Okajima, Folia Anat. Jpn., 67(6): 443-44i, March, 1991

Classification of the Abdominal Splanchnic Nerves -A Preliminary Attempt to Re-evaluate Their Nomenclatures-

By

K. MAKINO, T. K. YAMADA and K. KUMAKI

Undergraduate School of Medicine, Niigata University and Department of Anatomy, Niigata University School of Medicine

-Received for Publication , October 23, 1990-

Key Words: Abdominal Splanchnic Nerve, Gross Anatomy, PNA

Summary: The abdominal splanchnic nerves were observed in 22 cadavers (41 sides). The purpose of the study is to give more accurate definition to each nerve, for there are uncertainties in the nomenclature of these nerves. According to PNA, the abdominal splanchnic nerves are classified into three categories, on the basis of their sizes and their levels, namely Nn. splanchnici major, minor, and imus. Although Mitchell (1935) had already claimed that more attention should be given to the levels of ganglia which gave rise to these nerves, no revision has ever been made. Moreover, there still remains the matter of their destinations, which are more significant in defining them. Therefore, in addition to the conventional criteria for the classification, destinations of the nerves were taken into consideration. In the present study, 36 out of 41 sides were grouped into four types according to the said criteria. 5 exceptional cases were interpreted as results of minor modifications of these four types. Naturally, what is important in describing these nerves is to give clear idea about the actual condition of them. It is expected to give more reasonable nomenclature to these nerves based on the present result.

In the conventional scheme of gross anatomy, the ganglion, enters the abdomen medial to the sympathetic abdominal splanchnic nerves have been classified into trunk, and ends in the renal plexus. three; Nn. splanchnici major, minor, and imus These three splanchnic nerves have been named (minimus) (Kopsch, 1950; Elze, 1960; Beninghof and mainly according to their sizes. As early as in 1930's, GOrttler, 1967), or the greater (the great), the lesser (the Mitchell (1935, 1953) criticized this, because they didn't small), and the lowest (the least, the smallest) splanchnic indicate the levels of the ganglia which sent the fibers nerves (Schafer and Symington, 1909; Jackson, 1914; to these splanchnic nerves, and the so-called lowest Williams et al., 1989). splanchnic nerve is not always the smallest. He N. splanchnicus major (the greater or the great suggested, to avoid confusion, they would be better splanchnic nerve) is formed by the union of roots which termed the superior, the middle, and the inferior are given off by the thoracic ganglia from the fifth or splanchnic nerves, or the superior and the inferior when sixth to the ninth or tenth inclusive. It descends only two are present (1935). obliquely along the bodies of the vertebrae, supplies fine However, it is not so often that a single case has the branches to the descending thoracic aorta, perforates greater, the lesser, and the lowest splanchnic nerves in the crus of the diaphragm, and ends mainly in the celiac a complete set (cf Fig. 1). None of these classifications ganglion, but some of the fibers may occasionally be took the destination of these nerves into account, e.g., followed to the suprarenal body and the aorticorenal as will be shown later, Mitchell's "inferior splanchnic ganglion. nerve" does not always end in the fixed destination. N. splanchnicus minor (the lesser or the small Three kinds of the "inferior splanchnic nerves" are splanchnic nerve) is formed by one to three roots from identified on the basis of their destinations. the ninth and tenth or the tenth and eleventh thoracic An adequate classification of the splanchnic nerves ganglia, or from the neighbouring part of the trunk. is thus expected for the reasonable nomenclature. In It pierces the crus of the diaphragm with the greater the present paper, the origin and the destination of these splanchnic nerve, or separately, and ends in the nerves are taken into consideration as a preliminary a orticorenal ganglion. analysis for establishing a more acceptable N. y)latichnicus imus (the lowest, the least, or the nomenclature of the splanchnic nerves. smallest splanchnic nerve) arises from the last thoracic 444 K. Makino et al.

Fig. 1. An example where typical topographic relations of the abdominal splanchnic nerves to major organs are shown. In the right side, a splanchnic nerve arises from four ganglia, perforates the crus of the diaphragm, and ends in the celiac ganglion (CG). The other arises from the last thoracic ganglion, pierces the crus of the diaphragm with the sympathetic trunk, and enters the renal plexus (RP). In the left side, one splanchnic nerve which is formed by three roots passes the crus of the diaphragm and ends in the celiac ganglion. The other arises from the last thoracic ganglion, perforates the crus of the diaphragm with the sympathetic trunk, and divides into two branches. One of the branches ends in the aorticorenal ganglion (AG); the other joins the renal plexus. These two cases represented more than half the cases observed in this study, but did not satisfy the conventional definitions.

