Simulation of cellular packing in non-proliferative epithelia.

The physical laws governing the morphogenesis of biological tissues remain largely misunderstood. In particular, the role of the mechanical interactions occurring in this process needs to be better understood and studied. Inner follicular cells surrounding the oocytes of Ciona intestinalis form an epithelial monolayer resulting from an accretion process (without mitosis or apoptosis). This epithelium is elementary and useful for morphogenesis studies: the cells exhibit polygon packing with a specific but non-systematically repeatable topology (i.e. the distribution of pentagons, hexagons and heptagons changes). To understand the role of mechanical forces in tissue formation, we propose an innovative "2D spherical" model based on the physics of divided media. This approach simulates the cellular mechanical behavior and epithelium structuration by allowing cells to adopt a large variety of shapes and to self-organize in response to mechanical interactions. The numerical parameters considered in the model are derived from experimental data in order to perform pertinent and realistic simulations. The results obtained are compared to biological observations using the same counting method to characterize epithelium topology. Numerical and experimental data appear close enough to validate the model. It is then used for exploratory studies dealing with "Tissue Development Speed" variation, which is not easily attainable by experimentation. We show that the formation speed of the tissue influences its topology and hence its packing organization.

Mechanical model of cytoskeleton structuration during cell adhesion and spreading.

The biomechanical behavior of an adherent cell is intimately dependent on its cytoskeleton structure. Several models have been proposed to study this structure taking into account its existing internal forces. However, the structural and geometrical complexities of the cytoskeleton's filamentous networks lead to difficulties for determining a biologically realistic architecture. The objective of this paper is to present a mechanical model, combined with a numerical method, devoted to the form-finding of the cytoskeleton structure (shape and internal forces) when a cell adheres on a substrate. The cell is modeled as a granular medium, using rigid spheres (grains) corresponding to intracellular cross-linking proteins and distant mechanical interactions to reproduce the cytoskeleton filament internal forces. At the initial state (i.e., before adhesion), these interactions are tacit. The adhesion phenomenon is then simulated by considering microtubules growing from the centrosome towards transmembrane integrin-like receptors. The simulated cell shape changes in this process and results in a mechanically equilibrated structure with traction and compression forces, in interaction with the substrate reactions. This leads to a compressive microtubule network and a corresponding tensile actin-filament network. The results provide coherent shape and forces information for developing a mechanical model of the cytoskeleton structure, which can be exploitable in future biomechanical studies of adherent cells.

[Cancer of the gastric antrum. What can be expected from the systematic enlargement of the excision? Retrospective study of 73 cases]. / Cancers de l'antre gastrique. Que peut-on attendre de l'élargissement de principe des exérèses? Etude rétrospective de 73 cas.

The results of 73 consecutive curative resections for adenocarcinoma of the gastric antrum (37 distal subtotal gastrectomies and 36 electively extended total gastrectomies) are presented. The location and size of the tumour and the degree of lymph node involvement were similar in both groups (excluding superficial carcinomas), but the patients with subtotal gastrectomy were significantly older than the others (mean age : 70.5 and 59 years respectively). The operative mortality rate was 13.6% in each group, but the post-operative hospital stay was longer for total gastrectomy patients. The five-year survival rate overall (including operative deaths) was 44.3%. There was no difference in survival rate between the two types of operation (49.7% for subtotal, and 45.6% for total gastrectomy, operative deaths excluded). Survival was related to the degree of parietal spread and nodal involvement. These results are in favour of subtotal gastrectomy for antral adenocarcinoma.

[Left internal paraduodenal hernia: a case in a young adult]. / Hernie interne paraduodénale gauche: une observation chez l'adulte jeune.

The authors report the case of a left paraduodenal hernia which involved almost the entire small intestine in a 15 year old girl who presented with recurrence episodes of acute abdominal pain associated with König's syndrome. Radiologic examination (plain film of the abdomen and upper GI series with small bowel follow-through) was suspicious, but did not establish the diagnosis due to unfamiliarity with the radiologic appearance of the condition. The roentgenograms are shown as well as the intraoperative findings. Anatomic, pathophysiologic, clinical, and radiologic characteristics are reviewed.

[Surgery for excision of malignant duodenocolic fistulas. Review of the literature apropos of a case]. / La chirurgie d'exérèse des fistules duodéno-coliques malignes. Revue de la littérature à propos d'un cas.

Malignant duodenocolic fistula is nearly exclusively the fact of carcinoma of the hepatic flexure; it is one of the most uncommon and particular evolutive complication, because of its rapid nutritional disturbances and difficult surgical management. The authors report the case of a 78 year old man, still alive 18 months after a one staged right colectomy and pancreatico duodenectomy. The analysis of 26 others cases from literature treated with the same procedure or, most frequently, with right colectomy and partial duodenectomy allows to discuss indications and results of radical surgery: though it is possible at least in half cases, it represent a much better functional solution compared to complex by-pass procedures: more over its seems to be prognostically justifiable: out of 23 curative resected patients in this series, 6 at least (26%) are still alive from 9 to 26 years after.

[Duodenal varices. Review of the literature apropos of a case]. / Les varices duodénales. Revue de la littérature à propos d'une observation.

The authors report a case of digestive hemorrhage secondary to isolated duodenal varicosities, in a patient with ethylic cirrhosis. The diagnosis done through optical fibroscope was confirmed by arteriography. The evolution was unfavorable. Lesions were corroborated by autopsy. A review of the literature is done, about the 22 cases already published. With the help of these cases to authors stress the points that can lead to the good diagnosis and what therapeutical management should be done.

[Digestive complications of radiotherapy of gynecologic cancers: therapeutic possibilities]. / Les complications digestives de la radiothérapie des cancers gyécologiques : possibilités thérapeutiques.

It appears that there are a certain number of complications in the digestive tract that still occur in spite of improvements in techniques of irradiation therapy. They may only appear a few months or even a few years after the treatment, and sometimes they only appear when the initial growth is considered to have been cured. The clinical picture is dominated by the appearance of fistulae, of adhesions and of stenoses which give rise to sub-acute or sometimes acute obstructions. From the anatomical point of view all elements of the digestive tube are affected with a predominance of the fibro-hyaline elements of the muscles and the arteries. The possibilities for surgical treatment are limited. Excision with anastomosis would seem to be more risky than diversion. We have had to operate on ten of our eleven patients, of whom six died and only one of these directly because of recurrence of the initial growth. Only prevention can lessen the mortality of these severe complications.

[Digestive endometriosis. Current concepts]. / L'endométriose digestive. Conceptions actuelles.

Endometriosis involving the digestive tract accounts for 1% of all cases of the disease. There is a marked predominance in the recto-sigmoid and terminal ileal loops. Symptomatology is dominated by disturbances in intestinal transit, sub-occlusion or acute obstruction, pain worsening at the time of menstruation and by a haemorrhagic rectal discharge again accompanying menstruation. Apart from classical aetiopathogenic theories such as grafting onto the digestive tract by tubal, lymph vessel or venous propagation, it would appear that prostaglandins and in particular a change in the (formula; see text) ratio may play a large role. Operative resection of localised stenosis combined with oophorectomy, if the latter is possible in view of the patient's age, or prolonged medical treatment with progestational agents or even better Danazol results in cure and avoids recurrences.