[ 357 ]

THE PRENATAL DEVELOPMENT OF THE ABDOMINALPARA-AORTIC BODIES IN MAN

By R. E. COUPLANDDepartment of Anatomy, University of Leeds

INTRODUCTION

The adrenaline secreting cells of the human foetus are found in two situations, viz.in the adrenal glands and associated with the sympathetic nervous system outside,these structures. These cells are usually demonstrated histologically by making useof the chromaffin reaction and are known as chromaffin cells or phaeochromocytes.

In the abdomen of the foetus the extra-adrenal phaeochromocytes are foundeither in small non-encapsulated groups in sympathetic ganglia, or in encapsulatedmasses in the prevertebral sympathetic plexuses, the latter being the more commonarrangement. The encapsulated collections of cells are usually referred to as' paraganglia', but in this work (for reasons which will be discussed later) the latterterm has been replaced by 'para-aortic bodies'.

HISTORICAL SURVEY

Stilling (1890) observed extra-adrenal chromaffin cells lying in the midst of theabdominal sympathetic plexuses of the rabbit, cat and dog.

Zuckerkandl (1901) described extra-adrenal chromaffin cells in the abdominalsympathetic plexuses of the human foetus and described in detail collections of thesecells closely related to the origin of the inferior mesenteric artery. These are nowusually referred to as the 'organs of Zuckerkandl'.Bonnamour & Pinatelle (1902) confirmed Zuckerkandl's findings and described

chromaffin bodies in children up to the age of 6 years. Kohn (1902) reviewed theliterature relating to the chromaffin bodies of vertebrates, and in 1903 published hisclassical paper on the development of the paraganglia in man, rabbit and cat; inthe latter paper the development of chromaffin cells from the sympathetic anlagewas clearly described.Vincent (1910) described the adrenal and extra-adrenal chromaffin tissues of the

dog, cat and rabbit, and showed that in the dog the extra-adrenal tissue containeda pressor substance.

Zuckerkandl (1912) reviewed the literature relating to chromaffin tissues, andmade contributions in the field of the postnatal fate of these structures.From 1925 onward, an important series of papers was published, all relating to

the development of the para-aortic bodies in man. Ivanoff (1925) described thedevelopment and postnatal degeneration of the 'paraganglia'. Wrete (1927)observed the continuity of the chromaffin bodies of the para-aortic region with thechromaffin tissue of the adrenal glands. Keene & Hewer (1927) observed thecommon origin of the intra- and extra-adrenal chromaffin cells from the sympatheticanlage. Iwanow (1930, 1932) described in detail the morphology and embryologyof the 'paraganglia' in man.

358 R. E. CouplandThe descriptive works of Kohn (1903) and later workers established the common

origin of the cells of the adrenal medulla and para-aortic bodies from the sympatheticanlage. This concept was supported experimentally by the work of Van Campenhout(1930) on amphibians, and Hammond & Yntema (1947) on chicks.

Hollingshead (1937) showed that extra-adrenal chromaffin tissue was innervatedby pre-ganglionic sympathetic nerve fibres, and in 1940 reviewed the literaturerelating to these structures. Van Campenhout (1946) included 'paraganglia' underthe heading 'epithelio-neural bodies'.

It has recently been shown (West, Shepherd & Hunter, 1951) that the pressorsubstance present in the organs of Zuckerkandl of the newborn infant is pre-dominantly noradrenaline.

NOMENCLATURE

Kohn (1900, 1902, 1903) referred to the extra-adrenal collections of chromaffin cellsas ' paraganglia'. Within this term he included those structures which were developedfrom the sympathetic anlage, which were topographically related to the sympatheticnervous system and which were composed of chromaffin cells; the carotid body wasincluded, and he wrote (1902): 'Die carotisdruse ist ein chromaffiner Korper oder einParaganglia und richtiger als Paraganglion caroticum zu bezeichnen'. Kohn'sinclusion of the carotid body amongst the 'paraganglia' has not, however, beenconfirmed by subsequent workers (M6nkeberg, 1905; De Castro, 1926, 1928; Boyd,1937; Gosses, 1937). There is general agreement that neither developmentally (Boyd,1937) nor functionally (Christie, 1933; Gosses, 1937) does this structure justifyinclusion amongst the chromaffin organs.The term 'paraganglion' may, therefore, be applied in either a specific sense as

implied by Kohn (1900, 1902, 1903) and used by Boyd (1937) and Hammond (1941)to describe chromaffin structures developed from and topographically related to thesympathetic nervous system-the carotid body being excluded for the reasons givenabove-or non-specifically as used by Goormaghtigh (1936). The latter authorextended the term further by including 'vagal paraganglia' of the mouse andrecognized three types of paraganglia, viz. orthosympathetic, parasympathetic(vagal) and sensory (carotid body).Because of the lack of uniformity in the interpretation of the term 'paraganglia',

it has been replaced in the present investigation by the topographical term 'para-aortic bodies'. A para-aortic body is defined as an encapsulated collection ofchromaffin cells lying in intimate contact with the sympathetic nervous system andyielding a pressor substance after extraction.

THE CHROMAFFIN REACTION

Henle (1865) observed a brown coloration in the cells of the adrenal medulla aftertreatment with chromic acid or chrome salts. This reaction was referred to byStilling (1890) as the 'chromaphil' reaction and by Kohn (1900) as the 'chromaffin'reaction.

