Tatsuo KASAI, Shoji CHIBA, Takao SUZUKI and Yuko OKUNO

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1 Okajimas Folia Anat. Jpn., 66 (4): , October, 1989 Cutaneous Branches from the Dorsal Rami of the Cervical Nerves, with Emphasis on their Positional Relations to the Semispinalis Cervicis By Tatsuo KASAI, Shoji CHIBA, Takao SUZUKI and Yuko OKUNO Department of Anatomy, Hirosaki University Medical School, Hirosaki 036, Japan -Received for Publication, March 2, Key words: Cutaneous branch, Cervical nerve, Dorsal ramus, Semispinalis cervicis Summary: The courses of the cutaneous branches arising from the dorsal rami of the cervical and the upper thoracic nerves were examined on 61 sides in 31 human adults, and their positional relations to the semispinalis cervicis muscle were particularly noted. Absence of the cutaneous branch from the dorsal rami of the lower cervical nerves was observed in 60 of the 61 cases; and in the one remaining case, all the cervical nerves except C1 gave off a cutaneous branch. A difference in course of the cutaneous branches was clearly observed between those from the upper cervical and the upper thoracic segments. That is, those of the former passed superficial to the semispinalis cervicis, whereas those of the latter were situated deep to it. The absence of cutaneous branches of the lower cervical segments could be classified into two types: continuous absence and alternate absence. In the former, which was observed in 53 cases (87%), cutaneous branches were absent in continuous segments. In the latter, which was observed in 7 cases (11%), they were absent in alternate segments. Dermatome problems are discussed on the basis of the present results. Keegan- Garrett's chart could be supported in the one exceptional case only. It is well known that in the lower segments of the cervical nerves, cutaneous branches of the dorsal rami are usually absent. In this study, the cutaneous branches arising from the dorsal rami of the upper cervical and the upper thoracic segments were dissected, and the differences in course of these branches were examined, particularly as regards their positional relation to the semispinalis cervicis. In previous papers by others, no precise descriptions have been given for the courses of these branches. Materials and Methods The authors dissected 61 sides of 31 Japanese adults. After removing the back skin by routine methods, the cutaneous branches were carefully dissected. Special attention was paid not to miss small branches, although if some of them were missed, they could be found during subsequent dissection of the deep part. In this study, the dorsal ramus of the first cervical nerve was not particularly noticed, because even when it gave off a cutaneous branch (its frequency of appearance is 6% according to Kumaki (1981)), it showed no positional relation to the semispinalis 153

2 154 T. Kasai et al. cervicis. Findings Among the 61 cases examined, absence of the cutaneous branch from the dorsal rami of the lower cervical nerves was observed in 60 cases. In the one remaining case, all the dorsal rami of the cervical nerves except Cl gave off a branch. This case will be discussed in detail below. Two types of absence of the cutaneous branch could be classified. One of them was a continuous absence, which was found in 53 cases, where the cutaneous branches were absent in continuous segments of the cervical nerves. The other type was an alternate absence (7 cases), where the branches were absent in alternate segments. 1) Continuous absence: As shown in Table 1, the most frequent pattern was that where the cutaneous branch was lacking in segments C6, C7 and C8 (33%), and the next in frequency was that with absence in C6 and C7 (17%). The fmdings coincided mostly with the descriptions given in standard textbooks. The most remarkable observation was that a difference in course of the cutaneous branches was observed between those from the upper cervical and the upper thoracic nerves. In the former, they passed between the semispinales cervicis and capitis before they emerged in the subcutaneous tissue close to the dorsal midline Table 1. Absence of cutaneous branches in continuous segments of the cervical nerves. A total of 53 of the present 61 cases belonged to this eroup. Fig. 1. Dorsal aspect of the left side of the cervical region. In this case, the courses of the cutaneous branches from the dorsal rami of the cervical nerves were typical. Segments C6, C7 and C8 failed to have a cutaneous branch. The upper cervical segments (C2-05) gave off cutaneous branches which passed superficial to the semispialis cervicis, while those from the upper thoracic segments were situated deep to it.

