DISTRIBUTION OF HUMAN COLONIC LYMPHATICS IN NORMAL, HYPERPLASTIC, AND ADENOMATOUS TISSUE

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1 GASTROENTEROLOGY Copyright 1973 by The Williams & Wilkins Co. Vol. 64, No.1 Printed in U.S.A. DISTRIBUTION OF HUMAN COLONIC LYMPHATICS IN NORMAL, HYPERPLASTIC, AND ADENOMATOUS TISSUE Its relationship to metastasis from small carcinomas in pedunculated adenomas, with two case reports CECILIA M. FENOGLIO, M.D., GORDON I. KAYE, PH.D., AND NATHAN LANE, M.D. F. Higginson Cabot Laboratory of the Division of Surgical Pathology, Departments of Surgery and Pathology, College of Physicians and Surgeons, Columbia University, New York, New York Prompted by 2 cases of lymphatic metastasis from focal carcinoma in the head of pedunculated adenomas, lymphatics were studied in the colonic mucosa in normal, hyperplastic, and adenomatous tissue utilizing light and electron microscopic techniques. In all three tissues there is a lymphatic plexus associated with the muscularis mucosae, but there are no lymphatics above this level. This explains why lymphatic metastases from superficial intramucosal foci of carcinoma in adenomas do not occur. In lobules of adenomatous tissue, the total distance between the free surface and the muscularis mucosae may be considerably increased, and a focus of carcinoma in adenomatous tissue must at least reach the muscularis mucosae and its lymphatics in order to metastasize. This lack of lymphatics contrasts with the profusion of blood capillaries at the mucosal surface. This may be an example of a more general biological phenomenon in that other sites also concerned with water and ion transport, such as the renal glomerulus, the gallbladder mucosa, choroid plexus, and ciliary body lack lymphatics but exhibit a rich blood capillary network at their transporting surfaces. The occurrence of small carcinomas in adenomatous polyps of the large intestine without invasion of the pedicle is more than a morphological curiosity. Although this is an uncommon event, a number of cases in which such carcinomas exhibit metastatic spread have recently been re- ported. }-8 One of these was presented in an earlier work from this laboratory. 2 When that case was reported it was noted that focal carcinoma in the head of such polyps must not only invade the lamina propria of the adenomatous tissue, but must reach the submucosal stroma of the Received June 19, Accepted August 24, Address requests for reprints to: Dr. Cecilia M. Fenoglio, Surgical Pathology, College of Physicians and Surgeons of Columbia University, New York, New York This work was supported in part by Research Grant AM from the National Institutes of Arthritis and Metabolic Diseases, National Institutes of Health, United States Public Health Service, by 51 Grants P-362 and ET-15F from the American Cancer Society, and by a gift from Mr. and Mrs. Jacques Weber. Dr. Kaye is recipient of a Career Scientist Award of the Health Research Council of the City of New York under Contract The authors wish to express their appreciation to Drs. Raffaele Lattes, Robert Pascal, and John Fenoglio for their suggestions.