Ogata & Ogata (1923) reviewed the literature relating to the chromaffin reaction,and, after comparing the changes produced by the action of potassium dichromate

Prenatal development of the abdominal para-aortic bodies in man 359on solutions of adrenaline and on cells of the adrenal medulla, concluded that thebrown coloration was due to the production of chromium compounds in the affectedcells.

Gerard, Cordier & Lison (1930) considered that the reaction was independent ofthe presence of chrome compounds and was due to the oxidation of adrenaline andrelated substances, with the formation of quinones and brown tar-like derivatives.This work was confirmed by Bennett (1941) who suggested that the term 'chromaffinreaction' should be replaced by 'fuscogenic reaction'. Van Campenhout (1946)suggested that 'reaction of Henle' would be a preferable term.

In the present investigation the older term 'chromaffin reaction' is retained asbeing one in general use and most suitable, and refers to the brown colorationproduced by the action of potassium dichromate upon cells which contain a pressorsubstance (adrenaline or noradrenaline).

MATERIAL AND METHODS

Eighteen human foetuses and five newborn infants were used. The sizes (in mm.) ofthe former were: 8, 12, 14 (two), 16 (two), 19-5, 27, 46, 52, 55, 84, 92, 108, 135, 142,150 and 270.Only very fresh material was used; this was obtained whenever possible after

hysterotomy or after medical induction of abortion. All specimens of 16 mm. andless were fixed in Bouin or formol-saline, the 52 mm. foetus was fixed in Bouin andthe 150 mm. foetus in Zenker. All other foetal material was fixed in formol-dichromate (neutral formaldehyde 5 %, potassium dichromate 3 %). Fixation wasaccomplished by injection and immersion. The larger foetuses were evisceratedprior to immersion. All specimens between 8 and 19-5 mm. were sectioned seriallyat 8-10/t, as were the posterior abdominal walls of foetuses of 27, 52, 92, 108, 142,150 and 270 mm. The other foetuses were examined macroscopically after treatmentby the Wislocki method (1922) which bleaches all structures except those givinga positive chromaffin reaction.The five infants all died within 1 day of birth, three were premature weighing

31b. 6oz. and 31b. lOoz. (two); in these pregnancy had reached the 32nd week. Theothers weighed 7 lb. and 7 lb. 6 oz. and pregnancy had reached full term. Fromthese five infants the posterior abdominal viscera were excised en masse and thetissue immersed for 3 days in formol-dichromate. The posterior abdominal wallof one 3 lb. 10 oz. infant was sectioned serially at 12,; the others were examinedmacroscopically after treatment by the Wislocki method.

Sections were stained either with haematoxylin and eosin, or by Masson trichrome(iron haematoxylin, Ponceau acid-fuchsin, aniline blue) or Giemsa methods forspecial purposes.

OBSERVATIONS

8 mm. stage

At this stage the sympathetic anlage forms a chain along the dorso-lateral aspectof the abdominal aorta (PI. 1, fig. 1). A few primitive sympathetic cells (sympa-thogonia) may be observed extending ventrally on both sides of the abdominalaorta but a pre-aortic plexus is not observed.

360 R. E. CouplanrdIn sections cut at and just cranial to the origin of the coeliac artery, the rudiments

of the epithelial adrenal glands may be observed, closely related to columnar cells,which line the coelom on each side of the mesentery.

12 mm. stageThe sympathetic anlage has extended into the pre-aortic region and a definite

pre-aortic plexus exists. The epithelial adrenals have increased in size and on theirmedial aspects are closely related to sympathetic elements-primitive cells andfibres. The sympathetic chains lie relatively nearer the vertebral bodies and fartherfrom the aorta than at the 8 mm. stage.

14 mm. stageSections at the level of the adrenal glands show .the early invasion of these

structures by nerve fibres and primitive sympathetic cells (P1. 1, fig. 2).The pre-aortic plexus is well defined (P1. 1, fig. 3), but there is no evidence of

cellular differentiation within the sympathetic anlage in any area.The primitive cells are characterized by small intensely basophilic nuclei (4-6/,u)

in which scattered granules of chromatin are just visible; the cytoplasm is scanty.

16 mm. stageAt 16 mm. the invasion of the adrenal glands by sympathetic elements is more

advanced and some of the cells on the medial aspects of these structures, and in thepre-aortic plexus, are arranged in characteristic whorls (P1. I, fig. 4). The morecentral cells within the whorls have moderately basophilic ovoid nuclei, 6-8,u indiameter, in which a few chromatin granules may be observed; the amount ofcytoplasm is greater than in the primitive cells. These cells are phaeochromoblasts.Primitive cells persist in the peripheral zones of the whorls.

19-5 mm. stageThe whorls of phaeochromoblasts are larger and more numerous than in embryos

of 16 mm. The largest are situated on each side of the mid-line in the pre-aortic region(Text-fig. 1, P1. 2, fig. 6) and are related to the origin of the inferior mesentericartery; smaller structures are found in other parts of the pre-aortic plexus (P1. 2,fig. 5), along the medial aspects of the adrenal glands and kidneys and extend intothe pelvis.

Primitive cells may be observed in the peripheral zones of the whorls andfrequently exhibit mitosis; they are, however, relatively less numerous than in the16 mm. stage. Occasional mitotic figures are seen in the more central phaeochromo-blasts. The structures are poorly vascularized. Nerve fibres, primitive sympatheticcells and a few phaeochromoblasts can be traced into the medial aspects of the adrenalglands (Plate 3, fig. 7).

