Imaging the Vermiform Appendix

Near the ileocecal valve, at the junction of the small intestine and large intestine, lies a blind-ended tube and possible homeostatic regulator called the vermiform appendix. The organ can cause several abdominal maladies that, if left untreated, can result in a complicated recovery or death. Imaging professionals should understand the structure and function of the entire gastrointestinal tract to provide optimal care for patients undergoing diagnostic imaging. This article provides a brief overview of gastrointestinal anatomy, appendix physiology and function, clinical evaluation, appendix imaging, and treatment of appendicitis.

The vermiform appendix: not a useless organ

The appendix has often been seen more as a nuisance rather than an important part of the human anatomy. Early misconceptions have led to the indiscriminate removal of the appendix from the body. Long thought to be an evolutionary remnant of little significance to normal physiology, the appendix has more recently been identified as an important component of mammalian mucosal immune function, particularly B-lymphocyte-mediated immune responses and extrathymically derived T-lymphocytes. This structure helps in the proper movement and removal of waste matter in the digestive system, contains lymphatic vessels that regulate pathogens, and lastly, might even produce early defences that prevent deadly diseases. The appendix is one of the guardians of the internal environment of the body from the hostile external environment.

Multiple myenteric networks in the human appendix

The general histological organization of the appendix, including its innervation, is believed to be generally similar to that of the large intestine. However, several authors described an unusual arrangement of the myenteric ganglia within the appendiceal muscle, but conflicting reports do not allow clear conclusions on this matter. The aim of this work was to examine the appendiceal innervation in detail. The myenteric plexus of the human appendix was examined using sections and whole mount preparations. Human small and large intestines were used for comparison. The nerves were stained using immunohistochemistry, enzyme histochemistry for NADPH-diaphorase, and vital staining with 4-(4-diethylaminostyryl)-methylpyridinium iodide. Appendices from rabbits were also studied. In most cases, the innervation of the external muscle of the appendix consisted of three concentric networks of ganglia. These networks were located both between the circular and longitudinal muscle layers and within them. The middle network made connections with the other two. Such arrangement was not observed in the human small and large intestines. The myenteric plexus in the rabbit appendix displayed a much smaller degree of three-dimensional distribution compared with that of the human appendix. It is concluded that the myenteric plexus in the human appendix consists of several distinct networks, and appears to be unique in comparison with the other parts of the intestine.

Implications of removing a normal appendix

BACKGROUND

The diagnosis of acute appendicitis remains difficult and therefore 15-30% of the removed appendices appear to be normal. The aim of this study was to investigate morbidity, mortality and costs of removing a normal appendix in patients with suspected appendicitis.

PATIENTS AND METHODS

Retrospective study of patients who underwent a negative appendectomy for suspected appendicitis in the period 1991-1999 with a median follow-up of 4.4 years. Patients who underwent an elective appendectomy or appendectomy for other reasons were excluded.

RESULTS

In 285 patients (70% women, 30% men) a normal appendix was removed. In 192 (67%) patients a muscle-splitting incision was performed, in 6 (2%) a median laparotomy, and in 51 (18%) the normal appendix was removed by laparoscopy. In 36 patients (13%) a diagnostic laparoscopy was converted to a muscle-splitting incision. Complications occurred in 16 (6%) patients, in 5 (2%) a re-operation was needed. The mean hospital stay was 4.4 (SE 2.8) days, in case of complications 7.4 (SE 4.2) days. The mean extra hospital costs of a negative appendectomy were EUR 2712.

CONCLUSION

The removal of a normal appendix has considerable complications and costs. In an attempt to prevent these costs, extra diagnostic tools should be considered. Expensive diagnostic tools such as diagnostic laparoscopy should be used selectively in order not to further increase costs.

Nitrergic hyperinnervation in appendicitis and in appendices histologically classified as normal

CONTEXT

The pathogenesis of appendicitis remains poorly understood. Despite new diagnostic techniques, appendices removed from patients with suspected appendicitis often appear histologically normal on conventional examination. There is increasing evidence of involvement of the enteric nervous system in immune regulation and in inflammatory responses in the gastrointestinal system.

OBJECTIVE

To investigate the nitrergic innervation of (a) acutely inflamed appendices, (b) appendices classified as histologically normal from patients with a clinical diagnosis of appendicitis, and (c) normal control appendix specimens, using the whole-mount preparation technique.