2 52 FENOGLIO ET AL. Vol. 64, No.1 head of the polyp before metastasis will occur. At that time the following statement was made: "It is an interesting biologic observation that intramucosal carcinoma or carcinoma-in-situ may 'invade' the lamina propria of the adenomatous tissue, but, despite the presence of venules, capillaries and lymphatic vessels in the lamina propria, metastasis will not occur." Although the presence of blood capillaries in the lamina propria is very evident by light microscopy, the inclusion oflymphatic vessels in this statement represented an assumption that lymphatics would be present where capillaries were present. However, in light of subsequent electron microscopic observations, it now appears that this assumption was unfounded and that in the colon, although blood capillaries are numerous, no lymphatics permeate the lamina propria of either normal, hyperplastic, or adenomatous mucosa. Thus, in the colonic mucosa there is a dichotomy in the distribution of blood and lymphatic capillaries. This report presents the results of an anatomical study of the mucosal lymphatic distribution of normal, hyperplastic, and adenomatous colonic tissue. The study was prompted by 2 additional cases of metastasis from focal carcinoma in the head of adenomatous polyps. These cases will be briefly presented since the pattern of lymphangitic involvement helped elucidate the distribution of these lymphatics. Our aims were three: (a) to study the distribution of lymphatics in the mucosa of normal colon; (b) to study the distribution of lymphatics in the mucosa and submucosa of adenomatous tissue so as to localize the most superficial lymphatics available for entrance by carcinoma cells; and (c) to determine whether there are any fundamental differences in the distribution of lymphatics in normal, hyperplastic, and adenomatous mucosa. In addition, during the course of the study, the inverse relationship between the degree of differentiation of foci of carcinoma in adenomas and the possibility of metastasis was again noted,9 a phenomenon with possible therapeutic implication. Case Reports Clinicopathological Aspects Case 1 (N. R.). (The pathological terminology to be used is the same as that used in our earlier report. 2 For the sake of clarity, we are reproducing as fig. 1 a diagram from that article.) A 58-year-old female was seen at Columbia Presbyterian Medical Center in November 1967 for painful hemorrhoids. A barium enema at that time showed two polyps, one in the sigmoid and one in the descending colon. In April, 1967 she underwent colotomy and polypectomy. Because an invasive carcinoma was found in one of the adenomatous polyps and, because of her general good health, she subsequently underwent segmental sigmoid resection. She recovered uneventfully, and remains free of metastatic disease. The more distal of the two polyps measured 1.4 cm in its maximal diameter; the stalk measured 0.4 cm in length. Serial block sections showed an adenomatous polyp containing a focus of poorly differentiated carcinoma which invaded through the muscularis mucosae into the submucosa of the head of the polyp (fig. 2a). Some areas of the carcinomatous epithelium showed subgland formation, loss of polarity, and nuclear anaplasia; poor differentiation was shown in that neoplastic cells occasionally formed almost solid sheets without recognizable glandular formations (fig. 2b). The characteristic cytological appearance of adenomatous epithelium displacing normal epithelium is seen in figure 3a. The analagous replacement of adenomatous epithelium by carcinoma is seen in figure 3b. Carcinoma was found in a lymphatic of the stalk (fig. 4a). The sigmoid resection was not remarkable except for a hard nodule measuring 0.5 cm in diameter in the mesentery 1.5 cm from the site of the polyp. Microscopically, this was a lymph node containing poorly differentiated adenocarcinoma histologically resembling that found in the polyp (fig. 4b). Forty-four other lymph nodes were negative. Case 2 (S.G.). A 58-year-old female had an episode of rectal bleeding; air contrast

3 January 1973 DISTRIBUTION OF HUMAN COLONIC LYMPHATICS 53 FIG. 1. Semidiagrammatic representation of an adenomatous polyp containing a focus of invasive carcinoma. The labeling indicates the morphological criteria by which the terms used in this report are defined. Line X-Y connects the points of junction of normal (stalk) and adenomatous (neoplastic) epithelium and is taken, therefore, as the boundary between the head and stalk. Areas Sand S' are the submucosa of the stalk and head, respectively. M illustrates the looplike boundary by bundles of muscularis mucosae. This boundary separates the adenomatous tissue from the submucosa of the head. In situ (see i~et) refers to carcinomatous tissue restricted to the zone superficial to the boundary indicated by bundles of the muscularis mucosae. INV (see inset) indicates the earliest anatomic stage of invasive carcinoma in which the submucosa of only the head has been involved. Note: the distance from the free surface to the muscularis mucosae is many times increased in the lobules of adenomatous tissue as compared with the same distance in normal mucosa. The diagram is representative of the differences in these distances as seen in histological sections. (Reprinted with the courtesy of the American Journal of Clinical Pathology 48: 172, 1967.) study showed a 3-cm pedunculated lesion in the midsigmoid. In November, 1970 she underwent transabdominal colotomy and polypectomy; exploratory laparotomy was negative. Focal carcinoma in a pedunculated adenoma was found. Since there was extensive lymphatic permeation of the stalk she subsequently underwent partial colectomy. One year later, there was a 6-cm stricture in the proximal sigmoid near the anastomotic site. At laparotomy a left lower quadrant carcinomatous mass invading the musculature of the anterior abdominal wall was found. In addition, there was diffuse peritoneal seeding and recurrent carcinoma was documented histologically. Two weeks postoperatively she was discharged from the hospital on 5 fluorouracil. The head of the adenomatous polyp