27 mm. stageThe arrangement of phaeochromoblasts is as in the previous stages. The cell

whorls have increased in size, vascularization is taking place, but there is no evidenceof further differentiation.

Prenatal development of the abdominal para-aortic bodies in man 361

46-55 mm. stageBetween the 27 and 46 mm. stages, the majority of the phaeochromoblasts of the

cell whorls and adrenal glands undergo further differentiation.The change is again characterized by a decrease in nuclear basophilia-this

results in the chromatin granules and threads becoming more obvious, and, togetherwith a small nucleolus, they impart a 'dusty' appearance to the nucleus. The

0 05 1I 1 1 1 I IL I

mm.0 1 2

19.5 mm. 46 mm.mm.

Fig. 1. Fig. 2.

Text-fig. 1. Reconstruction of a 19-5 mm. human foetus, whorls of phaeochromoblasts stippled.AD, adrenal gland; CA, coeliac axis; SM, superior mesenteric artery; IM, inferior mesentericartery; MT, metanephros.

Text-fig. 2. Reconstruction of a 46 mm. human foetus showing the distribution of the para-aorticbodies. Phaeochromocytes are extending from a para-aortic body into the right adrenal gland.KD, kidney. Other abbreviations as in Text-fig. 1.

nuclei are round or ovoid and approximately the same size (6-8,u) as those of thephaeochromoblasts. Associated with the nuclear change there is an increase inthe amount of cytoplasm and the cells become rearranged with the formationof cords.A positive chromaffin reaction is not observed in microscopic sections at this stage,

but in all other respects the cells are identical with those of older foetuses which dogive a positive reaction, and are regarded as being phaeochromocytes. A positivereaction was observed in a gross specimen of 55 mm.

362 R. E. CouplandAssociated with the cellular differentiation there is a marked increase in the

vascularity of the structures, and networks of sinusoidal capillaries may be observed.The cords of phaeochromocytes and associated network of capillary blood vesselsare surrounded by a thin capsule (PI. 3, fig. 8). From this stage onwards the termpara-aortic body is used to describe these structures.

In sections through the adrenal glands of 46 and 52 mm. foetuses, phaeochromo-cytes are observed extending from cranial para-aortic bodies into the adrenal glands(Text-figs. 2, 3; PI. 4, fig. 9).

CAAD -

* - SM

o *O

KD

52 mm.0 1 2 3 0 1 2 3 92mm.

1 I I 1 2 m

mm. mm.Fig. 3. Fig. 4.

Text-fig. 3. Reconstruction of a 52 mm. human foetus. Para-aortic bodies stippled. Phaeochro-mocytes are extending from two cranial para-aortic bodies into the adrenal glands.

Text-fig. 4. Reconstruction of a 92 mm. human foetus. Para-aortic bodies stippled.

Large numbers of primitive sympathetic cells may be seen in the sympatheticchains and in the prevertebral plexuses, and are commonly arranged in rosettefashion. They are also present in the peripheral zones of all para-aortic bodies(PI. 3, fig. 8).The first sign of differentiation of primitive cells into sympathoblasts is noted at

46 mm., and occurs in the pre-vertebral plexus around the origin of the superiormesenteric artery. This differentiation is also characterized by a decrease in nuclearbasophilia and the early cells are individually indistinguishable from phaeochromo-blasts.The arrangement of para-aortic bodies at 46 and 52 mm. (Text-figs. 2 and 3)

corresponds in general with the cell whorls of the 19'5 mm. embryo. They extend in

Prenatal development of the abdominal para-aortic bodies in man 363a cranio-caudal direction from the diaphragm to the pelvis and laterally as far asthe uro-genital structures. They can be divided into:

(1) A median group of structures closely related to the aorta and in the mid-lineof the pelvis.

(2) and (3) Two lateral groups which are in close proximity to the adrenal glands,kidneys, ureters and lateral pelvic walls.Each of these groups is further divisible into:(a) Large bodies which correspond in position with the cell whorls of the 19-5 mm.

embryo and which in larger foetuses are macroscopic.(b) Small bodies which do not correspond with the cell whorls of the 19'5 mm.

embryo and which are always microscopic. The small bodies in the inter-adrenalarea are usually deeply embedded in the sympathetic plexuses.The largest bodies are members of the median group, and are in relation to the

origin of the inferior mesenteric artery-these are the bodies commonly called theorgans of Zuckerkandl.

Para-aortic bodies are associated with the aortic, adrenal, renal and testicular orovarian plexuses. They are also present in the pelvis near the midline posteriorly,and lying lateral to the rectum, associated with the extensions of the pelvicsympathetic plexus. Bodies are not seen in relation to the gangliated sympatheticchains at this stage.

84-92 mm. stageThe para-aortic bodies increase in size as the foetus grows. Primitive cells are

still present at the periphery of the bodies but are less numerous than in theearlier stages.The primitive cells lying in the ganglia of the sympathetic chains have begun to

differentiate, but chromaffin cells are not observed in these ganglia at this stage.Phaeochromocytes of the adrenal glands and para-aortic bodies give a positive

chromaffin reaction. Primitive cells can still be traced along nerve fibres into theadrenal glands, and form well-defined clusters and an occasional rosette in theinterior of the glands.

