Unusual spontaneous intraperitoneal hemorrhage: three case reports.

Introduction and importance: Spontaneous hemoperitoneum (SH) is a rare, life-threatening condition characterized by nontraumatic and non-iatrogenic intraperitoneal bleeding. This article explores three unique cases of SH, shedding light on unusual causes and emphasizing the critical role of diagnostic imaging and exploratory laparotomy in management. METHODS: The study was a retrospective single-center non-consecutive case series. RESULTS: We report three distinct cases of SH, each originating from uncommon sources: rupture of greater omentum arterio-venous malformation, a branch of the left gastric artery, and pathological splenic rupture. Clinical evaluation, diagnostic imaging, and surgical interventions are detailed for each case. CONCLUSION: These rare cases underscore the diverse etiologies of SH, including idiopathic omental bleeding, gastric intramural hematoma, and atraumatic splenic rupture. Enhanced CT imaging plays a crucial role in diagnosis, enabling the characterization of underlying pathologies. Exploratory laparotomy proves to be an essential treatment option for unstable patients with suspected or confirmed diagnoses of SH.

Primary omental infarction - a benign cause of acute abdomen.

Objectives: Omental infarction (OI) is an uncommon cause of acute abdominal pain. A high index of clinical suspicion is required for diagnosis of OI as the incidence is less than 1 %, presenting with abdominal pain. We report primary OI's clinical and radiological profile from a single tertiary care hospital in India. Methods: In this retrospective cross-sectional study, the electronic medical and radiology records of patients with abdominal pain were reviewed over seven years (2015-2022). Variables were systematically collected and analyzed. Results: A total of 22 patients diagnosed with primary OI were included in this study. Male preponderance (63.6 %) was noted with a mean age of 47.45 years (SD ± 13.84; range: 18-72 years). Most patients belonged to class I obesity (according to the Asia-Pacific body mass index classification) with a mean BMI of 26.56 kg/m2 (SD ± 3.21 kg/m2). All patients had abdominal pain as the primary symptom, with a mean duration of 8.64 days (SD ± 10.15; range: 1-42 days). The most common locations of pain were the right hypochondrium (27.3 %) and diffuse (27.3 %), followed by the right iliac fossa (18.1 %). Most (95.45 %, n=21/22) patients were treated conservatively, and only one required surgical intervention. Conclusions: Primary OI is a rare and benign cause of acute abdomen. Obesity is a risk factor but does not correlate with the size or severity of OI. Radiological imaging, like a computed tomography (CT) scan, is essential for diagnosis. A conservative management line should be the first approach in treating primary OI before considering surgical options.

Morphological differences between the lesser and the greater omenta in albino rats.

BACKGROUND: Publications report that all mammals have two omenta, namely, lesser omentum and greater omentum. Basically, these organs, which share the same name except for the adjective "lesser" or "greater," should not differ from each other. However, no clear description of the structure of the lesser omentum, as well as comparative morphological analysis between the lesser and greater omenta have been found in the literature, which necessitates a thorough investigation. Therefore, the aim of our study was to analyze the morphofunctional differences between the greater and lesser omenta in albino rats. METHOD: The experiment involved 20 mature male albino rats, weighing 298,28±7,36 grams. The material for our study were preparations of lesser and greater omenta, fixed in 10 % of neutral buffered formalin. Paraffin sections were stained with hematoxylin-eosin and Van Gieson stain. RESULTS: The findings of the study showed that the greater omentum in albino rats, unlike other derivatives of the omentum (ligaments and mesenteries), represents a free extension (mostly from the greater curvature of the stomach), in the form of an "apron," into a specific depth of the peritoneal cavity, duplicating the serous membrane. This duplication is characterized by the composition of two structurally interdependent formations. These include vascular-fatty arcades, associated with lymphoid nodules known as milky spots, and binding serous-reticular membranes. The findings of the study of the lesser omentum have established that in all cases it is located beneath the liver and becomes visualized only after hepatolifting. It is presented in the form of two ligaments: hepatoduodenal and hepatogastric, which contain two main structured formations, which we called vascular-fatty spurs, between these spurs, serous-reticular membranes are located. CONCLUSION: despite having similar names, the lesser omentum, a derivative of the peritoneum, is fundamentally different. As it is well known, the lesser omentum is represented by ligaments that extend from the liver hilus to the lesser curvature of the stomach and the duodenum. Due to this arrangement, the lesser omentum lacks the mobile activity characteristic of the greater omentum, which plays a crucial role in rapid response to damage in the gastrointestinal tract. Despite sharing the same names, both formations differ in shape, morphological structure, development and function.