PATIENTS AND DESIGN

Full-thickness specimens were collected from 28 acutely inflamed appendices (age range, 3.2-13.4 years), 31 histologically normal appendices removed from patients (age range, 5.7-13.6 years) with suspected appendicitis, and 23 histologically normal appendices from patients (age range, newborn to 12.1 years) undergoing elective abdominal surgery (controls). Whole-mount preparation using nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry and neuronal nitric oxide synthase immunohistochemistry were performed. The density of myenteric plexus was measured with a computerized analysis system.

RESULTS

The density of myenteric plexus in normal appendix specimens was similar to that of large bowel from the newborn period up to 3 years of age; this density decreased significantly thereafter. The myenteric plexus of normal appendix specimens from patients older than 4 years demonstrated smaller ganglia connected by thin nerve bundles, compared to larger ganglia and nerve bundles in large bowel. Significant neuronal hypertrophy was found in 55% of acutely inflamed and 41% of histologically classified normal appendix specimens. The myenteric plexus of these appendix specimens had even thicker nerve bundles connecting an increased number of ganglion cells.

CONCLUSIONS

Differences in the architecture of the myenteric plexus in patients older than 3 years suggest an altered function and motility of appendix in the early years of life. The significant increase in neuronal components of the myenteric plexus in a high proportion of acutely inflamed and histologically normal appendix specimens is unlikely to have developed during a single acute inflammatory episode. This suggests an underlying chronic abnormality as a secondary response to chronic luminal obstruction or repeated inflammatory episodes in the histologically normal appendix.

[Appendectomy reduces the risk of development of ulcerative colitis]

The etiology and pathogenesis of ulcerative colitis are still unclear. There is, however, a growing consensus that the disease is characterized by a complex interaction between genetic and environmental influences. Many studies in the last few years have suggested that appendectomy reduces the risk of development and improves the course of ulcerative colitis. The underlying mechanism of this effect is unknown. The appendix seems to play a more important role in the development and modulation of the mucosal immune system than believed so far.

Role of appendix and spleen in experimental colitis

There is growing clinical evidence suggesting that certain secondary lymphoid tissues (e.g., appendix and spleen) contribute to the initiation and/or perpetuation of ulcerative colitis. In this study, the importance of secondary lymphoid tissues in inducing colitis was assessed experimentally by removing the spleen and/or appendix (or sham operation) prior to inducing colitis in mice. Feeding 2.5% dextran sulphate sodium (DSS) in drinking water over 7 days induced colitis. Clinical disease activity was assessed based on weight loss, stool consistency, and presence of blood in stools. Additional measurements included white blood cell count and hematocrit, and myeloperoxidase activity (MPO) in colon samples. Colonic injury was assessed by histology and computerized image analysis. DSS treatment in sham-operated mice produced colitis associated with weight loss, bloody diarrhea, and mucosal ulceration. Clinical assessment of DSS-treated mice subjected to appendectomy or combined appendectomy/splenectomy exhibited a delayed onset and course of disease activity. Histomorphologic examination revealed significantly lower damage scores and a reduction in ulcerated mucosal surface area. Colonic MPO activity, which correlated with tissue injury and disease activity, was lowest in appendectomized mice. No beneficial effects of splenectomy were observed after 7 days of colitis. These findings support the hypothesis that appendicular lymphoid tissue, but not the spleen, contributes to the development of colitis.

[The useless appendectomy]

The appendectomy is still the most frequent operation in general surgery, being after performed without complete investigation. Because the appendix, through its lymphoid tissue with implication in the immunoglobuline secretion, has an important role in immunitary system criteria were searched to justify the appendectomy and to reduce the number of useless appendectomies, the proportion of the normal appendices being around 15%. Instead the basic triad-fever over 38 degrees C, parietal reaction and leucocitosis over 10.000/ml--measuring of reactive protein C, echography, CT, laparoscopy and antileucocite antibody labelled with TC99, would contribute to a better selection of patients for appendectomy. Surgeon's responsibility regarding the technique and the moment of operation, oblige him to take the proper decision.

Is appendectomy a causative factor in ulcerative colitis?

There are strong indicators that the aetiology of inflammatory bowel disease should be regarded as multifactorial, involving an interaction between genetic and environmental factors which give rise to an inadequate immunological response. During the past decade at least seven case-control studies have shown an inverse association between appendectomy and ulcerative colitis. Conclusions have been that either ulcerative colitis protects against appendicitis, or appendectomy protects against ulcerative colitis. The immunological function of the appendix is not well known, but experimental studies suggest that the appendix is possibly an important site for priming of the cells involved in the development of inflammatory bowel disease. Experimental and prospective cohort studies are needed to provide more insight in a possible relation between ulcerative colitis and the appendix.

