I
Volume 68 February 1975
77
Section of Laryngology President J A B Thomas FRCS
Meeting 21 June 1974 with the Section of Otology at-The Welsh National School of
Medicine, Cardiff
The Significance and Management of Metastatic Lymph Nodes in the Neck Major A J S Burge (Catterick Military Hospital, Catterick Camp, Yorkshire)
Histological Changes in Cervical Lymph Nodes Following Clinical Irradiation The practice of irradiating lymph node fields draining cancer sites is widespread. Where clinically involved nodes are present the object is to devitalize and encapsulate the metastatic tissue. In the absence of clinical metastases 'sterilizing' or 'prophylactic' courses are given, with the presumed aim of destroying microscopic tumour deposits in nodes. Taylor & Nathanson (1942) pointed out in their book on lymph node metastases: 'It is a common clinical observation that when metastases are present in the regional nodes, in most instances only relatively few nodes are actually involved, even with types of cancer which show the greatest propensity to form metastases.' Thus any irradiation of neck fields is likely to irradiate many nodes which are not involved in cancer. The purpose of this paper is to examine the effects of radiation on such uninvolved nodes. Earlier Investigations In man: Earlier investigations in man showed that irradiation produces rapid destruction of lymphocytes but spares initially the reticuloendothelial (RE) cells (Warthin 1906). Loss of germinal centres occurs during irradiation and there is a progressive fall in the number of follicles with increasing dosage (Taussig 1940). Inflammatory reactions with swollen medullary cords and hypernmia is a constant finding (Quick & Cutler 1925, Brown et al. 1951, Gorton
1957). The structure of the node is not altered in the early period after irradiation. Late changes of
hyalinization, reticular swelling and fibrosis with reduction or disappearance of lymph follicles occurs (Rutledge & Fletcher 1958). Most investigators felt that these changes were not sufficiently characteristic to be able to say with certainty on histological examination whether any particular node had been irradiated, and to what dosage (McGregor 1934, Morton 1945, Henricksen 1954). In animals: Most experiments have involved the use of single dose 3000 rads irradiation, or whole body irradiation, hence results are not strictly comparable with those from the fractionated regimes used in man. The destructive effect of small doses of radiation on lymphocytes is confirmed (Heineke 1903, Albertini 1932, De Bruyn 1948, Imamura 1959). Rapid repopulation of nodes occurs in the absence of local mitotic activity (Pape & Jellinek 1950, Pape & Piringer-Kuchinga 1956), presumably by blood borne lymphocytes from lymphoid tissue elsewhere in the body (Yoffey & Courtice 1956). In rats the disappearance of granulated mast cells from irradiated nodes was the most
characteristic postirradiation change. Thereafter, irradiated nodes were smaller with fewer follicles and an increase in fibrous tissue. This effect increased with time after irradiation (Engeset 1964). Lymphangiography and perfusion experiments with contrast media, carbon particles and cells of various origins, e.g. toad erythrocytes and Walker carcinoma cells, showed that radiation does not block the passage of lymph through lymph vessels and nodes in the early months after irradiation (Teneff & Stoppani 1935, Engeset 1964). The barrier function of nodes is partly damaged by radiation since up to 25% of cells which would normally be held up in nodes pass through (Engeset 1964).