Malignant Extrarenal Rhabdoid tumor derived from the greater omentum: A case report and literature review.

BACKGROUND: Malignant extrarenal rhabdoid tumor (MERT) is a rare and highly metastatic tumor, which is more than 75% of patients dying within 6 months of initial diagnosis, and it often leads to misdiagnosis and delayed treatment. CASE: This paper reports a 16-year-old girl who presented with the chief complaint of acute abdominal pain. She underwent laparoscopic exploration and excisional biopsy, then pathological examination and immunohistochemistry revealed "extrarenal malignant rhabdomyoma." One month after operation, she died of intra-abdominal hemorrhage and multiple organ dysfunction. CONCLUSION: MERT were often misdiagnosed and had a poor prognosis. The surgery and chemotherapy are usually beneficial to prolong the survival time of patients with MERT.

Case report: A rare case of omental extrarenal rhabdoid tumor and review of the literature.

Extrarenal rhabdoid tumor of the greater omentum is extremely rare, with only sporadic reports and limited documentation of its ultrasonographic findings. Here, we report a case of an extrarenal rhabdoid tumor of the greater omentum in a 16-year-old girl and review the relevant literature. It was found that the disease mainly occurred in female children and adolescents, and mainly manifested as lower abdominal pain and a large abdominal cystic or solid hemorrhagic mass. The clinical characteristics include a high degree of malignancy and mortality. Ultrasound shows some malignant features, but it is not specific; thus, it is easy to be misdiagnosed in the clinic.

Morphological Characteristics of the Results of Experimental Modeling of Septic Peritonitis

SUMMARY: Experimental studies devoted to the study of the mechanisms of the pathogenesis of acute peritonitis and the development of new methods of medical and surgical treatment are becoming increasingly relevant. Today, experimental medicine knows many different ways to modeling septic peritonitis and eliminate it, but the role of the local immune system is underestimated, whereas it takes a direct part in inflammation. The objective of our work to study morphological features of results of experimental modeling of septic peritonitis in white rats. The study included 15 sexually mature white male rats weighing 276.75±6.56 grams. A simulation of septic peritonitis was performed by perforating the upper part of the cecum with four punctures with a G16 injection needle. As a result of the experiment, after examination of the peritoneal cavity, all 15 animals were diagnosed with omentum tamponade of perforated damage to the caecum. In 11 cases, the perforated wall of the caecum was covered by the greater omentum (73.34 %), and in the other 4 animals, tamponade was performed by one of the epididymal omentum (26.66 %). The initial stage of tamponade with the greater or epididymal omentums of a perforated caecum begins on the first day of the experiment and consists of tight interstitial consolidation between them, as well as in the invasion of blood vessels from the omentum side to the focus of infection, which ensure the delivery of the appropriate immunocompetent cells. As a result of this process, intensive lymphoid infiltrates are formed in this area, as well as the growth of adipose tissue, which isolates the inflammatory focus from the peritoneal cavity with a thick layer.

Las investigaciones experimentales dedicadas al estudio de los mecanismos de patogénesis de la peritonitis aguda y el desarrollo de nuevos métodos de tratamiento médico y quirúrgico son cada vez más relevantes. Hoy en día, la medicina experimental conoce muchas formas diferentes de modelar la peritonitis séptica y eliminarla, pero se subestima el papel del sistema inmunológico local, mientras que él participa directamente en la inflamación. El objetivo de nuestro trabajo fue estudiar las características morfológicas de los resultados del modelado experimental de peritonitis séptica en ratas blancas. El estudio incluyó 15 ratas macho blancas, sexualmente maduras que pesaban 276,75 ± 6,56 gramos. Se realizó una simulación de peritonitis séptica perforando la parte superior del ciego con cuatro punciones con una aguja de inyección G16. Como resultado del experimento, después del examen de la cavidad peritoneal, a los 15 animales se les diagnosticó taponamiento del omento o lesión perforada del ciego. En 11 casos, la pared perforada del ciego fue recubierta por el omento mayor (73,34 %), y en los otros 4 animales el taponamiento se realizó por uno de los epidídimos (26,66 %). La etapa inicial del taponamiento con omento mayor o epidídimo de un ciego perforado comienza el primer día del experimento y consiste en una estrecha consolidación intersticial entre ellos, así como en la invasión de los vasos sanguíneos desde el lado del omento hasta el foco de infección, que aseguran la entrega de las células inmunocompetentes apropiadas. Como resultado de este proceso, se forman intensos infiltrados linfoides en esta zona, así como el crecimiento de tejido adiposo, que aísla el foco inflamatorio de la cavidad peritoneal con una gruesa capa.