4 A A 20 FIG. 2, a and b. From the serial block sections, this one showed the maximum depth of invasion by the focal carcinoma (C) into the submucosa of the head of this adenomatous polyp (arrows). The junction of head and stalk (dotted line) is well below this level. The zones, indicated by A, are classical benign adenomatous tissue. The stalk consists of normal "pulled up" mucosa and submucosa. In b, the poorly differentiated carcinomatous tissue, seen here in contrast with the well differentiated tubules on the left, is representative of the most malignant component of the specimen (x 160). 54

5 JanlUlry 1973 DISTRIBUTION OF HUMAN COLONIC LYMPHATICS 55 FIG. 3, a and b. In a, the adenomatous epithelium displaces the normal epithelium at the junction of the head and stalk (arrow) (x 180). In b, poorly differentiated carcinomatous tissue on the right appears to be dis placing (arrows) better differentiated neoplastic epithelium, just as the adenomatous epithelium displaced the normal in a ( x 235). measured 3 cm in maximum diameter; the stalk measured 0.4 cm. For the most part it was composed of typical adenomatous tissue in' which there was a focus of carcinoma that invaded the submucosa of the head of'the polyp in a manner topographically similar to case 1. The focus of the carcinoma was partly well differentiated, but also had a more anaplastic population of cells, as in the 1st case. Masses of anaplastic tumor appeared to displace better differentiated neoplastic elements (fig. 5a) and anaplastic cells diffusely permeated the lymphatics of the head and stalk (fig. 5b). Microscopic examination of the sigmoid resection specimen showed neoplastic cells within serosal lymphatics. Metastases were present in all of the epicolic and paracolic lymph nodes, but the nodes from the "high point" of the mesosigmoid were negative. Comment In both cases there was extensive carcinoma in the lamina propria of the adenomas, but the carcinoma was in lymphatics only at the level of the muscularis mucosae and submucosa. Therefore, the question arose whether lymphatics might be absent in the lamina propria. Since, in colonic carcinoma, metastasis is usually initially via the lymphatics, might the absence of lymphatics be' one reason why carcinoma confined to the mucosa does not metastasize? Our study in regard to these questions is presented at this point. Materials and Methods Of several approaches suggested for the study of lymphatics we have used the following three methods: (a) light microscopic examination of dilated lymphatics in a variety of congested and edematous colonic tissues; (b) electron microscopic examination of surgically removed normal, hyperplastic, and adenomatous tissues; and (c) light microscopic examination of surgical colonic specimens demonstrating extensive carcinomatous permeation of the lymphatics. Light Microscopy "Normal" mucosal samples were chosen from cases in which dilated lymphatics could

6 56 FENOGLIO ET AL. Vol. 64, No.1 FIG. 4, a and b. Carcinoma in a lymphatic (arrow) of the stalk (a) is regarded as a genuine finding since a lymph node metastasis was present (b) (a, x 160; b, x 150). be seen. Usually these were colons removed for a localized pathological process. These samples included areas of mucosa at a distance from carcinomas, diverticula, polyps, and intramural tumors. Two hundred-fifty normal specimens were examined. From 300 randomly chosen polyps from the diagnostic files of the Division of Surgical Pathology, 80 examples of adenomatous polyps and 50 examples of hyperplastic polyps showing dilated lymphatics were studied. The necessity of using specimens with di-

7 FIG. 5, a and b. As in case 1 (fig. 3b), portions of better differentiated neoplastic glands appear to be displaced by poorly differentiated carcinoma (arrow). The latter also exhibits remarkable lymphatic permeation (b). Some of the carcinoma in the lamina propria is within perivascular lymphatics at the level of the muscularis mucosae (MM) (a, x 170; b, x 2(0). 57

