Future Directions.

Recent findings related to the mesentery clarified the organisation of the abdomen at the foundational level. The Mesenteric-based model of abdominal anatomy articlulates a foundation that re-unites scientific and clinical approaches to the abdomen in health and disease. Importantly, recent advances are a reminder that we must always question dogma. The peritoneal-based dogma of conventional anatomy remained unquestioned for too long. With time, the mesenteric-based dogma will also be altered and improved on. Anatomy, and hence surgery, must always be considered as works in progress.

The Mesentery-Past, Present, and Future.

This article summarizes the events that shaped our current understanding of the mesentery and the abdomen. The story of how this evolved is intriguing at several levels. It speaks to considerable personal commitment on the part of the pioneers involved. It explains how scientific and clinical fields went different directions with respect to anatomy and clinical practice. It demonstrates that it is no longer acceptable to adhere unquestioningly to models of abdominal anatomy and surgery. The article concludes with a brief description of the Mesenteric Model of abdominal anatomy, and of how this now presents an opportunity to unify scientific and clinical approaches to the latter.

The Development of the Mesenteric Model of Abdominal Anatomy.

Recent advances in mesenteric anatomy have clarified the shape of the mesentery in adulthood. A key finding is the recognition of mesenteric continuity, which extends from the oesophagogastric junction to the mesorectal level. All abdominal digestive organs develop within, or on, the mesentery and in adulthood remain directly connected to the mesentery. Identification of mesenteric continuity has enabled division of the abdomen into two separate compartments. These are the mesenteric domain (upon which the abdominal digestive system is centered) and the non-mesenteric domain, which comprises the urogenital system, musculoskeletal frame, and great vessels. Given this anatomical endpoint differs significantly from conventional descriptions, a reappraisal of mesenteric developmental anatomy was recently performed. The following narrative review summarizes recent advances in abdominal embryology and mesenteric morphogenesis. It also examines the developmental basis for compartmentalizing the abdomen into two separate domains along mesenteric lines.

The Mesentery in Robot-Assisted Total Mesorectal Excision.

In recent decades, surgery for rectal cancer has evolved from an operation normally performed under poor vision with a lot of blood loss, relatively high morbidity, and mortality to a safer operation. Currently, minimally invasive rectal procedures are performed with limited blood loss, reduced morbidity, and minimal mortality. The main cause is better knowledge of anatomy and adhering to the principle of operating along embryological planes. Surgery has become surgery of compartments, more so than that of organs. So, rectal cancer surgery has evolved to mesorectal cancer surgery as propagated by Heald and others. The focus on the mesentery of the rectum has led to renewed attention to the anatomy of the fascia surrounding the rectum. Better magnification during laparoscopy and improved optimal three-dimensional (3D) vision during robot-assisted surgery have contributed to the refinement of total mesorectal excision (TME). In this chapter, we describe how to perform a robot-assisted TME with particular attention to the mesentery. Specific points of focus and problem solving are discussed.

Urogenital function following robotic and laparoscopic rectal cancer surgery: meta-analysis.

BACKGROUND: Mixed results are reported on clinical and cancer outcomes in laparoscopic rectal cancer surgery (LRCS) compared with robotic rectal cancer surgery (RRCS). However, more favourable functional outcomes are reported following RRCS. This study compared urinary and sexual function following RRCS and LRCS in male and female patients. METHODS: A systematic review and meta-analysis of urinary and sexual function after RRCS and LRCS was performed following PRISMA and MOOSE guidelines, and registered prospectively with PROSPERO (ID:CRD42020164285). The functional outcome reporting tools most commonly included: the International Prostate Symptom Score (IPSS), International Index of Erectile Function (IIEF) and Female Sexual Function Index (FSFI). Mean scores and changes in mean scores from baseline were analysed using RevMan version 5.3. RESULTS: Ten studies were included reporting on 1286 patients. Some 672 patients underwent LRCS, of whom 380 (56.5 per cent) were men and 116 (17.3 per cent) were women (gender not specified in 176 patients, 26.2 per cent). A total of 614 patients underwent RRCS, of whom 356 (58.0 per cent) were men and 83 (13.5 per cent) were women (gender not specified in 175 patients, 28.5 per cent). Regarding urinary function in men at 6 months after surgery, IPSS scores were significantly better in the RRCS group than in the LRCS group (mean difference (MD) -1.36, 95 per cent c.i. -2.31 to -0.40; P = 0.005), a trend that persisted at 12 months (MD -1.08, -1.85 to -0.30; P = 0.007). ΔIIEF scores significantly favoured RRCS at 6 months [MD -3.11 (95%CI -5.77, -0.44) P <0.021] and 12 months [MD -2.76 (95%CI -3.63, -1.88) P <0.001] post-operatively. Mixed urinary and sexual function outcomes were reported for women. CONCLUSION: This meta-analysis identified more favourable urinary and erectile function in men who undergo robotic compared with conventional laparoscopic surgery for rectal cancer. Outcomes in women did not identify a consistently more favourable outcome in either group. As robotic rectal cancer surgery may offer more favourable functional outcomes it should be considered and discussed with patients.

