Anatomy of the ileum-intestinal tract of the human fetus at 16–22 weeks of ontogenesis



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Abstract

Aim – to obtain new data on the quantitative macromicroscopic anatomy of the iliac-intestinal region in the intermediate fetal period of human ontogenesis from the 16th to the 22nd week of development.

Material and methods. The study was performed on 30 subjects of both sexes (18 female and 12 male fetuses) using the following methods: macro- and microscopic preparation, N.I. Pirogov sawing, histotopographic method, morphometry, and variation-statistical methods. All the morphometric data obtained were subjected to variation-statistical processing in Windows XP-based Excel 2010 and Statistics 13.0 application software packages. When testing statistical hypotheses in this study, the critical level of statistical significance (p) was assumed to be 0.05. The Student’s t-test was used to assess the reliability. A set of tools for macromicroscopic preparation of the fetus was used.

Results. During the period of development in question, the position of the ileum has slight vertical deviations, which affects the formation and magnitude of the angle between the ileum and the cecum, as well as between the ileum and the ascending colon. The predominant shape of the cecum is cylindrical (80%), less often conical (20%). There is an uneven growth of the walls of the cecum, where the lateral wall prevails over the medial one, which is associated with the formation of flap structures. The ileo-intestinal opening is oval in shape, the frenules are weakly pronounced, with a more pronounced ileo-colon lip. Semilunar folds are differentiated on the mucous membrane of the cecum from 16-17 weeks, and a free muscle band is also determined. The omental and mesenteric bands are not pronounced. There is no morphological boundary between the appendix and the cecum. From 19-20 weeks, the presence of 1-2 gausters is noted. The quantitative parameters of the iliac-intestinal region are characterized by a gradual twofold increase in values.