8 58 FENOGLIO ET AL. Vol. 64, No.1 lated lymphatics for light microscopic studies is due to the fact that many lymphatics are normally collapsed and not visible. An example of such a lymphatic that would not have been visible with the light microscope is shown in figure 6. In tissues with dilated lymphatics, there exists the theoretical possibility that a new production of lymphatics has occurred at sites where there were none normally. This possibility was excluded by electron microscopic studies of non-edematous tissues (see below). Electron Microscopy Surgically removed specimens, received fresh in the operating room, were studied electron microscopically. On all pedunculated lesions, a specimen from the tip and from the junction of the head and stalk was taken. Usually one-half of each small non-pedunculated hyperplastic polyp was taken. In addition to 28 specimens of normal mucosa, 20 adenomatous polyps and 21 hyperplastic polyps were examined with the electron microscope. Carcinomatous Autoinjection Ten cases of carcinoma of the colon were selected which showed lymphatic permeation adjacent to the tumor. These were studied in the routine sections taken from such specimens in this laboratory. However, in relation to the question of the lymphatic distribution in the lamina propria and submucosa of adenomatous tissue, the 2 cases described above, which ex- FIG. 6. The lymphatic across the top of the electron micrograph is almost completely collapsed and would not be distinguisable with the light microscope. The potential lumen is indicated by the arrows. L, lumen; MM, muscularis mucosae (x 19,850).

9 January 1973 DISTRIBUTION OF HUMAN COLONIC LYMPHATICS 59 hibited lymphatic permeation were studied in detail. This was done by preparing subserial sections of both specimens. Results Light Microscopy The most superficial lymphatics are identifiable as irregular, thin-walled spaces lined by flattened endothelium without muscle or adventitia. At the level of the muscularis mucosae, such lymphatics are easily distinguished from blood vessels by their large diameters, relative to their thin walls (fig. 7). The presence or absence of blood is not generally helpful in distinguishing between blood and lymphatic capillaries in surgically handled tissues. (1) In the normal mucosa, lymphatics were seen as a network immediately superficial to, within, and below the muscularis mucosae (figs. 8, a and b, and 9a). Some blunt-ended lymphatic loops extended upward for a short distance, to abut on the base of a crypt. No lymphatic was identified in the lamina propria above the lowest one-sixth of the crypt. In all cases the lymphatics maintained an intimate association with the muscularis mucosae. (2) In the hyperplastic polyps, the association of the most superficial lymphatics FIG. 7. The irregular shape, large caliber, and thin wall of the lymphatic contrast with the opposite features of the blood capillary. L, lymphatic, C, capillary (x 880).

10 60 FENOGLIO ET AL. Vol. 64, No.1 FIG. 8. (see also fig. 9). a, The most superficial lymphatics form a plexus at the level of the muscularis mucosae (x 50). b, As indicated by the letters, the lymphatic channels are found just above (LA), within (L W), and deep (LD) to the muscularis mucosae (x 350). C, blood capillary. c, Typically, the most superficiallymphatic channels only reach to the level of the base of crypts (x 140). with the fibers of the muscularis mucosae was the same as the normal. A minor change appeared to be only an architectural one; i.e., the hyperplastic mucosa was associated with a slight elevation of the muscularis mucosae and its lymphatics (figs. 9b and loa). (3) In small adenomas, where the eleva-