Ex vivo specimen MRI and pathology confirm a rectosigmoid mesenteric waist at the junction of the mesorectum and mesocolon.

AIM: Continuity of the mesentery has recently been established and may provide an anatomical basis for optimal colorectal resectional surgery. Preliminary data from operative specimen measurements suggest there is a tapering in the mesentery of the distal sigmoid. A mesenteric waist in this area may be a risk factor for local recurrence of colorectal cancer. This study aimed to investigate the anatomical characteristics of the mesentery at the colorectal junction. METHOD: In this cross-sectional study, 20 patients were recruited. After planned colorectal resection, the surgical specimens were scanned in a MRI system and subsequently dissected and photographed as per national pathology guidelines. Mesenteric surface area and linear measurements were compared between MRI and pathology to establish the presence and location of a mesenteric waist. RESULTS: Specimen analysis confirmed that a narrowing in the mesenteric surface area was consistently apparent at the rectosigmoid junction. Above the anterior peritoneal reflection, the surface area and posterior distance of the mesentery of the upper rectum initially decreased before increasing as the mesentery of the sigmoid colon. These anatomical properties created the appearance of a mesenteric 'waist' at the rectosigmoid junction. Using the anterior reflection as a reference landmark, the rectosigmoid waist occurred at a mean height of 23.6 and 21.7 mm on MRI and pathology, respectively. CONCLUSION: A rectosigmoid waist occurs at the junction of the mesorectum and mesocolon, and is a mesenteric landmark for the rectum that is present on both radiology and pathology.

Resectional surgery for malignant disease of abdominal digestive organs is not surgery of the organ itself, but also that of the mesenteric organ.

Despite large strides in molecular oncology, surgery remains the bedrock in the management of visceral cancer. The primacy of surgery cannot be understated and a mesenteric (i.e. ontogenetic) approach is particularly beneficial to patients. Heald greatly advanced the management of rectal cancer with his description of the anatomical foundation of total mesorectal excision (TME), dramatically improving outcomes worldwide with this mesenteric-based approach. Moreover, complete mesocolic excision (CME) based on similar principles is becoming popular. Introduced by Hohenberger, CME resembles TME insofar as it emphasises strictly anatomical dissection along embryological planes to detach an intact (i.e. "complete") mesentery with peritoneal envelope. CME also incorporates "central" vascular ligation (CVL) which broadly correlates with the "D3 lymphadenectomy" of Eastern literature. As many surgeons already practise anatomical and mesenteric-based surgery, it is unclear how the putative benefits of CME (including CVL) arise. Herein, we argue that these may relate to a more extensive resection of the mesentery, and thus mesenteric tumour deposits within the connective tissue lattice of the mesentery, and not necessarily the lymphadenectomy alone. We believe the connective tissue interface between the bowel wall and mesentery provides an alternative mode of spread of pathogenic elements. Whilst this remains a suggestion only, it would explain the histological independence of tumour deposits and why a greater mesenterectomy could be associated with benefits in survival. If this argument holds, it follows that resectional surgery for digestive organ malignancy is not surgery of the organ itself (or lymphatics only), but also that of the contiguous mesentery.

Direct mechanical characterization of prostate tissue-a systematic review.

BACKGROUND: Direct mechanical characterization of tissue is the application of engineering techniques to biological tissue to ascertain stiffness or elasticity, which can change in response to disease states. A number of papers have been published on the application of these techniques to prostate tissue with a range of results reported. There is a marked variability in the results depending on testing techniques and disease state of the prostate tissue. We aimed to clarify the utility of direct mechanical characterization of prostate tissue in identifying disease states. METHODS: A systematic review of the published literature regarding direct mechanical characterization of prostate tissue was undertaking according to PRISMA guidelines. RESULTS: A variety of testing methods have been used, including compression, indentation, and tensile testing, as well as some indirect testing techniques, such as shear-wave elastography. There is strong evidence of significant stiffness differences between cancerous and non-cancerous prostate tissue, as well as correlations with prostate cancer stage. There is a correlation with increasing prostate stiffness and increasing lower urinary tract symptoms in patients with benign prostate hyperplasia. There is a wide variation in the testing methods and protocols used in the literature making direct comparison between papers difficult. Most studies utilise ex-vivo or cadaveric tissue, while none incorporate in vivo testing. CONCLUSION: Direct mechanical assessment of prostate tissue permits a better understanding of the pathological and physiological changes that are occurring within the tissue. Further work is needed to include prospective and in vivo data to aid medical device design and investigate non-surgical methods of managing prostate disease.