78 Proc. roy. Soc. Med. Volume 68 February 1975
2
Present Investigations Scope and material: The present investigation attempts to relate histological changes to radiation doses in cervical lymph nodes. The material consisted of 38 radical neck dissections performed in the year 1973-74 with or without en bloc resection of the primary tumour. All cases had received radiation to the neck either as part of the field of radiation to the primary tumour or as deliberate irradiation of- the cervical nodes. Primary tumours involved most sites in the head and neck. It was felt that the presence of tumour in any of the nodes in the lymphatic field might alter the behaviour of neighbouring nodes, especially when tumour necrosis after radiation might take place. All cases where clinically palpable nodes had been found before treatment were therefore set aside. All nodes were then examined histologically and those with microscopic tumour or necrotic debris suggestive of tumour breakdown eliminated. It is interesting to note that of 30 cases with clinically involved nodes, only 19 had evidence on histological examination of tumour, past or present. Eight cases had neither clinical pretreatment nor histological posttreatment metastases. Changes in these nodes could therefore be attributable either to radiotherapy or to reaction to the primary tumour. Most of the primaries in this series were infected to some extent. Reactive hyperplasia was therefore to be expected in both irradiated and unirradiated nodes; any differences between the two groups in individual patients could be fairly attributed to radiation change alone. Methods: Nodes removed from neck dissection specimens could be located spatially by their relation to the accessory nerve, omohyoid muscle, upper and lower ends of the jugular vein, and in some cases to the attached larynx or mandible. The position of each node was recorded on a standard chart. Radiation fields were determined by examining the field X-rays taken on the radiotherapy machine during treatment. Plotting the fields on the standard node chart showed which nodes were clearly within, and which clearly outside, the radiation field. Borderline nodes were discarded. Reference to the dose contour diagram gives the amount of radiation at various depths in the head and neck as a percentage of the incident dose. The position of each irradiated node was estimated on its relevant dose contour diagram. From the 8 cases free of metastasis a total of 114 nodes were obtained after eliminating those which were borderline. Of these, 81 were clearly inside radiation fields, 33 unirradiated nodes being used as controls. The dose received by the irradiated nodes was calculated by multiplying
the total incident dose by the contour line passing through the node and dividing by 100. Findings: (1) Subjective impressions of radiation effects were gained by simple comparisons of irradiated and non-irradiated nodes from individual patients. The nodes were stained with hiematoxylin and eosin, reticulin, and Unna-Pappenheim stains. The latter shows mast cells. No difference in mast cell population was seen in the 2 groups, contrary to Engeset's (1964) observations in rats. (2) Control nodes: The histology of the nodes presented a variety of appearances. The controls varied from small nodes with infrequent small follicles and increased fibrous tissue (particularly in the elderly) to large nodes with brisk reactive hyperplasia. In some nodes the germinal centres were large and pale, in others the medullary cords were swollen, blood vessels dilated and macrophages containing cellular debris were seen. These changes occurred in nodes removed 3 to 28 days after irradiation in their immediate vicinity. (3) Irradiated nodes: Nodes receiving less than 1000 rads had all the above features. Some follicles appeared to have fewer lymphocyte layers in the periphery so that the germinal centres appeared large and relatively acellular. At 1500 rads normal follicles could still be found. Others appeared disrupted with no germinal centres. Still others had eosinophilic material between the cells of the germinal centres - this probably represents an inflammatory exudate. Medullary cords remained swollen with macrophages and lymphocytes. The reticuloendothelial cells appeared normal. Capillary dilatation seemed much less than in the unirradiated nodes. At over 2000 rads disrupted follicles with no germinal centres was the rule, even 35 days after completion of radiotherapy. Increasing fibrosis appeared in nodes removed 35 days after 3000 rads, with strands of fibrous tissue forming throughout the node. This fibrosis was not seen in control nodes from the same patient. Follicles remained small with no
germinal centres.