From the foot-mouth reflex to the hand-mouth reflex. A continuum of responses to appendicular compression

We studied the mouth opening response to appendicular compression in two groups of children. This study was performed with the intention of testing the semiologic role of the act of mouth opening following stimulation of various regions, based on the hand mouth reflex of Babkin. Group I was formed by 33 normal children who underwent monthly follow up assessments since birth; and group II consisted of 50 children older than 6 months of age, known to have a neurologic deficit and a neuro-psychomotor development equivalent to that of a child in the first trimester of life. We observed that the normal mouth opening response in group I was more pronounced following compression of the hand and forearm when compared to compression of the arm (p < 0.001). This response could persist for as long as the first 6 months of life. We were not able to elicit a mouth opening response following compression of the lower limb in this group. Among children from group II, we observed mouth opening responses to stimulation of all limb segments. Within the upper limb, the response was more pronounced following compression of the hand in comparison to the forearm (p < 0.01), and forearm in comparison to the proximal arm (p < 0.01). Stimulation of the foot was more effective in eliciting a mouth opening response when compared to equivalent stimulation of the lower leg (p < 0.05). However, there was no statistical difference when responses to stimulation of the lower leg and thigh were compared. The presence of the previously unreported foot-mouth response may serve as an indicator of central nervous system compromise and could be associated with a poorer prognosis. We believe that our observations of the specific foot-mouth response patterns may serve as a marker of early neuro-psychomotor development dysfunction during childhood.

The effect of acute ligation of the rabbit appendix on antioxidant enzymes

The role of oxygen free radicals (OFR) in the pathogenesis of many diseases is known. This experimental study was planned to investigate the role of OFR in acute abdominal inflammation. In this study, 20 adult rabbits were used. They were divided into two groups with 10 rabbits in each. In the study group, blood samples were taken from peripheral and mesenteric veins and then their appendices were ligated; after 24 h, blood samples were taken again and the appendices were resected. The same procedures were carried out in the control group, except for ligation of the appendices. Superoxide dismutase,catalase and glutathione peroxidase (GPX) activities were measured in all blood samples. The activities of catalase and GPX were increased postoperatively in peripheral and mesenteric blood samples in the experimental group. The catalase activity was increased in the control group. These results suggest that OFR increased sufficiently to activate the enzymatic defense system in acute appendicitis.

Rabbit IgH sequences in appendix germinal centers: VH diversification by gene conversion-like and hypermutation mechanisms

Although the rabbit IgH locus contains approximately 100 VH genes, the majority of B cells rearrange VH1. To produce a primary repertoire containing a sufficient number of protective antibodies, rearranged VH1-DH-JH sequences may diversify within rabbit B cells in an organ that functions like a chicken bursa, sheep ileal Peyer's patch, or both. It was suggested many years ago that the rabbit appendix could be a bursal equivalent. To reexamine this possibility, we analyzed rearranged heavy chain variable region sequences in B cells from light and dark zones of appendix germinal centers from 6-week-old rabbits. Our findings indicate that antibody diversification occurs by gene conversion-like and somatic hypermutation mechanisms in appendix germinal centers of young rabbits.

Assessment of gut intraepithelial lymphocytes during late gestation and the neonatal period

Intraepithelial lymphocyte counts (IEL % enterocytes) were carried out in histological samples of jejunal, ileal and appendiceal mucosa of 39 neonates, aged from birth to 28 days. Correlations between IEL counts and developmental factors, namely gestational age, birth weight and intrauterine growth, as well as neonatal infections or feeding state were performed. No significant differences were observed among neonates grouped according to birth weight, intrauterine growth or neonatal infections. The pattern of feeding, however was associated with significantly higher IEL counts (p < 0.02) in the ileum in oral/enterally fed neonates than in the unfed or parenterally fed. Full-term neonates also had higher counts in the ileum (p < 0.02). In this group, oral/enterally fed neonates had the higher values. Thus, besides in utero development, the pattern of feeding might be considered as an important modulating factor on IEL postnatal expansion.