Bodies exist in the same sites as in the 52 mm. foetus, i.e. in all parts of the pre-vertebral plexuses (Text-fig. 4). There is a slight increase in number of the smallbodies between and posterior to the adrenal glands.

108-150 mm. stageThe general distribution of para-aortic bodies (Text-figs. 5-7) is the same as in the

earlier stages. There is a gradual increase in the size of the large bodies and in thenumber of the small ones. As the former increase in size the connective tissuestroma becomes obvious. In foetuses of 108 and 150 mm. para-aortic bodies maybe seen lying in the centre of developing lymph nodes (P1. 4, fig. 10). The position ofthese bodies is indicated by arrows in Text-figs. 5 and 7.

In the same foetuses and in a 142 mm. foetus nerve fibres were observed traversinglymph nodes.

In foetuses of 142 and 150 mm. the organs ofZuckerkandl are united by an isthmus(Text-figs. 6 and 7), and in the larger foetus have a maximum length of 6 mm. Thelargest para-aortic body of the lateral groups is 2-8 mm. long.

In a 108 mm. foetus a small non-encapsulated collection of chromaffin cells isobserved in a ganglion of the sympathetic chain.

Primitive sympathetic cells exist in the peripheral zones of all para-aortic bodiesbut become less numerous as the age of the foetus increases.

270 mm. to full termA foetus of 270 mm. was sectioned after removal of kidneys and right adrenal

gland. During this manipulation a number of the bodies belonging to the lateralgroups was inadvertently removed, and this fact explains their absence inText-fig. 8.

0 1 2 3 4 5 0 1 2 3 4 5X _L_j l 108 mm. mm 142 mm.mm. mm.

Fig. 5. Fig. 6.

Text-fig. 5. Reconstruction of a 108 mm. human foetus. Para-aortic bodies stippled. The arrowsindicate sites of close association between chromaffin and lymphoid tissue.

Text-fig. 6. Reconstruction of a 142 mm. human foetus. Para-aortic bodies stippled. The organsof Zuckerkandl are connected by an isthmus.

Primitive sympathetic cells are not observed in the peripheral zones of para-aortic bodies during this stage, and mitotic figures are absent.

In a 270 mm. foetus (Text-fig. 8) the majority of the pre-aortic chromaffin tissueis arranged as an elongated body 16 mm. long, extending from just caudal to theorigin of the superior mesenteric artery to the origin of the inferior mesenteric artery.Bodies of 1-1 5 mm. in length exist near the midline of the pelvis and are associatedwith the fibres of the pelvic plexus; similar structures lie along the lateral extensionsof this plexus and lie between the rectum and lateral pelvic walls. In two 3 lb. 10 oz.

364 B. E. Coupland

Prenatal development of the abdominal para-aortic bodies in man 365premature infants (Text-fig. 9), the organs of Zuckerkandl are united by isthmusesand have a maximum length of 5 and 8 mm.; the larger bodies of the lateral groupsare 2 mm. long. The total amount of extra-adrenal chromaffin tissue present ina 3 lb. 10 oz. infant (Text-fig. 9) appears to be approximately the same as thatpresent in a 150 mm. foetus (Text-fig. 7).

AD

0*

0 1 2 3 4 5 S m/1012345 ~~~~~~~150mm.mm. 0 1 2 34 5

L~~-L-J-J 270 mm.

Fig. 7. Fig. 8.

Text-fig. 7. Reconstruction of a 150 mm. human foetus. Para-aortic bodies stippled. The arrowindicates a body which is closely related to lymphoid tissue. The organs of Zuckerkandl areconnected by an isthmus.

Text-fig. 8. Reconstruction of a 270 mm. human foetus, showing the more medially placed para-aortic bodies (stippled). The arrows indicate sites of close association between chromaffin andlymphoid tissue.

In a 7 lb. one-day-old infant the organs of Zuckerkandl measure 10 mm. in lengthand are unconnected; in a 7 lb. 6 oz. infant the structures are united by an isthmusand have a maximum length of 11 mm.

Primitive cells still form a prominent feature of the adrenal medulla and may betraced along nerve fibres from the periphery of the cortex to the interior of theglands in a 270 mm. foetus.

Non-encapsulated collections of phaeochromocytes are observed in the gangliaof the prevertebral plexuses and the sympathetic chains of a 270 mm. foetus anda 3 lb. 10 oz. premature infant. A small para-aortic body is also found associatedwith a ganglion of the sympathetic chain in the former specimen.The close association between lymphoid tissue and chromaffin tissue is more

widespread at this stage than in the preceding one; the sites of such association areindicated by arrows in Text-figs. 8 and 9.

This association takes two forms:(1) Para-aortic bodies are seen lying in the centre of lymph nodes.(2) The two structures lie side by side in contact with each other.

CA .A

SM~~~~~~

IN a n tC KD

0 1 2 3 4 5 3 lb. 10 oz. premature..1 I IL "

mm.

Text-fig. 9. Reconstruction of the posterior abdominal wall of a 3 lb. 10 oz. premature infant.Para-aortic bodies stippled. Arrows indicate sites of close association between chromaffinand lymphoid tissue. The organs of Zuckerkandl are connected by an isthmus.

At the points of contact, the capsules of the para-aortic bodies are incomplete,and lymphocytes may be observed infiltrating the chromaffin tissue by directextension (P1. 4, fig. 11). Perivascular collections of lymphocytes are also oc-casionally observed.The larger bodies have a well-developed connective tissue stroma and a rich blood

supply; the phaeochromocytes are arranged in cords between capillary bloodvessels.

