THE WNWETEACH...
The Anatomy of the Peritoneum RUFUS M. CLARKE
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Rufus M . Clarke, M A , MD, PH.D, is Foundation Professor of Anatomy, Unzuersity of Newcastle Newcastle NS W 2308, Australia.
T h e author describes two educational strategies for helping students to understand the complex threedimensional structure of the peritoneal cavity and the developmental changes by which that structure arises. T h e first strategy consists of a series of conducted circular tours round the peritoneal lining of the postnatal abdomen. T h e second is a demonstration of the developmental history of the placing of the gut and its peritoneum using a model. Visualizing three-dimensional relationships in the peritoneal cavity has always been a difficult task for medical students; the difficulty is compounded by the complex space-time relationship of the embryological development of the mesenteries, omenta, fossae and folds of the peritoneum. The authors of embryological textbooks have attempted to help by giving wordy descriptions, supplemented by numerous diagrams. The inadequacies of the latter attest to the difficulties of representing three dimensions in only two. Some of these difficulties can be overcome by the use of animated film sequences, which also allow portrayal of the continuity of developmental changes in time; however, students often find these difficult to comprehend, except after repeated screenings, because of difficulties in becoming and staying orientated, and because of the sheer concentration of visual information which is contained in the film. It therefore seemed logical to attempt to improve the efficiency of learning by replacing the missing third dimension through the use of specimens, by providing an alternative learning experience to the book or lecture, and by increasing student participation in the learning process. Purpose This paper describes two educational strategies to help students with the anatomy and embryology of the peritoneum. I used them in the Department of Human Morphology in the University of Nottingham Medical 130
School from 1970 to 1975. They have not yet been implemented in the curriculum of the Newcastle (NSW) University Faculty of Medicine on account of its different curricular structure. The first strategy consists of a series of conducted circular tours round the peritoneal lining of the postnatal abdomen; the second is a demonstration of the developmental history of the placing of the gut and its peritoneum through the use of a model. In Nottingham, as in many schools, the anatomy of the abdomen is studied about midway through the basic medical science (preclinical) course. Thus, the students have some familiarity with anatomical terminology and concepts; in particular, they have studied the pleural and pericardial cavities and their development. Students learn anatomy by attending lectures and demonstrations and through dissection. Emphasis is placed on applied and living anatomy. The anatomy of the peritoneum is learned in the context of an integrated course on the alimentary system (AS). The two strategies to be described, together with a brief lecture on the development of the gut, constituted the first class in the AS course, lasting three hours. Strategy 1-Guided
Tours of the Cadaver Abdomen
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Students undertaking dissection classes at Nottingham were guided by a staff member who used a radiomicrophone public address system with a closed circuit television (CCTV) display. The usual pattern was a brief broadcast burst of instructions and guidance, followed by an opportunity for students to carry out the dissection or analysis, under the direction of demonstrators. Because the first class in the AS course had to form the anatomical basis for subsequent physiological and biochemical classes, it was necessary to proceed straight to the gut and peritoneum. The abdomen was opened by a cruciate incision, leaving the umbilicus in the right upper quadrant. Students were then given a guided tour of the abdominal viscera, proceeding from stomach to rectum. They returned later to a study of the anterior abdominal wall. Medical Teacher V o l 2 No 3 1980
T h e strategy adopted to accustom students to the general layout of the peritoneum was to ask them to imagine themselves in the role of an insect walking about on the peritoneum, and to undertake a series of circular tours, each ultimately arriving back at the starting place .thus demonstrating the continuity of parietal and visceral peritoneum). T h e route of the tour was displayed as a diagram on the television screen, and talked through jlowly, so that the students had the chance to follow the route on the cadaver in front of them. Three tours were undertaken.
