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The glossopharyngeal and vagus nerves arise from the posterior aspect of the superior third of the ol-ive anterior to the choroid plexus, extending from

the foramen of Luschka and traveling laterally to enter the jugular foramen. The jugular foramen is divided into an anteromedial pars nervosa and posterolateral pars venosum compartment by the jugular spine (intrajugu-lar process). In this foramen, the nerves traverse with a sheath of connective tissue that extends from the dura to the pericranium.4 The glossopharyngeal and vagus nerves are often separated in the jugular foramen by a fibrous crest (dural septum), thereby separating the jugu-lar foramen into a glossopharyngeal and vagal meatus. This septum varies in width from 0.5 to 4.9 mm.2 Linn et al.5 termed the glossopharyngeal meatus a “small internal auditory canal.” The inferior petrosal sinus travels with the glossopharygeal nerve in one canal or each travels separately in its own bony canal.4

During the formation of the skull, no rigid separa-tion of the fibers of the glossopharyngeal, vagus, acces-sory, and hypoglossal nerves exists. Additionally, the lower cranial nerves merge during development through a common ganglion crest.7 Therefore, it is not surprising that these nerves may communicate along their length.

To our knowledge, intracranial connections between the glossopharyngeal and vagus nerves have not been previously reported. Since these connections may have relevance during microvascular procedures of this area, the present study aimed at observing such connections.

MethodsDuring a microvascular decompression for hemifa-

cial spasm, the senior author (A.C.G.) noted a connec-tion between the glossopharyngeal and vagus nerves. To

Intraoperative and anatomical descriptions of intracranial connections between the glossopharyngeal and vagus nerves: clinical implications

Laboratory investigationR. Shane TubbS, M.S., P.a.-C., Ph.D.,1 MaRTin M. MoRTazavi, M.D.,1 MaRioS LoukaS, M.D., Ph.D.,2 MohaMMaDaLi M. Shoja, M.D.,3 anD aaRon a. Cohen-GaDoL, M.D., M.SC.3

1Pediatric Neurosurgery, Children’s Hospital, Birmingham, Alabama; 2Department of Anatomical Sciences, St. George’s University, Grenada; and 3Goodman Campbell Brain and Spine, Indiana University Department of Neurological Surgery, Indianapolis, Indiana

Object. Knowledge of the variations in the nerves of the posterior cranial fossa may be important during skull base approaches. To the authors’ knowledge, intracranial neural interconnections between the glossopharyngeal and vagus nerves have not been previously investigated.

Methods. The senior author (A.C.G.) noted the presence of an intracranial interneural connection between the glossopharyngeal and vagus nerves during microvascular decompression surgery in a patient suffering from hemi-facial spasm. To further investigate the approximate incidence and significance of such an interneural connection, the authors studied 40 adult human cadavers (80 sides) and prospectively evaluated 16 additional patients during microvascular procedures of the posterior cranial fossa.

Results. In the cadavers, the incidence of intracranial neural connections between the glossopharyngeal and vagus nerves was 2.5%. The only such connection found in our series of living patients was in the patient in whom the connection was initially identified. These interconnections were more common on the left side. Based on our findings, we classified these neural connections as Types I and II. In the cadavers, the length and width of this con-nection were approximately 9 mm and 1 mm, respectively. Histological analysis of these connections verified their neural content.

Conclusions. Although these connections are rare and the significance is unknown, knowledge of them may prove useful to surgeons who operate in the posterior fossa region so that they may avoid inadvertent traction or transection of these interconnections. Additionally, such connections might be considered in patients with recalcitrant neuralgia af-ter microvascular decompression and rhizotomy of the glossopharyngeal nerve. (DOI: 10.3171/2011.2.JNS101757)

key WoRDS      •      variation      •      anatomy      •      intracranial connection      •      neurosurgery

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investigate this further, prospective observations were made during 16 consecutive posterior fossa microvas-cular decompressive procedures for glossopharyngeal/geniculate neuralgia and hemifacial spasm regarding the presence of any interneural connection among the lower cranial nerves. This cohort was composed of 4 male and 12 female adult patients. Of these, 6 underwent explor-atory posterior fossa surgery on the left side and 10 on the right side.