3 Cutaneous Branch of Dorsal Ramus of Cervical Nerve 155 of the trunk, whereas in the latter, they passed deeply between the semispinalis cervicis and the multifidus. In other words, the cutaneous branches of the former passed superficial to the semispinalis cervicis, whereas those of the latter were situated deep to it. Thus, the cutaneous branches took different courses from each other, interposing the lower cervical segments from which no cutaneous branches arose. This situation was confirmed in 36 of the 53 cases of continuous absence (Figs. 1 and 2A). In another 15 cases, however, the most caudal branch of the upper cervical segments pierced through the semispinalis cervicis (Fig. 2B). In the remaining 2 cases, the most caudal branch passed deep to the muscle, like those of the upper thoracic segments (Fig. 2C). 2) Alternate absence: 7 cases belonged to this group (Table 2). In these cases, cutaneous branches emerged, being interposed between the segments from which no cutaneous branches arose. In total, 8 interposed cutaneous branches were noted in the 7 cases, of which 5 passed deep tothe semispinalis cervicis, 2 superficial to it and the remaining one pierced through the muscle (Fig. 2D). Fig. 2. Schematic representation showing the courses of the cutaneous branch es arising from the upper cervical and the upper thoracic segments. Their positional relations to the semispinalis cervicis were particularly noted. The lower cervical segments, being interposed between them, have no cutaneous b ranches. Cases A, B and C in this figure show a continuous absence of the cutaneo us branch. Dorsal aspect of the left side. A: The most typical case, as shown in Fig. 1. The frequency of appearance was 5907o. B : The course of the cutaneous branches are mostly the same as those in the p receding case. However, the most caudal branch of the upp er cervical segments pierces through the semispinalis cervicis. 25% C: The most caudal branch of the upper cervical segments passes deep to the muscle, like those arising from the upper th oracic segments. 3%. D: Alternate absence of cutaneous branches in the lower cervical segments. In this case, segment C6 supplies a cutaneous branch which passes deep to the semispinalis cervi cis, whereas C5, C7 and C8 do not. 11%

4 156 T. Kasai et al. Table 2. Alternate absence of cutaneous branches from the dorsal rami of the cervical segments. Seven cases were observed in the present study, in which cutaneous branches arose in alternate segments. Each segment listed in the table gave off a cutaneous branch, while the interposed one(s) did not. In each case, the most caudal segment of the upper cervical region and the most cranial one of the lower cervical or upper thoracic region are also shown. The course of the cutaneous branches from the interposed segments is shown in parentheses as follows: D, passed deep to the semispinalis cervicis; P, pierced through the muscle; and 5, passed superficial to it. 3) Case in which all the dorsal rami of the cervical segments except Cl gave off a cutaneous branch (Fig. 3): In this exceptional case, the cutaneous branches arising from C3 to C6 passed superficial to the semispinalis cervicis, and those from C7 and C8 pierced through the muscle. The more caudal branches passed deep to it. Discussion Most textbooks of anatomy have indicated that the dorsal rami of C6, C7 and C8 fail to develop cutaneous branches, and this situation was confirmed by Johnston (1909), Shinji (1936) and Pearson et al. (1963, 1965). The present authors also obtained similar finding most frequently, as shown in Table 1. Concerning the course of cutaneous branches arising from the dorsal ramus of the Fig. 3. A rare case in which all the cervical nerves except Cl gave off cutaneous branches from their dorsal rami. This situation was found in only one of the 61 cases examined (2%). Dorsal aspect of the right side. spinal nerve, it has been said that the medial branch generally passes between the semispinalis and the multifidus. In this study, those arising from the upper thoracic segments were confirmed as typically passing between, the two muscles (deep to the semispinalis cervicis), but those from the upper cervical segments caudal to C2 were observed to pass between the semispinales cervicis and

5 Cutaneous Branch of Dorsal Ramus of Cervical Nerve 157 capitis (superficial to the former). Although a few exceptional branches were noted in the most caudal one of the upper cervical segments as stated above, it can be concluded that the courses of the cutaneous branches differed between those from the upper cervical and the upper thoracic segments. Recently, Sato (1973, 1982) presented a diagram illustrating the cross-sectional arrangement of the paravertebral musculature in the thoracic and lumbar regions. He reached his conclusions by modifying Nishi's typological concept (1963) which was based on findings for the tail musculature of the shark. Sato also showed the course of the dorsal rami of the spinal nerves in his figures. The present authors, following Sato's results, give a schematic diagram of the cervical region in Fig. 4, incorporating the findings of the present investigation, particularly emphasizing the courses of the cutaneous branches. As can be seen from the serial diagrams of Sato and the present authors, the courses of the medial branches become deeper caudally. Dermatome charts have been presented by several authors such as Sherrington (1893), Head (1893, 1900), Bolk (1898) and Foerster (1929, 1936). These authors performed their studies by physiological or clinical methods in living man and the monkey, except for Bolk who carried out dissection of infants. Keegan and Garrett (1948) also presented a new chart obtained by clinical investigation of human bodies, and this has been cited in many textbooks. Keegan-Garrett's chart differed from the others in that the dermatome of the upper extremity was shown to consist of a continuous series of segments which extended from the dorsal mid-line of the trunk. In other words, Keegan and Garrett denied the existence of the posterior axial line in the upper extremity. An axial line has been defined as that of demarcation separating two dermatomes supplied from discontinuous spinal segments. From the anatomical standpoint, the posterior axial line means a deficiency of cutaneous branches from the dorsal rami of the cervical nerves. As stated above, in only one of the cases examined in this study, did all the cervical nerves except Cl give off cutaneous branches. This case is clearly rather rare (roughly 2% in this study), and Shinji (1936) previously also reported one similar case among his 10 cases. Keegan- Garrett's dermatome chart may be supported only by such exceptional cases. In the majority Fig. 4. Schematic diagram showing the cross-sectional arrangement of the paravertebral dorsal musculature and the courses of the cutaneous branches arising from the medial branches of the dorsal rami of the spinal nerves. Modified from Sato (1973, 1982).

