Comparative Medicine Vol 61, No 5 Copyright 2011 October 2011 by the American Association for Laboratory Animal Science Pages 453–456

Case Report Horner Syndrome After Carotid Sheath Surgery in a Pig: Anatomic Study of Cervical Sympathetic Chain

Peng Ding,1,* Ralph P Tufano,2 Regina Campbell- Malone,1 Wallace Feng,1 Sang Jun Kim,1 and Rebecca Z German1

In an experimental model, iatrogenic Horner syndrome developed after a right carotid sheath surgery in an infant pig (Sus scrofa). Horner syndrome is a classic clinical triad consisting of ipsilateral eyelid ptosis, pupil miosis, and facial anhydrosis. This syndrome results from cervical sympathetic chain (CSC) paresis and usually is acquired in humans. To determine whether the development of Horner syndrome in this situation could be attributed to pig anatomy, we compared the anatomy of the CSC in pigs and humans, by using 10 infant (age, 1 to 3 wk) pig cadavers. The CSC and cranial cervical sympathetic ganglion (CCG) were dissected bilaterally under a surgical microscope. These structures were consistently within the carotid sheaths of the pigs. In contrast, the CSC and CCG are outside the carotid sheath in humans. Awareness of the anatomic variation of the CSC and CCG within the carotid sheath in the pig and the possibility of the same variation in humans may help surgeons to identify and preserve important structures while performing cervical surgery in pigs and humans. Furthermore, this knowledge can aid in the diagnosis and prognosis of schwannoma.

Abbreviations: CCG, cranial cervical sympathetic ganglion; CSC, cervical sympathetic chain; NG, nodose ganglion.

Horner syndrome is a classic clinical triad consisting of ipsilat- carotid artery, innervates the sphincter of the pupil and Müller eral eyelid ptosis (which is usually mild), pupil miosis, and facial muscle. The other branch follows the (A. anhydrosis (which may or may not be present, depending on the cervicalis externa) to supply other facial areas.19 location of the lesion).This syndrome results from cervical sym- Even though the CSC is located deep in the upper , the in- pathetic chain (CSC) paresis and can be congenital or acquired. cidence of iatrogenic Horner syndrome, stemming from surgery, Congenital causes of Horner syndrome account for less than 5% is reported to be 10% to 18.5%15 in humans. Surgeries that can of all cases. Acquired Horner syndrome can be caused by vasa cause iatrogenic Horner syndrome include thyroidectomy, coro- nervorum occlusion, tumor invasion, infection, or trauma or may nary bypass surgery, carotid endarterectomy, spine surgery, and present as an iatrogenic sequela of surgery.17 Horner syndrome cervical sympathectomy or thoracoscopic sympathicotomy.12,15 was characterized first in humans by Friedrich Horner in 1869.11 It Because of the relatively high incidence of iatrogenic Horner syn- has been previously identified in other mammals including guin- drome in patients, the information gained from animal models ea pigs, rats, mice, hamsters, and rabbits after superior cervical can be useful for understanding the specific iatrogenic causes in ganglionectomy.1,14 Only one case of iatrogenic Horner syndrome both animals and humans. Further, data on incidence in animal in pigs (Sus scrofa), which was caused by inflammation after ca- models may be useful in developing models for research of this rotid artery surgery, 10 has been reported previously. problem. In humans, the CSC ascending from thoracic cavity courses in In this study, we report a case of Horner syndrome occurring the prevertebral space posterior to the carotid sheath and anterior after carotid sheath surgery in a pig. In addition to documenting to the longus colli and longus capitis muscles. The CSC has 2 or the problem in the living animal, we performed 20 detailed post- 3 ganglia, with the superior cervical sympathetic ganglion be- mortem evaluations (including the piglet with Horner syndrome) ing the largest. The superior cervical sympathetic ganglion lies to assess the anatomic relationship among the CSC, cranial cervi- adjacent to the second and third cervical vertebrae. The internal cal sympathetic ganglion (CCG; ganglion cervical cranial), and carotid artery (A. cervicalis interna) and sheath lie anterior, and the carotid sheath. longus capitis is posterior.20 The superior cervical sympathetic ganglion has 2 main branches ascending to the face and cranium, Case Report each branch of which includes both postganglionic vasomotor The subject was one of a set of female pigs obtained from Tom and sudomotor fibers. One branch, which follows the internal Morris Farms (Reisterstown, MD) as part of a swallowing study. The pig was 18 d old and weighted 5.44 kg at the time of arrival at Received: 20 Jan 2011. Revision requested: 22 Feb 2011. Accepted: 08 May 2011. our vivarium. The pig was housed in a separate indoor cage and Departments of 1Physical Medicine and Rehabilitation and 2Otolaryngology-Head and environmental conditions were maintained as recommended in Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, Maryland. the Guide for the Care and Use of Laboratory Animals.9 It was fed 5 *Corresponding author. Email: [email protected]