At over 4000 rads the dominant picture, especially where radiation preceded excision by several months, was of increasing hyalinization of parts of the node, and increasing fibrous tissue formation. In many cases no recognizable lymphoid tissue could be found, the node being converted to a small hard fibrous nodule. (4) Objective findings: Follicle diameters were measured using the vernier scale on the microscope table. Average follicle sizes were deter,nined at different radiation intensities, and plotted against dose received (Fig 1). Up to 3000 rads little change in follicle size occurs. The apparent
Section ofLaryngology
3 1RRADIATED NODES AVERAGE FOLLICLE SIZE AT DIFFERING RADIATION INTENSITIES Follicle Size (arbitrary units) 3.403.00-
2.60 -
*
2.20
Average follicle size In normal nodes
v
1.80-
*
1.40*
5
10
15
20 25 30 35 40 45 Radiation Dose (100 rads)
50
55 60
Fig 1 Histological changes in lymph nodes after radiation in man
increase in size between 1000 and 2000 rads probably represents cedema rather than any increase in the absolute number of cells. At over 3000 rads the average follicle size shows a steady decline. Since follicles are spheres, and only their diameter has been measured, the actual decrease in lymphoid tissue is much greater than shown. (5) Mitotic activity: Few mitotic figures were found either in the irradiated nodes or in the controls. This lack of mitotic activity agrees with findings in animals that repopulation of the node following destruction of lymphocytes by radiation occurs from elsewhere. Peripheral lymph - that draining into nodes - containing few lymphocytes (Yoffey & Courtice 1956) so that blood-borne lymphocytes from spleen, marrow, thymus, &c., are those which repopulate the node. Such cells will have arisen in areas distant from the antigens of the tumour. Discussion Tumours are antigenic (Southam & Moore 1958, Hammond et al. 1967). Host reaction to tumour is characterized by histological changes associated with immune responses (Hamlin 1968). There is no doubt that the small lymphocyte is intimately concerned in the immune response, both in its own right and as a precursor of other cells with immune functions (Gowans 1965, Gowans & McGregor 1965). The effect of radiation in reducing the lymphocyte population of the tumour's local lymphatic field must reduce the quantitative response to the tumour. Lymphocytes exposed to antigen require a period of time in which to develop and pass on the necessary immune response. The time relations of this process are not known. The time-relations of graft-rejection phenomena suggest this period may be measured in days rather than hours. Daily doses of radiation will destroy successive waves of populating lymphocytes before they can develop immune competence against tumour antigens. Hamlin (1968) showed
79
that the poorer survival in patients having postoperative radiation in carcinoma of the breast is related to depression of the immune response. W H Bond (reported in World Medicine 17 October 1967, p 68) has stated that postoperative irradiation does not increase the survival time in patients with nodal metastases and may, in fact, shorten the survival period of those patients without nodal metastases. Summary Clinical radiation in man is shown to have similar effects to single dose irradiation in animals. While it is not possible by examining individual nodes to estimate the dose of radiation they have received, progressive changes with increasing doses can be seen leading to loss of lymphoid tissue and replacement by fibrous tissue. Functional changes probably occur, leading to loss of the filtering power of the nodes and their by-pass by anastomotic lymph channels. The purpose of this paper is in no way an appeal to discard radiation as a form of treatment for cancer. The destructive effects of radiation have been known for some time, but the significance of the regional nodes in the immune response to tumour has only recently been considered. A reappraisal is required of the way radiation therapy is given, so that as much as possible of the immune mechanism may be left undamaged. REFERENCES Albertini A V (1932) Beitrdge zurpathologischen Anatomie und zur allgemeinen Pathologie 89, 183-288 Brown W E, Meschan I, Kerekas E & Sadler J M (1951) American Journal of Obstetrics and Gynecology 62, 871-889 De Bruyn P P H (1948) In: Histopathology of Irradiation from External and Internal Sources. Ed. W Bloom. McGraw-Hill, New York; Chapter 8 Engeset A (1964) Acta radiologica Suppl. 