To further investigate the approximate incidence and significance of such an interneural connection, we stud-ied 80 sides from 40 cadavers (23 male and 17 female) aged 39–88 years old (mean 73.5 years) at death. Twen-ty-five of the cadavers were formalin-fixed and 15 were unembalmed; none harbored any sign of an intracranial pathological condition. After the bone over the posterior fossa was removed with a drill (Midas Rex, Medtronic), brain retractors were positioned to retract the cerebellum medially, and the arachnoid membranes over the lower cranial nerves were dissected using microsurgical tech-niques. These nerves were then inspected from their exit zone to the jugular foramen and interconnections among them were investigated. Specifically, we sought any neu-ral connections between the glossopharyngeal and vagus nerves using a surgical microscope (Zeiss). When seen, histological analysis (H & E staining) of these connec-tions was performed.

ResultsOur initial surgical patient was observed to harbor

a connection between the glossopharyngeal and vagus nerves during a posterior fossa exploration for hemifa-cial spasm on the left side. This connection was more oblique than those subsequently identified in the cadavers that we studied and traveled from the glossopharyngeal nerve medially to join the vagus nerve laterally (Fig. 1). No other such connections were observed between the glossopharyngeal and vagus nerves in any of the other 16 patients included in this study.

Among the cadavers, 2 sides (2.5%) were found to

have neural connections between the intracranial intra-cisternal segments of the glossopharyngeal and vagus nerves (Fig. 2). These were identified on the right side of an embalmed male cadaver and the left side of an unem-balmed female cadaver. Both of these connections were more or less vertical in nature and occurred as the nerve began to traverse the jugular foramen. The length and width of these connections were approximately 9 mm and 1 mm, respectively. Histological analysis of these connec-tions verified their neural content.

We classified these 2 forms of glossopharyngeal nerve to vagus nerve connections as Types I (occurring in 66% of the observed instances) and II (occurring in 33%). Type I designates the more vertical connecting fibers and Type II the more oblique connecting fibers (Figs. 1 and 2). Two of the 3 intraneural connections were seen on the left side.

DiscussionWe found that intracranial connections between the

glossopharyngeal and vagus nerves exist and are seen as potentially two types, one more vertical and the other more oblique. The neural anastomotic network between the lower cranial nerves shows individual variability, and knowledge of the anatomy, including such neural con-nections as reported herein, may be important during skull base surgery such as microvascular decompression and various nerve transfer procedures, as well as for un-derstanding the pathophysiology of skull base and neck disorders. Of note, upper fibers of the vagus nerve are often transected for surgical treatment of glossopharyn-geal neuralgia.6 However, the significance of such neural interconnections is unknown and warrants further inves-tigation. We would hypothesize that such connections represent embryologically misguided fibers from the glossopharyngeal nerve to the vagus nerve or vice versa.

Extracranial connections between the glossopha-ryngeal and vagus nerves have been described. Such ex-tracranial connections have been referred to as the ansa of van Haller1 or the glossopharyngeo–pneumogastric

Fig. 1. Left: Photograph obtained in cadaveric specimen demonstrating a vertical connection (traveling over instrument) be-tween the right glossopharyngeal and vagus nerves (Type I connection). Right: Schematic drawing of the Type I connection.

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anastomosis.3 This anastomosis is formed by the joining of a small branch of the glossopharyngeal nerve (ramus communicans cum nervo glossopharyngeo) with the au-ricular branch of the vagus nerve. Such communication may also be seen at the level of the tympanic plexus where branches of the glossopharyngeal and vagus nerves come into contact.