Primary Omental Torsion in Children in the Laparoscopy Era: What Have we Learned so far?

BACKGROUND/AIM: Primary omental torsion is uncommon, mimicking appendicitis and other acute abdominal pathologies. It often escapes diagnosis on imaging investigation or conventional open laparotomy. This study aimed to evaluate the effect of laparoscopy on the various parameters of this entity, including incidence, diagnosis, and treatment. MATERIALS AND METHODS: A systematic review was performed, including PubMed and Scopus databases, without a time limit, following the PRISMA principles. A total of 16 articles from January 2000 to December 2023, corresponding to 56 children with primary omental torsion, complied with the research criteria. RESULTS: Primary omental torsion was associated with obesity. Symptoms were right abdomen oriented, often compared to those of acute appendicitis. Preoperative ultrasound displayed low diagnostic accuracy, whereas computerized tomography diagnosed only two thirds of cases. In all patients, the vermiform appendix was normal. CONCLUSION: Laparoscopy affected both diagnosis and treatment of primary omental torsion in children. Easy peritoneal cavity access rendered possible the diagnosis of cases previously discharged as abdominal pain of unknown etiology. Combined with the increased pediatric obesity, it also affected primary omental torsion incidence. The recent pathogenetic theories may be better supported today, as laparoscopy provides a detailed view in situ, and facilitates harvesting of fat tissue from the omentum for molecular investigation. The diagnostic efficiency of laparoscopy is superior to ultrasonography and computerized tomography. Finally, the removal of the ischemic omentum is technically easier compared to the open laparotomy alternative with all the technical difficulties of traction of a vulnerable hemorrhagic tissue through a small incision.

Parasitic leiomyoma of the greater omentum: a case report and literature review.

Parasitic leiomyomas (PL), also known as free leiomyomas, which occur outside the uterus and rarely happen in clinical practice. They are usually reported in women of reproductive age who underwent hysterectomy or myomectomy and frequently present with symptoms such as abdominal pain and distention. In fact, it is hard to determine the nature of the mass according to the imaging examination and clinical manifestation. At present, the most common treatment involves an abdominal or laparoscopic surgery in order to remove the mass and perform the next step of treatment based on the histological diagnosis. In this case report, we describe a 35-year-old woman with a 12.4 × 9.3 × 9.8 cm3 PL with blood supply from the greater omentum. Considering the prolonged menstruation of the patient, she underwent the hysteroscopic and laparotomy exploration. The mass was confirmed as smooth leiomyoma with necrosis by the immunohistochemical examination. The patient had a good recovery and being discharged seven days after the surgery. The patient is still in the follow-up.

Omental fibroma combined with right indirect inguinal hernia masquerades as a scrotal tumor: A case report.

BACKGROUND: The most common causes of scrotal enlargement in patients include primary tumor of the scrotum, inflammation, hydrocele of the tunica vaginalis, and indirect inguinal hernia; scrotal enlargement caused by external tumors of the scrotum is rare. The patient had both a greater omentum tumor and an inguinal hernia, and the tumor protruded into the scrotum through the hernia sac, which is even rarer. Moreover, omental tumors are mostly metastatic, and primary omental fibroma is rare. CASE SUMMARY: Here, we report a rare case of a 25-year-old young man with scrotal enlargement and pain for 3 months. Preoperative examination and multidisciplinary discussions considered intra-abdominal tumor displacement and inguinal hernia, and intraoperative exploration confirmed that the greater omentum tumor protruded into the scrotum. Therefore, tumor resection and tension-free inguinal hernia repair were performed. The final diagnosis was benign fibroma of the greater omentum accompanied by an indirect inguinal hernia. CONCLUSION: This unusual presentation of a common inguinal hernia disease illustrates the necessity of performing detailed history taking, physical examination, and imaging before surgery.