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times daily with a milk replacement formula (Solustart pig milk replacer, Land O Lakes, St Paul, MN). Fresh water was provided ad libitum. Vital signs were tested daily by the veterinarian and indicated that the pig was healthy prior to surgery. All procedures on the living pig were approved by the Johns Hopkins IACUC (protocol number, SW07M14). For surgery, anesthesia was induced with inhaled isoflurane at 5% by face mask. The pig was intubated, and anesthesia was maintained with 3.5% to 5% isoflurane in 100% 2O as a carrier gas. The isoflurane level was adjusted to maintain anesthesia with stable hemodynamics. Heart rate, aortic blood pressure, respira- tory rate, and electrocardiographic data were continuously moni- tored throughout the procedure. Under sterile conditions, we performed the anterior approach to expose the cranial laryngeal nerve (N. laryngeus cranialis) in the lateral thyrohyoid membrane (membrana thyrohyoidea). We traced this nerve laterally to the ca- rotid sheath, which we opened. The right nodose ganglion (NG; ganglion distal) and its branch, the cranial laryngeal nerve, were exposed at the thyrohyoid membrane level within the sheath. During further dissection of the cervical (N. vagus cervicalis) caudally, we found another nerve medial and parallel to the cervical vagus nerve tracing between the cervical vagus nerve Figure 1. Horner syndrome in the pig. (A) Right side ptosis. (B) Left and internal (V. jugulari interna) within the sheath. side normal eyelid. (C) Horner syndrome pig. (D) Right carotid sheath This nerve was injured inadvertently by the microforceps tips structures postmortem. Cervical sympathetic chain (CSC) was located during the phase of the dissection. Within 12 h after surgery, the medial and dorsal to the cervical vagus nerve (CV) and nodose ganglion pig presented with a drooping right upper eyelid. Ophthalmo- (NG). The start of the cranial laryngeal nerve (CLN) from the NG had logic examination revealed 3 mm of ptosis and 1 mm of miosis been ligated with a black suture during the surgery. CCA, common ca- on the right side (Figure 1). Analgesics and antibiotics were ad- rotid artery; CLA, cranial laryngeal artery; H, hyoid bone; TC, thyroid ministered after surgery to decrease the pain and infective risk. cartilage; TM, thyrohyoid membrane. We delivered buprenorphine (0.01 mg/kg IM twice daily) at 0800 and 1700 and meloxicam (0.4 mg/kg IM daily) and amoxicillin Results (20 mg/kg IM daily) at 1700. The pig showed no distress or pain The basic arrangement of the carotid sheath was constant in after surgery. all dissected pigs. In all 20 cases, the CSC lay within the carotid At 3 d after surgery, no recovery had occurred and the pig sheath. The CSC ascended between the cervical vagus nerve and was euthanized by intracardiac injection of sodium pentobarbi- the , arriving at the CCG which was cranial, tal (greater than 200 mg/kg) under deep isoflurane anesthesia. dorsal, and medial to the NG. For all 20 specimens, the CCG was Postmortem evaluation confirmed that the nerve injured during located on the ventral and medial surface of the internal carotid surgery was the CSC caudal to the CCG within the carotid sheath. artery adjacent to the bifurcation of the On the basis of the physical examination and anatomic findings, (A. cervicalis profunda) at the level of the first and second cervi- the diagnosis of Horner syndrome was indicated and classified as cal vertebrae. The CCG was fusiform or flattened triangular in a preganglionic lesion. shape and reddish or gray in color. The CCG was larger than the NG. In all 20 dissections, the NG was reddish in color and ovoid Materials and Methods in shape. The CCG had 2 main branches traveling cranially: one Materials. The cadaver study included 10 pig specimens (age, with the for innervations of the face, and 1 to 3 wk) obtained from Tom Morris Farms (Reisterstown, MD). the other traveling with the external carotid artery. Within the All dissections involved recently euthanized animals. All dissec- carotid sheath, from cranial to caudal direction between the tions within and related to the carotid sheath were done by using base and thyrohyoid membrane level, there were the CCG, the bi- microdissection surgical tools and a surgical microscope (OPMI furcation of the common carotid artery, and the NG. From ventral CS-NC, Carl Zeiss, Oberkochen, Germany). Photos were taken to dorsal direction, there were the common carotid artery and cra- with a digital camera (Coolpix 8700, Nikon, Melville, NY) con- nial laryngeal artery, the NG and cranial laryngeal nerve, the CSC nected to the surgical microscope. and the internal jugular vein at the level of the NG, and the exter- Dissection method of fresh cadaver specimens. We used an an- nal carotid artery, the CCG, the internal carotid artery, and the cer- terior approach to dissect the structures within the carotid sheath vical vagus nerve above the NG at the level of the CCG (Figure 2). bilaterally between the skull base and thyrohyoid membrane. The The bifurcation of the common carotid artery was located at the major stages were documented by digital images taken from the level of the greater cornu of the hyoid bone. The stable relation- lateral and ventral aspects to preserve the relationships among ship among the cervical vagus nerve–NG, CSC–CCG, common the vessels, nerves, and surrounding structures. Both sides of all carotid artery, and internal jugular vein within the carotid sheath 10 cadavers were dissected, for a sample size of 20. is shown in a schematic diagram (Figure 3).