Rhoton6 stated that a large glossopharyngeal nerve diameter may be associated with a small diameter of the upper vagus nerve rootlets or vice versa as these two nerves arise from the same nuclei and have similar func-tions. We have found that stimulation of the glossopha-ryngeal nerve gives results comparable to those of vagus nerve stimulation in aborting seizures in an animal mod-el.8 Such findings lend credence to alternative pathways to the nucleus tractus solitarius via glossopharyngeal nerve to vagus nerve connections.

The intrancranial intracisternal interconnections be-tween the glossopharyngeal and vagus nerves described herein may be more common than previously described because such small connections among intracisternal seg-ments of the cranial nerves may be underappreciated and

missed during removal of the embalmed brain from the cranial vault. We do not believe that our findings regard-ing these interconnections were due to fixation of soft tissues because both fixed and unfixed specimens were found to have these interconnections.

ConclusionsAlthough apparently uncommon and having an un-

known function, knowledge of neural interconnections between the glossopharyngeal and vagus nerves might prove useful to surgeons who operate in the posterior cra-nial fossa so that they may avoid inadvertent traction or transection of these connections.

Disclosure

The authors report no conflict of interest concerning the mate-rials or methods used in this study or the findings specified in this paper.

Author contributions to the study and manuscript preparation include the following. Conception and design: Cohen-Gadol, Tubbs. Acquisition of data: all authors. Analysis and interpretation of data: all authors. Drafting the article: Cohen-Gadol, Tubbs. Critically re vising the article: Cohen-Gadol, Tubbs. Reviewed final version of the manuscript and approved it for submission: all authors. Study supervision: Cohen-Gadol.

References

1. Brown H: Anatomy of the spinal accessory nerve plexus: rel-evance to head and neck cancer and atherosclerosis. Exp Biol Med (Maywood) 227:570–578, 2002

2. de Oliveira E, Rhoton AL Jr, Peace D: Microsurgical anatomy of the region of the foramen magnum. Surg Neurol 24:293–352, 1985

3. Kawai K: Terminal distribution of the branch termed Ramus communicans cum nervo glossopharyngeo of the facial nerve and its morphological significance. Acta Anat  (Basel) 153: 57–63, 1995

4. Lang J (ed): Skull Base and Related Structures: Atlas of Clinical Anatomy. Stuttgart: Schattauer, 1995

5. Linn J, Peters F, Moriggl B, Naidich TP, Brückmann H, Yous-ry I: The jugular foramen: imaging strategy and detailed anat-omy at 3T. AJNR Am J Neuroradiol 30:34–41, 2009

6. Rhoton AL: Microsurgical anatomy of posterior fossa cranial nerves, in Barrow DL (ed): Surgery of the Cranial Nerves of the Posterior Fossa. Park Ridge, IL: American Association of Neurological Surgeons, 1993, pp 1–103

7. Streeter GL: The development of the cranial and spinal nerves in the occipital region of the human embryo. Am J Anat 4: 83–116, 1904

8. Tubbs RS, Patwardhan RV, Wellons JC III, Oakes WJ: Cor-tical representation of Hering’s nerve: a possible anatomical pathway for seizure cessation following electrical stimulation. Pediatr Neurosurg 37:235–239, 2002

Manuscript submitted October 14, 2010.Accepted February 9, 2011.Please include this information when citing this paper: pub-

lished online March 11, 2011; DOI: 10.3171/2011.2.JNS101757.Address correspondence to: Aaron A. Cohen-Gadol, M.D.,

M.Sc., Goodman Campbell Brain and Spine, Indiana University Department of Neurological Surgery, 1801 North Senate Blvd, Suite 610, Indianapolis, Indiana 46202. email: acohenmd@gmail.com.

Fig. 2. Upper: Intraoperative photograph demonstrating a Type II connection in a patient undergoing microvascular decompression for left hemifacial spasm as reported herein. Lower: Schematic drawing of the Type II connection.