Materials and Methods splanchnic nerve were determined. The courses and the destinations of these nerves were also examined. There Intensive observations were made on 41 sides of 22 was no significant difference dependent on sex or side. cadavers (male: 24 sides/13 bodies, female: 17 sides/9 bodies) in the student course of dissection at Niigata University School of Medicine. Three sides were ex- Results cluded because they were not suitable for the observa- tion. The dissection was carried out according to the Classification of the splanchnic flaws: On the de- manual of human dissection by Yamada and Mannen tailed observations, the patterns of the abdominal splanchnic nerves in 36 out of 41 sides were groupcd (1987). After the routine observations, levels of ganglia into four types (Type A to D; Fig. 2). In each t pc, which gave rise to the nerve $il-)er consisting each main branches are numbered according to the order of Clasitication of the Abdominal Splanehnic Nerves 445

Fig. 2. Classification of the abdominal splanchnic nerves based on their origins and destinations; every case is represented as the right side. Type A (15/41 sides, 36.6%) is composed of two abdominal splanchnic nerves (A-1, A-2). A-1 arises from the higher level of the sympathetic trunk than A-2 does. A-1 ends in the celiac ganglion (CG) and A-2 in the renal plexus (RP). Type B (9/41 sides, 22.0,7o) is also consisted of two abdominal splanchnic nerves. B-1 is similar to A-1 in its origin, route and destination. B-2 divides into two branches after passing the diaphragm; one of them joins the aorticorenal ganglion (AG) and the other the renal plexus. Type C (6/41 sides, 14.607o) is consisted of three. C-1, C-2, and C-3 arise from the sympathetic trunk in a descending order. C-1 is similar to A-1 and B-1. C-2 descends between C-1 and the sympathetic trunk and ends in the aorticorenal ganglion. C-3, after piercing the diaphragm with the sympathetic trunk, ends in the renal plexus. Conventional definition of the splanchnic nerves seems to correspond to this type, however, the occurrence is rather low (14.6070). Type D (6/41 sides, 14.607o) has two abdominal splanchnic nerves. D-1 is similar to A-1. D-2 descends between D-1 and the sympathetic trunk and ends in the aorticorenal ganglion. their bifurcations. Type D: Two abdominal splanchnic nerves constitute Type A: 15 out of 41 sides (36.6%) represent the type the type D (6/41 sides, 14.607o). The D-1 arises from A, which is composed of two abdominal splanchnic higher part of the sympathetic trunk than the D-2. The nerves (A-1, A-2). The A-1 arises from the higher level D-1 is similar to the A-1 in its route. The D-2 descends of the sympathetic trunk than the A-2 does. The A-1 between the D-1 and the sympathetic trunk and ends descends obliquely forward over the bodies of the in the aorticorenal ganglion. vertebrae, and ends in the celiac ganglion (CG) after Exceptional cases: Five exceptional cases which are perforating the crus of the diaphragm. The A-2 passes not classified into type A to type D are shown the diaphragm with the sympathetic trunk or medial schematically in Fig. 3. to it, and ends in the renal plexus (RP). Ex-1: This could be interpreted as a modified case Type B: The type B (9/41 sides, 22.007o) is also con- of the type A. In this case, extra connections were found sisted of two abdominal splanchnic nerves. The B-1 between the A-1 and the renal plexus, and between the arises from the higher part of the sympathetic trunk A-2 and the celiac ganglion. than the B-2. The B-1 is similar to the A-1 in its route Ex-2: All the branches from the thoracic ganglia and destination. The B-2 descends between the B-I and lower than Th5 unites to form one common trunk. This the sympathetic trunk and divides into two branches trunk bifurcates after passing through the diaphragm; after passing the diaphragm. One of them joins the one is for the celiac ganglion, the other joins the renal aorticorenal ganglion (AG) and the other the renal plexus. This case also resembles to the type A. plexus. Ex-3: A portion of B-2 which should end in the Type C: Three abdominal splanchnic nerves con- aorticorenal ganglion unites with the B-1. stitute the type C (6/41 sides, 14.607o).The C-1, the C-2, Ex-4: In the type C, a part of C-2 unites with the C-3. and the C-3 arise from the sympathetic trunk in a Ex-5: Also in the type C, the C-2 divides into two descending order. The C-1 is similar to the A-1 in its branches after passing the diaphragm. One of the route. The C-2 descends between the C-1 and the branches ends in the celiac ganglion and the other in sympathetic trunk, piercing the diaphragm with the C-1 the renal plexus. or a little lateral to it, and ends in the aorticorenal Further analyses on the splanchnic nerve-is and their ganglion. The C-3 pierces the diaphragm with the relation to the other splanchnic nerves: The highest s mpathetic trunk and ends in the renal plexus. Con- splanchnic nerve which flows into the celiac ganglion tional scheme on the splanchnic nerves, which in types A, B, C, and D and in five exceptional cases tsstimes threc branches, seems to correspond to this will be designated as the splanchnic nerve- l in the type, however, the occurrence is rattler low (14.6%) as following. Since the "splanchnic ner\ "s in all the dcs(1 ibed above. cases examined indicate similar characteristics in their 446 K. Makino et al.