The appendix functions as a mammalian bursal equivalent in the developing rabbit

In this paper we present genomic DNA sequence and histological evidence that the appendix is a site of diversification of the rabbit's primary antibody repertoire. By 6 weeks after birth, the B cell follicular regions of the rabbit appendix and the distribution of the resident lymphoid cells bear a strong morphological resemblance to similar regions within two primary lymphoid tissues, the chicken bursa and the sheep ileal Peyer's patch. However, similarities between the rabbit appendix, chicken bursa and sheep ileal Peyer's patch end as these animals reach adulthood. The rabbit appendix undergoes morphological and cellular distribution changes as it matures taking on the appearance of a secondary lymphoid tissue, while the sheep ileal Peyer's patch and the chicken bursa both involute. We determined DNA sequences of PCR amplified rearranged variable region genes from germinal center B cells of 6 week old rabbits isolated from several different appendix dark zones and light zones. There was a trend toward a higher degree of diversification from the germ-line VH gene DNA sequence in dark zones than light zones. It is likely that both gene conversion and somatic hypermutation are responsible for the nucleotide changes we observed. Our findings suggest that the rabbit appendix functions as a mammalian bursal equivalent early in development. As the rabbit matures, the appendix appears to evolve into a secondary lymphoid tissue resembling secondary GALT in appearance and possibly in function.

Role of leukocyte CD11/CD18 complex in endotoxic and septic shock in rabbits

Two models of sepsis were investigated using rabbits. In the first model, rabbits given lipopolysaccharide (LPS) were treated with saline (group II) or CD18 monoclonal antibody (MAb) 60.3 (group III). Group I animals received no LPS. Cardiac output was maintained by infusion of lactated Ringer solution with group II (95 +/- 68 ml/kg) requiring significantly more than group I (0 +/- 0 ml/kg) or group III (39 +/- 27 ml/kg). Lung permeability indexes in groups II (median 0.002, range 0.023) and III (median 0.0035, range 0.053) were not different but were significantly greater than group I (median 0.0007, range 0.001). In the second model, peritonitis was produced by devascularizing the appendix, leaving it in situ for 19 h, and then performing an appendectomy. Saline or MAb 60.3 treatment was at appendectomy and every 12 h for 3 days. Survival was significantly greater in the MAb 60.3-treated group at day 10 (90 vs. 40%). Lung permeability was increased at day 2 and was not different between groups. Day 1 fluid requirements were greater in the saline-treated group. These data are consistent with MAb 60.3 protection of systemic but not pulmonary circulation in two models of sepsis.

Neuropeptides in the human appendix. Distribution and motor effects

At present our knowledge of enteric peptide-containing neurons in man is limited. In this study we have used human appendices removed at surgery to examine the peptidergic innervation by immunocytochemistry, immunochemistry, and pharmacological in vitro experiments. Immunocytochemistry revealed a variety of peptide-containing nerve fiber populations in the human appendix. VIP/PHI-, VIP/PHI/NPY-, SP/NKA-, galanin-, and enkephalin-containing nerve fibers were numerous; CGRP- and GRP-containing nerve fibers were moderate in number, while only scattered NPY-, enkephalin/BAM-, and somatostatin-containing nerve fibers could be found. No CCK-, dynorphin A-, or dynorphin B-immunoreactive nerve fibers could be detected. The coexistence of VIP/PHI, SP/NKA, and enkaphalin/BAM can be anticipated from the known sequence of their respective precursors. However, the coexistence of VIP/PHI and NPY was unexpected but corroborates previous observations in other species. Interestingly, SP and CGRP did not seem to coexist in nerve fibers of the human appendix. Immunochemistry (RIA and HPLC) confirmed the presence of VIP, NPY, SP, galanin, CGRP, GRP, enkephalin, and somatostatin. Motor activity studies suggest that acetylcholine plays a major role in the electrically evoked contractions, since atropine suppressed these contractions. Galanin (10(-8)-10(-6) M) and GRP (10(-9)-10(-7) M) caused concentration-dependent contractions that were unaffected by tetrodotoxin and thus probably reflect a direct action on smooth muscle receptors. GRP (10(-9) M) enhanced the electrically induced cholinergic contraction (to 193 +/- 24%), while met-enkephalin (10(-6) M) reduced it (to 54 +/- 6%). Both peptides failed to affect the contractile response to exogenous acetylcholine and probably act to modulate the release of acetylcholine. NPY, VIP, CGRP, SP, and somatostatin failed to induce contraction or to affect the electrically evoked contractions.