11 January 1973 DISTRIBUTION OF HUMAN COLONIC LYMPHATICS 61 HYPERPLASTIC POLYP ADENOMATOUS POLYP ADENOMATOUS POLYP ( CROSS SECTION ) FIG. 9. Diagrammatic summary. a, The normal colonic mucosa shows a lymphatic plexus around the muscularis mucosae. From this, some blind loops extend upward for a short distance into the lamina propria, but no lymphatics are seen above the level of the base of the crypts. b, In hyperplastic polyps the basic anatomic relationships are preserved. The major change is an architectural one in which the fibers of the muscularis are elevated. c, In the adenomatous polyp there is a disorganization of the fibers of the muscularis mucosae; this change is more marked in the larger polyps. The basic anatomic relationship of muscularis mucosae and lymphatics is preserved. d, In a cross section taken through the head of an adenomatous polyp (dotted line in c), lymphatics can be seen, but only in association with the "pulled up" fibers of the muscularis mucosae; they are not otherwise found. tion of the growth was minimal, the lymphatic distribution was identical to that in the normal or hyperplastic mucosa. In larger polypoid growths, where there was a neoplastic proliferation of epithelium on a stalk of normal tissue, the lymphatics of the lamina propria of the adenoma also proved to be associated with the fibers of the muscularis mucosae. In these instances, not only was there an architectural change, whereby smooth muscle fibers of the muscularis mucosae were elevated into the head of the neoplasm, but the muscularis mucosae was tremendously frayed at the junction of the head and stalk (figs. 9c and lob). The association of the lymphatics with these frayed fibers was seen to best advantage when a cross section through the head of the adenomatous polyp passed at a level in which these "pulled up" fibers of the muscularis mucosae were present (fig. 9el). In this plane, it was clear that while the lymphatics of the lamina propria of the adenoma could be found associated with these fibers, there were no lymphatics in a more superficial location. Electron Microscopy When the normal, hyperplastic, and adenomatous tissues were examined with the electron microscope, lymphatics were only seen associated with the muscularis mucosae or with the bases of the crypts. The electron microscopic studies provided the ultimate criteria used to differentiate the blood and lymph vessels. These criteria are well recognized and are

12 62 FENOGLIO ET AL. Vol. 64, No.1 FIG. 10, a and b (see also fig. 9). At the base of the hyperplastic polyps (a) superficial fibers of the muscularis mucosae with their associated lymphatics may be "pulled up" a short distance toward the intercryptal lamina propria. In adenomas (b), elevation of the neoplastic crypts and "pulling up" of fibers of the muscularis mucosae (M) may be quite marked and lymphatics may accompany them (arrows) (a, x 88; b, x 88). summarized in figures 11 and 12. As was evident by light microscopy, blood capillaries were noted at all levels of the lamina propria, in normal, hyperplastic, and adenomatous tissue. Carcinomatous Autoinjection Intramural lymphatic spread of carcinoma cells in normal mucosa adjacent to carcinomas provided further confirmation of the above results. There was permeation of the lymphatic network associated with the muscularis mucosae, but there was no evidence of lymphatics above the level of the base of the crypts (fig. 13). Lymphangitic spread of carcinoma in adenomatous tissue was extensively present in the 2nd case described above (figs. 5a and b). Numerous involved lymphatics were present in association with the frayed strands of the muscularis mucosae in the head of the adenoma, but again, the lamina propria of the adenomatous zone superficial to these fibers was free of such involvement. These results confirmed the light and electron microscope findings concerning the distribution of lymphatics in adenomatous tissue. Discussion Although the distribution of intramucosal lymphatics of the small intestine is well described in any number of histology texts, the localization of lymphatics in the mucosa of the large intestine has been controversial. Patzelt,20 on the basis of injection studies, states that the situation is similar to that seen in the small intestine. Renyi-Vamos and Szinay,21 while acknowledging the unanimity of this opinion

13 January 1973 DISTRIBUTION OF HUMAN COLONIC LYMPHATICS 63 FIG. 11, a and b. A blood capillary (a) is characterized by regular contours, a regular lamina densa, the presence of fenestrations, and the absence of anchoring filaments. F, fenestrations (x 11,300). A lymphatic (b) is characterized by irregular contours, an irregular or absent (arrows) lamina densa, and anchoring filaments. LD, lamina densa; AF, anchoring filaments; L, lumen (b, x 2800). prior to their study, could only demonstrate lymphatics in the submucosa but not in the muscularis mucosae or lamina propria. In other studies, the lymphatics have been described as a network between the muscularis mucosae and the bases of the intestinal glands. 22, 23 The most recent of these 24 employed multiple techniques to examine rabbit intestine. These included direct injection of dyes into the lymphatic vessels, intraarterial injection of dyes and silver nitrate, and the addition of pepsin to the dyes to facilitate their exodus from the blood vessels. Because of the obvious risk of introduction of artifact associated with injection and digestion methods we thought it advisable to study the distribution of lymphatics in normal and abnormal colonic mucosa in its "natural state" by light and electron microscopy. Ultrastructural differences between lymphatic and blood capillaries have been described and allow for accurate discrimination between the two types of vessels. The generalization to be drawn from our study is that the lymphatics of the colonic mucosa are only associated with the muscularis mucosae, and extend no higher than the bases of the crypts of Lieberkiihn (fig. 9). In hyperplastic and adenomatous polyps the apparently more superficial position of some lymphatics occurs only in association with the displacement of some fibers of the muscularis mucosae into the polyp. The basic relationship of the lymphatics to these fibers remains the same