454 Horner syndrome in a pig

Figure 2. Right side carotid sheath of pig specimen showing the struc- tures and relationship among the cranial cervical sympathetic ganglion (CCG), cervical sympathetic chain (CSC), NG (nodose ganglion), CV (cervical vagus nerve), CCA (common carotid artery), internal jugular vein (IJV), and cranial laryngeal nerve (CLN).

Discussion On the basis of human anatomy, we expected that the CCG and CSC in pigs would be located outside of the carotid sheath posteriorly.20 In our postmortem assessment of the pig that devel- oped Horner syndrome after surgery, we found the CSC nerve medial to the cervical vagus nerve and caudal to the cranial laryngeal nerve within the carotid sheath, which we hypothesized was the external laryngeal nerve (N. laryngeus externa). Following this nerve cranially, we saw this nerve was not a branch from either the cervical vagus nerve or NG but instead was the CCG. Further postmortem evaluation of other pigs supported this as- signment. The dissection of additional specimens indicated that the CCG and CSC routinely coursed within the carotid sheath in Figure 3. Schematic diagram showing anatomic structures of the right a constant position in the pig. The CCG lay on the medial and common carotid sheath. The ventral red structure is the common carotid ventral surface of the internal carotid artery close to the bifurca- artery (CCA) with its 2 branches, the internal carotid artery (ICA) and external carotid artery (ECA). The nodose ganglion (NG) and cervical tion of the common carotid artery at the level of first to second vagus nerve (CV) are dorsal and medial to the CCA. The internal jugu- cervical vertebrae. lar vein (IJV) locates most dorsally within the sheath. The cervical sym- In dogs, similar to pigs, the CSC is located in the carotid sheath pathetic chain (CSC) goes cranially between the CV and IJV within the associated with the vagus nerve in the neck and cranially termi- carotid sheath and then curves dorsally to the cranial laryngeal nerve nates in the CCG.4 In macaque monkeys, the CCG is consistently (CLN), arriving at the cranial cervical sympathetic ganglion (CCG). The positioned dorsally (medial to) the bifurcation of the common CCG lies ventral and medial to the ICA, and immediately adjacent to the carotid artery and between the first and second cervical verte- bifurcation of the CCA. It has 2 main branches sending sympathetic fib- brae.8 In humans, the CCG and CSC are embedded in the prever- ers cranially innervating the face and cranium along the ICA and ECA separately. The bifurcation of the CCA is at the level of the great cornu of tebral posterior to the carotid sheath adjoining the second 20 the hyoid bone. CLA, cranial laryngeal artery; ELN, external laryngeal and third cervical vertebrae. Compared with the position of the nerve; ILN, internal laryngeal nerve; TM, thyrohyoid membrane. Figure CCG close to the jugular foramen in infant pigs, the NG is located printed with permission from Bricelyn Strauch. caudal to the carotid bifurcation, at the level of the thyrohyoid membrane (Figure 3). This position in pigs is different from that in humans and rats. In humans, the vagus nerve is joined by the the iatrogenic Horner syndrome cases observed in patients after cranial portion of the and enlarges into the NG cervical surgery. after it exits from the jugular foramen.20 In rats, the NG is located Anatomic variation of the CSC–CCG can affect the accuracy between the posterior lacerated foramen and the carotid bifurca- of diagnosing schwannoma. Pain and neurologic symptoms are tion.7 uncommon in schwannoma unless the lesion has become large. Most studies and textbooks of human anatomy are explicit that Dysfunction in the nerve of origin may result from axons being the CSC and CCG have stable anatomic position and are located stretched over the tumor capsule. In addition, adjacent nerves outside the carotid sheath.2,20 Our study shows that the location may be affected by direct pressure from the tumor. Therefore, a of the CSC in pigs differs from that of humans. However, the CSC specific nerve dysfunction does not necessarily indicate the exact 6 has been reported within the carotid sheath in 2 of 12 cases in a site of the origin of the tumor. Because most patients have few human cadaver study.13 Therefore, the anatomic variation that oc- symptoms, the anatomic locations of these nerves are significant curs in pigs can occur in humans. Such anatomic variation of the in understanding the differential diagnosis of schwannoma based CSC in humans may contribute to the development of some of on imaging diagnostic modalities like computed tomography and MRI.3,5 Clinically, the differential diagnosis of schwannoma deriv-