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Introduction. The morphological basis for many types of pathology of the ileocecal intestine is already laid at the stage of prenatal ontogenesis [Slobodyan O.M., Pronyaev D.V., 2013; Antonenko F.F. et al. 2022; Kelsen J.R., Baldassano R.N., 2017] and affect the functioning of various systems of internal organs [Vorobyov V. V., 2004; Isakov Yu.F. Dronov A.F., 2009; Pujari A.A., Methi R.N., Khare N., 2008; Soomro S., Mughal S.A., 2013]. 
Congenital malformations of the intestine (malformation, intestinal inversion, blind-colon invagination, intestinal obstruction and atresia) account for 3-6%, of which malformations of the colon are the most common. Modern diagnostics makes it possible to clearly visualize the human fetal intestine and perform early endoscopic intestinal diagnostics in newborns and young children [Zheleznov L. M. et al., 2010; Shepelev A.N. et al., 2015, 2019; Kozlova Yu.A. et al., 2017; Nambu R., Hagiwara Si.[et al.], 2019]. 
The available data from literary sources mainly address the issues of the formation of composite formations of the ileum separately, the anatomy and morphometry of the cecum, the appendix in the fetal period of development, as well as the anatomy of the ileum angle of newborns, children and adults. There are practically no questions in the scientific literature that highlight the features of the anatomy of the iliac-intestinal tract during the fetal period of human ontogenesis as a whole. There is little information on the position of the appendix, the state and position of the ileocecal angle in the intermediate fetal period of development, there is no work on the quantitative macromicroscopic anatomy of the ileocerebral intestine in the fetal period of human ontogenesis, while the processes of formation of the ileocerebral intestine of the human fetus and the movement of the thin (from right to left, behind the superior mesenteric artery) and thick intestines (from left to right of the same artery), which is called the turn of the intestine, they end in the intermediate fetal period of ontogenesis [Rigoard P., [et al.] 2009; Ueda Y., [et al.], 2020]. From 16-20 weeks, the beginning of the functioning of the gastrointestinal tract of the fetus as a digestive organ [Sachs F.F. et al., 1994; Aminova G.G., 2001; Moldavskaya A.A., 2006; Bokonbayeva S. J. et al., 2008; Moore P., 2016, Sadler J., 2020], which is generally the basis for studying and replenishing the knowledge base on the fetal anatomy of the ileum and the prevention of many of its congenital injuries. As is known, the ileum-intestinal tract is a zone located between the small and large intestine and connects the terminal segment of the ileum, the cecum with a vermiform process and the ileum-intestinal flap (Bauginia flap), as well as the initial part of the ascending colon [Maksimenkov, A. N., 1972; Rylyuk, A. F., 1997; Poptsova T. A. et al., 2023; Kutia S.A. [et al. 2019]. This department is often accompanied by intrauterine malformations.
In this regard, the purpose of the study is determined: to obtain new data on the quantitative macromicroscopic anatomy of the iliac-intestinal region in the intermediate fetal period of human ontogenesis from the 16th to the 22nd week of its development.
Materials and methods. The entire study was performed on 30 subjects of both sexes (18 female fetuses, 12 male fetuses). Human fetal torsos from the fetal collection of the Department of Human Anatomy of OrGMU were used. The present study was conducted on the basis of the Department of Human Anatomy of the Federal State Budgetary Educational Institution of Higher Medical Education of the Ministry of Health of the Russian Federation from 2019 to 2024. The study was carried out in compliance with all ethical and legal standards. A positive conclusion of the LEK OrGMU dated 16.10.2019 No. 237 was received. The objects are divided into 3 age groups: 16-17 weeks (10 drugs), 18-19 weeks (10 drugs), 20-22 weeks (10 drugs). The selected age range almost completely corresponds to the terms of the second trimester of pregnancy and the intermediate fetal period of human ontogenesis [Kolesnikov L.L., Shevlyuk N.N., Erofeeva L.M., 2014]. According to Order No. 1130 n dated October 20, 2020 "On approval of the Procedure for providing medical care in the field of Obstetrics and Gynecology", the period of screening ultrasound of the fetus coincides with the specified gestation period. The paper uses archival material from the archive of the Department of Human Anatomy of OrGMU.
The following research methods were used in the work: the method of macro- and microscopic preparation, the method of sawing according to N.I. Pirogov in three mutually perpendicular planes, histotopographic method, morphometry method, variational and statistical methods of processing the obtained data (mean value (X), standard error of the average value (Sx), standard deviation (σ), lowest parameter value (min), highest parameter value (max), growth rate (TR) and the growth rate (TP) [Ageeva V.A., 2007], as well as the intensity of growth (IR) [Sokolov V.V., Chaplygina E.V., Sokolova N.G., 2005]. The work uses a set of tools and devices for macromicroscopic dissection of the fetal torso (a stand for dissecting the fetal torso, a magnifying magnifier and illuminated eyepieces, digital vernier calipers, a set of microscopic instruments (microscopy scissors, tweezers, scalpel and medical bayonet probe).
Results. 
When the anterior abdominal wall of the fetus is opened, a macroscopic examination of the zone of the ileum and the intestinal tract clearly identifies the site of transition from the terminal ileum to the caecum, the caecum with a vermiform appendix and the ileum opening (Figure 3-4). The position of the iliac-intestinal region has a slight deviation vertically (deviates somewhat laterally). In addition, the area of the iliococcal (ileocecal) angle is well suited for studying and conducting macroscopy and measurements. 
During the observation period, in the majority of observations (80%), the ileum enters the lumen of the cecum, obliquely, or the direction of entry is defined as horizontal with an angle of 90 ° (in 20% of observations). In the fundus area, the cecum passes into a vermiform process in the medial direction (75% of observations) or laterally (15%) without a clear boundary. 
A tight contact is determined between the medial wall of the cecum and the lateral wall of the ileum. In this case, the so-called ileocalcular angle is formed. Depending on the features of the entrance of the terminal part of the ileum into the cecum, this angle will vary. The direction of the cecum and ascending colon follows a unidirectional axis, slightly medially deviated from the vertical. In this case, the ileum enters the cecum mainly into the medial wall and is directed horizontally, forming an angle between the ileum and the ascending colon equal to 90-115 °, while forming an angle (ileocecal) between the ileum and the cecum equal to 27-40 °. 
The direction of the cecum and the ascending colon follows the same axis, with some deviation from the vertical to the lateral side (the cecum deviates to the lateral side), while the terminal portion of the ileum enters the caecum in the obliquely cranial direction, and the posterior- the medial wall of the cecum body. At the same time, the angle between the ileum and the ascending colon is 70-80°, and the angle between the cecum and the ileum becomes 30-60 °. 
The cecum in fetuses at 16-17 weeks of development is a bulging intestinal tube, its shape is cylindrical. It is located in the right iliac region of the fetus, in the area between the ilio-lumbar muscle and the anterior abdominal wall. The axis of direction of the ascending colon and cecum is determined, where the axis of the cecum is a continuation of the axis of the ascending colon. At 16-22 weeks, the cecum adjoins the medial or posterior walls to the anterior surface of the ileum. In most cases, it shares the mesentery with the ileum. The cecum is placed just below the right kidney of the fetus, touching its lateral or posterior wall with the medial part of the anterior surface of the right kidney. 
During these periods of ontogenesis, the shape of the cecum has a certain significance. At week 16-22 of the study period, the cecum is a moderately swollen area of the proximal colon, in which the formed bottom and small body are determined. In the middle and end of the observations, the cecum is a well-defined formation, where the predominant shape is cylindrical (80%), less often conical, with a slightly expanded saccate bottom (20%). It is located in the right iliac fossa of the fetus. In the cecum, from the 16th to the 22nd week of development, a body with medial, lateral, anterior and posterior walls, as well as a bottom (dome), is isolated. In the studied observation period, the bottom of the cecum in most cases (75%) was located cranially (ventrolaterally and ventromedially), or caudally (15%) (ventrolaterally and ventromedially). 
The length of the cecum (from the end of the ascending colon to the mouth of the appendix) will change during the observation period from 1.0‒1.50 mm (average values were 1.16±0.25 mm) to 3.0‒3.60 mm (average values were 3.24±0.27 mm), with a growth rate of 2.1 times and an increase of 82%. The width of the cecum varies, respectively, from 0.50‒0.70 mm (average values were 0.62 ±0.09 mm) to 2.0‒2.60 mm (average values were 2.35±0.24 mm) with a growth rate of 2.1 times and an IQ of 135%. No sex differences were found.

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About the authors

Tatyana A. Vasileva

Orenburg State Medical University

Author for correspondence.
Email: tatianavasileva-1997@list.ru
ORCID iD: 0009-0000-5320-4320

MD, assistant at the Department of Hospital Surgery

Russian Federation, Orenburg

Elvira N. Galeeva

Orenburg State Medical University

Email: tatianavasileva-1997@list.ru
ORCID iD: 0000-0001-8930-5975

MD, Dr. Sci. (Medicine), Associate Professor, Professor of the Department of Human Anatomy

Russian Federation, Orenburg

Victoriya A. Galiakbarova

Orenburg State Medical University

Email: tatianavasileva-1997@list.ru
ORCID iD: 0000-0001-6361-0605

MD, Cand. Sci. (Medicine), senior lecturer at the Department of Human Anatomy

Russian Federation, Orenburg

Anastasiya A. Grigoreva

Orenburg State Medical University

Email: tatianavasileva-1997@list.ru
ORCID iD: 0009-0009-4011-5148

6th year student at the Faculty of Medicine

Russian Federation, Orenburg

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