14 64 FENOGLIO ET AL. Vol. 64, No.1 FIG. 12. As opposed to blood capillaries, the junctional zones between adjacent endothelial cells of lymphatic capillaries are poorly developed and open junctions may be seen (inset). Note again the absence of the lamina densa, L, lumen (x 32,500; inset, x 36,000). FIG. 13. The lymphangitic spread of cancer cells adjacent to a large carcinoma of the colon is seen. Tumor-filled lymphatics have the same distribution as in the normal mucosa (figs. 8a and 9a). None were observed above the level of the base of the crypts ( x 80). (fig. 9), there being thus no real difference in lymphatic distribution among normal, hyperplastic, and adenomatous mucosa. We feel that this displacement of the muscularis mucosae and its lymphatics in polyps is probably a passive phenomenon and not an integral part of the proliferative process. Since there are no known examples of purely intramucosal carcinoma in adenomas giving rise to lymphatic metastasis, this knowledge of lymphatic distribution provides some insight into the anatomical site at which the process of lymphatic metastasis can begin. While realizing that far more must be involved in the biology of the metastatic process than the mere availability of vascular channels, lymphatics do have to be present for lymphatic metastases to occur. Thus, a focus of intramucosal carcinoma in an adenoma must invade at least to the level of the muscularis mucosae to enter lymphatics, and, in the case of large lobules of adenomatous tissue, this distance may be many times greater than in normal mucosa (fig. 1). Moreover, carcinomatous change may occur near the free surface of adenomatous tissue, the furthest point from the muscularis mucosae. There is another factor mentioned by