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Tour 1 - Transverse Section through the Mzd-abdomen The picture displayed on the tclevision scrcen is a transverse section of the abdomen at about the level of thc fourth lumbar vertebra (e.g. Figure 1 ) . This level illustrates the uncomplicated 'primitive' stage with the jmall intestine and its dorsal mesentcry. The tour starts on the parietal peritoneum of thc anterior abdominal wall and passes laterally onto the posterior abdominal wall. T h e paracolic gutters and their ,ignificancr are identified, and the concept of rrtroperitoneal organs is introduced. T h e insect, on its tour. climbs the hill created by the paravertebral muscles and the bodies of the lumbar vertebrae. before travcrsing t h e rncsentery. rounding the small bowel and sliding down the mesentcry on the other side. This part of the tour is uscd to show how disentangling the small bowel until it lies parallel with the root of its mesentery, with the mesentcry untwistcd, enables the surgeon to identify thc oral and aboral ends of a loop of small bowel. 'l'he tour continues over the posterior, lateral and anterior a b dominal walls to end where it started. After this broadcast, students arc given a few moments to retrace the tour for themselves. and to consult a demonstrator if necessary.
Figure 1. Transverse section of the mzd-abdomen, showing the arrangement of the peritoneum After Snell, R S., Clinical Anatomy for Medical Students, Lzffle Brown, Boston, 1973. I
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Median umbilical ligament
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/Lateral umblllcal ligament
Greater omentum
Tour 2-Sagittal Section T h e picture displayed on the television screen is one such as that shown in Figure 2. This more complicated tour again starts on the a n terior abdominal wall and proceeds inferiorly, following the peritoneum over t h e bladder to the recto-uterine or recto-vesical pouch (pointing out the relationship of the former to the posterior fornix of the vagina, and of both to the finger examining per rectum). T h e climb to the sacral promontory illustrates its importance as a watershed for peritoneal fluid in the supine position. T h e role of the transverse mesocolon in separating supra- and inframesocolic compartments is well seen, and the likely sequclae of perforation of different parts of the gut can be discussed. In this tour it is preferable not to enter the lesser sac. In the undissected cadaver i t is oftcn difficult to trace the peritoneal rcflections off the liver, and it is wise to have some spare cadavers ready if u n suspected peritoneal pathology obscures the normal anatomy. T h e tour again concludes on the anterior abdominal wall, and students are given time to retrace thc tour for themsclves.
TOUT 3- Transverse Section through the Lesser Sac T h e picture displayed is a transverse section at the level of the twelfth thoracic vertebra (Figure 3). Starting on the anterior abdominal wall in the midline, t h e tour progresses to the right, and traverses the falciform ligament and inferior surfacc of the liver to the right subhepatic space (pouch of Rutherford Morison). T h e right subphrcnic space cannot usually be explored. but the tour passes over the right kidney and through the entrance into t h e lesser sac. Once the lesser omentum has been identified, its relationship to the lesser sac noted, and the structures in its free border palpated, the lesser sac can be better explored by perforating the lesser omentum with a finger. This manoeuvre facilitates digital investigation of the recesses of the lesser sac, especially the inferior recess, which is closed inferiorly by fusion of the layers of the greater omentum. T h e tour continues over the anterior surface of the lesser omentum and over the stomach to the spleen, demonstrating in turn tbc gastrosplenic and lienorenal ligaments. From the left kidney t h e tour concludes by passing anteriorly along the parietal peritoneum to the mid line. This tour is more complex, and students often need some time to fathom the mysteries of the lesser sac.
Strategy 2-Modelling the Embryology
Aoria
.Medical Teacher V o l 2 No 3 I980
Inferiorvena cava
T h e educational strategy described here aims to recapitulate the positional changes undergone by the gut and peritoneum during development from the primitive fore-, mid. and hindgut stage to the postnatal disposition, by the use of a model large enough to demonstrate to the classes of 48 students in Nottingham during the era in question. T h e session started with a lecture which described the organogenesis of the gut 131
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Figure 2. Sagittal section of the female abdomen, showing the arrangement of the peritoneum. After Snell. R . S . , Clinical Anatomy for Medical Students, Little Brown, Boston, 1973. tube. T h e model was then demonstrated, and sub. sequently made available in a classroom for students to test their understanding of the processes.
Fi.gure 3. Trunsuerse section ofthe abdomen through the lesser sac. After Snell, R . s., Clinical Anatomy for Medical Students, Little Brown, Boston, 1973.
Development of the Peritoneal Caw'ty Many of the idiosyncrasies of the postnatal peritoneum are seated in their developmental history. and students often find a knowledge of the latter to be helpful in a p preciating the former. In deriding upon the order of learning, the assumption has been that students will be able to understand developmental anatomy more readily if they already have some idea of the final outcome, i.e. picture. ?'herefore, the second the gross anatomical strategy aims at gving students a three-dimensional insight into the dynamic processes of gut and peritoneal embryology .