In gross specimens the para-aortic bodies are intimately connected with the nervefibres of the prevertebral plexuses. In unfixed material they have a pinkish colourwhich is slightly different from the grey of the nearby lymph nodes, but they canonly be identified with certainty after fixation in formol-dichromate and bleachingby the Wislocki method.

366 R. E. Coupland

Prenatal development of the abdominal para-aortic bodies in man 367

THE BLOOD SUPPLY OF THE PARA-AORTIC BODIESIn general, it may be said that arterial blood is derived from the nearest artery andthe venous drainage is into a neighbouring vein. Branches of the aorta, superiormesenteric, inferior mesenteric and testicular or ovarian arteries have been tracedto bodies in the older foetuses. In a 46 mm. foetus the large para-aortic bodies aresupplied by branches of the aorta, the mesenteric arteries or the lateral splanchnicarteries (P1. 3, fig. 8). These findings are in accord with the observations of Zucker-kandl (1901) and Iwanow (1932).

THE CHROMAFFIN REACTIONA positive chromaffin reaction was first observed in a gross specimen of 55 mm. afterfixation in formol-dichromate and bleaching by the Wislocki method. In micro-scopic sections a reaction was first observed in the adrenal glands and para-aorticbodies of a 92 mm. foetus and was noted in all larger specimens. The intensity of thebrown coloration varied from cell to cell. The lack of uniformity in the colorationof the phaeochromocytes may be due to the cells being in different phases of asecretary cycle, as described by Bennett (1941).The presence of a pressor principle in the para-aortic bodies and adrenal glands

of four foetuses between the sizes of 70 and 107 mm. was demonstrated by injectingextracts of these structures-obtained by the method of Holton (1949)-intra-venously into chloralosed cats, and making simultaneous recordings of changes inthe blood pressure and contractions of the nictitating membrane.

DISCUSSIONIt is generally accepted that the chromaffin cells and sympathetic neurones arederived from the sympathetic anlage. The earlier work relating to the developmentof the chromaffin system (Kohn, 1903; Zuckerkandl, 1912) is characterized by a lackof uniformity in nomenclature relating to the various stages in the differentiationof the primitive cells. Kohn (1903) described 'chromaffinen Zellen' in a 19f5 mm.embryo and reported their subsequent change in size and staining reactions asfurther differentiation occurred, but retained the original name. Zuckerkandl (1912)referred to the primitive cells as 'sympathoblasts' or 'chromaffinoblasts', and allsubsequent derivatives of the latter cells as 'chromaffin bodies'.

In this paper the small basophilic cells of the sympathetic anlage are referred toas primitive sympathetic cells; in the 14-16 mm. stage, these cells differentiate intolarger less basophilic cells which are referred to as phaeochromoblasts. The latterundergo further differentiation in foetuses of between 27 and 46 mm. with theformation of phaeochromocytes. This change is again characterized by a reductionin nuclear basophilia. Mitotic figures have been observed in primitive cells andphaeochromoblasts but not in phaeochromocytes.Kohn (1903) observed 'paraganglia' in a 19-5 mm. embryo, and although he

referred to changes in cell type and vascularity as development continued, thesame term was retained throughout. Zuckerkandl (1912) made similar observations.Iwanow (1930, 1932) described the appearance of 'paraganglia' at the 30 mm. stage,but did not use this term to describe the groups of phaeochromoblasts which wereobserved in the same situations in embryos of between 17 and 30 mm. Kohn and

Anatomy 86 25

368 R. E. CouplandZuckerkandl did not recognize the two-stage differentiation of phaeochromocytes,and referred to all collections of cells (other than neurones and their precursors)which are developmentally and topographically related to the sympathetic nervoussystem as 'paraganglia' or 'chromaffin bodies'. Iwanow included within this termonly those structures which are morphologically similar to the 'paraganglia' of theolder foetus and child, which are composed predominantly of phaeochromocytes,have a well-developed vascular network and which are probably functionally active.The second interpretation is accepted by the present writer.The formation of para-aortic bodies is characterized not only by a differentiation

of the cells but also by the appearance of a well-developed vascular network whichis in the main composed of sinusoidal capillaries. Throughout intra-uterine life thestructures have a rich blood supply derived from neighbouring arteries: in the earlystages from the aorta, unpaired branches of the aorta, and lateral splanchnicarteries, and in the later stages from the aorta and unpaired branches, and deriva-tives of the lateral splanchnic vessels (testicular, ovarian and renal arteries). Thevenous drainage is into nearby veins.The extension of primitive sympathetic elements into the adrenal glands is well

recognized. Wrete (1927) observed the continuity between the chromaffin tissue ofthe cranial para-aortic bodies and the adrenal glands of foetuses of 21-1, 37-8 and39*4 mm. During the present investigation three types of cells have been observedinvading the adrenal glands:

(1) Primitive cells between the stages of 14 and 270 mm. (P1. 1, fig. 2, PI. 3, fig. 7).(2) Phaeochromoblasts at the 19-5 mm. stage (PI. 3, fig. 7).(3) Phaeochromocytes at the 46-52 mm. stage (P1. 4, fig. 9).The phaeochromocytes of the bodies and adrenal medulla, after fixation in Bouin,

formol-dichromate and Zenker, and staining with haematoxylin and eosin anda Masson trichrome method, are structurally identical.