Fig. 3. Schematic drawings of the five exceptional cases which cannot be grouped into type A to type D. Ex-1: This could be interpreted as a modified case of type A. In this case, extra connections were found between A-1 and the renal plexus, and A-2 and the celiac ganglion. Ex-2: All the branches from the thoracic ganglia lower than Th5 unites to form one common trunk. This bifurcates after passing through the diaphragm; one is for the celiac ganglion, the other joins the renal plexus. This case also resembles to type A. Ex-3: A portion of B-2 which should end in the aorticorenal ganglion unites with B-1. Ex-4: In type C, a part of C-2 unites with C-3. Ex-5: In type C, C-2 divides into two branches after passing the diaphragm. One of the branches ends in the celiac ganglion and the other in the renal plexus.

List of abbreviations

AG : aorticorenal ganglion Table 1. The analysis of the roots which constitute the splanchnic CG : celiac ganglion nerve-1, The highest segment, the lowest segment, the K : kidney total number of segments, and the segment levels incor- RG : renal ganglion porated in the splanchnic nerve-1 are listed to show the range of this nerve. RP : renal plexus

courses and destinations, further analyses on their origins were made (Table 1). The range of the ganglia which gave rise to the "splanchnic nerve-1"s was from the fifth to the tenth (Ggl. 5 to Ggl. 10) to the eighth to the eleventh (Ggl. 8 to Ggl. 11) thoracic ganglia (Ggl. 5 to Ggl. 11). Correlations between the lowest level of the splanchnic nerve-1 and the levels of ganglia constituting the other branches in Type A to Type D were analyzed (Table 2). Naturally, when the splanchnic nerve-1 con- tains more segments, those in the other nerves are small. Thus, the composition of the splanchnic nerve-1 affects those of the other splanchnic nerves. Classification of the Abdominal Splanchnic Nerves 447

Table 2. The relations between the lowest ganglion level of the splanchnic nerve-I and the levels of all the ganglia that constitute the rest of the splanchnic nerve/s in each type. Their frequencies are indicated as number of the sides. (X-1) represents the level of the lowest ganglion constituting the A-1 to the D-1, and (X-2) or (X-3) indicates the ganglia that constitute the branches respectively.