The Model
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T h e principles of construction of the model are depicted in Figure 4 , which should be examined in conjunction with this description. On a 20 mm blockboard base ( 1 ) (500 m m X 700 rnm approx.) was mounted a 12 m m slieet of insulation board (2) (500 rnm x 1,000 mm apprjx), into which pins could easily be stuck. This sheet represents the posterior abdominal wall. T h e top ( 3 ) , also of insulation board (500 m m X 500 m m approx.), represents the diaphragm. Stiffening gussets (4) are needed, and a carrying handle is also advantageous (not depicted). Medical Teacher V o l 2 N o 3 1980
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Indications Treatment of all grades of hypertension when oral antihypertensive therapy is indicated Dosage and Administration The recommended starting dose is lOOmg three times daily If necessary, this may be increased gradually at intervals of one or two weeks A daily dosage of 600mg is usually adequate but severe cases may require up to 2,400mg daily Once the optimum dosage is established a twice daily dosage regimen can be used TrandateTablets should preferably be taken after food For transfer of patients from other antihypertensive therapy see Data Sheet Trandate therapy is not applicable to children Contra-indications There are no known absolute contra-indications Warning There have been reports of skin rashes and/or dry eyes associated with the use of beta.adrenoceptor blocking drugs The reported incidence is small and in most cases the symptoms have cleared when the treatment was withdrawn. Discontinuatlon of the drug should be considered if any such reaction is not otherwise explicable Cessation of therapy with a beta adrenoceptor blocking drug should be gradual Precautions Trandate should not be given to patients with uncompensated or digitalis resistant heart failure or with atrioventricular block The presence of severe liver disease may necessitate reduced doses of Trandate Care should be taken in asthmatic patients and others prone to bronchospasm Unnecessary administration of drugs during the first trimester of pregnancy is undesirable Side effects If the recommended dosage instructions are followed side effects are infrequent and usually transient.Those that have been reported include headache, tiredness dizziness, depressed mood and lethargy, difficulty in micturition, epigastric pain, nausea and vomiting, a tingling sensation in the scalp, and, in a very few patients, a lichenoid rash Trandate Tablets lOOmg PL 0045/0106, Trandate Tablets 200mg PL 0045/0107, TrdndateTablets 400mg PL 0045/0109 Full prescribing information is available on request Trandate is a trade mark of Allen & Hanburys Ltd London E2 6LA
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Figure 4. Diagrammatic reprehentation of the model used to demonstrate the deuelopment of the postnatal posztzon of the gut and its mesenter-zes. See text f o r detazls
In the midline of the posterior abdominal wall runs a length of plastic covered curtain wire ( 5 ) (the spiralwound, slightly extensible variety); it is secured to a screw eye in the base, and led through a small hole in the insulation board top. Before being finally fixed in place, the wire is threaded through a 1,500 to 1,800 mm length of tubular open weave bandage (6) (Tubegauz) of large size (400 mm circumference approx.). This represents the primitive dorsal mesentery, and the curtain wire represents its root. In the anterior free border of the mesentery is lightly sewn a length of heavy gauge black plastic sheet (7) (width 30 mm approx.). This represents the primitive gut tube; tubing would perhaps be more realistic, but tends to be too rigid to be formed into colonic and duodenal flexures. Two modifications (not depicted) have to be built in to the dorsal mesogastrium: first, a small fist-sized lump of polystyrene foam, suitably coloured with emulsion paint, is inserted to represent the spleen; secondly, a n apron-shaped double layer of Tubegauz has to be sewn into a defect created between stomach and spleen, to represent the greater omentum. A further sheet of Tubegauz (not depicted) is sewn on to represent the ventral mesentery of the primitive foregut. In its inferior free border it bears a (plastic strip) bile duct, which leads to a large, red, wedge-shaped lump of polystyrene foam, the liver.
Medical Teacher V o l 2 No 3 1980
Finally, red plasric strip representations of the three arteries of supply (8) to the fore-, mid- and hindgut are zewn i n t o the dorsal mesentery, the coeliac artery passing close to the spleen. T h e only remaining requirement is a profuse supply of m a p pins (12 m m shaft, 3 m m glass head).