These findings support the concept that the phaeochromocytes of the adrenalmedulla and para-aortic bodies are identical developmentally and structurally.

In the course of the present work the differentiation of primitive sympatheticcells into sympathoblasts was first noted in the prevertebral ganglia of a 46 mm.foetus; differentiation of the cells of the gangliated chains was first observed ata later stage (92 mm.). The sympathoblasts are initially indistinguishable fromphaeochromoblasts, but enlarge relatively quickly and develop at least one largenucleolus, after which the two types can be readily recognized. Phaeochromocyteswere first observed in the ganglia of the sympathetic chains in a foetus of 108 mm.It would, therefore, appear that the primitive cells of the gangliated chains differ-entiate into both chromaffin and nervous elements at a later stage of developmentthan those present in the prevertebral plexuses; this is in keeping with the observa-tions of Kohn (1903) and Lucas Keene & Hewer (1927).The close association between lymphoid tissue and chromaffin tissue in the

human foetus does not appear to have been reported previously. Ivanoff (1925)reported a perivascular lymphoid infiltration of the chromaffin bodies of childrenaged 2-3 years. This was associated with hyaline and fibrous degeneration. Thefinding of para-aortic bodies in the centres of lymph nodes (PI. 4, fig. 10) in foetusesof 108 and 150 mm. may be fortuitous, as sympathetic nerve fibres are commonly

Prenatal development of the abdominal para-aortic bodies in man 369observed traversing lymph nodes at the same stage and in older foetuses. Thisexplanation would also be adequate for the side to side apposition noted in olderfoetuses and in a 3 lb. 10 oz. infant, but does not explain the direct lymphocyticinvasion and perivascular infiltration noted in the older specimens (PI. 4, fig. 11).As associated signs of degeneration were not observed, the significance of thesefindings is not clear. The organs of Zuckerkandl were unaffected in all specimens.

It is generally accepted that macroscopic para-aortic bodies are not observed inthe adult. Lucas Keene & Hewer (1927) observed an increase in fibrous tissue in theorgans of Zuckerkandl of a full-term foetus and considered that the change wasa sign of degeneration. Bonnamour & Pinatelle (1902) observed normal bodies inchildren of 5-6 years of age, but found that the appearances were variable. Zucker-kandl (1912) found microscopic evidence of degenerated chromaffin bodies in anadult aged 39 years and of hyaline degeneration of these structures in a child aged2 years. Ivanoff (1925) reported that the para-aortic bodies reach maximumdevelopment in children between 12 and 18 months of age and that after that timeatrophy occurred.

In the present investigation an increase in connective tissue stroma was observedin the larger bodies of foetuses of and above 150 mm. in length. This is not regardedas a sign of degeneration but as a normal response to the increase in bulk of thestructures. Cellular degeneration was not observed during intra-uterine life.

Primitive cells are associated with the peripheral zones of all the para-aorticbodies of foetuses up to 150 mm. and disappear in the period between 150 and270 mm. This disappearance coincides with the apparent cessation of growth of allbodies except the organs of Zuckerkandl. Mitotic figures have not been observed inmicroscopic sections of the para-aortic bodies of a 270 mm. foetus or a 3 lb. 10 oz.infant.A slight increase in the size of the organs of Zuckerkandl towards the end of

intra-uterine life has been observed during the present investigation, and agreeswith the findings of Zuckerkandl (1901), Bonnamour & Pinatelle (1902) and Iwanow(1932). Bonnamour & Pinatelle (1902) stated that mitotic figures were not observedin these structures at this stage but described amitotic nuclear division. In thepresent series neither mitotic nor amitotie division has been observed, and the increaseappears to be due in part to an increase in connective tissue stroma and blood vessels.

Zuckerkandl (1901), Bonnamour & Pinatelle (1902) and Iwanow (1930, 1932)described in detail the variations in shape of the organs of Zuckerkandl. Observa-tions made during this investigation indicate that the cell whorls of the 16 and19-5 mm embryos develop on a more or less bilaterally symmetrical pattern, with-out extension across the midline (Text-fig. 1, PI. 2, figs. 5, 6). This pattern is followedinitially by the large para-aortic bodies of the smaller foetuses (Text-figs. 2, 3),but as the primitive cells at the periphery of these structures differentiate, the organsof Zuckerkandl commonly unite across the midline with the formation ofan isthmus.An isthmus was first observed in a 142 mm. foetus (Text-fig. 6) and is present infive out of seven of the older specimens examined.

Phaeochromocytes have been observed singly and in small non-encapsulatedgroups in the sympathetic ganglia (prevertebral and of the sympathetic chains) infoetuses of 108 and 270 mm. and in a 3 lb. 10 oz. premature infant. Only one small

25-2

370 R .Culnpara-aortic body was observed in relation to the gangliated chains of all specimensexamined; this was found in a foetus of 270 mm. These findings indicate that thepara-aortic bodies in the abdomen of the human foetus are largely confined to theprevertebral plexuses. Zuckerkandl (1912) wrote: 'These bodies may occur where-ever there are sympathetic ganglia.' This statement may well be extended in thelight of the present work to read that the para-aortic bodies are found in all parts ofthe prevertebral sympathetic plexuses of the abdomen and pelvis and less commonlyin association with the sympathetic chains.