Discussion by taking the destinations into consideration (Fig. 2). The abdominal splanchnic nerve-1 is mostly formed There has been an established definition on the by 3 or 4 ganglia from the 6th thoracic ganglion (Ggl. abdominal nerves, the greater, the lesser and the lowest 6) to Ggl. 10 (Table 2). The abdominal splanchnic splanchnic nerves. These three splanchnic nerves have nerve-1 always exists, passes through the regular course, been named mainly according to their sizes. However, and ends in the celiac ganglion, though the composi- it is not satisfactory to classify the abdominal splanchnic tion of the splanchnic nerve-1 is not always constant. nerves according only to their sizes, and these three The abdominal splanchnic nerve-1 affects the other splanchnic nerves do not always exist in a single side nerves in the level of their segments and the ways of of a human body. In this respect, Mitchell (1935) their bifurcation. Details are given as follows: The level already pointed out that the names of these nerves were of the lowest ganglion which constitute the A-1 is unsatisfactory because the so-called lowest splanchnic calculated as 10.3 on average in the type A. In the B-1 nerve is not always the smallest. He suggested that they it is 10.0, and in the C-1, 8.7 (Table 2). This result should have been termed not by their sizes, but by their suggests that proportion of the fibers from the lower levels. He defined them as the superior, the middle, and segments increase in the order of the C-1, the B-1 and the inferior splanchnic nerves, or the superior and the the A-1. In 7 sides out of 15 the A-2 arises solely from inferior when only two are present (Mitchell, 1935). Ggl. 12. In 6 sides out of 9 the roots of the B-2 include However, his classification which paid more attention Ggl. 11. The C-2s arise mostly from Ggl. 10 or 11, and to the levels, in addition to their sizes, is still unsatis- the C-3s from Ggl. 12. Therefore, it is presumed that factory, because three kinds of "the inferior splanchnic union of the lower part of the A-1 and the A-2 produces nerve's were found in respect to their destinations. the B-2, and the C-2 is thought to include lower part Thus, there is no reliable classification nor nomen- of the A-1 and higher part of the A-2. clature for the abdominal splanchnic nerves. As is The A-1, the B-1, the C-1 and the D-1 end in the mentioned before, cases with traditional splanchnic celiac ganglion; the A-2 and the C-3 in the renal plexus; nerves were found only in 14.6°7o of the samples the B-2 both in the aorticorenal ganglion and the renal examined. plexus; and the C-2 in the aorticorenal ganglion. These It is inevitable to refer not only to the origins and facts suggest that the higher segment of the thoracic the courses, but also to the destinations of the ganglia ends in the celiac ganglion, the lower segment abdominal splanchnic nerves. In the present study, in the renal plexus and the middle segment in the intensive observations were made to classify the aorticorenal ganglion. 11)(lominal splanchnic nerves more accurately. Four Type D is unique, in that the fibers through the IVj)c5 of the abdominal splanchnic nerves were found aorticorenal ganglion, and those from the lumbar 448 K. Makino et al. ganglia, or from the cord in a few exceptional cases, basis of intensive observation in accordance with the compensate for the nerve from the thoracic ganglia to level, the course, and the destination of these nerves. the renal plexus in types A, B and C. But with due con- It is expected that the more reasonable nomenclature sideration of the fact that the D-2s scarcely include the will be established according to the present fibers from Ggl. 12, the type D can be concluded as classification. the type C lacking the C-3. Considering these, the fibers might be given and taken between type A and type B, type B and type C, Acknowledgments and type C and type D during the ontogenetic processes. That is, type A, type B, type C and type D may change The authors wish to thank Ms. Shannon Wellwood their types mutually. for her kind co-operation in writing English . Figures The Ex-3 is interpreted as the type B when the branch were prepared with indispensable co-operation of Mr. of the B-2, which ends in the aorticorenal ganglion, Kin'ya Ishimoto. unites with the B-1, or as the type A in which the A-2 unites with the A-1. This case can be thought of as the intermediate type between the type A and the type B. References The Ex-4 can be understood as the type B, if the 1) Elze, C.: Anatomie des Menschen. Band 3. 2nd ed. 352-353. nerve from Ggl. 12 unites with the nerve from Ggl. 10 Springer, Berlin, 1960. before it separates into two branches, or as the type 2) Beninghof, A. & Gdrttler, K.: Lehrbuch der Anatomie des C without communication between the nerve from Ggl. Menschen. Band 3. 8th ed. 376-378. Urban & Schwarzenberg, 10 and from Ggl. 12. Miinchen, 1967. 3) Jackson, C. M.: Morris's human anatomy. 5th ed. 1037-1039. P. Blakiston's Son, Philadelphia, 1914. 4) Kopsch, F. R.: Lehrbuch und Atlas der Anatomie des Conclusion Menschen. Band 3. 17th ed. 327. Georg Thieme, Leipzig, 1950. 5) Mitchell, G. A. G.: The innervation of the kidney, ureter, The abdominal splanchnic nerves have been named testicle and epididymis. J. Anat., 70: 10-32, 1935. mainly according to the sizes, but Mitchell (1935), 6) Mitchell, G. A. G.: Anatomy of the autonomic nervous system. criticizing this for the lack of information on the levels 240-245. E. & S. Livingston, Edinburgh and London, 1953. 7) Schafer, E. A. & Symington, J.: Quain's Elements of Anatomy. of origins, took an additional account of the levels in vol. 3. part 2. 11th ed. 160. Longmans, London, 1909. order to avoid confusion. However, such nomenclature, 8) Williams, P. L., Warwick, R., Dyson, M. & Bannister, L. H.: still, is not satisfactory. The course and the destination Gray's anatomy. 37th ed. 1162-1163. Churchill Livingstone, should also be taken into account for more reasonable Edinburgh & London, 1989. 9) Yamada, M. & Mannen, H.: Jissyu Kaibougaku (anatomy for nomenclature. In the present paper, the abdominal the dissectors). Nankodo, Tokyo, 1985. (in Japanese) splanchnic nerves were grouped into four types on the