Abdomen agudo por torsión de epiplón mayor simulando una apendicitis aguda / Acute abdomen due to torsion of greather omentun simulating acute appendicitis

La torsión del epiplón mayor es una patología poco frecuente con una clínica inespecífica, por lo que históricamente su diagnóstico es realizado en el quirófano ya que simula patologías como la apendicitis o colecistitis. Los métodos auxiliares de diagnóstico como las ecografías o las tomografías son de mucha utilidad para la sospecha de esta patología, aunque no cuenta con signos patognomónicos de la enfermedad, las imágenes asociadas a la clínica del paciente pueden llevar a un diagnóstico preciso. Presentamos el caso de un paciente joven de sexo masculino, que acudió al servicio de urgencias por cuadro de dolor abdominal tipo cólico de moderada intensidad en fosa iliaca derecha, acompañado de sensación febril, sin alteración de la analítica sanguínea, sin hallazgo de valor en la ecografía abdominal, que ante la persistencia del dolor y la fiebre se realizó una tomografía contrastada en la que se observó un empastamiento del epiplón sometiéndose a una laparoscopía exploradora con el hallazgo de una torsión del epiplón mayor.

Torsion of the greater omentum is a rare pathology with non-specific symptoms, so historically its diagnosis is made in the operating room since it simulates pathologies such as appendicitis or cholecystitis. Auxiliary diagnostic methods such as ultrasound or tomography are of very useful for the suspicion of this pathology, although it does not have pathognomonic signs of the disease, the images associated with the patient's symptoms can lead to a precise diagnosis. We present the case of a young male patient who came to the emergency department due to moderately intense colic-like abdominal pain in the right iliac fossa, accompanied by a feverish sensation, without alterations in blood tests, without any finding of value in the abdominal ultrasound, due to the persistence of pain and fever, a contrast-enhanced tomography was performed in which a filling of the omentum was observed, undergoing an exploratory laparoscopy with the discovery of a torsion of the greater omentum.

Incarcerated umbilical hernia in a patient with cirrhotic ascites in combination with chronic lymphocytic leukemia: a case report.

Umbilical hernia is a common type of extra-abdominal hernia in adults. However, chronic granulocytic leukemia in combination with cirrhotic ascites and renal insufficiency is less common. The patient reported here had both indications and contraindications for emergency surgery; therefore, the treatment options were subject to debate. We report the case of a man in his 60s who had a strangulated umbilical hernia, with overlying purple-colored infected and necrotic skin. The area was painful, but his bowel movements were normal. Patients underwent comprehensive conservative management, and remote follow-ups via telephone and video conferencing for a period of 60 days, during which the incarcerated contents of the hernia eventually retracted and his pain was relieved, such that there were no longer indications for emergency surgery. In addition, his skin infection disappeared and his quality of life improved, and therefore the treatment outcomes were good. Thus, we provide evidence that not all incarcerated umbilical hernias require emergency surgery, but may respond well to conservative treatment when the contents do not include intestinal loops or other critical organs.

General Morphological Characteristics of the Results of Experimental Modeling of Aseptic Peritonitis.

BACKGROUND: Aseptic peritonitis is a reaction of the local immune system aimed at rejection of a foreign body, which, having antigenic properties, does not (unlike a pathogen) counteract the immune system. The suture materials, namely catgut thread, used in intracavitary surgical operations possess xenogenic properties and can be used for antigenic stimulation of the immune system of the peritoneal cavity. Consequently, we decided to use a catgut suture for antigenic stimulation of the immune system of the peritoneal cavity and to study the morphological features of the results of experimental modeling of aseptic peritonitis in albino rats. METHOD: The study involved 15 Wistar albino male rats, weighing 286,13 ± 6,26 g. To study the dynamics of destructive changes made by the catgut implant in the peritoneal cavity of the experimental animals, the animals were assigned into three groups in accordance with the time interval of their euthanasia at 3, 7, and 14 days of the experiment. RESULTS: After modeling an aseptic peritonitis, the investigation the abdominal cavity showed that in four out of five animals of the first group, that is, on day 3 of the experiment, the catgut implant had adhered to the greater omentum. The search for the fifth implant led to an unexpected discovery: we found it conjoined with the second derivative of the visceral peritoneum, similar in structure to the greater omentum, but related to the testes. On day 7, the implant embedded into the peritoneal cavity of the animals, had adhered to the serous formations of the testes in all five cases (100%, three of them - to the left epididymal omentum, and another two - to the right one). On day 14 (n = 5) it was found that in three cases it had adhered to the serous formations of the testes (60%, one of them to the left epididymal omentum, another two - to the right one) and in two cases it had adhered to the greater omentum (40%). CONCLUSION: During the experiment on implantation of a xenogenic substrate in the form of flat bundles made from the catgut thread into the peritoneal cavity of sexually mature male rats, it was found for the first time that their acceptors were not only the greater omentum, but also two derivatives of the peritoneum, homeomorphic to it and associated with the epididymides, which we reasonably called epididymal omenta and described in details.