SUMMARY1. The adrenal medulla and extra-adrenal chromaffin tissues of the human foetus

develop from sympathetic elements.2. Primitive sympathetic cells situated in the pre-aortic region begin to differ-

entiate into phaeochromoblasts between the 14 and 16 mm. stages. The phaeo-chromoblasts are arranged in whorls. In the peripheral zones of the whorlsprimitive cells may be observed.

3. Between the 27 and 46 mm. stage the phaeochromoblasts undergo furtherdifferentiation with the formation of phaeochromocytes. This change is accompaniedby an increase in the vascularity of the structures, and the whorl-like formation ofcells is replaced by cell cords. From this stage onwards the structures are referredto as para-aortic bodies.

4. Primitive sympathetic cells, phaeochromoblasts and phaeochromocytes havebeen observed extending into the adrenal glands.

5. All para-aortic bodies except the organs of Zuckerkandl appear to attaina maximum size between the 150 and 270 mm. stages. The organs of Zuckerkandlcontinue to enlarge up to the end of intra-uterine life. Para-aortic bodies may befound in all parts of the abdominal and pelvic prevertebral sympathetic plexuses,and less commonly in association with the sympathetic chains.

6. A close association between lymphoid tissue and para-aortic bodies has beennoted in foetuses of and after the 108 mm. stage.

In conclusion I should like to thank Prof. A. Durward for his advice, encourage-ment and instructive criticism throughout this investigation; the staffs of theDepartments of Gynaecology and Pathology, St James's Hospital, Leeds, who haveprovided the foetal material; Prof. R. A. Willis, who allowed me to examine an8 and a 12 mm. embryo; and Prof. W. A. Bain and the staff of the Department ofPharmacology for advice and facilities placed at my disposal during the per-formance of bio-assays.

I am indebted to Mr R. Adkin for help in the preparation of the histologicalmaterial and to Mr C. N. England who produced the photographic plates.

REFERENCESBENNETT, H. S. (1941). Cytological manifestations of secretion in the adrenal medulla of the cat.

Amer. J. Anat. 69, 333-381.BONNAMOUR & PINATELLE (1902). Note sur l'organe para-sympathique de Zuckerkandl. Bibliogr.

anat. 11, 127-136.BOYD, J. D. (1937). The development of the human carotid body. Contr. Embryol. Carneg. Instn.

26, 1-1.

370 R. E. Coupland

Prenatal development of the abdominal para-aortic bodies in man 371CHRISTIE, R. V. (1933). The functions of the carotid gland (glomus caroticum). Endocrinology, 17,

421 444.DE CASTRO, F. (1926). Sur la structure et l'innervation de la glande intercarotidienne (glomus

caroticum) de l'homme et des mammiflres, et sur un nouveau system d'innervation autonomedu nerf glosso-pharyngien. Trab. Lab. Invest. biol. Univ. Madr. 24, 365-432.

DE CASTRO, F. (1928). Sur la structure et l'innervation du sinus carotidien de l'homme et desmammifteres. Nouveaux faits sur l'innervation et la fonction du glomus caroticum. Trab. Lab.Invest. biol. Univ. Madr. 25, 131-380.

GERARD, P., CORDIER, R. & LISON, L. (1930). Sur la nature de la reaction chromaffine. Bull.Histol. Tech. micr. 7, 133-139.

GOORMAGHTIGH, N. (1936). On the existence of abdominal vagal paraganglia in the adult mouse.J. Anat., Lond., 71, 77-90.

GossEs, J. (1937). The glomus caroticum. Acta nWerl. morph. 1, 38-42.HAMMOND, W. S. (1941). The development of the aortic arch bodies in the cat. Amer. J. Anat.

69, 265-293.HAMMOND, W. S. & YNTEMA, C. L. (1947). Depletions in the thoraco-lumbar sympathetic system

following removal of the neural crest in the chick. J. comp. Neurol. 86, 237-253.HENLE, J. (1865). Ueber das Gewebe der Nebenniere und der Hypophysis. Z. rat. Med. 24,

143-152.HOLLINGSHEAD, W. H. (1937). The innervation of the abdominal chromaffin tissue. J. comp.

Neurol. 67, 133-143.HOLLINGSHEAD, W. H. (1940). Chromaffin tissue and paraganglia. Quart. Rev. Biol. 15, 156-171.HOLTON, PAMELA (1949). Noradrenaline in tumours of the adrenal medulla. J. Physiol. 108,

525-529.IVANOFF, G. (1925). Zur Frage uber die Genese und Reduktion der Paraganglien des Menschen.

Z. ges. Anat. 1. Z. Anat. EntwGesch. 77, 234-244.IWANOW, G. (1930). Variabilitaten der abdominalen Paraganglien in Kindesalter. Z.ges. Anat. 1.

Z. Anat. EntwGesch. 91, 405-441.IWANOW, G. (1932). Das chromaffine und interrenale System des Menschen. Z.ges. Anat. 3. Ergebn.

Anat. EntwGesch. 29, 87-280.KEENE, M. F. LUCAS & HEWER, E. E. (1927). Observations on the development of the human

suprarenal gland. J. Anat., Lond., 61, 302-324.KOHN, A. (1900). Ueber den Bau und die Entwicklung der sog. Carotisdruse. Arch. mikr. Anat.