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ing from the vagus nerve, CSC, or carotid body is an important features and postoperative neurologic outcome. Laryngoscope step for surgeons for surgical planning and ultimate prognosis for 118:1579–1582. a patient. In schwannoma of the vagus nerve, the schwannoma 4. De Lahunta A, Glass E. 2009. Veterinary neuroanatomy and clinical neurology. St Louis (MO): Saunders Elsevier. can grow between the common carotid artery and internal jugular 5. Furukawa M, Furukawa MK, Katoh K, Tsukuda M. 1996. Differen- vein or between the internal carotid artery and internal jugular tiation between schwannoma of the vagus nerve and schwannoma of vein. Both result in an increase in the distance (separation) be- the cervical sympathetic chain by imaging diagnosis. Laryngoscope tween the artery and vein. In schwannoma of the CSC, the tumor 106:1548–1552. can be posterior to the jugular vein and common carotid artery 6. Ganesan S, Harar RP, Owen RA, Dawkins RS, Prior AJ. 1997. or internal carotid artery, with no separation.5 Imaging studies that Horner’s syndrome: a rare presentation of cervical sympathetic reveal a splaying of the carotid bifurcation are usually indicative chain schwannoma. J Laryngol Otol 111:493–495. 7. Hoyes AD, Barber P, Jagessar H. 1982. Location in the nodose of schwannoma of the carotid body. One group of authors re- ganglion of the perikarya of neurons whose axons distribute in the ported an accurate diagnosis at a rate of 83% prior to surgery in epithelium of the rat . J Anat 134:265–271. 12 schwannoma patients.16 Another study involved 8 cases with 8. Kawashima T, Sato K, Akita K, Sasaki H. 2005. Comparative ana- CSC schwannoma as a cause of splaying of the carotid bifurca- tomical study of the autonomic cardiac nervous system in macaque tion.18 This finding may be further evidence of anatomic variation monkeys. J Morphol 266:112–124. in humans with the CSC inside the carotid sheath, as our current 9. Institute for Laboratory Animal Research. 1996. Guide for the care and use of laboratory animals. Washington (DC): National Acad- study has shown in pigs. emies Press. Awareness of the anatomic variation of the CSC–CCG with- 10. Lembo TM, Wright KC, Cromeens DM, Price RE. 2001. Iatrogenic in the carotid sheath in pigs and the possible occurrence of this Horner’s syndrome in an experimental pig. Contemp Top Lab Anim variant in humans may help in identifying and preserving these Sci 40:33–35. important structures during cervical surgery in both pigs and 11. Leuchter I, Becker M, Mickel R, Dulguerov P. 2002. Horner’s syn- human patients. Inadvertent damage to the CSC–CCG in surgery drome and thyroid neoplasms. ORL J Otorhinolaryngol Relat Spec may result in Horner syndrome. Furthermore, understanding the 64:49–52. 12. Lu J, Ebraheim NA, Nadim Y, Huntoon M. 2000. Anterior anatomy of these structures may help in explaining and evaluat- approach to the cervical spine: surgical anatomy. Orthopedics ing clinical diagnosis and prognosis of schwannoma. Improving 23:841–845. of the knowledge of anatomic variations is crucial for both clinical 13. Lyons AJ, Mills CC. 1998. Anatomical variants of the cervical sym- and veterinary surgeons and researchers. pathetic chain to be considered during neck dissection. Br J Oral Maxillofac Surg 36:180–182. 14. Marfurt CF, Ellis LC. 1993. Immunohistochemical localiza- Acknowledgments tion of tyrosine hydroxylase in corneal nerves. J Comp Neurol We thank Dr Christine G Gourin for sharing her expertise in the field 336:517–531. of head and neck surgery. We thank Bricelyn Strauch for the illustration 15. Patel S, Ilsen PF. 2003. Acquired Horner’s syndrome: clinical review. of Figure 3. 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