Changes in Peristomal Skin Condition and User Experience of a Novel Ostomy Barrier Ring With Assisted Flow: A 6-Week Feasibility Study.

PURPOSE: This purpose of this study was to evaluate a novel barrier ring with an assisted flow mechanism by assessing changes in peristomal moisture-associated skin damage (MASD) and perceptions of comfort, security, handling, and discretion in persons with an ileostomy for 6 months or longer. DESIGN: Single-arm, open-labeled feasibility study. SUBJECTS AND SETTINGS: Twenty participants (aged ≥18 years) with an ileostomy for 6 months or more participated in the study and 12 completed data collection. The primary reason for dropouts concerned compatibility issues with the barrier ring when used with certain convex pouching systems. METHODS: Participants used the barrier ring along with their normal ostomy pouching system for a period of 6 weeks. Changes in skin condition were assessed using the Ostomy Skin Tool (OST). Participants' perception of the barrier rings' comfort, security, handling, and discretion were also recorded on a 10-point scale, where participants would offer a low score if their experience was negative and a higher score if their experience was positive. Participants changed pouches and barrier rings at their own discretion. For participants who completed the study, the average skin condition and median ratings of comfort, security, handling, and discretion at 6 weeks were compared to baseline values. RESULTS: Twelve of the 20 participants (60%) completed the study. For those who completed, the mean score on the OST decreased from 6.2 ± 1.90 (mean ± SD) at baseline to 3.4 ±1.73 at 6 weeks, indicating a mean reduction of 2.8 (95% CI, -1.6 to -3.9; P < .001). The peristomal skin condition of 9 participants improved, whereas 3 experienced no change. All participants who completed the study rated comfort, handling, security, and discretion highly (median score 10 at baseline and at 6 weeks). CONCLUSIONS: Study findings indicate the novel ostomy barrier ring may reduce levels of peristomal MASD in persons living with an ileostomy, though a more extensive trial with a control group is recommended.

Do Inflammatory Indices Play a Role in Distinguishing between Uncomplicated and Complicated Diverticulitis?

BACKGROUND: The usefulness of inflammatory indices in assessment of the severity of acute diverticulitis remains unestablished. The aim of this study was to determine whether inflammatory indices and hematological ratios could be utilised to differentiate between uncomplicated and complicated diverticulitis. METHODS: Hematological and inflammatory indices were recorded for each admission with CT confirmed acute diverticulitis (101 complicated, 127 uncomplicated). Cases were divided into training (n = 57) and test sets (n = 171). A classification and regression tree (CART) analysis was employed in the training set to identify optimal inflammatory marker cut-off points associated with complicated diverticulitis. Samples (test set) were then categorized as (A) greater than and (B) less than CART identified cut-off points. The predictive properties of inflammatory marker cut-off points in distinguishing severity of diverticulitis were assessed using a univariate logistic regression analysis, summary receiver operating characteristic curves and confusion matrix generation. RESULTS: C-reactive protein >109 mg/ml (OR 3.07, 95% CI 1.43-6.61, p = 0.004, area under the curve; AUC = 0.64) and white cell lymphocyte ratio (WLR) >17.72 (OR 4.23, 95% CI 1.95-9.17, p < 0.001, AUC = 0.64) were the most accurate parameters in distinguishing complicated and uncomplicated disease. WCC >21 × 109/l (p = 0.02, AUC = 0.60) and lymphocyte count >0.55 × 109/l (p = 0.009, AUC = 0.60) were less accurate. CONCLUSION: Widely used inflammatory indices are useful in the depiction of complicated diverticulitis. The indices cut-off points highlighted in this study should be considered at the time of diagnosis in combination with radiological features of complicated diverticulitis.

The effect of purse-string approximation versus linear approximation of ileostomy reversal wounds on morbidity rates and patient satisfaction: the 'STOMA' trial.