56, 81-148.KOHN, A. (1902). Das chromaffine Gewebe. Z. ges. Anat. 3. Ergebn. Anat. EntwGesch. 12, 253-348.KOHN, A. (1903). Die Paraganglien. Arch. mikr. Anat. 62, 263-365.MONKEBERG, I. G. (1905). Die Tumoren der Glandula carotica. Beitr. path. Anat. 38, 1-66.OGATA, T. & OGATA, A. (1923). tber die Henle'sche Chromreaktion der sogenannten chromaffinen

Zellen und den mikrochemischen Nachweis des Adrenalins. Beitr. path. Anat. 71, 376-387.STILLING, H. (1890). A propos de quelques experiences nouvelles sur la maladie d'Addison.

Rev. Medecine, 10, 808-831.VAN CAMPENHOUT, E. (1930). Contribution to the problem of the development of the sympathetic

nervous system. J. exp. Zool. 56, 295-320.VAN CAMPENHOUT, E. (1946). The epithelio-neural bodies. Quart. Rev. Biol. 21, 327-47.VINCENT, SWALE (1910). The chromaphil tissues and the adrenal medulla. Proc. Roy. Soc. B, 82,

502-515.WEST, G. B., SHEPHERD, D. M. & HUNTER R. B. (1951). Adrenaline and nor-adrenaline concentra-

tions in the adrenal glands at different ages and in some diseases. Lancet, ii, 966-969.WISLOCKI, G. B. (1922). Note on a modification of the chromaffin reaction, with observations on

the occurrence of abdominal chromaffin bodies in mammals. Johns Hopk. Hosp. Bull. 33,359-361.

WRETE, M. (1927). Beitrage zur Kenntnis von der Entwicklung des chromaffinen Gewebes derBauchregion beim Menschen. Z. mikr.-anat. Forsch. 9, 79-98.

ZUCKERKANDL, E. (1901). Ueber Nebenorgane des Sympathicus in Retroperitonaealraum desMenschen. Anat. Anz. 15, 97-107.

ZUCKERKANDL, E. (1912). The development of the chromaffin organs and of the suprarenal glands.Keibel and Mall's Manual of Human Embryology, 2, 157-179. U.S.A.: Lippincott and Co.

372 R. E. Coupland

EXPLANATION OF PLATES

AbbreviationsAO, aorta; AD, adrenal gland; LA, lateral splanchnic artery; PAB, para-aortic body; PB,

phaeochromoblasts; SN, primitive sympathetic cells and fibres; SP, primitive sympathetic cells.

PLATE 1Fig. 1. Transverse section of an 8 mm. human foetus taken immediately cranial to the origin of

the coeliac artery. The sympathetic anlage forms a chain on the dorso-lateral aspect of theabdominal aorta. The rudiment of the developing adrenal gland is closely related to columnarcells (C), which line the adjacent coelom. Haematoxylin and eosin. x 140.

Fig. 2. Section of a 14 mm. human foetus at the level of the origin of the coeliac artery. Primitivesympathetic cells and nerve fibres are invading the medial aspects of the adrenal glands.Haematoxylin and eosin. x 130.

Fig. 3. Transverse section of a 14 mm. human foetus mid-way between the origins of the superiorand inferior mesenteric arteries. The pre-aortic plexus is composed entirely of primitive cellsand nerve fibres. Haematoxylin and eosin. x 140.

Fig. 4. Transverse section of a 16 mm. human foetus mid-way between the origins of the superiorand inferior mesenteric arteries, showing a pre-aortic whorl of phaeochromoblasts. Haema-toxylin and eosin. x 140.

PLATE 2Fig. 5. Transverse section of a 19-5 mm. human foetus between the origins of the superior and

inferior mesenteric arteries-nearer the former. Whorls of phaeochromoblasts lie in the pre-aortic region, primitive cells are found at the periphery of these structures. Haematoxylinand eosin. x 140.

Fig. 6. Transverse section of a 19-5 mm. human foetus immediately cranial to the origin of theinferior mesenteric artery, showing two large whorls of phaeochromoblasts. Haematoxylinand eosin. x 140.

PLATE 3Fig. 7. Transverse section of a 19-5 mm. human foetus between the origins of the coeliac and

superior mesenteric arteries. Sympathetic nerve fibres and primitive cells are invading themedial aspect of the adrenal gland. A few phaeochromoblasts may also be observed extendingfrom the lateral whorl of phaeochromoblasts into this structure (EXT). Haematoxylin andeosin. x 140.

Fig. 8. Transverse section of a 46 mm. human foetus between the origins of the superior andinferior mesenteric arteries. Two large para-aortic bodies are situated in the pre-aortic regionon each side of the mid-line. Primitive sympathetic cells may be observed in the peripheralzones of one body. A lateral splanchnic artery is supplying the body on the left. Haema-toxylin and eosin. x 130.

PLATE 4Fig. 9. 52 mm. human foetus. Shows the medial aspect of the right adrenal gland with associated

para-aortic bodies and primitive cells. Phaeochromocytes may be traced from the largestpara-aortic body into the adrenal gland. Masson. x 140.

Fig. 10. 108 mm. human foetus. A para-aortic body may be observed lying inside a developinglymph node. Haematoxylin and eosin. x 160.

Fig. 11. 270 mm. human foetus. A large para-aortic body (right) is in contact with a mass oflymphoid tissue. Lymphocytes are infiltrating the para-aortic body. Haematoxylin andeosin. x 160.

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