be closed in transversal direction with absorbable threads. After the reinsertion of the navel the region of the operation will be closed with subcutaneous und intracutaneous seams.

The randomisation succeeded via block randomisation at a ratio of 1 to 1. A randomisation list with SAS®-Makros "Randomisation Tables" by M. Stout is already created. There is one list for Wuerzburg and one for Kitzingen. In total there are 72 assignments created, instead of 50. But upon consultation the recruitment will be stopped after the 50th patient. According to the calculations of the epidemiological departement of the University of Wuerzburg there are 22 patients needed in each arm, that means 44 patients in total to reach the confidence interval. The patient data will be imported to EuraHS. This data entry is based on the ethics committee vote of the medical departement of Wuerzburg dated the 31th of july 2012 (application number 256/11) and the renewal of the 21st of july 2015.

If there´s an increased complication rate in one of the groups or the morphology of the MRI-visible meshes is found unsatisfactory the study will be cancelled.

The patient data will be recorded via pseudonyms.

Inclusion Criteria:

• umbilical hernia > 0,4 cm; <= 3 cm
• BMI > 20; < 51

Exclusion Criteria:

• emergency operation
• previous abdominal operation
• epigastric hernia in more than 3 cm distance of the umbilical hernia
• ascites
• hepatic insufficiency
• periumbilical skin disease
• incisional umbilical hernia
• claustrophobia
• contraindications concerning the MRI examination