BACKGROUND: Ileostomy reversal is associated with surgical site infection (SSI) rates as high as 37%. Recent literature suggests that employing a purse-string approximation (PSA) of the reversal wound reduces this rate of SSI. Thus we wished to perform a randomised controlled trial to compare SSI rates in purse-string versus linear closure (PLC) wounds following ileostomy reversal. METHODS: A randomised, controlled trial was conducted at University Hospital Limerick. Sixty-one patients undergoing ileostomy reversal were included. Thirty-four patients were randomised to PSA and 27 patients to linear closure. The primary endpoint was incidence of SSI and secondary endpoints measured were quality of life and satisfaction with cosmesis. Statistical analysis was performed on a per protocol basis using SPSS version 22.0. RESULTS: Three patients in the PSA group developed an SSI compared to 8 in the PLC group at 30 days (8 vs 30%, p = 0.03). The mean time to SSI diagnosis was faster in the PSA group (3 vs 12.3 days, p = 0.08). Patients who developed SSI experienced a longer mean length of stay (6.8 vs 11.4 days, p = 0.012). On multivariate analysis, PLC was the only predictive factor of SSI formation (p < 0.001). There was no difference in patient satisfaction between the two study groups (p = 0.14). CONCLUSIONS: PSA of wounds following ileostomy reversal significantly reduces SSI formation compared to linear approximation without any effect on patient satisfaction.

Using fluorescence lymphangiography to define the ileocolic mesentery: proof of concept for the watershed area using real-time imaging.

Recent advances in mesenteric science have demonstrated that the mesentery is a continuous structure with a 'watershed' area at the mesenteric apex between the right colon and terminal ileum, where lymphatic flow can proceed either proximally or distally. With this new understanding of the anatomy, functional features are emerging, which can have an impact on surgical management. Fluorescence lymphangiography or lymphoscintigraphy with indocyanine green allows real-time visualization of lymphatic channels, which highlights sentinel lymph nodes and may facilitate identification of the ideal margins for mesenteric lymphadenectomy during bowel resection for colon cancer. By using this novel technology, it is possible to demonstrate a watershed area in the ileocolic region and may facilitate more precise mesenteric dissection. In the present study, we provide proof of concept for the ileocolic watershed area using fluorescence lymphangiography.

Initial experience with a dual-console robotic-assisted platform for training in colorectal surgery.

BACKGROUND: Minimally invasive surgery is associated with several patient-related benefits, including reduced length of hospital stay and reduced blood loss. Robotic-assisted surgery offers many advantages when compared with standard laparoscopic procedures, including a stable three-dimensional binocular camera platform, motion smoothing and motion scaling, improved dexterity and ergonomics. There are limited data on the effectiveness of the dual-console DaVinci Xi platform for teaching resident surgeons. The goal of this study was to examine preliminary outcomes following the introduction of a dual-console robotic platform in our institution. METHODS: A retrospective review of our prospectively maintained patient database was performed. The first ten dual-console resident-performed procedures in colorectal surgery were compared with matched cases performed on a single console by the trainer. Patient demographics, operative times and patient outcomes were compared. RESULTS: Twenty patients were included in this study. There was no significant difference in console time (p = 0.46) or total operative time (p = 0.52) when residents and trainers were compared. Patient outcomes were equivalent, with no difference in length of stay, morbidity or mortality. CONCLUSIONS: The DaVinci Xi dual-console platform is a safe and effective platform for training junior surgeons. The dual-console system has the potential to alter surgical training pathways.

An appraisal of the computed axial tomographic appearance of the human mesentery based on mesenteric contiguity from the duodenojejunal flexure to the mesorectal level.

OBJECTIVE: The human mesentery is now regarded as contiguous from the duodenojejunal (DJ) to anorectal level. This interpretation prompts re-appraisal of computed tomography (CT) images of the mesentery. METHODS: A digital model and reference atlas of the mesentery were generated using the full-colour data set of the Visible Human Project (VHP). Seventy one normal abdominal CT images were examined to identify mesenteric regions. CT appearances were correlated with cadaveric and histological appearances at corresponding levels. RESULTS: Ascending, descending and sigmoid mesocolons were identifiable in 75%, 86% and 88% of the CTs, respectively. Flexural contiguity was evident in 66%, 68%, 71% and 80% for the ileocaecal, hepatic, splenic and rectosigmoid flexures, respectively. A posterior mesocolic boundary corresponding to the anterior renal fascia was evident in 40% and 54% of cases on the right and left, respectively. The anterior pararenal space (in front of the boundary) corresponded to the mesocolon. CONCLUSIONS: Using the VHP, a mesenteric digital model and reference atlas were developed. This enabled re-appraisal of CT images of the mesentery, in which contiguous flexural and non-flexural mesenteric regions were repeatedly identifiable. The anterior pararenal space corresponded to the mesocolon. KEY POINTS: The Visible Human Project (VHP) allows direct identification of mesenteric structures. Correlating CT and VHP allows identification of flexural and non-flexural mesenteric components. Radiologic appearance of intraperitoneal structures is assessed, starting from a mesenteric platform.