299, 5-125 Gorton G (1957) Progress in Gynacology 3, 594-603 Gowans J L (1965) British Medical Bulletin 21, 106 Gowans J L & McGregor D D (1965) Progress in Allergy 9, 1 Hamlin I M E (1968) Cancer 22,383-401 Hammond W G, Fisher J C & Rolley R T (1967) Surgery (St Louis) 62, 124 Heineke H (1903) Manchener medizinische. Wochenschrift 48, 2090-2092 Henricksen E (1954) In: Surgical Treatment of Cancer of the Cervix. Ed. J V Meigs. Grune & Stratton, New York; pp 65-117 Imamura H (1959) Okajimasfolia anatomicajaponica 32, 289-301 McGregor L (1934) Acta radiologica (Stockholm) 15, 129-152 Morton D G (1945) American Journal of Obstetrics & Gynecology 49, 19-31 Pape R & Jellinek N (1950) Radiologia Austriaca 3, 43-62 Pape R & Piringer-Kuchinka A (1956) Strahlentherapie 101, 523-535 Quick D & Cutler M (1925) American Journal of Roentgenology 14, 529-540 Rutledge F N & Fletcher G H (1958) American Journal of Obstetrics & Gynecology 76, 321-334 Southam C M & Moore A E (1958) Annals of the New York Academy of Sciences 73,635 Taussig F J (1940) American Journal of Roentgenology 43, 539-543 Taylor G W & Nathanson I T (1942) Lymph Node Metastases. Incidence and Surgical Treatment in Neoplastic Disease. Oxford University Press, London; p 10 Teneff S & Stoppani F (1935) Radiologica medica (Torino) 22,768-787 Warthin A S (1906) International Clinics 4, 243-277 Yoffey J M & Courtice F C (1956) Lymphatics, Lymph and Lymphoid Tissue. 2nd edn. Arnold, London; pp 510
Volume 68 February 1975
77
Section of Laryngology President J A B Thomas FRCS
Meeting 21 June 1974 with the Section of Otology at-The Welsh National School of
Medicine, Cardiff
The Significance and Management of Metastatic Lymph Nodes in the Neck Major A J S Burge (Catterick Military Hospital, Catterick Camp, Yorkshire)
Histological Changes in Cervical Lymph Nodes Following Clinical Irradiation The practice of irradiating lymph node fields draining cancer sites is widespread. Where clinically involved nodes are present the object is to devitalize and encapsulate the metastatic tissue. In the absence of clinical metastases 'sterilizing' or 'prophylactic' courses are given, with the presumed aim of destroying microscopic tumour deposits in nodes. Taylor & Nathanson (1942) pointed out in their book on lymph node metastases: 'It is a common clinical observation that when metastases are present in the regional nodes, in most instances only relatively few nodes are actually involved, even with types of cancer which show the greatest propensity to form metastases.' Thus any irradiation of neck fields is likely to irradiate many nodes which are not involved in cancer. The purpose of this paper is to examine the effects of radiation on such uninvolved nodes. Earlier Investigations In man: Earlier investigations in man showed that irradiation produces rapid destruction of lymphocytes but spares initially the reticuloendothelial (RE) cells (Warthin 1906). Loss of germinal centres occurs during irradiation and there is a progressive fall in the number of follicles with increasing dosage (Taussig 1940). Inflammatory reactions with swollen medullary cords and hypernmia is a constant finding (Quick & Cutler 1925, Brown et al. 1951, Gorton
1957). The structure of the node is not altered in the early period after irradiation. Late changes of
hyalinization, reticular swelling and fibrosis with reduction or disappearance of lymph follicles occurs (Rutledge & Fletcher 1958). Most investigators felt that these changes were not sufficiently characteristic to be able to say with certainty on histological examination whether any particular node had been irradiated, and to what dosage (McGregor 1934, Morton 1945, Henricksen 1954). In animals: Most experiments have involved the use of single dose 3000 rads irradiation, or whole body irradiation, hence results are not strictly comparable with those from the fractionated regimes used in man. The destructive effect of small doses of radiation on lymphocytes is confirmed (Heineke 1903, Albertini 1932, De Bruyn 1948, Imamura 1959). Rapid repopulation of nodes occurs in the absence of local mitotic activity (Pape & Jellinek 1950, Pape & Piringer-Kuchinga 1956), presumably by blood borne lymphocytes from lymphoid tissue elsewhere in the body (Yoffey & Courtice 1956). In rats the disappearance of granulated mast cells from irradiated nodes was the most
characteristic postirradiation change. Thereafter, irradiated nodes were smaller with fewer follicles and an increase in fibrous tissue. This effect increased with time after irradiation (Engeset 1964). Lymphangiography and perfusion experiments with contrast media, carbon particles and cells of various origins, e.g. toad erythrocytes and Walker carcinoma cells, showed that radiation does not block the passage of lymph through lymph vessels and nodes in the early months after irradiation (Teneff & Stoppani 1935, Engeset 1964). The barrier function of nodes is partly damaged by radiation since up to 25% of cells which would normally be held up in nodes pass through (Engeset 1964).