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How the Model is Used Before starting, the liver has to be pinned or sewn to the diaphragm; in the absence of this fixation, thc ensuing ptosis cffcctively hinders any further development! T h e parts of thc model arc first explained, then the umbilical herniation of the gut is easily modelled because the length of the gut substantially exceeds the length of the root of its mesentery. Care should be taken at this stage to ensure that t h e segment of gut which is the destination of the end of the superior mesenteric artcry (the site of Meckel’s diverticulum) is the most herniated segment. T h e hernia is then progressively reduced by pinning the ends of the gut to the posterior abdominal wall. T h e stomach is twisted, throwing the spleen and greater omentum to the left. and the superior part of the duodenum is pinned in front of thc midline, followed by the rest of the duodenum as far as the duodenojejunal junction, twisting the duodenum so that the bile duct passes posterior to i t . Redundant mesentery of retroperitoncal structures is tucked and pinned behind them. Inferiorly, the rectum is pinned in the midline, and the root of thc sigmoid mesocolon pinned down as an i n verted V . T h e roots of mesenteries are best highlighted by using pins of a different coloured head. T h e descending colon is pinned out to the left (explaining the mechanism of zygosis, and showing. in passing, how the colon can be surgically mobilized). T h e root of the transverse mesocolon is pinned across in front of the duodenum, and the transverse colon allowed to hang down. taking care not to trap the greater omentum behind these structurcs. T h e ascending colon is similarly fixed a n d , if the proportions have been correctly judged, one is left with the small intestine, w i t h the superior mesenteric artery ending in its distal quarter. T h e root of the mesentery is pinned out, curving obliquely across the posterior abdominal wall. T h e final stage is to fuse the posterior layer of the greater omentum w i t h the anterior surface of the transverse mesocolon by the use of a couple of safety pins. While all this is going o n , one also has to provide a running commentary, and to keep out of the way, so that the audience can see what is happening. A t the e n d , i t is wise to recapitulate the structures and their relationships, and to point out such features as thc lesser sac by passing a couple of fingers into i t from the right, behind the bile duct in the free border of the lesser omentum. The model can, of course, be used to demonstrate the development of congenital anomalies. After the structures h a v been unpinned, and the model restored to its ‘primitive’ condition, students are encouraged to t r y modelling the developmental sequence for themselves.
.Medical Teacher V o l 2 N o 3 1980
Alterna i j ve Serdngs Effective use of these strategies is not confined to the classroom setting described. Familiarity with the threedimensional arrangement of the peritoneum in the adult requires a cadaver (or a postmortem specimen), but could equally well be conducted by a demonstrator and a group of students with a series of diagrams on a handout or a blackboard, or could be incorporated into a selfinstructional package, for example with an audiotape and workbook. Similarly, the model can be used by a demonstrator with small groups, or for self-instruction. Its use for large groups would be restricted, unlcss i t were constructed on a much larger scale, so that those a t t h e back could see. Evaluation of these Educational Strategies N o formal evaluation was carried out, partly because of the difficulties of objective testing of the knowledge and understanding acquired, and partly because these strategies representcd only a small segment of the course. Student acceptability of both strategies seemed high, probably because of the bizarre notion of imagining oneself crawling about in the peritoneal cavity, and because of the novelty of the demonstration as opposed to a lecture. However, few students availed themselves of the opportunity to experiment with the model in the days after the class.
Summary Two educational strategies have been described for helping students to understand the complex threedimensional structure of the peritoneal cavity, and the developmental changes by which that structure arises. Students learn the gross structure by undertaking three circular tours around the peritoneal lining of the a b domen, two transversc and one sagittal. T h e e m bryological development of the relationships is demonstrated using a model of the g u t and its adnexae and its mesenteries. These strategics are certainly a c ceptable to students, but their educational efficacy has not been tested.
F u r t h e r Reading Snell. R. S . . Clinical A n a f o m y for Medical StudenLJ, Liitlr Brown Boston. 1973
Acknowledgements I thank Profrssor Rex Coupldnd Univrrsiiy of Nottinsham. for freedom in he rrcative in education I thank Associate Profecsnr Charles F.ngel and Dr Derek Wdrdk for constru(itve criririmi of the manuscripr a n d Mr John Slnqlr for his hrlp with Figure I
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