Neoadjuvant therapy does not affect lymph node ratio in rectal cancer.

AIMS: Recently, lymph-node ratio (LNR) has emerged as a prognostic tool in staging rectal cancer. Studies to date have demonstrated threshold values above and below which survival is differentially altered. Neoadjuvant therapy significantly reduces the number of lymph node retrieved. The aim of the present study was to determine the effect of neoadjuvant therapy on LNR and its prognostic properties. METHODS: Consecutive patients who underwent curative rectal cancer resections in a single institution from 2007 to 2010 were reviewed. LNR was stratified into five subgroups of 0, 0.01-0.17, 0.18-0.41, 0.42-0.69 and 0.7-1.0 based on a previous study. The effect of neoadjuvant therapy on lymph node retrieval, LNR, locoregional (LR) and systemic recurrence (SR), disease-free (DFS) and overall survival (OS) was compared between patients who did (Neoadjuvant) and did not (Surgery Alone) receive neoadjuvant therapy. RESULTS: Neoadjuvant and Surgery Alone groups were comparable in gender, age and tumour stage. The number of lymph nodes retrieved were significantly lower in the Neoadjuvant group (p < 0.01). However, LNR remained similar in both groups (p = 0.36). There was no statistical difference in the DFS and OS between the Neoadjuvant and Surgery Alone groups at the various LNR cut off values in patients with AJCC Stage 3 tumours. CONCLUSIONS: LNR ratio remains unaltered despite reduced lymph node retrieval after neoadjuvant therapy in rectal cancer. LNR may therefore be a more reliable prognostic indicator in this subgroup of patients.

Identification of the optimal visual recording system in open abdominal surgery - a prospective observational study.

INTRODUCTION: Current methodologies used to record and render the surgeon's point of view in open operative surgery remain limited. Chief among these limitations is a failure to demonstrate, in high definition and magnification, the planar roadmap that surgeons utilise in colorectal surgery. The high magnification and high resolution views provided during laparoscopic surgery simultaneously capture the planar road map and surgeon's point of view. We developed an arm-mounted external laparoscope (exoscope) system and compared its performance against multiple standard recording modalities. METHODS: Following ethical approval and informed consent, open colorectal procedures were recorded using five separate methodologies. Each methodology was assessed and compared. RESULTS: Most of the methodologies utilised scored poorly at one if not more levels. The arm-mounted external laparoscope (exoscope) scored highest in rendering the surgeon's point of view while simultaneously achieving high resolution and high magnification rendition of operative field (p < .001). This methodology was tested in a number of operative contexts within which it reproducibly and consistently scored highly. CONCLUSIONS: The arm-mounted exoscope is the optimal means of rendering the surgeon's point of view of anatomic planes during open colorectal surgery.

Spatial variation of the colonic microbiota in patients with ulcerative colitis and control volunteers.

OBJECTIVES: The relevance of spatial composition in the microbial changes associated with UC is unclear. We coupled luminal brush samples, mucosal biopsies and laser capture microdissection with deep sequencing of the gut microbiota to develop an integrated spatial assessment of the microbial community in controls and UC. DESIGN: A total of 98 samples were sequenced to a mean depth of 31,642 reads from nine individuals, four control volunteers undergoing routine colonoscopy and five patients undergoing surgical colectomy for medically-refractory UC. Samples were retrieved at four colorectal locations, incorporating the luminal microbiota, mucus gel layer and whole mucosal biopsies. RESULTS: Interpersonal variability accounted for approximately half of the total variance. Surprisingly, within individuals, asymmetric Eigenvector map analysis demonstrated differentiation between the luminal and mucus gel microbiota, in both controls and UC, with no differentiation between colorectal regions. At a taxonomic level, differentiation was evident between both cohorts, as well as between the luminal and mucosal compartments, with a small group of taxa uniquely discriminating the luminal and mucosal microbiota in colitis. There was no correlation between regional inflammation and a breakdown in this spatial differentiation or bacterial diversity. CONCLUSIONS: Our study demonstrates a conserved spatial structure to the colonic microbiota, differentiating the luminal and mucosal communities, within the context of marked interpersonal variability. While elements of this structure overlap between UC and control volunteers, there are differences between the two groups, both in terms of the overall taxonomic composition and how spatial structure is ascribable to distinct taxa.