78 Proc. roy. Soc. Med. Volume 68 February 1975
2
Present Investigations Scope and material: The present investigation attempts to relate histological changes to radiation doses in cervical lymph nodes. The material consisted of 38 radical neck dissections performed in the year 1973-74 with or without en bloc resection of the primary tumour. All cases had received radiation to the neck either as part of the field of radiation to the primary tumour or as deliberate irradiation of- the cervical nodes. Primary tumours involved most sites in the head and neck. It was felt that the presence of tumour in any of the nodes in the lymphatic field might alter the behaviour of neighbouring nodes, especially when tumour necrosis after radiation might take place. All cases where clinically palpable nodes had been found before treatment were therefore set aside. All nodes were then examined histologically and those with microscopic tumour or necrotic debris suggestive of tumour breakdown eliminated. It is interesting to note that of 30 cases with clinically involved nodes, only 19 had evidence on histological examination of tumour, past or present. Eight cases had neither clinical pretreatment nor histological posttreatment metastases. Changes in these nodes could therefore be attributable either to radiotherapy or to reaction to the primary tumour. Most of the primaries in this series were infected to some extent. Reactive hyperplasia was therefore to be expected in both irradiated and unirradiated nodes; any differences between the two groups in individual patients could be fairly attributed to radiation change alone. Methods: Nodes removed from neck dissection specimens could be located spatially by their relation to the accessory nerve, omohyoid muscle, upper and lower ends of the jugular vein, and in some cases to the attached larynx or mandible. The position of each node was recorded on a standard chart. Radiation fields were determined by examining the field X-rays taken on the radiotherapy machine during treatment. Plotting the fields on the standard node chart showed which nodes were clearly within, and which clearly outside, the radiation field. Borderline nodes were discarded. Reference to the dose contour diagram gives the amount of radiation at various depths in the head and neck as a percentage of the incident dose. The position of each irradiated node was estimated on its relevant dose contour diagram. From the 8 cases free of metastasis a total of 114 nodes were obtained after eliminating those which were borderline. Of these, 81 were clearly inside radiation fields, 33 unirradiated nodes being used as controls. The dose received by the irradiated nodes was calculated by multiplying
the total incident dose by the contour line passing through the node and dividing by 100. Findings: (1) Subjective impressions of radiation effects were gained by simple comparisons of irradiated and non-irradiated nodes from individual patients. The nodes were stained with hiematoxylin and eosin, reticulin, and Unna-Pappenheim stains. The latter shows mast cells. No difference in mast cell population was seen in the 2 groups, contrary to Engeset's (1964) observations in rats. (2) Control nodes: The histology of the nodes presented a variety of appearances. The controls varied from small nodes with infrequent small follicles and increased fibrous tissue (particularly in the elderly) to large nodes with brisk reactive hyperplasia. In some nodes the germinal centres were large and pale, in others the medullary cords were swollen, blood vessels dilated and macrophages containing cellular debris were seen. These changes occurred in nodes removed 3 to 28 days after irradiation in their immediate vicinity. (3) Irradiated nodes: Nodes receiving less than 1000 rads had all the above features. Some follicles appeared to have fewer lymphocyte layers in the periphery so that the germinal centres appeared large and relatively acellular. At 1500 rads normal follicles could still be found. Others appeared disrupted with no germinal centres. Still others had eosinophilic material between the cells of the germinal centres - this probably represents an inflammatory exudate. Medullary cords remained swollen with macrophages and lymphocytes. The reticuloendothelial cells appeared normal. Capillary dilatation seemed much less than in the unirradiated nodes. At over 2000 rads disrupted follicles with no germinal centres was the rule, even 35 days after completion of radiotherapy. Increasing fibrosis appeared in nodes removed 35 days after 3000 rads, with strands of fibrous tissue forming throughout the node. This fibrosis was not seen in control nodes from the same patient. Follicles remained small with no
germinal centres.
At over 4000 rads the dominant picture, especially where radiation preceded excision by several months, was of increasing hyalinization of parts of the node, and increasing fibrous tissue formation. In many cases no recognizable lymphoid tissue could be found, the node being converted to a small hard fibrous nodule. (4) Objective findings: Follicle diameters were measured using the vernier scale on the microscope table. Average follicle sizes were deter,nined at different radiation intensities, and plotted against dose received (Fig 1). Up to 3000 rads little change in follicle size occurs. The apparent