6 158 T. Kasai et al. of cases, some segments of the lower cervical region lack cutaneous branches from their dorsal rami, showing the existence of the posterior axial line. The discrepancy concerning the posterior axial line of the upper extremity could be made clear by the present dissection studies. The question remains, however, of whether the distributive area of some cutaneous nerves arising from the ventral rami of the spinal nerves extends as far backwards as the dorsal mid-line of the trunk, as shown in the case of Shinji (1936), so that the existence of the posterior axial line might be excluded, even though cutaneous branches from the dorsal rami of the cervical nerves are lacking. Such cases, however, are considered to be rare, although further investigations of this point are needed. It has generally been said that determination of the dermatome cannot be performed satisfactorily by anatomical dissection because of the difficulty in tracing each component of the segmental nerves peripherally (Eke, 1961). Minute dissection as performed here and in the authors' previous study (Kasai et al., 1982) can, however, contribute usefully to the dermatome problem. References 1) Bolk, L.: Die segmentale Differenzierung des menschlichen Rumpfes und seiner Extremitdten. Morph. Jahrb., 26: , ) Elze, C.: Die anatomischen Grundlagen der Headschen Zonen. Zeitschr. f. Anat. u. Entwicklgsch., 122: , ) Foerster, 0.: Die kutanen Distributionsgebiete der sensiblen Nerven. Handbuch der Neurologie, Erganzungs-Bd. zweiter Band, von Lewandowsky, , ) Foerster, 0.: Die Dermatome. Bumke und Foerster, Handbuch der Neurologie, Bd. 5, , ) Head, H.: On the disturbances of sensation with special reference to the pain of visceral disease. Brain, 16: 1-133, ) Head, H. and Campbell, A.W.: The pathology of herpes zoster and its bearing on sensory localisation. Brain, 23: , ) Johnston, H.M.: The cutaneous branches of the posterior primary divisions of the spinal nerves, and their distribution in the skin. J. Anat. Physiol., 43: 80-92, ) Kasai, T., Chiba, S. and Tsunoda, T.: Mor- phological investigation of the peripheral distribution of cutaneous nerves in the upper extremity. Okajimas Folia Anat. Jap., 58: , ) Keegan, J.J. and Garrett, F.D.: The segmental distribution of the cutaneous nerves in the limbs of man. Anat. Rec., 102: , ) Kumaki, K.: The lateral occipital nerve (a new definition). Medicine and Biology, 102: 33-38, (in Japanese). 11) Nishi, S.: Systematisierung der spinalen Stammuskeln des Menschen im Licht der typologischen Anatomic. Gumma J. Med. Sci., 12: 1-5, ) Pearson, A.A., Sauter, R.W. and Bass, J.J.: Cutaneous branches of the dorsal (primary) rami of the cervical nerve. Am. J. Anat., 112: , ) Pearson, A.A., Sauter, R.W. and Buckley, T.F.: Further observations on the cutaneous branches of the dorsal primary rami of the spinal nerves. Am. J. Anat., 118: , ) Sato, T.: A new classification of the transversospinalis system: Preliminary report. Proc. Japan Acad., 49: 51-56, ) Sato, T. and Nakazawa, S.: Morphological classification of the muscular tubercles of the vertebrae. Okajimas Folia Anat. Jap., 58: , ) Sherrington, C.S.: Experiments in examination of the peripheral distribution of the fibers of the posterior roots of some spinal nerves. Phil. Trans. Roy. Soc. London, Ser. B, , ) Shinji, M.: Pri la hautteritorioj de Rami posteriores de Nervi spinales. Tokyo Igakukai Shi, 50: , (in Japanese) Abbreviations for figures C: cervical vertebra IC: iliocostalis IS: interspinalis L: lumbar vertebra LA: longissimus capitis LC: longissimus cervicis LO: longissimus M: multifidus

7 Cutaneous Branch of Dorsal Ramus of Cervical Nerve 159 MB: multifidus brevis ML: multifidus longus RB: rotatoris brevis RL: rotatoris longus SMA: semispinalis capitis SMC: semispinalis cervicis SP: splenius SPA: splenius capitis SPC: splenius cervicis T: thoracic vertebra