[The effect of histamine and histamine H1 and H2 receptor blockers on the tone of the longitudinal muscles in the human appendix]

The aims of this study were to determine whether the effect of histamine on a smooth musculature of the human appendix is mediated by histamine H1-receptors only or whether histamine H2-receptors are involved, as well. The obtained results indicate histamine increases tonus in musculature; however, histamine H1-receptor antagonist (promethazine) decreases tonus. Histamine H2-receptor antagonist (cimetidine) has caused a mild increase in tonus of musculature what indicates that it has a certain intrinsic activity. By blocking histamine receptors with H1 and H2 antagonists which were used either separately or together before cumulative histamine concentrations, it has been concluded that histamine actions are exerted not exclusively by H1-receptors but also histamine H2-receptor antagonists can significantly decrease the tonicizing effect of histamine.

[The effect of prostaglandin F2 alpha and indomethacin on the musculature of the human appendix]

In their research, the authors have tried to determine possible differences in effects of prostaglandin F2 alpha on longitudinal musculature tonus in normal and inflamed human appendix and the extent to which it is possible to react on prostaglandin effect by indomethacin. The obtained results indicate that PGF2 alpha increases tonus in human appendix musculature; however, the change is more pronounced in a normal appendix musculature. Even more, indomethacin prevents spasms caused by PGF2 alpha in musculature of both normal and inflamed appendix significantly. This indicates that, in addition to its influence on prostaglandin synthesis indomethacin also has another mechanism of activity, may be even at the level of prostaglandin receptors.

Acute appendicitis in the rabbit. An experimental study

With the purpose of devising an experimental model of acute appendicitis, the vermiform appendix in five rabbits was lightly compressed with a specially designed metal clamp, and in five others it was firmly ligated proximally. Based on these experiments, a final model was evolved, with a firm ligature midway on the vermiform process. This model was tested in 15 rabbits and proved to be reliable in provoking acute inflammation in one part, while the rest of the appendix remained unaffected. The literature is reviewed.

Experimental model for the study of the human appendix

A simple and reproducible model for the experimental study of the normally functioning human appendix is described. The appendix removed from a human is transplanted into a nude mouse and is kept vital for at least 4 hours. This model is an improvement on previous models. It corresponds well with the working of the normal human appendix as regards tissue type and characteristics. Results are easily quantified and a paired control is possible in the experimental animal. This simplifies the experimental design and statistical calculations. The model can be used to gain additional information about the pathophysiology of the human appendix and the possible influence of drugs on this organ.

The aging gastrointestinal tract, liver, and pancreas

This article summarizes the age-related structural and functional alterations in the esophagus, stomach, small and large intestines, liver, pancreas, and vermiform appendix. Also considered are the possible relationships of these changes with the disturbance of homeostatic mechanisms and proneness to certain diseases in the aged.

Functional histology of appendix

The appendix is a prominent example of gut associated lymphoepithelial tissue, whose function is to react to the wide variety of antigens present in the gastrointestinal tract. It is composed of a large number of repeating units, the lymphoid follicles, each of which is divided into an apical dome, a large basal nodule with a germinal center, and laterally extending thymus dependent areas. The dome epithelium consists mainly of columnar absorptive cells and of specialized follicle associated epithelial (FAE) cells which are efficient at transporting material from the lumen to the underlying lymphoid tissue, and may also transport macromolecules from the lymphoid follicle into the lumen. The dome epithelium normally has large numbers of lymphocytes within it, as well as smaller numbers of macrophages and plasma cells. Macrophages, and perhaps FAE cells, are capable of processing and presenting antigens to reactive lymphocytes. Lymphocyte proliferation and differentiation in response to antigenic stimulation begins in the lymphoid follicles, but most of the lymphocytes leave by the lymphatics, migrate through lymph nodes and spleen, frequently to complete differentiation into IgA-secreting plasma cells in the lamina propria of mucosal surfaces. Normal function of appendix probably helps suppress potentially destructive humoral antibody responses while promoting local immunity.

Germinal centres and the origin of the B-cell system. I. Germinal centres in the rabbit appendix

Regeneration of follicular structures in the rabbit spleen after a single dose of 450 rads whole body X-irradiation was shown to be dependent upon the presence of the appendix.

Results obtained were in favour of a stream of cells—probably derived from appendix germinal centres—to follicular structures in the spleen, in particular to the lymphocyte corona and marginal zone but excluding germinal centres.

Recovery of the antibody forming potential following X-irradiation was equally shown to be dependent upon the presence of the appendix.

It was concluded that following 450 rads whole body X-irradiation the appendix contributes to the recovery of the antibody forming capacity of the spleen by the production of antibody-forming cell precursors; these latter cells are presumably identical with the follicle replenishing class of lymphocytes derived from appendix germinal centres.

Composition and source of secretion from lymphoid aggregations in the rabbit gut

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