Solitary Fibrous Tumor of the Peritoneal Cavity and Greater Omentum: Case Report and Review of the Literature.

Background: The solitary fibrous tumor is a rare soft tissue mesenchymal tumor which typically arises from the pleura but may be found anywhere in the body. Abdominal localizations are very rare. The solitary fibrous tumor is classified into two forms, pleural and extrapleural, and morphologically they resemble each other. The diagnostics of the tumor is usually accidental because usually there are no clinical symptoms. The main treatment of the solitary fibrous tumor is the surgical removal of the tumor while radiotherapy treatment and chemotherapy outcomes remain unclear due to the rarity of the tumor and lack of data. Case presentation: We report the case of the 32-year-old man who was diagnosed with the solitary fibrous tumor of the peritoneal cavity. Laparotomy was performed. A grayish-white, stiff, coarse-grained tumor about 11 cm in diameter of the greater omentum was found and radical omentectomy with tumor removal were performed. Postoperative course was uneventful and the patient is well with no signs of recurrence on the CT scan of the chest and abdomen and MRI of the pelvis at 6 months after surgery. Conclusions: The solitary fibrous tumor is a rare condition. It is a borderline-malignant tumor but may cause serious complications if not treated. Due to the absence of clinical symptoms, the tumor is usually detected accidentally. The radical surgical removal of the tumor is the most optimal treatment.

CT and MR imaging of the greater omentum: Pictorial essay.

The greater omentum is a unique anatomical structure that serves a critical function in the containment of inflammatory and infectious processes within the abdominal cavity. It is also a common site of involvement by metastases, as well as the primary location for various pathologic lesions of clinical significance. Its fibroadipose composition, large size, and position in the most anterior aspect of abdomen allow accurate visualization of the greater omentum on CT and MR images. Careful evaluation of the greater omentum can provide important clues to the diagnosis of the underlying abdominal disorder. The aim of this article is to present the normal appearance of the greater omentum, and the wide spectrum of its pathological features as demonstrated on CT and MRI of the abdomen.

Torsion of the Greater Omentum: A Mimicker of Acute Appendicitis.

Torsion of the greater omentum is rare and difficult to diagnose preoperatively. There are operative or non-operative treatment options. Operative management is often done for patients with abdominal pain in the right lower quadrant because omental torsion is misdiagnosed as appendicitis. If omental torsion is accurately diagnosed, previous reports suggest that symptoms may improve 12-120 hours after non-operative management of a primary omental torsion. Here, we report a successful case of surgical treatment for torsion of the greater omentum after non-operative treatment was ineffective. Thus, considering the severity of the pain and operative risk, a laparoscopic omentectomy may be feasible to relieve the severe abdominal pain promptly.

Isolated greater omentum solid mass, a rare manifestation of hydatid disease; A Case Report and Review of Literature.

Background: Echinococcus granulosus causes hydatid disease, which is found in various countries of the world, including Iran. The liver and lungs are prevalent involved structures in hydatid disease. One of the least common sites in hydatid disease seems to be the omentum. Seven cases of mesenteric, diaphragmatic, omental, pelvic, and retroperitoneal hydatid cysts have been reported in Iran within last 20 years. The appearance of hydatid disease as a primary mass in the greater omentum without hepatic involvement is very rare and no similar case was introduced in Iran in our searches. Case Presentation: Our patient was a 33-year-old woman who underwent a diagnostic laparoscopy due to abdominal pain and an abdominal mass. During laparoscopy, there was a solid mass with a size of about 10 × 5 cm in the greater omentum that was resected. The histopathological examination of the mass showed the hydatid disease. Conclusion: The hydatid cyst can appear anywhere on the body, and no part of the body is guarded. Since these uncommon locations often cause nonspecific symptoms, the hydatid cyst should be included in the differential diagnosing of omental cysts, particularly in endemic countries like Iran.

Differences in histomorphology and expression of key lipid regulated genes of four adipose tissues from Tibetan pigs.