Section ofLaryngology
3 1RRADIATED NODES AVERAGE FOLLICLE SIZE AT DIFFERING RADIATION INTENSITIES Follicle Size (arbitrary units) 3.403.00-
2.60 -
*
2.20
Average follicle size In normal nodes
v
1.80-
*
1.40*
5
10
15
20 25 30 35 40 45 Radiation Dose (100 rads)
50
55 60
Fig 1 Histological changes in lymph nodes after radiation in man
increase in size between 1000 and 2000 rads probably represents cedema rather than any increase in the absolute number of cells. At over 3000 rads the average follicle size shows a steady decline. Since follicles are spheres, and only their diameter has been measured, the actual decrease in lymphoid tissue is much greater than shown. (5) Mitotic activity: Few mitotic figures were found either in the irradiated nodes or in the controls. This lack of mitotic activity agrees with findings in animals that repopulation of the node following destruction of lymphocytes by radiation occurs from elsewhere. Peripheral lymph - that draining into nodes - containing few lymphocytes (Yoffey & Courtice 1956) so that blood-borne lymphocytes from spleen, marrow, thymus, &c., are those which repopulate the node. Such cells will have arisen in areas distant from the antigens of the tumour. Discussion Tumours are antigenic (Southam & Moore 1958, Hammond et al. 1967). Host reaction to tumour is characterized by histological changes associated with immune responses (Hamlin 1968). There is no doubt that the small lymphocyte is intimately concerned in the immune response, both in its own right and as a precursor of other cells with immune functions (Gowans 1965, Gowans & McGregor 1965). The effect of radiation in reducing the lymphocyte population of the tumour's local lymphatic field must reduce the quantitative response to the tumour. Lymphocytes exposed to antigen require a period of time in which to develop and pass on the necessary immune response. The time relations of this process are not known. The time-relations of graft-rejection phenomena suggest this period may be measured in days rather than hours. Daily doses of radiation will destroy successive waves of populating lymphocytes before they can develop immune competence against tumour antigens. Hamlin (1968) showed
79
that the poorer survival in patients having postoperative radiation in carcinoma of the breast is related to depression of the immune response. W H Bond (reported in World Medicine 17 October 1967, p 68) has stated that postoperative irradiation does not increase the survival time in patients with nodal metastases and may, in fact, shorten the survival period of those patients without nodal metastases. Summary Clinical radiation in man is shown to have similar effects to single dose irradiation in animals. While it is not possible by examining individual nodes to estimate the dose of radiation they have received, progressive changes with increasing doses can be seen leading to loss of lymphoid tissue and replacement by fibrous tissue. Functional changes probably occur, leading to loss of the filtering power of the nodes and their by-pass by anastomotic lymph channels. The purpose of this paper is in no way an appeal to discard radiation as a form of treatment for cancer. The destructive effects of radiation have been known for some time, but the significance of the regional nodes in the immune response to tumour has only recently been considered. A reappraisal is required of the way radiation therapy is given, so that as much as possible of the immune mechanism may be left undamaged. REFERENCES Albertini A V (1932) Beitrdge zurpathologischen Anatomie und zur allgemeinen Pathologie 89, 183-288 Brown W E, Meschan I, Kerekas E & Sadler J M (1951) American Journal of Obstetrics and Gynecology 62, 871-889 De Bruyn P P H (1948) In: Histopathology of Irradiation from External and Internal Sources. Ed. W Bloom. McGraw-Hill, New York; Chapter 8 Engeset A (1964) Acta radiologica Suppl. 299, 5-125 Gorton G (1957) Progress in Gynacology 3, 594-603 Gowans J L (1965) British Medical Bulletin 21, 106 Gowans J L & McGregor D D (1965) Progress in Allergy 9, 1 Hamlin I M E (1968) Cancer 22,383-401 Hammond W G, Fisher J C & Rolley R T (1967) Surgery (St Louis) 62, 124 Heineke H (1903) Manchener medizinische. Wochenschrift 48, 2090-2092 Henricksen E (1954) In: Surgical Treatment of Cancer of the Cervix. Ed. J V Meigs. Grune & Stratton, New York; pp 65-117 Imamura H (1959) Okajimasfolia anatomicajaponica 32, 289-301 McGregor L (1934) Acta radiologica (Stockholm) 15, 129-152 Morton D G (1945) American Journal of Obstetrics & Gynecology 49, 19-31 Pape R & Jellinek N (1950) Radiologia Austriaca 3, 43-62 Pape R & Piringer-Kuchinka A (1956) Strahlentherapie 101, 523-535 Quick D & Cutler M (1925) American Journal of Roentgenology 14, 529-540 Rutledge F N & Fletcher G H (1958) American Journal of Obstetrics & Gynecology 76, 321-334 Southam C M & Moore A E (1958) Annals of the New York Academy of Sciences 73,635 Taussig F J (1940) American Journal of Roentgenology 43, 539-543 Taylor G W & Nathanson I T (1942) Lymph Node Metastases. Incidence and Surgical Treatment in Neoplastic Disease. Oxford University Press, London; p 10 Teneff S & Stoppani F (1935) Radiologica medica (Torino) 22,768-787 Warthin A S (1906) International Clinics 4, 243-277 Yoffey J M & Courtice F C (1956) Lymphatics, Lymph and Lymphoid Tissue. 2nd edn. Arnold, London; pp 510