15 January 1973 DISTRIBUTION OF HUMAN COLONIC LYMPHATICS 65 Morson and Bussey,25 and illustrated by the 2 cases included in this report that is relevant to lymphatic metastasis from pedunculated lesions, namely, the lack of differentiation of the carcinoma. Morson and Bussey stated "that when small early cancers, as defined above, do metastasize, they usually are anaplastic or poorly differentiated adenocarcinoma." 25 The 2 cases presently described contained extensive foci of poorly differentiated carcinoma and it is possible that their aggressive biological ability to invade the most superficially available lymphatics is a reflection of their lack of histological differentiation. These cases, together with Morson's observations, make the finding of poor differentiation in carcinomas in adenomatous polyps of potential therapeutic importance. As a rule, when an adenomatous polyp is removed by polypectomy, focal carcinoma, if found, will be moderately or well differentiated, even if the focus is invasive. If it is confined to the head of the lesion, there is clearly no indication to consider additional (radical) surgery. However, we have now learned that if such a focus of invasive carcinoma, even if confined to the head of the polyp, is poorly differentiated, invasion of lymphatics and metastasis can occur. Data are insufficient to quantitate this phenomenon, but clearly such specimens deserve additional sectioning and careful examination for invasion of the lymphatics. In any case, the possibility of additional radical surgery cannot automatically be dismissed. A point of more general interest that emerged from this study is the dichotomy in the distribution of the blood capillaries versus the lymphatic capillaries in the colonic mucosa. The former are profusely distributed as a plexus under the free surface epithelium (perhaps to deal most effectively with solute and water transport), while the latter (not needed for absorption as they are in the small intestine) are not present superficial to the level of the muscularis mucosae. Perhaps this is an example of a more general phenomenon since other structures concerned principally with water and ion transport, such as the renal glomerulus (G. Godman, personal communication), choroid plexus (G. Kaye, unpublished data), ciliary body (unpublished data), and gallbladder mucosa, 26 also have blood capillaries immediately at the transporting surface but do not have lymphatics at this site. REFERENCES 1. Palacios R, Wellman K: Adenomatous polyps of colonic adenocarcinoma and pulmonary metastases. Gastroenterology 51:82-86, Lane N, Kaye GI: Pedunculated adenomatous polyps of the colon with carcinoma, lymph node metastasis and suture line recurrence. Am J Clin Pathol 48: , Krauss FT: Pedunculated adenomatous polyps with carcinoma in the tip and metastasis to lymph nodes. Dis Colon 8: , Silverberg SS: Locally malignant adenomatous polyps of the colon and rectum. Surg Gynecol Obstet 131: , Manheimer LH: Metastasis to the liver from a colonic polyp. N Engl J Med 272: , Helwig EB: Adenomas and the pathogenesis of cancer of the colon and rectum. Dis Colon Rectum 2:5-17, Starr GF: Adenomatous polyps and polypoid carcinoma of the large intestine. Am J Clin Pathol, 29: , Scarborough R, Dockerey M, Gershon-Cohen G, et al: Adenomatous polyps of the rectum and the colon. Dis Colon Rectum 8:85-96, Morson BC: Malignant lesions of the large intestine. Br J Surg 55: , Rusznyak I, Foldi M, Szabo G: Lymphatics and Lymph Circulation; Physiology and Pathology. Second edition. Oxford, Pergamon Press, Kline IK: Lymphatic pathways in the heart. Arch Pathol 88: , Dobbins WO: The intestinal mucosal lymphatics in man. Gastroenterology 51: , Palay AL, Karlin LJ: An electron microscopic study of the intestinal villus. J Biophys Biochem Cytol 5: , Casley-Smith JR, Florey HW: The structure of normal small lymphatics. Q J Exp Physiol 46: , Ottaviani G, Azzali G: Ultrastructure des capillaires lymphatiques. Symposium International Morphologic Histochemie Paroi Vascus. Fribourg, Switzerland, 1965, p Casley-Smith JR: An electron microscopic study of injured and abnormally permeable lymphatics. Ann NY Acad Sci 116: , Leak LV, Burke JF: Ultrastructural studies on the lymphatic anchoring filaments. J Cell Bioi 36: ,1968

16 66 FENOGLIO ET AL. Vol. 64, No Leak LV, Burke JF: Fine structure of the lymphatic capillary and the adjoining connective tissue area. Am J Anat 118: , Casley-Smith JR: The fine structure of the lymphatics under some pathological conditions, New Trends in Basic Lymphology. Experientia (suppl 14). Proceedings of a symposium held at Charlers (Belgium) July 11-13, Edited JM Collette, G Jantet, E Schoffeniels. Basel, Birchauser-Verlag, Patzelt V: Die Blut-und Lymphgefusse des Marmes, Handbuch der Mikroskopischen Anatomie des Menshen, Verdaungsapparat, part 3, Berlin, J Springer Verlag, 1936, p Renyi-Vamos F, Szinay GY: Das lymphgefassystem des coecums. Acta Anat 34: , Shimizu S Cited by Kamei Y: The distribution and relative location of the lymphatic and blood vessels in the mucosa of the rabbit colon. Nagoya Med J 15: , Ottaviani G Cited by Kamei Y: The distribution and relative location of the lymphatic and blood vessels in the mucosa of the rabbit colon. Nagoya Med J 15: , Kamei Y: The distribution and relative location of the lymphatic and blood vessels in the mucosa of the rabbit colon. Nagoya Med J 15: , Morson BC, Bussey HJR: Predisposing causes of intestinal cancer, Current Problems in Surgery. Chicago, Year Book Medical Publishers, Rappaport A: Anatomic Considerations in Diseases of the Liver. Edited by L Schiff. Philadelphia, AB Lippincott Co, 1969