Tibetan pigs, an indigenous pig breed in China, have high overall fat deposition and flavorful and tasty meat. They are thus good models for studying adipogenesis. Few studies have been conducted focusing on expression of lipid regulated genes in different adipose tissues of Tibetan pigs. Therefore, we compared the difference of histomorphology and expression level of lipid regulated genes through qPCR and western blot in subcutaneous fat, perirenal fat, omental adipose tissue, and inguinal fat of Tibetan pigs. Our results showed that the area of subcutaneous adipocytes in Tibetan pigs was smaller, while the other three adipose tissues (perirenal fat, greater omentum fat, inguinal fat) had cell areas of similar size. The gene expression of FABP4, FASN, FABP3, and ME1 in subcutaneous fat was significantly higher than that in perirenal fat. Furthermore, the protein expression of FABP4 was significantly lower in subcutaneous fat than in perirenal fat (p < 0.05), and the expression of FASN was higher in greater omentum fat than in subcutaneous fat (p = 0.084). The difference in adipocyte cell size and expression of lipid-regulated genes in adipose tissues from the various parts of the pig body is likely due to the different cellular lipid metabolic processes. Specially, FABP4 and FASN may be involved in the regulation of fat deposition in different adipose tissues of Tibetan pigs.

The greater omentum and similar serous formations of testis in male white rats.

BACKGROUND: The greater omentum of white rats appears, in basic morphological features (in miniature), to be homologous to the greater omentum of humans. We study of the greater omentum reaction to the catgut implant. After implantation of the catgut thread, it turned out that not only the greater omentum, but also serous formations similar to it, related to the testicles, are involved in the covering of the implant. The aim of the study was to study the general plan of the structure and the principles of morphometric analysis of serous formations of testis in white male rats. MATERIALS AND METHODS: The experiment involved 15 white male rats of reproductive age, weighing from 284 to 334 grams. RESULTS: It has been established that each testicle of white rats has serous (peritoneal derivatives) formations of two types. One of them is a typical mesentery, with which each testicle is separately fixed to the posterior wall of the pelvic cavity, and the other formation is a free regrowth of a duplication of the serous membrane. It was called the epididymal omentum. According to the algorithm for studying the greater omentum in our previous works, it is noteworthy that the area of the greater omentum is noticeably inferior to the area of the epididymal omentums (F = 0.239; p = 0.006). So, if the average value of the area of the greater omentum is 2766.51 ± 388.12 mm2, then the same indicator of the epididymal omentum reaches 4383.36 ± 793.56 mm2, with their approximately the same thickness (F = 1.35; p = 0.291). CONCLUSIONS: It has been established that the greater omentum has two, homeomorphic to it, derivatives of the peritoneum, associated with the epididymis, which were justifiably called epididymal omentums and were fully described in the literature for the first time.

Uterine Serosal Inclusion Cysts with Greater Omentum Involvement in a Cat.

A 7-year-old nulliparous Chinchilla queen was admitted to a veterinary clinic for routine ovariohysterectomy. Examination of the uterus, greater omentum and varicose ovarian veins revealed multiple thin-walled cysts filled with a transparent fluid over the serosal surfaces of these organs. Histologically, the cysts were of variable size, filled with a small amount of mucinous fluid, and had thin walls that contained hypocellular collagen and a few small calibre vessels. The inner and outer epithelium of the cyst walls and the cells that lined the uterine serosa were immunopositive for cytokeratin and vimentin, suggesting a mesothelial origin. Alpha-smooth muscle actin immunolabelling was patchy or continuous in smooth muscle in the wall of many of the cysts.

Anatomy of the vitelline vein remnant in human embryos and fetuses.

PURPOSE: To demonstrate the entire course of the human vitelline vein (VV) in specimens after degeneration of the yolk sac. METHODS: Sagittal and horizontal histological sections from 8 embryos and 19 fetuses (gestational age approximately 6-12 weeks; crown-rump length 11-61 mm) were examined. RESULTS: Two types of VV remnants were observed: a long VV on the right superior side of the mesentery of the jejunum (VV1) and a short VV on the left inferior side of the mesentery (VV2). The VV1, observed in 12 specimens, was 20-30 microns in diameter and ran dorsally between the right liver lobe and the jejunum, subsequently merging with an initial superior mesenteric vein on the pancreatic head immediately below the superior portion of the duodenum. The VV2, observed in four specimens, passed dorsally between loops of the ileum on the left side of the mesentery of the ileum and connected to the mesentery. Many of the VVs did not originate from the umbilical cord but suddenly started in the sack of physiological herniation. At 10-12 weeks, after herniation, the VVs originated from the umbilicus and were involved by the expanding greater omentum. CONCLUSIONS: The right-sided and left-sided VVs seemed to correspond to right and left VV remnants, respectively, and both took an upstream course outside the mesentery of the jejunum and ileum. The right VV upstream portion was likely to disappear later than the left one, but the timing of degeneration varied greatly among individuals, depending on the topographical relationship between the right liver lobe and the jejunum.